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UBC Theses and Dissertations

Modified atmosphere packaging of sweet cherries Thomson, Carrie Ann 1989

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MODIFIED ATMOSPHERE PACKAGING OF SWEET CHERRIES by CARRIE ANN THOMSON B . S c , THE UNIVERSITY OF GUELPH, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Food S c i e n c e ) We a c c e p t t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d THE UNIVERSITY OF A p r i l (c) C a r r i e Ann BRITISH COLUMBIA 1989 Thomson, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Food S c i e n c e The University of British Columbia Vancouver, Canada Date 2 7 A p r i l , 19 89  DE-6 (2/88) ABSTRACT M o d i f i e d atmosphere packag ing (MAP) i n v o l v e s the s t o r a g e of p e r i s h a b l e commodit ies i n atmospheres c o n t a i n i n g h i g h e r carbon d i o x i d e and lower oxygen l e v e l s than i n a i r . When combined w i t h r e f r i g e r a t i o n t e m p e r a t u r e s , MAP t e c h n i q u e s r e s u l t i n an a p p r e c i a b l e e x t e n s i o n of the p o s t - h a r v e s t l i f e of f r u i t s and v e g e t a b l e s . M o d i f i e d atmosphere packag ing s torage t r i a l s performed in t h i s s t u d y i n v o l v e d packag ing sweet c h e r r i e s i n four p l a s t i c f i l m s , c o v e r i n g a range of gas p e r m e a b i l i t i e s , c o u p l e d w i t h o s torage a t 1 C . C h e r r i e s packaged i n p l a s t i c produce bags o b t a i n e d from a l o c a l supermarket s erved as the c o n t r o l t reatment f o r the exper iment . A v a r i e t y of c h e m i c a l and p h y s i c a l c h a r a c t e r i s t i c s of the s t o r e d f r u i t was a n a l y z e d and v a l u e s were compared to those o b t a i n e d f o r u n s t o r e d f r e s h f r u i t . D e v i a t i o n of v a l u e s from those o b t a i n e d f o r zero s t o r a g e f r u i t was taken as a measure of c h e r r y d e t e r i o r a t i o n . Sensory a n a l y s i s was performed f o r a s s e s s i n g c h e r r y q u a l i t y . S torage of c h e r r i e s i n f i l m s r a n g i n g from medium-high to h i g h gas p e r m e a b i l i t i e s r e s u l t e d i n i n t e r n a l a e r o b i c atmospheres w i t h e l e v a t e d c a r b o n d i o x i d e l e v e l s . c h e r r i e s i n these packages d i s p l a y e d s u p e r i o r q u a l i t y r e t e n t i o n over the s torage p e r i o d as compared to o ther t r e a t m e n t s , and c o u l d be s t o r e d s u c c e s s f u l l y f o r up to s i x weeks. Whi le the c o n t r o l c h e r r i e s r e t a i n e d t h e i r a c c e p t a b l e q u a l i t y f o r about f i v e i i weeks, mold growth was apparent a f t e r t h i s s t o r a g e t i m e . Storage of c h e r r i e s i n medium-low p e r m e a b i l i t y f i l m s r e s u l t e d i n the a c c u m u l a t i o n of v e r y h i g h l e v e l s of c a r b o n d i o x i d e w i t h i n the packages . C h e r r i e s i n these packages d e t e r i o r a t e d more q u i c k l y than c h e r r i e s s t o r e d l n the h i g h e r p e r m e a b i l i t y f i l m s , but remained m a r g i n a l l y a c c e p t a b l e a t the end of e i g h t weeks of s t o r a g e . Carbon d i o x i d e l e v e l s rose and oxygen l e v e l s f e l l q u i c k l y i n the low p e r m e a b i l i t y f i l m packages . The q u a l i t y of the c h e r r i e s i n these packages d i m i n i s h e d v e r y r a p i d l y , and f r u i t was u n a c c e p t a b l e a f t e r four weeks of s t o r a g e . I t i s proposed from these f i n d i n g s t h a t the low oxygen and h i g h c a r b o n d i o x i d e l e v e l s w i t h i n the h i g h and medium-high p e r m e a b i l i t y packages s lowed p r o d u c t r e s p i r a t i o n , t h e r e b y e x t e n d i n g the e f f e c t i v e s t o r a g e p e r i o d of the f r u i t . The i n h i b i t i o n of s p o i l a g e organisms under these atmospheres l i k e l y a l s o p l a y e d a r o l e i n m i t i g a t i n g q u a l i t y changes . TABLE OF CONTENTS Page A b s t r a c t i t T a b l e of Contents i v L i s t of T a b l e s v i i i L i s t of F i g u r e s x i Acknowledgements x i i i 1. INTRODUCTION 1 2. LITERATURE REVIEW 3 2.1 M o d i f i e d Atmosphere Packag ing - G e n e r a l Aspec t s 3 2.2 O b j e c t i v e s of M o d i f i e d Atmosphere Packag ing 6 2 . 2 . 1 R e d u c t i o n i n P r o d u c t R e s p i r a t i o n Rate 7 2 .2 .2 E t h y l e n e B i o s y n t h e s i s and A c t i o n . . . . 10 2 . 2 . 3 C o m p o s i t i o n a l Changes 11 2 .2 .4 Water Loss 13 2 . 2 . 5 E f f e c t s of MAP on P h y s i o l o g i c a l D i s o r d e r s 13 2 . 2 . 6 E f f e c t s of MAP on Mold Growth 14 2.3 C h e r r y S torage 17 2.4 Atmosphere M o d i f i c a t i o n and Sweet C h e r r y Storage 19 2.5 C h e m i c a l C o n s t i t u e n t s of C h e r r i e s 25 2 . 5 . 1 P h e n o l i c Compounds 25 2 .5 .2 A n t h o c y a n i n s - Occurrence and A n a l y s i s 30 2 . 5 . 3 O r g a n i c A c i d s and T h e i r D e t e r m i n a t i o n 31 2 . 5 . 3 . 1 G e n e r a l B i o c h e m i s t r y and the E f f e c t s of MAP on O r g a n i c A c i d L e v e l s i n F r u i t s and V e g e t a b l e s 31 2 . 5 . 3 . 2 O r g a n i c A c i d s A n a l y s i s 36 i v Page 3. MATERIALS AND METHODS 40 3.1 I n t r o d u c t i o n 40 3.2 C h e r r y Packag ing 40 3.3 Package Headspace A n a l y s i s 41 3.4 Mold Development D u r i n g Storage 43 3.5 F r u i t Weight Changes D u r i n g Storage 45 3.6 P h y s i c a l A n a l y s e s 45 3 . 6 . 1 O b j e c t i v e E v a l u a t i o n of c h e r r y T e x t u r e 45 3 .6 .2 C h e r r y F r u i t S u r f a c e C o l o u r 46 3.7 Chemica l A n a l y s e s 48 3 . 7 . 1 C h e r r y J u i c e E x t r a c t i o n 48 3 . 7 . 1 . 1 D e t e r m i n a t i o n of C h e r r y pH . 48 3 . 7 . 1 . 2 P e r c e n t S o l u b l e S o l i d s D e t e r m i n a t i o n 49 3 . 7 . 1 . 3 P e r c e n t T i t r a t a b l e A c i d i t y D e t e r m i n a t i o n 49 3 . 7 . 1 . 4 P e r c e n t S o l u b l e S o l i d s / P e r c e n t T i t r a t a b l e A c i d i t y R a t i o 49 3 . 7 . 1 . 5 P h e n o l i c Content of C h e r r i e s 50 3 .7 .2 T o t a l A n t h o c y a n i n s A n a l y s i s 50 3 . 7 . 2 . 1 E x t r a c t i o n Procedure 51 3 . 7 . 2 . 2 C a l c u l a t i o n s 52 3 . 7 . 3 O r g a n i c A c i d s A n a l y s i s 55 3 . 7 . 3 . 1 Sample P r e p a r a t i o n 55 3 . 7 . 3 . 2 P r e p a r a t i o n of Standards . . . 56 3 . 7 . 3 . 3 HPLC I n s t r u m e n t a t i o n . . . . . . . 57 3.8 Sensory E v a l u a t i o n 58 3.9 S t a t i s t i c a l A n a l y s i s 60 V Page 4. RESULTS AND DISCUSSION 62 4.1 E f f e c t of s t o r a g e Time and Package on Headspace C o m p o s i t i o n 62 4.2 Mold Development i n C h e r r i e s D u r i n g MAP Storage 72 4.3 C h e r r y Weight Loss D u r i n g Storage 74 4.4 E f f e c t of S torage Time and Package on F r u i t T e x t u r e as Determined U s i n g the I n s t r o n . . . . 76 4.5 E f f e c t of S torage Time and Package on C h e r r y S u r f a c e C o l o u r ( R e f l e c t a n c e Measurements) 86 4.6 E f f e c t of S torage Time and Package on C h e r r y pH, P e r c e n t T i t r a t a b l e A c i d i t y , P e r c e n t S o l u b l e S o l i d s , and P e r c e n t S o l u b l e S o l i d s / P e r c e n t T i t r a t a b l e A c i d i t y R a t i o s 98 4 . 6 . 1 pH Changes 98 4 .6 .2 P e r c e n t T i t r a t a b l e A c i d i t y Changes . . 101 4 .6 .3 P e r c e n t S o l u b l e S o l i d s Changes 105 4 .6 .4 Changes i n P e r c e n t S o l u b l e S o l i d s / P e r c e n t T i t r a t a b l e A c i d i t y R a t i o s . . . 108 4.7 E f f e c t of S torage Time and Package on T o t a l A n t h o c y a n i n s Content s of C h e r r i e s . . . . I l l 4.8 E f f e c t of S torage Time and Package on the T o t a l P h e n o l i c s Content of C h e r r i e s 118 4.9 E f f e c t of S torage Time and Package on the O r g a n i c A c i d P r o f i l e s of C h e r r y F r u i t 122 4.10 s e n s o r y A n a l y s i s 132 5. CONCLUSIONS AND RECOMMENDATIONS 156 5.1 Summary of R e s e a r c h F i n d i n g s and C o n c l u s i o n s 156 5.2 Recommendations f o r F u r t h e r Research 157 6. REFERENCES 159 v i Page 7. APPENDICES 167 Appendix A : S tandard Curves f o r O r g a n i c A c i d s i n Sweet C h e r r i e s 167 Appendix B : Sensory E v a l u a t i o n Form f o r C h e r r i e s 168 v i i LIST OF TABLES Page T a b l e 2.1 P h y s i o l o g i c a l D i s o r d e r s of F r u i t s and V e g e t a b l e s 15 T a b l e 2.2 The P r i n c i p a l P h e n o l i c Compounds of Sweet C h e r r i e s (Prunus avium s p . ) 29 T a b l e 3.1 P r o p e r t i e s of the Packag ing F i l m s 42 T a b l e 4.1 P e r c e n t Carbon D i o x i d e L e v e l s i n c h e r r y Packages D u r i n g Storage a t 1 ° C 65 T a b l e 4.2 P e r c e n t Oxygen L e v e l s i n C h e r r y Packages D u r i n g Storage a t 1 ° C 67 T a b l e 4.3 Changes i n C h e r r y Weights Under V a r i o u s Packag ing C o n d i t i o n s 75 T a b l e 4.4 B i o y i e l d Va lues (N) of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s 79 T a b l e 4 .5 F i rmness V a l u e s (N/m) of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s 81 T a b l e 4.6 Deformat ion Va lues (mm) of C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 84 T a b l e 4.7 Hunter L V a l u e s of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s 91 T a b l e 4.8 Hunter b Va lues of C h e r r i e s Under V a r i o u s P a c k a g i n g c o n d i t i o n s 94 T a b l e 4.9 Hunter a V a l u e s of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s 97 T a b l e 4.10 pH V a l u e s of C h e r r i e s Under V a r i o u s P a c k a g i n g c o n d i t i o n s 100 T a b l e 4.11 P e r c e n t T i t r a t a b l e A c i d i t y L e v e l s (as M a l i c A c i d ) of C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 103 T a b l e 4.12 P e r c e n t S o l u b l e S o l i d s L e v e l s of C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 107 T a b l e 4.13 P e r c e n t S o l u b l e S o l i d s / P e r c e n t T i t r a t a b l e A c i d i t y R a t i o s for C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 110 v i i i Page T a b l e 4.14 T o t a l A n t h o c y a n i n Contents of C h e r r i e s (mg c y a n i d i n - 3 - g a l a c t o s i d e / 1 0 0 e d i b l e f r u i t ) Under V a r i o u s Packag ing C o n d i t i o n s 114 T a b l e 4.15 T o t a l P h e n o l i c Content of C h e r r i e s (mg G a l l i c A c i d / 1 0 0 mL J u i c e ) Under V a r i o u s Packag ing C o n d i t i o n s 120 T a b l e 4.16 M a l i c A c i d Content of C h e r r i e s (mg/100 g E d i b l e F r u i t ) under v a r i o u s Packag ing C o n d i t i o n s 125 T a b l e 4.17 S u c c i n i c A c i d c o n t e n t of C h e r r i e s (mg/100 g E d i b l e F r u i t ) Under V a r i o u s Packag ing C o n d i t i o n s 128 T a b l e 4.18 Q u i n i c A c i d Content of C h e r r i e s (mg/100 g E d i b l e F r u i t ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s 131 T a b l e 4.19 Formic A c i d Content of C h e r r i e s (mg/100 g E d i b l e F r u i t ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s 134 T a b l e 4.20 Sensory F irmness Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 137 T a b l e 4.21 Sensory C o l o u r Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 139 T a b l e 4.22 Sensory Appearance Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 140 T a b l e 4.23 Sensory T e x t u r e Scores f o r C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s 145 T a b l e 4.24 Sensory Sweetness Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 146 T a b l e 4.25 Sensory Aroma Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 148 T a b l e 4.26 Sensory B i t t e r n e s s Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 150 T a b l e 4.27 Sensory O f f - F l a v o u r Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 152 i x Page T a b l e 4.28 Sensory O v e r a l l A c c e p t a b i l i t y Scores f o r C h e r r i e s Under V a r i o u s Packag ing C o n d i t i o n s 155 X L I S T OF FIGURES Page F i g . 2.1 The Krebs C y c l e 9 F i g . 2.2 B i o s y n t h e s i s of Cinnamlc A c i d s 28 F i g . 2.3 S t r u c t u r a l T r a n s f o r m a t i o n s of A n t h o c y a n i n s w i t h pH 32 F i g . 3.1 Sample Gas Chromatogram of Package Headspace 44 F i g . 3.2 T y p i c a l F o r c e - D e f o r m a t i o n Curve for an I n d i v i d u a l C h e r r y F r u i t 47 F i g . 3.3 HPLC Chromatogram of O r g a n i c A c i d S tandards 59 F i g . 4.1 Changes i n Carbon D i o x i d e C o n c e n t r a t i o n s i n F i l m Packages of C h e r r i e s D u r i n g Storage a t 1 ° C 64 F i g . 4.2 Changes i n Oxygen C o n c e n t r a t i o n s i n F i l m Packages of C h e r r i e s D u r i n g Storage a t 1 ° C 66 F i g . 4.3 The Krebs C y c l e and Some A s s o c i a t e d Pathways 69 F i g . 4.4 Changes i n C h e r r y B i o y i e l d Va lues D u r i n g S torage a t 1 ° C 78 F i g . 4.5 Changes i n C h e r r y F irmness Values D u r i n g S torage a t l ° c 80 F i g . 4.6 Changes i n C h e r r y Deformat ion Values D u r i n g S torage a t 1 ° C 83 F i g . 4.7 The Hunter L , a , b C o l o u r S o l i d 87 F i g . 4.8 Changes i n Hunter L v a l u e s of C h e r r i e s D u r i n g Storage a t l ° c 90 F i g . 4.9 Changes i n Hunter a Va lues of C h e r r i e s D u r i n g S torage a t 1 ° C 93 F i g . 4.10 Changes i n Hunter b V a l u e s of C h e r r i e s D u r i n g Storage a t 1 ° C 96 x i Page F i g . 4.11 Changes i n C h e r r y pH Values D u r i n g Storage a t 1*C 99 F i g . 4.12 Changes i n P e r c e n t T i t r a t a b l e A c i d i t y L e v e l s i n C h e r r i e s D u r i n g Storage a t 1 ° C 102 F i g . 4.13 Changes i n P e r c e n t S o l u b l e S o l i d s L e v e l s l n C h e r r i e s D u r i n g Storage a t 1 ° C 106 F i g . 4.14 Changes i n P e r c e n t S o l u b l e S o l i d s / P e r c e n t T i t r a t a b l e A c i d i t y R a t i o s i n C h e r r i e s D u r i n g Storage a t l ^ C 109 F i g . 4.15 Changes i n T o t a l A n t h o c y a n i n s Contents of C h e r r i e s D u r i n g S torage a t 1 ° C 113 F i g . 4.16 R e a c t i o n of A c e t a l d e h y d e (I) w i t h C a t e c h i n ( I I ) and C y a n i d i n - 3 - g l u c o s i d e ( I I I ) 117 F i g . 4.17 Changes i n T o t a l P h e n o l i c s Contents of C h e r r i e s D u r i n g Storage a t 1 ° C 119 F i g . 4.18 T y p i c a l HPLC Chromatogram of O r g a n i c A c i d s l n C h e r r y E x t r a c t s 123 F i g . 4.19 Changes i n M a l i c A c i d L e v e l s i n C h e r r i e s D u r i n g S torage a t 1° C 124 F i g . 4.20 Changes i n S u c c i n i c A c i d L e v e l s i n C h e r r i e s D u r i n g S torage a t 1 ° C 127 F i g . 4.21 Changes i n Q u i n i c A c i d L e v e l s i n C h e r r i e s D u r i n g Storage a t 1 ° C 130 F i g . 4.22 Changes i n Formic A c i d L e v e l s i n C h e r r i e s D u r i n g Storage a t 1 C 133 F i g . 4.23 Changes i n Sensory F irmness Scores f o r C h e r r i e s D u r i n g S torage a t 1° C 136 F i g . 4.24 Changes i n Sensory T e x t u r e Scores f o r C h e r r i e s D u r i n g S torage a t 1° C 143 F i g . 4.25 Changes i n Sensory O f f - F l a v o u r Scores f o r C h e r r i e s D u r i n g S torage a t 1 ° C 151 F i g . 4.26 Changes i n Sensory O v e r a l l A c c e p t a b i l i t y Scores f o r C h e r r i e s D u r i n g Storage a t 1 ° C 154 x i i ACKNOWLEDGEMENTS I would l i k e to express my thanks to my t h e s i s r e s e a r c h s u p e r v i s o r , D r . W i l l i a m P o w r i e , Department of Food S c i e n c e , f o r h i s s uppor t throughout the course of t h i s s t u d y , and p a r t i c u l a r l y f o r h i s a s s i s t a n c e i n e x p e d i t i n g the c o m p l e t i o n of t h i s m a n u s c r i p t . Thanks i s a l s o extended to the members of my s u p e r v i s o r y committee , D r s . Brent S k u r a , David K i t t s , and Ruth Wu, a l l of the Department of Food S c i e n c e , for t h e i r h e l p f u l sugges t ions d u r i n g the p r e p a r a t i o n of t h i s t h e s i s . The t e c h n i c a l a s s i s t a n c e of Mr. Sherman Yee was v e r y much a p p r e c i a t e d . x i i i 1.0 INTRODUCTION The s t o r a g e l i f e of c h e r r i e s under c o n v e n t i o n a l r e f r i g e r a t e d c o n d i t i o n s i s n o r m a l l y l i m i t e d to two to three weeks, p r i m a r i l y due to the r a p i d development o£ mold (Anderson and Hardenburg , 1977; Salunkhe and D e s a i , 1984) . Rapid water l o s s from h a r v e s t e d f r u i t a l s o l eads to a d e t e r i o r a t i o n of p r o d u c t q u a l i t y (Drake et a l _ . , 1988) . M o d i f i e d atmosphere packag ing (MAP) i n v o l v e s packag ing h i g h l y p e r i s h a b l e foods i n f i l m bags of s e l e c t i v e p e r m e a b i l i t i e s . The product may be b l a n k e t e d w i t h an atmosphere r i c h i n carbon d i o x i d e and wi th lower oxygen l e v e l s than those found i n a i r . A l t e r n a t i v e l y , packages c o n t a i n i n g o n l y a i r may be s e a l e d , i n which case the c o n t i n u e d r e s p i r a t i o n of the p r o d u c t generates the m o d i f i e d atmosphere . In both types of sys tems , the c o m b i n a t i o n of the m o d i f i e d atmosphere w i t h c h i l l i n g temperatures r e t a r d s f r u i t senescence as w e l l as pa thogen- induced decay . C h e r r i e s are a major f r u i t produced i n B r i t i s h C o l u m b i a . However, the s h o r t h a r v e s t season and the l i m i t e d s t o r a g e l i f e causes markets to become f l o o d e d , l e a d i n g to low economic r e t u r n s f o r growers . I f MAP can be used to extend the p o s t -h a r v e s t l i f e of c h e r r i e s , i t would e f f e c t i v e l y i n c r e a s e the l e n g t h of the c h e r r y m a r k e t i n g s eason , c a u s i n g a change i n the t y p i c a l supply/demand c u r v e , t h e r e b y a l l o w i n g the p r o d u c t to c a p t u r e a h i g h e r p r i c e i n the m a r k e t p l a c e . F u r t h e r m o r e , MAP e x t e n s i o n of c h e r r y s t o r a g e l i f e may expand the g e o g r a p h i c a l 1 boundar ie s f o r d i s t r i b u t i o n , e n a b l i n g the use of s u r f a c e d i s t r i b u t i o n channe l s as opposed to expens ive a i r f r e i g h t . The o b j e c t i v e of t h i s s t u d y was to e v a l u a t e the e f f e c t i v e n e s s of four p l a s t i c f i l m s of v a r i o u s p e r m e a b i l i t i e s i n e x t e n d i n g c h e r r y s t o r a g e l i f e . T h i s was a c h i e v e d by m o n i t o r i n g changes i n c h e m i c a l , p h y s i c a l , and s e n s o r y a t t r i b u t e s of the f r u i t over an e ight-week s t o r a g e p e r i o d . 2 2. LITERATURE REVIEW 2.1 MODIFIED ATMOSPHERE PACKAGING - GENERAL ASPECTS M o d i f i e d atmosphere packag ing (MAP) i n v o l v e s i n t r o d u c i n g a whole or c u t commodity i n t o a package system i n which the a i r s u r r o u n d i n g the commodity i s d i s p l a c e d by a s p e c i f i c mix ture and volume of gases p r i o r to s e a l i n g (Powrie , 1988) . MAP d i f f e r s from c o n t r o l l e d atmosphere packaging (CAP) or s t o r a g e (CAS) by the f a c t t h a t t h e r e i s no c o n t r o l of the c o m p o s i t i o n of the i n t e r n a l gas mixture once the package i s s e a l e d (Wol fe , 1984) . Whi le r e s e a r c h has c o n c e n t r a t e d l a r g e l y on bulk s t o r a g e of h o r t i c u l t u r a l commodit ies under MA or CA c o n d i t i o n s , r e c e n t t r e n d s have been towards the development of MA w i t h i n r e t a i l packages ( B a l l a n t y n e , 1986) . T e c h n o l o g i c a l advances a l l o w i n g f o r s m a l l e r amounts of goods to be packaged i n MA c o n d i t i o n s (Wol fe , 1984) , as w e l l as advances i n the d e s i g n and manufacture of p o l y m e r i c f i l m s w i t h a wide range of gas p e r m e a b i l i t i e s have r e s u l t e d i n a he ightened i n t e r e s t i n d e v e l o p i n g MA t e c h n o l o g y (Zagory and K a d e r , 1988) . With the r e t a i l d i s t r i b u t i o n of MAP commodi t i e s , the consumer i s a b l e to take the p r o d u c t home, where the b e n e f i t s of MA c o n t i n u e to be r e a l i z e d u n t i l the package i s opened. T h i s a l l o w s for m a x i m i z a t i o n of the q u a l i t y s t a b i l i z i n g b e n e f i t s of the t e c h n o l o g y and the a s s o c i a t e d economic r e t u r n s ( B e l l , 1986) . A f u r t h e r impetus f o r the development of MAP t e c h n o l o g y has been 3 the r e c e n t t r e n d of consumers to demand f r e s h produce (Myers , 1989) . MAP I n v o l v e s m a n i p u l a t i o n of oxygen and carbon d i o x i d e c o n c e n t r a t i o n s i n the atmosphere s u r r o u n d i n g the commodity. Other gases , such as carbon monoxide, e t h y l e n e , p r o p y l e n e , and a c e t y l e n e may a l s o be used i n some a p p l i c a t i o n s (Wol fe , 1984) . The p r e c i s e c o m p o s i t i o n of the gas mixture to be used i n MAP of h o r t i c u l t u r a l p r o d u c t s i s commodity-dependent . However, the atmosphere g e n e r a l l y i n c l u d e s e l e v a t e d l e v e l s of carbon d i o x i d e and reduced l e v e l s of oxygen as compared to a i r (Kader , 1986; Wol f e , 1984) . The optimum atmosphere c o m p o s i t i o n s h o u l d reduce the r a t e of p r o d u c t r e s p i r a t i o n and r i p e n i n g which l e a d to q u a l i t y d e t e r i o r a t i o n of the commodity (Zagory and K a d e r , 1988) D e s p i t e the f a c t t h a t the c o m p o s i t i o n of the atmosphere i s c o n t r o l l e d to w i t h i n s t r i c t l i m i t s a t the t ime of p a c k a g i n g , the atmosphere w i t h i n the package i s not s t a t i c d u r i n g s t o r a g e . The consumption of oxygen and g e n e r a t i o n of carbon d i o x i d e d u r i n g the c o n t i n u e d r e s p i r a t i o n of the p r o d u c t c o n t r i b u t e to the dynamic n a t u r e of the sys tem. Thus , the p r a c t i c a l o p t i m a l atmosphere c o m p o s i t i o n s h o u l d not be too c l o s e to t h a t of one t h a t i s i n j u r i o u s to the p r o d u c t (Zagory and K a d e r , 1988) . In the development of a MAP s t o r a g e reg ime , c o n s i d e r a t i o n must a l s o be g i v e n to t e m p e r a t u r e , which i s o u s u a l l y m a i n t a i n e d below 5 C ( B l e n f o r d , 1986) . MAP i s o n l y an a d j u n c t to e f f e c t i v e r e f r i g e r a t e d s t o r a g e . G e n e r a l l y , f r u i t s and v e g e t a b l e s w i l l l a s t l onger a t lower t e m p e r a t u r e s , p r o v i d e d 4 t h e i r lower temperature l i m i t s are not exceeded. The optimum s t o r a g e temperature i s one which d e l a y s the development of senescence and r e t a i n s q u a l i t y wi thout i n d u c i n g low- temperature or c h i l l i n g i n j u r y . T h i s optimum temperature i s dependent on the c o m p o s i t i o n of the atmosphere w i t h i n the package s u r r o u n d i n g a commodity (Zagory and K a d e r , 1988) . The c h o i c e of a packag ing m a t e r i a l i s a l s o important from the s t a n d p o i n t of gas p e r m e a b i l i t i e s . The gas t r a n s m i s s i o n c h a r a c t e r i s t i c s of the f i l m w i l l l a r g e l y de termine i t s e f f e c t i v e n e s s i n m a i n t a i n i n g the d e s i r e d in -package gas c o m p o s i t i o n . The temperature of s t o r a g e w i l l a f f e c t the gas t r a n s m i s s i o n r a t e s ; g e n e r a l l y , f i l m p e r m e a b i l i t y i n c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e , w i t h carbon d i o x i d e p e r m e a b i l i t y r e s p o n d i n g moreso than oxygen p e r m e a b i l i t y . The e n t i r e system must be c o n s i d e r e d as a whole , as opposed to c h o o s i n g each parameter i n d e p e n d e n t l y ( B e l l , 1986; B l e n f o r d , 1986) . With a f r e s h commodity i n a s e a l e d package , the c o n c e n t r a t i o n of oxygen decreases whi l e carbon d i o x i d e i n c r e a s e s . However, i f the f i l m i s permeable to these gases , as the l e v e l of c a r b o n d i o x i d e c o n t i n u e s to i n c r e a s e , i t d i f f u s e s out of the package a t an i n c r e a s i n g r a t e due to the e s t a b l i s h m e n t of a carbon d i o x i d e c o n c e n t r a t i o n g r a d i e n t a c r o s s the packag ing m a t e r i a l . S i m i l a r l y , as oxygen c o n t i n u e s to be d e p l e t e d from the atmosphere w i t h i n the package , a c o n c e n t r a t i o n g r a d i e n t w i l l be e s t a b l i s h e d between the i n t e r i o r and e x t e r i o r of the package . Oxygen w i l l d i f f u s e i n t o the 5 package a t a r a t e dependent on the magnitude of the oxygen d e f i c i t . I d e a l l y , an e q u i l i b r i u m c o n c e n t r a t i o n of both gases w i l l be e s t a b l i s h e d , where the r a t e of gas t r a n s m i s s i o n through the package i s e q u a l to the r a t e of p r o d u c t r e s p i r a t i o n . The e q u i l i b r i u m v a l u e s are dependent on a number of f a c t o r s , i n c l u d i n g the r e s p i r a t i o n r a t e of the p r o d u c t , package f i l l we ight , s u r f a c e area f o r gas exchange, and the gas t r a n s m i s s i o n v a l u e s of the f i l m a t the s t o r a g e temperature employed ( B a l l a n t y n e , 1986) . A p r e f e r r e d p l a s t i c f i l m i s one w i t h a p e r m e a b i l i t y t h a t a l l o w s a gas e q u i l i b r i u m to be e s t a b l i s h e d q u i c k l y w i t h u l t i m a t e low oxygen and e l e v a t e d carbon d i o x i d e c o n c e n t r a t i o n s . I f f i l m p e r m e a b i l i t y i s too low, a n a e r o b i c c o n d i t i o n s w i l l r e s u l t w i t h i n the package as oxygen i s d e p l e t e d through r e s p i r a t i o n . In h i g h l y permeable packages , l i t t l e or no m o d i f i c a t i o n of the atmosphere w i l l r e s u l t ( B a l l a n t y n e , 1986) . 2.2 OBJECTIVES OF MODIFIED ATMOSPHERE PACKAGING The a im of MAP i s to min imize the r a t e of q u a l i t y d e t e r i o r a t i o n to extend commodity s t o r a g e l i f e . S ince MAP a f f o r d s a g r e a t e r r e d u c t i o n i n r e s p i r a t i o n and r i p e n i n g r a t e s than r e f r i g e r a t i o n a l o n e , t h i s has o f t e n been p r o c l a i m e d as the p r i m a r y reason f o r the b e n e f i c i a l e f f e c t s of MAP; however, t h i s may be an o v e r - s i m p l i f i c a t i o n ( B e l l , 1986; Wol f e , 1986) . P o s t -h a r v e s t d e t e r i o r a t i o n of f r e s h produce can be caused by a 6 number of f a c t o r s i n a d d i t i o n to h i g h r e s p i r a t i o n r a t e , i n c l u d i n g m e t a b o l i c changes , growth and development , p h y s i c a l i n j u r i e s , water l o s s , p h y s i o l o g i c a l d i s o r d e r s , and p a t h o l o g i c a l breakdown. MAP may i n f l u e n c e each of these f a c t o r s e i t h e r d i r e c t l y or i n d i r e c t l y to l e n g t h e n the s t o r a g e l i f e of the commodity (Kader , 1986) , as d i s c u s s e d below. 2 . 2 . 1 REDUCTION IN PRODUCT RESPIRATION RATE Low oxygen t e n s i o n s s u r r o u n d i n g f r e s h f r u i t s and v e g e t a b l e s cause a r e d u c t i o n i n t h e i r r a t e s of r e s p i r a t i o n and e t h y l e n e p r o d u c t i o n (Kader , 1986) . However, the degree of i n h i b i t i o n i s not p r o p o r t i o n a l to the r e d u c t i o n i n oxygen l e v e l s . The r e s p i r a t o r y q u o t i e n t , d e f i n e d as the r a t i o of carbon d i o x i d e p r o d u c t i o n to oxygen consumpt ion , g e n e r a l l y remains s t a b l e u n t i l a c r i t i c a l minimum c o n c e n t r a t i o n of oxygen i s r e a c h e d . At oxygen l e v e l s below t h i s c r i t i c a l v a l u e , the i n h i b i t i o n of r e s p i r a t i o n and e t h y l e n e p r o d u c t i o n r a t e s i n c r e a s e s g r e a t l y ( Z e m l i a n u k h i n and Ivanov, 1978) . The r e d u c t i o n i n r e s p i r a t i o n r a t e appears to be due to a decrease i n the a c t i v i t y of ox idase s w i t h a low a f f i n i t y f o r oxygen such as a s c o r b i c a c i d o x i d a s e , p o l y p h e n o l o x i d a s e , and g l y c o l i c a c i d o x i d a s e , as opposed to the s u p p r e s s i o n of cytochrome o x i d a s e , which mediates the b a s a l metabo l i sm of the p r o d u c t ( B u r t o n , 1978) . Oxygen c o n c e n t r a t i o n s must be ma in ta ined above a minimum of about 1 to 3%, (the p r e c i s e l e v e l be ing dependent on the 7 commodity) , to a v o i d a s h i f t from a e r o b i c to a n a e r o b i c r e s p i r a t i o n . D u r i n g a n a e r o b i c r e s p i r a t i o n , p y r u v i c a c i d i s no longer o x i d i z e d through the Krebs c y c l e , but i s d e c a r b o x y l a t e d to form a c e t a l d e h y d e and u l t i m a t e l y e t h a n o l , which cause the development of o f f - f l a v o u r s , o f f - o d o u r s , and t i s s u e breakdown (Kader , 1986) . E l e v a t e d l e v e l s of carbon d i o x i d e may a l s o a c t to reduce the r e s p i r a t i o n r a t e . T h i s may be a r e s u l t of some u n c o u p l i n g e f f e c t of carbon d i o x i d e on o x i d a t i v e p h o s p h o r y l a t i o n , or the i n h i b i t i o n of some Krebs c y c l e enzymes (Monning, 1983) . The Krebs c y c l e i s the p r i n c i p a l pathway f o r c a r b o h y d r a t e and a c i d metabo l i sm under a e r o b i c c o n d i t i o n s , and r e s u l t s i n the g e n e r a t i o n of carbon d i o x i d e , water , and energy , as ATP ( F i g u r e 2 . 1 ) . I t s h o u l d be noted t h a t not a l l f r u i t s respond i n the same way to h i g h e r l e v e l s of c a r b o n d i o x i d e w i t h the r e s p i r a t i o n r a t e be ing reduced i n some f r u i t , wh i l e i t Increase s i n o t h e r s ( z e m l l a n u k h i n and Ivanov , 1978) . I t may be t h a t t h i s i s due to s t r e s s under h i g h carbon d i o x i d e t e n s i o n s . U l t r a s t r u c t u r a l changes i n the m i t o c h o n d r i a may a l s o be caused by h i g h carbon d i o x i d e c o n c e n t r a t i o n s ( F r e n k e l and P a t t e r s o n , 1977) . The maximum l e v e l of carbon d i o x i d e used i n MAP i s g e n e r a l l y about 20% carbon d i o x i d e ; however, t h i s i s dependent on the l e v e l of oxygen i n the atmosphere , as w e l l as the commodity i t s e l f (Kader , 1986) . C e r t a i n commodit ies have a 8 C H 3 C O ~ CoA = Acetylcoenzyme A CoA = Coenzyme A fc = Condensation enzyme fa = Aconitase fi = Isocitric enzyme fk = a-Ketoglutaric dehydrogenase fs = Succinic dehydrogenase ff = Fumarase fm = Malic dehydrogenase A F ' = Standard free energy change at pH7 F i g u r e 2.1 The Krebs C y c l e ( G a r d n e r , 1966) 9 v e r y low t o l e r a n c e f o r carbon d i o x i d e and undergo c a r b o n d i o x i d e damage under e l e v a t e d l e v e l s . 2 .2 .2 ETHYLENE BIOSYNTHESIS AND ACTION The gaseous c o m p o s i t i o n of the atmosphere w i l l a l t e r the r a t e and ex tent of e t h y l e n e b i o s y n t h e s i s (Kader , 1986; Z e m l l a n u k h i n and Ivanov, 1978). S ince e t h y l e n e i s a p l a n t hormone which r e g u l a t e s many a s p e c t s of growth , deve lopment , and senescence , and p l a y s a c e n t r a l r o l e l n the i n i t i a t i o n of r i p e n i n g , t h i s c o n t r o l can l e a d to Increased f r u i t s t o r a g e l i f e (Yang, 1985; K a d e r , 1986) . oxygen Is r e q u i r e d for e t h y l e n e p r o d u c t i o n and a c t i o n (Burg and B u r g , 1967; Burg and B u r g , 1969); t h e r e f o r e , decreases i n oxygen w i l l a f f e c t the r a t e s of these p r o c e s s e s . Increased c a r b o n d i o x i d e l e v e l s can r e d u c e , promote , or have no e f f e c t on e t h y l e n e p r o d u c t i o n r a t e s , depending on the p a r t i c u l a r f r u i t and the carbon d i o x i d e c o n c e n t r a t i o n . These e f f e c t s of oxygen and carbon d i o x i d e may be due to e f f e c t s on the enzyme systems i n v o l v e d i n e t h y l e n e b i o s y n t h e s i s (Kader , 1986) , p a r t i c u l a r l y the e t h y l e n e - f o r m i n g enzyme which e f f e c t s the c o n v e r s i o n of 1 - a m i n o - l - c y c l o p r o p a n e to e t h y l e n e (Yang, 1985) . In a d d i t i o n to i n f l u e n c i n g the r a t e of e t h y l e n e p r o d u c t i o n , h i g h l e v e l s of carbon d i o x i d e can a l s o i n f l u e n c e the response of f r e s h f r u i t s and v e g e t a b l e s to e t h y l e n e . For 10 example, s o f t e n i n g , i n c r e a s e d a b s c i s s i o n , and p h y s i o l o g i c a l d i s o r d e r s may be prevented or d e l a y e d under h i g h carbon d i o x i d e t e n s i o n s . Carbon d i o x i d e may compete w i t h e t h y l e n e f o r the b i n d i n g s i t e (Burg and B u r g , 1967) or i n h i b i t e t h y l e n e o x i d a t i o n to c a r b o n d i o x i d e v i a a feedback i n h i b i t i o n mechanism (Beyer , 1985) . 2 . 2 . 3 . COMPOSITIONAL CHANGES CA/MA can i n f l u e n c e the r a t e a t which c o m p o s i t i o n a l changes i n f r u i t s o c c u r , such as changes which i n f l u e n c e t h e i r c o l o u r , f l a v o u r , t e x t u r e . The r a t e o f b i o s y n t h e s i s and d e s t r u c t i o n of v a r i o u s p l a n t pigments i s a l t e r e d under CA/MAP c o n d i t i o n s . The l o s s of c h l o r o p h y l l i s s lowed down under CA/MA (Kader , 1986) , and c a r o t e n e d e g r a d a t i o n i n c a r r o t s i s reduced under low oxygen t e n s i o n ( B u r t o n , 1974) . The development of r e d c o l o u r i n tomatoes due to lycopene s y n t h e s i s i s prevented under c o n d i t i o n s of low oxygen and h i g h carbon d i o x i d e . However, once tomatoes are r e t u r n e d to a i r , lycopene b i o s y n t h e s i s resumes and the f r u i t deve lops normal c o l o u r i n g (Goodenough e t a l . , 1982) . I t i s g e n e r a l l y agreed t h a t the r a t e of a n t h o c y a n i n p r o d u c t i o n i n f r u i t s i s reduced under CA/MA c o n d i t i o n s (Kader , 1986) . With r e s p e c t to f r u i t t e x t u r e , CA/MA c o n d i t i o n s u s u a l l y d e l a y the s o f t e n i n g a s s o c i a t e d wi th r i p e n i n g and senescence . 11 I t appears t h a t e l e v a t e d carbon d i o x i d e l e v e l s i n the atmosphere i n c r e a s e s the r e t e n t i o n of f i rmness more than reduced oxygen l e v e l s , a l t h o u g h the mechanism i s u n c l e a r . I t may be due to a d e l a y i n the s y n t h e s i s of p o l y g a l a c t u r o n a s e , as has been demonstrated i n tomatoes . The reduced r e s p i r a t i o n r a t e under CA/MA may s u p p l y l e s s ATP to b i o s y n t h e t i c sys tems . The l a c k of p h o s p h o r y l a t e d molecu le s prevent s the t r a n s l a t i o n of preformed mRNA i n the f r u i t to enzyme p r o t e i n (Goodenough et a l . . , 1982) . Changes i n f r u i t and v e g e t a b l e c o n s t i t u e n t s , such as c a r b o h y d r a t e s , o r g a n i c a c i d s , p r o t e i n s and amino a c i d s , l i p i d s , and p h e n o l i c compounds w i l l i n f l u e n c e the f l a v o u r of the p r o d u c t . S i n c e CA/MA c o n d i t i o n s may upset the normal enzymic pathways of the f r u i t or v e g e t a b l e , i t f o l l o w s t h a t the s y n t h e s i s or d e g r a d a t i o n of compounds important i n f l a v o u r may be a l t e r e d . G e n e r a l l y , CA/MA m i t i g a t e changes i n these c o n s t i t u e n t s , t h e r e b y a i d i n g i n r e t a i n i n g f r e s h f l a v o u r . T h i s may be due i n p a r t to s u p p r e s s i o n of the Krebs c y c l e , which s lows down the d e p l e t i o n of c a r b o h y d r a t e and a c i d r e s e r v e s . I f the commodity i s exposed to a n a e r o b i c c o n d i t i o n s , however, o f f -f l a v o u r s and o f f - o d o u r s d e v e l o p due the p r o d u c t i o n of e t h a n o l , a c e t a l d e h y d e , and o ther l o w - m o l e c u l a r weight compounds from a n a e r o b i c r e s p i r a t i o n . Extended p e r i o d s of s t o r a g e under CA/MA c o n d i t i o n s can a l s o cause a decrease i n the r a t e of p r o d u c t i o n of v o l a t i l e s ( K a d e r , 1986) . Most s t u d i e s i n t o the e f f e c t s of CA/MA s t o r a g e of f r u i t s 12 and v e g e t a b l e s have g i v e n l i t t l e c o n s i d e r a t i o n to the e f f e c t s on n u t r i e n t r e t e n t i o n . I t i s known tha t such c o n d i t i o n s favour the r e t e n t i o n of v i t a m i n C (Kader , 1986) , and perhaps v i t a m i n A , as there i s l e s s o x i d a t i v e d e g r a d a t i o n of caro tene l n c a r r o t s i n low oxygen atmospheres (Burton 1974) . 2 .2 .4 WATER LOSS The packag ing m a t e r i a l a c t s as a p h y s i c a l b a r r i e r to water v a p o u r , w i t h i t s e f f e c t i v e n e s s i n t h i s c a p a c i t y b e i n g dependent on the m o i s t u r e vapour t r a n s m i s s i o n r a t e of the f i l m (Day, 1988) . T h i s a i d s i n the development and r e t e n t i o n of h i g h r e l a t i v e h u m i d i t i e s w i t h i n the packages , which are n e c e s s a r y for the r e t e n t i o n of t u r g o r l n f r u i t s and v e g e t a b l e s (Zagory and K a d e r , 1988) . Turgor i s an important f a c t o r a f f e c t i n g f r u i t appearance and t e x t u r e ; t h e r e f o r e , maintenance of t u r g o r d u r i n g s t o r a g e must be of prime c o n c e r n (Phan, 1987) . Condensa t ion of m o i s t u r e on the i n t e r n a l s u r f a c e of the package must be a v o i d e d as i t has an adverse a f f e c t on f i l m p e r m e a b i l i t y , which can r e s u l t i n the development of u n d e s i r a b l e a tmospheres . Some f i l m s used -in MAP a p p l i c a t i o n s c o n t a i n an a n t i - f o g compound to reduce the s u r f a c e t e n s i o n of water d r o p l e t s , c a u s i n g m o i s t u r e to spread more e v e n l y over the f i l m s u r f a c e (Day, 1988) . 2 . 2 . 5 EFFECTS OF MAP ON PHYSIOLOGICAL DISORDERS F r e s h f r u i t s and v e g e t a b l e s are s u s c e p t i b l e to a wide 13 v a r i e t y of p h y s i o l o g i c a l d i s o r d e r s which may be i n d u c e d , a l l e v i a t e d , or aggravated under MA/CA c o n d i t i o n s as shown i n T a b l e 2.1 (Kader , 1986) . 2 . 2 . 6 EFFECTS OF MAP ON MOLD GROWTH CA/MA s t o r a g e can reduce the i n c i d e n c e and s e v e r i t y of decay due to pathogens ( B r e c h t , 1980) . T h i s may be due to d i r e c t e f f e c t s of the atmosphere on pathogens , but i n most cases i s l i k e l y a t t r i b u t a b l e to the d e l a y e d r i p e n i n g of the f r u i t under such s t o r a g e c o n d i t i o n s , which r e n d e r s the f r u i t l e s s s u s c e p t i b l e to pathogen a t t a c k ( B u r t o n , 1978) . s i n c e decay r e s u l t s from an i n t e r a c t i o n between pathogen and h o s t , I t i s d i f f i c u l t t o de termine the p r e c i s e e f f e c t s of MA/CA c o n d i t i o n s on decay caused by pathogens ( B u r t o n , 1974) . The response of pure c u l t u r e s of pathogens to d i f f e r e n t atmospheres may d i f f e r from those i n a f r u i t - p a t h o g e n type of I n t e r a c t i o n ( F o l l s t a d , 1966) . I t i s g e n e r a l l y agreed t h a t carbon d i o x i d e i n s u f f i c i e n t c o n c e n t r a t i o n s can i n h i b i t the growth of s p o i l a g e molds ( H i n t l i a n and H o t c h k l s s , 1986); however, once c a r b o n d i o x i d e c o n c e n t r a t i o n s i n the atmosphere decrease to l e v e l s below 1%, molds resume t h e i r normal growth r a t e . W e l l s and Uota (1970) , s t u d i e d the e f f e c t s of MA on the g e r m i n a t i o n and growth of f i v e f u n g i ( A l t e r n a r i a t e n u i s , F u s a r l u m roseum, B o t r y t l s c l n e r e a , C l a d o s p o r i u m herbarum, and Rhlzopus s t o l o n i f e r ) , and found T a b l e 2.1 P h y s i o l o g i c a l S torage D i s o r d e r s of F r u i t s and V e g e t a b l e s D i s o r d e r s A l l e v i a t e d by C o n t r o l l e d / M o d i f i e d Atmospheres * R e d u c t i o n i n the s e v e r i t y of c h i l l i n g i n j u r y symptoms * R e d u c t i o n i n app le and pear s c a l d * R e d u c t i o n i n e t h y l e n e - i n d u c e d d i s o r d e r s D i s o r d e r s Aggravated by C o n t r o l l e d / M o d i f i e d Atmospheres * A g g r a v a t i o n of c h i l l i n g i n j u r y symptoms * A g g r a v a t i o n of c o m m o d i t y - s p e c i f i c d i s o r d e r s D i s o r d e r s Induced by C o n t r o l l e d / M o d i f i e d Atmospheres * Impaired r i p e n i n g * I n t e r n a l browning * E x t e r n a l brown d i s c o l o r a t i o n * S u r f a c e p i t t i n g * Increased s u c c i n i c a c i d ( K a d e r , 1986) 15 t h a t h i g h c o n c e n t r a t i o n s o f c a r b o n d i o x i d e suppressed m y c e l i a l growth i n most c u l t u r e s . The m y c e l i a l growth of A . t e n u i s , B. c i n e r e a , R. s t o l o n i f e r , and C . herbarum was i n h i b i t e d a p p r o x i m a t e l y 50% i n a 21% oxygen-20% carbon d i o x i d e atmosphere . However, under c o n d i t i o n s of l i m i t e d oxygen a v a i l a b i l i t y , c o n c e n t r a t i o n s of c a r b o n d i o x i d e s l i g h t l y above 0.03% g e n e r a l l y s t i m u l a t e d g e r m i n a t i o n and growth . Carbon d i o x i d e l e v e l s of g r e a t e r than 50% w i l l c o m p l e t e l y suppress f u n g a l r o t t i n g of b l a c k c u r r a n t s . However, i t must be noted t h a t not a l l commodit ies can w i t h s t a n d such h i g h carbon d i o x i d e l e v e l s ( B u r t o n , 1978). F r u i t t h a t e x h i b i t low t o l e r a n c e to carbon d i o x i d e undergo carbon d i o x i d e damage, which f a c i l i t a t e s the growth of f u n g i ( U l r i c h , 1975) . L e v e l s of c a r b o n d i o x i d e between 5 and 20% a c t to i n h i b i t mold growth by i n c r e a s i n g the l a g phase . The p r e c i s e mechanism of the i n h i b i t i o n i s not u n d e r s t o o d ; however, there are s e v e r a l p o s s i b l e e x p l a n a t i o n s : (1) carbon d i o x i d e i n t e r f e r e s w i t h c e r t a i n enzyme sys tems , most l i k e l y those i n v o l v e d i n s u c c i n a t e metabo l i sm; (2) c a r b o n d i o x i d e may cause a d e h y d r a t i o n of the c e l l membrane, thus impeding the passage of w a t e r - s o l u b l e food m a t e r i a l s i n t o the c e l l s ; (3) t h e r e may be a mass a c t i o n e f f e c t i n which carbon d i o x i d e i n t e r f e r e s w i th d e c a r b o x y l a t i o n . High c a r b o n d i o x i d e l e v e l s may a l s o i n c r e a s e g e r m i n a t i o n t imes ( C l a r k and T a k a c s , 1980) . U l r i c h (1975) i n d i c a t e d t h a t the growth of f u n g i i s r e t a r d e d under low oxygen t e n s i o n s , but t h a t the e f f e c t i s 16 s e l e c t i v e . S i m i l a r l y , Wel l s and Uota (1970) found t h a t oxygen l e v e l s of l e s s than 4% i n h i b i t e d the m y c e l i a l growth of most s p e c i e s s t u d i e d . F o l l s t a d (1966) had e a r l i e r i n d i c a t e d t h a t a t a tmospher i c oxygen l e v e l s of l e s s than 1%, the m y c e l i a l growth r a t e of f u n g a l c u l t u r e s d e c r e a s e d by up to 50%. I t was suggested t h a t i f low oxygen s t o r a g e i s t o be used t o c o n t r o l d e c a y , oxygen l e v e l s must be m a i n t a i n e d below 1%, w h i l e Burton (1974) i n d i c a t e d t h a t l e v e l s as low as 0.5% might be n e c e s s a r y . T h i s would p r e s e n t prob lems , as such an atmosphere would most l i k e l y l e a d to a s w i t c h to a n a e r o b i c r e s p i r a t i o n by the f r u i t , l e a d i n g to d e t e r i o r a t i o n of the commodity due to the a c c u m u l a t i o n o f the end p r o d u c t s of a n a e r o b i c r e s p i r a t i o n . i t becomes e v i d e n t t h a t a c a r e f u l ba lance must be s t r u c k between the l e v e l s of c a r b o n d i o x i d e and oxygen to c o n t r o l pathogen growth , and those which a d v e r s e l y a f f e c t the commodity. 2.3 CHERRY STORAGE Sweet c h e r r i e s (Prunus avium) are a v e r y p e r i s h a b l e commodity w i t h a v e r y s h o r t p o s t - h a r v e s t s t o r a g e l i f e i n c o n v e n t i o n a l c o l d s t o r a g e . Even w i t h good h a n d l i n g , the s t o r a g e l i f e of t h i s f r u i t i s l i m i t e d to a two-or three-week p e r i o d (Anderson and Hardenburg , 1977; Drake e_t a l . , 1988; Salunkhe and D e s a l , 1984) . T h e r e f o r e , r e l a t i v e l y l i t t l e t r u e c h e r r y s t o r a g e i s p r a c t i s e d ( P a t t e r s o n , 1981) . i t has u s u a l l y been the p r a c t i c e to g r a d e , pack , and s h i p the f r u i t as soon as p o s s i b l e a f t e r i t i s h a r v e s t e d , which i s i d e a l l y on the same 17 day . T h i s r e s u l t s i n a v e r y s h o r t m a r k e t i n g s e a s o n , i n which p o s t - h a r v e s t l o s s e s can be q u i t e h i g h ( P a t t e r s o n and M e l s t a d , 1977; sa lunkhe and D e s a i , 1984) . The s h o r t h a r v e s t p e r i o d c h a l l e n g e s marke t ing system c a p a c i t i e s ( P a t t e r s o n and M e l s t a d , 1977) . The two p r i n c i p a l modes o f p o s t - h a r v e s t d e t e r i o r a t i o n of sweet c h e r r i e s are water l o s s and the development of mold (Drake e_t a l _ . , 1988; Salunkhe and D e s a i , 1984) . Both the c h e r r y f r u i t and i t s stem c o n s i s t l a r g e l y of water , which i s l o s t r a p i d l y due to h i g h t r a n s p i r a t i o n r a t e s (Drake et_ a l . , 1988; Sharkey and P e g g i e , 1984) . The c h e r r y f r u i t has a v e r y poor moi s ture b a r r i e r ( s k i n ) ( P a t t e r s o n , 1981) . M o i s t u r e l o s s i s one of the most c r i t i c a l f a c t o r s a f f e c t i n g the appearance of both the f r u i t and the s tem. When m o i s t u r e i s l o s t , there i s subsequent s o f t e n i n g of the f r u i t and browning of the stem (Drake ejt a l . , 1988) . i n a d d i t i o n to the d e l e t e r i o u s e f f e c t s on c h e r r y appearance , m o i s t u r e l o s s a l s o r e p r e s e n t s a d i r e c t economic l o s s through weight l o s s . C h e r r i e s may l o s e up to 1.5% of t h e i r weight per hour i f exposed to wind d u r i n g t r a n s p o r t (Salunkhe and D e s a i , 1984) . P a t t e r s o n (1981) found t h a t c h e r r i e s l o s e weight a t the r a t e o f 1% per hour a t normal h u m i d i t y a t room t e m p e r a t u r e . Under the same c o n d i t i o n s , stems may l o s e 4% per h o u r . S i g n i f i c a n t p o s t - h a r v e s t l o s s e s of c h e r r i e s are a l s o a t t r i b u t a b l e to pathogen a t t a c k . The most common market d i s e a s e s of the c h e r r y are brown r o t , b lue mold r o t , A l t e r n a r l a r o t , C l a d o s p o r l u m r o t , g r a y mold r o t , and Rhlzopus r o t 18 (Salunkhe and D e s a i , 1984; R y a l l and P e n t z e r , 1974) . i n o r d e r to m i t i g a t e q u a l i t y d e t e r i o r a t i o n and a s s o c i a t e d p o s t - h a r v e s t l o s s e s o f sweet c h e r r y , good h a n d l i n g c o n d i t i o n s must be employed from the t ime of h a r v e s t . The c o n v e n t i o n a l s t o r a g e of c h e r r i e s i n v o l v e s p r e - c o o l i n g the f r u i t o to as near as 0 C as p o s s i b l e a f t e r h a r v e s t , and h o l d i n g i t a t o -1 to 0 C d u r i n g s t o r a g e (Anderson and Hardenburg , 1977; R y a l l and P e n t z e r , 1974) . While such low temperature treatment i s b e n e f i c i a l t o c h e r r y l o n g e v i t y , pro longed c o l d s t o r a g e may cause s u r f a c e p i t t i n g (Chen e t a l . , 1981; Salunkhe and D e s a i , 1984), a common p h y s i o l o g i c a l d i s o r d e r . L o n g , i r r e g u l a r l y -shaped brownish p i t s appear on the c h e r r y s k i n , and the f l e s h beneath these s p o t s t u r n s brown and d r i e s o u t , l e a v i n g s m a l l . c a v i t i e s which l e a d to a poor appearance of the f r u i t ( P o r r i t t et a l _ . , 1971) . 2.4 ATMOSPHERE MODIFICATION AND SWEET CHERRY STORAGE The MAP s t o r a g e of c h e r r i e s i s de s igned to reduce p o s t -h a r v e s t l o s s e s and i n c r e a s e t h e i r s torage l i f e . A v a r i e t y of s t u d i e s has been conducted i n v o l v i n g the CA s t o r a g e o f sweet c h e r r i e s ; however, i t appears t h a t no s t u d i e s have been performed to de termine the f e a s i b i l i t y of u s i n g MAP to extend the s t o r a g e l i f e of c h e r r i e s . Q u a l i t y f a c t o r s f o r c h e r r i e s i n c l u d e p e r c e n t s o l u b l e s o l i d s , t o t a l a c i d i t y and a c i d components, aroma components , 19 and p h e n o l i c c o n t e n t ( P o l l , 1986) . In a d d i t i o n , the c h e r r i e s shou ld be b r i g h t r e d (and dark r e d , i n the case of "Lambert" c h e r r i e s ) i n c o l o u r and have a g l o s s y s k i n . The f r u i t s h o u l d be plump w i t h f r e s h , green stems ( R y a l l and P e n t z e r , 1974) . I f MAP a i d s i n the maintenance of these c h a r a c t e r i s t i c s , i t o n l y f o l l o w s t h a t i t enhances the r e t e n t i o n of c h e r r y q u a l i t y . I t has been found t h a t the CAS of c h e r r i e s extends t h e i r s t o r a g e l i f e (Chen e t a l . , 1981; S ingh et a l . , 1970; P o r r i t t and Mason, 1965; Schomer and O l s e n , 1964). Recent r e s e a r c h has i n d i c a t e d t h a t MAP r e s u l t s i n a s i m i l a r e x t e n s i o n of c h e r r y s t o r a g e l i f e (Powrie e t a l . , 1987) . However, l i t t l e has been p u b l i s h e d r e g a r d i n g the p h y s i c o - c h e m i c a l changes o c c u r r i n g i n c h e r r y f r u i t s p e c i f i c a l l y under MAP s torage c o n d i t i o n s . Sweet c h e r r i e s t o l e r a t e v e r y h i g h c o n c e n t r a t i o n s of c a r b o n d i o x i d e i n t h e i r s t o r a g e atmospheres (Anderson and Hardenburg , 1977; P a t t e r s o n and M e l s t a d , 1977) . Thus d r y i c e has been added to c a r l o a d s of c h e r r i e s to augment c a r b o n d i o x i d e l e v e l s d u r i n g t r a n s p o r t (Schomer and O l s e n , 1964) . A n a t u r a l e x t e n s i o n of t h i s was the use of s e a l e d p o l y e t h y l e n e box l i n e r s to r e t a r d m o i s t u r e l o s s i n the f r u i t d u r i n g s h i p p i n g and to c r e a t e h i g h c a r b o n d i o x i d e and low i n oxygen atmospheres ( R y a l l and P e n t z e r , 1974) . Whi le the low oxygen t e n s i o n s u s u a l l y used i n CAS may favour c h e r r y l o n g e v i t y , Schomer and O l s e n (1964) sugges ted t h a t the b e n e f i c i a l e f f e c t s of CAS on "Lambert" c h e r r y s t o r a g e l i f e i s p r i n c i p a l l y a t t r i b u t a b l e to the i n c r e a s e d l e v e l s of carbon d i o x i d e . They found t h a t a low 20 (3%) l e v e l of oxygen wi thout carbon d i o x i d e had no b e n e f i c i a l e f f e c t on c h e r r y s t o r a g e l i f e . The bes t responses to CA are o b t a i n e d w i t h sound, h i g h q u a l i t y f r u i t t h a t has been prompt ly c o o l e d a f t e r h a r v e s t , and o t h a t has been m a i n t a i n e d a t a temperature of - 1 . 1 to 0 C d u r i n g the s t o r a g e p e r i o d . The major b e n e f i t s ga ined through the CAS of sweet c h e r r i e s are a s u p p r e s s i o n of decay , maintenance of f i r m n e s s , % s o l u b l e s o l i d s , pH, and t i t r a t a b l e a c i d i t y l e v e l s , r e d u c t i o n i n the r e s p i r a t i o n r a t e , and a s u p p r e s s i o n of a n t h o c y a n i n s y n t h e s i s ( P a t t e r s o n , 1981; Schomer and O l s e n , 1964; R y a l l and P e n t z e r , 1974; S k r y p n i k e_t a l . , 1985) . Sweet c h e r r i e s d e t e r i o r a t e q u i c k l y under c o n v e n t i o n a l r e f r i g e r a t i o n c o n d i t i o n s , l o s i n g c o l o u r and f l a v o u r , as w e l l as becoming moldy and w i t h e r e d ( R y a l l and P e n t z e r , 1974; sa lunkhe and D e s a i , 1984) . However, MA c o n d i t i o n s have been found to m a i n t a i n the f r e s h appearance of the f r u i t ( R y a l l and P e n t z e r , 1974) . Atmospheres c o n t a i n i n g 10% carbon d i o x i d e and reduced oxygen l e v e l s r e s u l t e d i n b e t t e r r e t e n t i o n of f l a v o u r , as compared t o c o n t r o l f r u i t (Schomer and O l s e n , (1964) . The e x t e n s i o n of c h e r r y s t o r a g e l i f e under CA c o n d i t i o n s i s l i k e l y due i n p a r t to an a l t e r a t i o n i n the r e s p i r a t i o n r a t e of the f r u i t . C h e r r i e s s t o r e d under CA c o n d i t i o n s d i s p l a y lower r e s p i r a t i o n r a t e s than f r u i t i n c o n v e n t i o n a l c o l d s t o r a g e (S ingh et a l . , 1970; P a t t e r s o n , 1981). P a t t e r s o n (1981) found t h a t a r e s i d u a l s u p p r e s s i o n of r e s p i r a t i o n r a t e remained p o s t -t r e a t m e n t , and may account for the f r e s h e r appearance of f r u i t 21 o a f t e r two days a t 20 C f o l l o w i n g s t o r a g e i n 10% carbon d i o x i d e as compared to f r u i t s t o r e d i n a i r (Schomer and O l s e n , 1964) . S ingh ejb al_. (1970) s t u d i e d the e f f e c t s of CAS on o r g a n i c a c i d s i n "Lambert" sweet c h e r r i e s . These r e s e a r c h e r s found t h a t the l e v e l o f a c i d i t y i n c r e a s e d under CAS as compared to f r u i t s t o r e d i n c o n v e n t i o n a l c o l d s t o r a g e . T h i s o b s e r v a t i o n i s i n c l o s e agreement w i t h the f i n d i n g s of Schomer and O l s e n (1964) t h a t c o n v e n t i o n a l l y s t o r e d c h e r r i e s l o s e a c i d i t y more q u i c k l y than CAS c h e r r i e s . The observed i n c r e a s e i n a c i d i t y r e p o r t e d by S i n g h e_t al_. (1970) was a t t r i b u t e d to a s u p p r e s s i o n of the r e s p i r a t o r y r a t e of the f r u i t , which l e a d to an a c c u m u l a t i o n of o r g a n i c a c i d s i n v o l v e d i n the Krebs c y c l e . The r e t e n t i o n of r e d c o l o u r by c h e r r i e s i s improved under CA c o n d i t i o n s (Chen e t a l _ . , 1981) . P a t t e r s o n (1981) i n d i c a t e d t h a t c h e r r i e s s t o r e d a t low temperature and under low oxygen, h i g h c a r b o n d i o x i d e , and low p r e s s u r e c o n d i t i o n s , undergo l e s s c o l o u r development than s i m i l a r samples s t o r e d i n a i r . Chen e t a l . (1981) i n v e s t i g a t e d the e f f e c t s of low oxygen and low temperature on c o l o u r r e t e n t i o n i n "Bing" sweet c h e r r i e s , and found t h a t f r u i t s t o r e d a t 0.5 to 2.0% oxygen i n the atmosphere m a i n t a i n e d b r i g h t e r c o l o u r than f r u i t s t o r e d i n a i r a t the same temperature a f t e r 35 days of s t o r a g e . S i m i l a r r e s u l t s were o b t a i n e d f o r c h e r r i e s s t o r e d i n a 10% oxygen and 20% carbon d i o x i d e atmosphere . S k r y p n i k e t a l . (1985) s t u d i e d the s t o r a g e of U k r a n l a n v a r i e t i e s of sweet c h e r r y i n atmospheres c o n t a i n i n g 5 or 8% c a r b o n d i o x i d e and found t h a t 22 they accumulated a n t h o c y a n i n s , which c o n t r i b u t e the red c o l o u r to c h e r r i e s , more s l o w l y than i n a i r . S ince the c o n c e n t r a t i o n of a n t h o c y a n i n s i n c r e a s e s r a p i d l y i n c h e r r i e s as they r e a c h m a t u r i t y (Van B u r e n , 1971) , i t may be t h a t the s u p p r e s s i o n of r i p e n i n g and senescence by m o d i f i c a t i o n of the atmosphere may account for the r e d u c t i o n i n a n t h o c y a n i n b i o s y n t h e s i s . At e x c e e d i n g l y h i g h l e v e l s of carbon d i o x i d e , carbon d i o x i d e i n j u r y may r e s u l t , c a u s i n g the d a r k e n i n g of the f r u i t to be hastened ( P a t t e r s o n and M e l s t a d , 1977) . C A - s t o r e d c h e r r i e s have been shown to r e t a i n a c c e p t a b l e t e x t u r e , w i t h f i rmness v a l u e s a c t u a l l y I n c r e a s i n g over an extended s t o r a g e p e r i o d as compared to c o n v e n t i o n a l l y s t o r e d f r u i t . Oxygen l e v e l s of l e s s than 10% appear to a c c e l e r a t e s o f t e n i n g , w h i l e 20% c a r b o n d i o x i d e a l l o w s f o r s u p e r i o r r e t e n t i o n of f r u i t f i rmness ( P a t t e r s o n , 1981) . Stem c o n d i t i o n i s an important q u a l i t y f a c t o r o f c h e r r i e s . They s h o u l d remain t u r g i d and g r e e n ; however, they q u i c k l y become s h r i v e l l e d and brown i n c o l o u r d u r i n g s t o r a g e (S iege lman, 1953) . The p r i n c i p a l cause of t h i s s h r i v e l l i n g and d i s c o l o r a t i o n i s water l o s s (Drake e t a l _ . , 1988) . S iege lman (1953) sugges ted t h a t browning i s due to an a c c u m u l a t i o n of brown pigments which mask the c h l o r o p h y l l . T h i s may occur v i a an enzyme-mediated r e a c t i o n , o c c u r r i n g as a r e s u l t o f i n j u r y to the s tem. i n j u r y to stems a l s o a c c e l e r a t e s m o i s t u r e l o s s (S iege lman , 1953) . Chen e_t al_. (1981) found t h a t low oxygen (0 .5 to 2.0%) c o n d i t i o n s a i d e d i n the r e t e n t i o n of the green 23 c o l o u r i n s tems. The r a p i d l o s s of m o i s t u r e from c h e r r y f r u i t and c h e r r y stems i s due to the h i g h r a t e of t r a n s p i r a t i o n and low m o i s t u r e b a r r i e r s . CAS may a i d i n c o n t r o l l i n g water l o s s by r e d u c i n g the r a t e of t r a n s p i r a t i o n . The ex tent of r e d u c t i o n i s h i g h l y dependent on the p e r m e a b i l i t y of the packag ing m a t e r i a l u s e d , as w e l l as the temperature of the s t o r a g e environment (Salunkhe and D e s a i , 1984) . packag ing f i l m s w i t h low water vapour t r a n s m i s s i o n r a t e s p r o v i d e environments f o r the r e t e n t i o n of f r u i t m o i s t u r e d u r i n g s t o r a g e . Sharkey and Peggie (1984) found t h a t the s t o r a g e of "Lambert" c h e r r i e s under c o n d i t i o n s of h i g h r e l a t i v e h u m i d i t y (RH) (95-99%) i n a i r m a i n t a i n e d greenness and t u r g i d l t y i n c h e r r y s tems. Schomer and O l s e n (1964) found an atmosphere c o n t a i n i n g 10% carbon d i o x i d e to be e f f e c t i v e i n r e t a i n i n g stem t u r g i d l t y d u r i n g the s t o r a g e of "Lambert" c h e r r i e s . Presumably h i g h RH w i t h i n the package i n c o n c e r t w i t h a tmospher i c gas components c o n t r i b u t e to the p r e s e r v a t i o n of stem q u a l i t y . CAS of c h e r r i e s i s r e p o r t e d l y e f f e c t i v e i n c o n t r o l l i n g f u n g a l r o t t i n g (Schomer and O l s e n , 1964; P a t t e r s o n and M e l s t a d , 1977) , t h e r e b y r e d u c i n g p o s t - h a r v e s t l o s s e s . Schomer and O l s e n (1964) found t h a t an atmosphere c o n t a i n i n g 10% c a r b o n d i o x i d e a t low temperatures reduced the i n c i d e n c e of decay due to mold as compared to c o n t r o l f r u i t i n a i r ; however, mold deve loped q u i c k l y upon removal of the f r u i t from s t o r a g e to a i r a t ambient t e m p e r a t u r e . 2 4 P a t t e r s o n and M e l s t a d (1977) I n d i c a t e d t h a t CAS reduced the amount of decay i n sweet c h e r r i e s d u r i n g an e ight -week s t o r a g e p e r i o d , wh i l e t h e r e was an a p p r e c i a b l e amount of decay i n c o n t r o l samples a f t e r o n l y f i v e weeks of s t o r a g e . I t was suggested t h a t the i n c r e a s e d l e v e l s of carbon d i o x i d e s u b s t a n t i a l l y i n h i b i t e d the growth of a l l m i c r o o r g a n i s m s . There i s l i t t l e documentat ion on the e f f e c t s of CAS on the s e n s o r y a t t r i b u t e s o f c h e r r y f r u i t . i n an e a r l y s t u d y by Schomer and O l s e n (1964) , I t was found t h a t a f t e r 50 days of s t o r a g e i n 10% c a r b o n d i o x i d e , the f l a v o u r d e c l i n e d to a f a i r r a t i n g but was s u p e r i o r to t h a t of the c o n t r o l f r u i t . P a t t e r s o n and M e l s t a d (1977) a l s o i n d i c a t e d t h a t CAS p r e s e r v e d the s e n s o r y q u a l i t y of c h e r r y f r u i t d u r i n g extended s t o r a g e . F r u i t s t o r e d i n 0 to 40% carbon d i o x i d e atmospheres r e t a i n e d an a c c e p t a b l e f l a v o u r , comparable to t h a t of f r e s h l y h a r v e s t e d f r u i t , through to the s i x t h week of s t o r a g e , a f t e r which f l a v o u r d e t e r i o r a t e d r a p i d l y . Samples s t o r e d i n 60% carbon d i o x i d e deve loped a s l i g h t o f f - f l a v o u r i n the f i r s t week, w i t h f l a v o u r becoming p r o g r e s s i v e l y worse w i t h i n c r e a s e d s t o r a g e t i m e . T h i s r e s u l t was l i k e l y due to a s h i f t to a n a e r o b i c r e s p i r a t i o n i n the f r u i t . 2 .5 CHEMICAL CONSTITUENTS OF CHERRIES 2 . 5 . 1 PHENOLIC COMPOUNDS The major importance of p h e n o l i c compounds i n f r u i t s i s 25 t h e i r c o n t r i b u t i o n t o f l a v o u r and c o l o u r . W i t h i n the g e n e r a l group of p h e n o l i c compounds, there are s e v e r a l c l a s s e s . These i n c l u d e a n t h o c y a n i n s , l e u c o - a n t h o c y a n i n s , f l a v o n o i d s , and c i n n a m l c a c i d d e r i v a t i v e s , such as c h l o r o g e n i c a c i d s . Cinnamic a c i d d e r i v a t i v e s and the f l a v i n s u s u a l l y predominate i n f r u i t s and are more u n i f o r m l y d i s t r i b u t e d throughout t i s s u e s than a n t h o c y a n i n s , which are o f t e n c o n c e n t r a t e d i n the s k i n (Van B u r e n , 1971) . The l e v e l s of p h e n o l i c compounds i n f r u i t s v a r y w i t h a number of f a c t o r s , such as s p e c i e s and v a r i e t y , as w e l l as w i th the degree of m a t u r i t y . The c o n c e n t r a t i o n of p h e n o l i c s i n f r u i t g e n e r a l l y decreases w i t h i n i n c r e a s i n g m a t u r i t y , due to f r u i t en largement , but the amount per f r u i t a c t u a l l y i n c r e a s e s (Van B u r e n , 1971) . P h e n o l i c compounds are produced In p l a n t s through a number of b i o s y n t h e t i c pathways. The main s t e p s i n c l u d e : (1) the f o r m a t i o n of c i n n a m i c a c i d s ; (2) the c o n d e n s a t i o n of a c y l groups to b u i l d the *A* phenyl r i n g ; and (3) t r a n s f o r m a t i o n s l e a d i n g to the v a r i o u s f l a v o n o i d s (Van B u r e n , 1971) . Cinnamic a c i d s are formed through the s h i k i m i c a c i d pathway v i a the c o n d e n s a t i o n of phospheno lpyruvate w i t h D-e r y t h r o s e - 4 - p h o s p h a t e to generate a h e p t u l o s o n i c a c i d . The h e p t u l o s o n l c a c i d i s c y c l i z e d to form 5 - d e h y d r o q u i n i c a c i d , an i n t e r m e d i a t e i n the f o r m a t i o n of both s h i k i m i c and q u i n i c a c i d s . The a d d i t i o n of a c e t y l and m a l o n y l groups to the C6:C3 s t r u c t u r e of c i n n a m i c a c i d s p r o v i d e s the carbons of the e v e n t u a l * A' pheny l r i n g . Condensa t ion r e q u i r e s the 26 p a r t i c i p i t a t i o n of Coenzyme A . H y d r o x y l a t i o n , m e t h y l a t i o n , and g l y c o s y l a t i o n of c i n n a m i c a c i d proceeds v i a a s e r i e s of enzyme-mediated r e a c t i o n s (Van B u r e n , 1971) ( F i g u r e 2 . 2 ) . The p h e n o l i c compounds i n sweet c h e r r i e s i n c l u d e c a t e c h l n s , p r o a n t h o c y a n i n s , hydroxyc innamic a c i d d e r i v a t i v e s , f l a v o n o l g l y c o s i d e s , and a n t h o c y a n l n s (Table 2 . 2 ) . The p -c o u m a r o y l q u i n i c a c i d s may c o n s t i t u t e more than h a l f of the t o t a l h y d r o x y c l n n a m o y l q u i n i c a c i d s p r e s e n t . Other c i n n a m i c a c i d d e r i v a t i v e s i n c l u d e e s t e r s of c a f f e i c , p - c o u m a r l c , and f e r u l i c a c i d s ( M o l l e r and Herrmann, 1983). I t i s h i g h l y u n l i k e l y t h a t p l a n t p h e n o l i c s p l a y a s i g n i f i c a n t r e s p i r a t o r y r o l e i n normal t i s s u e . However, they may undergo changes mediated by p o l y p h e n o l o x i d a s e (PPO). I t s major s u b s t r a t e s are hydroxyc innamic a c i d e s t e r s and monomeric and d i m e r i c f l a v a n s . Whi le t h e i r o x i d a t i o n p r o d u c t s are not p a r t i c u l a r l y d a r k , these p r o d u c t s can o x i d i z e o ther f r u i t components such as a n t h o c y a n l n s to s i g n i f i c a n t l y a f f e c t p r o d u c t c o l o u r (Van B u r e n , 1971) . MA c o n d i t i o n s a f f e c t the b i o s y n t h e s i s o f p h e n o l i c compounds. S i r l p h a n i c h and Kader (1985) found t h a t the t o t a l p h e n o l i c s i n l e t t u c e s t o r e d under e l e v a t e d c a r b o n d i o x i d e l e v e l s d i d not change s i g n i f i c a n t l y , but the t o t a l p h e n o l i c s i n c o n t r o l ( a i r ) samples i n c r e a s e d r a p i d l y by 50% from the o r i g i n a l l e v e l , and then remained s t a b l e . T h u s , they c o n c l u d e d t h a t c a r b o n d i o x i d e suppresses the p r o d u c t i o n of p h e n o l i c compounds i n p l a n t t i s s u e s . Carbon d i o x i d e i s assumed to have 27 COOH CHO COOH COPO.H, HCOH 6-0 i s ' CH 2 + HCOH ~ ~ * CHZ CHjOPOjHj HO4H H6OH HCOH QUINIC ACIO CHJOPOJHJ PHOSPHO-ENOlr PYRUVATE O-ERYTHROSE DAHP -1-PHOSPHATE COOH; COOH S-PHOSPHOSHIKIMIC ACIO SHIKIMIC ACIO 5- OEHYDROSHIKIUIC ACIO \ COOH CH, OH I COOH c=o H00C CH, 3- (ENOLPYRUVATE ETHER) Of PHOSPHOSHIKIUIC ACIO 0 NH2 CHj- C-CO0H CHj-CH-COOH OH PREPHENIC ACID L- PHENYLALANINE HC-CH-COOH OH P-COUMARIC ACID HC-CH-COOH CINNAMC ACIO F i g u r e 2.2 B i o s y n t h e s i s of c i n n a m i c A c i d s (Van B u r e n , 1971) 28 T a b l e 2.2 The P r i n c i p a l P h e n o l i c Compounds of sweet c h e r r i e s ( P r u n u 3 av ium s p . ) PHENOL PREDOMINANT COMPOUND F l a v a n s ( + ) - c a t e c h i n ( - ) - e p i c a t e c h i n Anthocyan ins C y a n i d i n - 3 - r u t i n o s i d e C y a n i d i n - 3 - g l u c o s i d e P e o n i d i n - 3 - g l u c o s i d e P e o n i d i n - 3 - r u t i n o s i d e F l a v a n o l G l y c o s i d e s Q u e r c e t i n - 3 - r u t i n o s i d e Cinnamic A c i d D e r i v a t i v e s 3 • - p - c o u m a r o y l q u i n i c a c i d 3 ' - c a f f e o y l q u i n i c a c i d S o u r c e s : deMan (1982) M o l l e r and Herrman (1983) Van Buren (1971) 29 I n h i b i t e d some s t e p ( s ) In the pathway o £ p h e n o l i c metabo l i sm a t a p o i n t where the h y d r o x y l group has not yet been i n c o r p o r a t e d , such as the c o n v e r s i o n of c i n n a m i c a c i d to 4 -hydroxyc innamic a c i d , b l o c k i n g the p r o d u c t i o n of new p h e n o l i c compounds. 2 .5 .2 ANTHOCYANINS - OCCURRENCE AND ANALYSIS A n t h o c y a n i n s are w a t e r - s o l u b l e pigments found as g l y c o s i d e s i n p l a n t m a t e r i a l . The c o l o u r of a g i v e n commodity c o n t a i n i n g a n t h o c y a n i n s i s I n f l u e n c e d by the type and c o n c e n t r a t i o n s of the a n t h o c y a n i n s presen t (Jackman e t a l . , 1987) . The major a n t h o c y a n i n s l n c h e r r i e s are l i s t e d i n T a b l e 2 .2 . The hue and i n t e n s i t y of c o l o u r of a n t h o c y a n i n s i s p H -dependent . At a pH of 1 .0 , a n t h o c y a n i n s (Acy) e x i s t l n the h i g h l y c o l o u r e d oxonium s a l t or f l a v y l i u m i o n form, which ranges from orange to r e d , wh i l e a t pH 4 . 5 , Acy e x i s t p r e d o m i n a n t l y i n the c o l o u r l e s s c a r b i n o l base form. At pH v a l u e s of 7 or 8, the anhydro q u i n o i d a l base form accounts for the b lue c o l o u r ( F i g u r e 2.3) ( W r o l s t a d , 1976) . The low pH of c h e r r i e s a s s u r e s t h a t the red f l a v y l i u m i o n form of a n t h o c y a n i n s w i l l predominate , l e n d i n g a r e d c o l o u r t o the f r u i t . T y p i c a l l y , Acy are measured a t pH 1 .0 , where t h e y are most s t r o n g l y c o l o u r e d . However, as has been demonstrated l n c r a n b e r r i e s and c h e r r i e s , a c o n s i d e r a b l e amount of brownish 30 d e g r a d a t i o n p r o d u c t s can accumulate d u r i n g s t o r a g e ( F u l e k i and F r a n c i s , 1968b; P o l e s e l l o and B o n z i n i , 1977) . A l t h o u g h these d e g r a d a t i o n p r o d u c t s have a b s o r p t i o n maxima i n the 400-440 nm r a n g e , they a l s o absorb to a c e r t a i n ex tent a t 510 nm. S i n c e TAcy measurements are n o r m a l l y made a t 510 nm (the a b s o r p t i o n maximum for A c y ) , the presence of brownish d e g r a d a t i o n p r o d u c t s c o u l d r e s u l t i n anomalous ly h i g h v a l u e s f o r TAcy b e i n g o b s e r v e d . In such c a s e s , a pH d i f f e r e n t i a l method i n v o l v i n g the measurement of Acy a t 510 nm on e x t r a c t s a t both pH 1.0 and pH 4.5 i s u sed , such t h a t d e g r a d a t i o n p r o d u c t s may be accounted for ( F u l e k i and F r a n c i s , 1968b) . 2 .5 .3 ORGANIC ACIDS AND THEIR DETERMINATION 2 . 5 . 3 . 1 GENERAL BIOCHEMISTRY AND THE EFFECTS OF MAP ON ORGANIC ACID LEVELS IN FRUITS AND VEGETABLES O r g a n i c a c i d s are Important c o n s t i t u e n t s i n p l a n t f o o d s , and p l a y a major r o l e i n d e t e r m i n i n g the f l a v o u r , s t a b i l i t y , and keep ing q u a l i t i e s of such foods ( P i c h a , 1985) . O r g a n i c a c i d s are i n a c o n s t a n t m e t a b o l i c f l u x i n most f r u i t s . G e n e r a l l y , the o v e r a l l a c i d i t i e s of f r u i t s d e c l i n e d u r i n g r i p e n i n g ( a l t h o u g h some I n d i v i d u a l a c i d s may i n c r e a s e ) , and tend to d i m i n i s h d u r i n g the f i n a l senescence of most p l a n t t i s s u e s (Haard , 1976) . As s u c h , i t has been proposed t h a t o r g a n i c a c i d s may s erve as an index of m a t u r i t y , r i p e n e s s , or s p o i l a g e i n c e r t a i n commodit ies ( P i c h a , 1985). 31 AH = F L A V Y L I U M C A T I O N ( R E D ) B = C A R B I N O L P S E U D O B A S E ( C O L O U R L E S S ) C = C H A L C O N E ( C O L O U R L E S S ) A = Q U I NO I D A L A N H Y D R O B A S E ( B L U E ) R 3 , R 5 = H, OH, OR 0CH 3 6 L Y = G L Y C O S Y L M O I E T Y F i g u r e 2.3 S t r u c t u r a l T r a n s f o r m a t i o n s of A n t h o c y a n i n s w i t h pH (adapted from B r o u l l l a r d and D e l a p o r t e , 1977) 32 A wide range of o r g a n i c a c i d s occur i n p l a n t t i s s u e . Many a r e p r e s e n t o n l y i n s m a l l q u a n t i t i e s , o c c u r r i n g p r i m a r i l y as i n t e r m e d i a t e s i n a v a r i e t y of m e t a b o l i c pathways, such as the Krebs c y c l e , the s h i k i m i c a c i d pathway and the g l y o x y l i c a c i d pathway. Other o r g a n i c a c i d s can o c c u r , and w h i l e t h e y may accumulate i n s i g n i f i c a n t amounts i n p l a n t t i s s u e s , they do not appear to have p h y s i o l o g i c a l s i g n i f i c a n c e and have not been l i n k e d to any m e t a b o l i c pathways (Haard , 1976) . O r g a n i c a c i d s are generated i n the Krebs c y c l e d u r i n g the a e r o b i c o x i d a t i o n of c a r b o h y d r a t e s , f a t s , and p r o t e i n s i n most b i o l o g i c a l systems ( P i c h a , 1985) , which account s f o r t h e i r d e c l i n e d u r i n g r i p e n i n g and senescence . s i n c e o r g a n i c a c i d s can a l t e r the metabo l i sm of p l a n t hormones, they are i m p l i c a t e d i n the c o n t r o l of senescence ( H a a r d , 1976) . The metabo l i sm (and thus l e v e l s ) of o r g a n i c a c i d s change w i t h m o d i f i c a t i o n s to the atmosphere s u r r o u n d i n g a commodity. F r u i t s p r e s e r v e d i n a c o n t r o l l e d gaseous environment g e n e r a l l y have a h i g h e r l e v e l of a c i d i t y than do those s t o r e d In a i r . T h i s r e d u c t i o n i n the l o s s of a c i d i t y In f r u i t s can have a profound i n f l u e n c e on the f l a v o u r of the s t o r e d commodity (Kader , 1986; M e t l i t s k i i e t a l . , 1983) . H igher t i t r a t a b l e a c i d i t y and lower pH v a l u e s are m a i n t a i n e d i n C A - s t o r e d f r u i t as compared to those v a l u e s observed i n f r u i t s t o r e d i n a i r (Kader , 1986) . The dynamics of o r g a n i c a c i d s i n C A - s t o r e d f r u i t s i s i n f l u e n c e d by a t l e a s t two f a c t o r s . The f i r s t of these i s the 33 proces s which i n h i b i t s the l o s s of a c i d i t y f o l l o w i n g the u s u a l r e d u c t i o n i n o v e r a l l metabol i sm observed i n C A - s t o r e d f r u i t s . In p a r t i c u l a r , the o x i d a t i v e metabol i sm of o r g a n i c a c i d s i s i n h i b i t e d under c o n d i t i o n s of CA s t o r a g e , l i k e l y due to the low oxygen c o n d i t i o n s n o r m a l l y employed ( M e t l i t s k i i e t a l . , 1983) . The l e v e l s of o r g a n i c a c i d s i n C A - s t o r e d f r u i t s are a l s o I n f l u e n c e d by the s y n t h e s i s of o r g a n i c a c i d s f o l l o w i n g the h e t e r o t r o p i c a s s i m i l a t i o n of carbon d i o x i d e . R a d i o - l a b e l l i n g 14 exper iments have shown t h a t h a l f of the CO absorbed i s used 2 i n the f o r m a t i o n of m a l i c a c i d , wh i l e some i s a l s o i n c o r p o r a t e d i n t o o ther o r g a n i c a c i d s and amino a c i d s ( M e t l i t s k i i e_t a l . , 1983) . The d e c a r b o x y l a t i o n of m a l i c a c i d to p y r u v i c a c i d by malate dehydrogenase i s i n h i b i t e d i n the presence of c a r b o n d i o x i d e , p r e v e n t i n g the decrease i n m a l i c a c i d p o o l s ( Z e m l l a n u k h i n and Ivanov, 1978). At h i g h enough c o n c e n t r a t i o n s of carbon d i o x i d e , the r e a c t i o n may be r e v e r s e d , t h e r e b y p r o d u c i n g m a l i c a c i d . Thus , m a l i c a c i d l e v e l s tend to be h igher i n C A - s t o r e d f r u i t s than i n f r u i t s s t o r e d i n a i r ( M e t l i t s k i i e t a j , . , 1983) . The s t o r a g e of some f r u i t s i n CA/MA c o n d i t i o n s l eads to an i n c r e a s e i n the l e v e l s of s u c c i n i c a c i d . Carbon d i o x i d e i n j u r y of a p p l e s i n s t o r a g e i s preceded by an Increase i n the l e v e l of s u c c i n i c a c i d s l n the t i s s u e (Monning, 1983) . S i m i l a r l y , the s t o r a g e of grapes i n atmospheres c o n t a i n i n g 5-15% carbon d i o x i d e r e s u l t s i n the a c c u m u l a t i o n of s u c c i n i c , 34 among o ther a c i d s (Kader , 1986) . T h i s may be due to the i n h i b i t i o n of the s u c c i n a t e dehydrogenase enzyme ( Z e m l i a n u k h i n and i v a n o v , 1978). Monning (1983) s t u d i e d the e f f e c t s of 5 and 10% carbon d i o x i d e of the a c t i v i t y of Krebs c y c l e enzymes and the l e v e l s of Krebs c y c l e a c i d s u s i n g r a d i o - l a b e l l e d s u c c i n i c a c i d , m a l i c a c i d , and g l u c o s e as s u b s t r a t e s . They found t h a t c o n t r o l samples showed h i g h e r r e s p i r a t i o n r a t e s and an i n c r e a s e i n the r a t e of c o n v e r s i o n of s u c c i n i c a c i d i n t o o ther Krebs c y c l e a c i d s , as compared to those samples s t o r e d i n c a r b o n d i o x i d e -r i c h a tmospheres . The same phenomenon h e l d t r u e f o r the uptake of other Krebs c y c l e a c i d s used as s u b s t r a t e s (Monning, 1983) . The e f f e c t s of e x c e e d i n g l y h i g h c o n c e n t r a t i o n s of carbon d i o x i d e on p l a n t metabo l i sm cannot be a t t r i b u t e d s o l e l y to the c r e a t i o n of an h y p o x i c s t a t e . Carbon d i o x i d e i s a v e r y a c t i v e c e l l m e t a b o l i t e , and has s p e c i f i c i n t e r a c t i o n w i t h c e l l s t r u c t u r e s . I t has a g r e a t e r e f f e c t on d i f f e r e n t r e s p i r a t o r y s u b s t r a t e s than does oxygen d e p r i v a t i o n ( Z e m l i a n u k h i n and Ivanov , 1978) . i n i n c r e a s e d c a r b o n d i o x i d e e n v i r o n m e n t s , p l a n t s not o n l y l i b e r a t e c a r b o n d i o x i d e i n r e s p i r a t i o n , but a l s o a s s i m i l a t e c a r b o n d i o x i d e from the environment and use i t i n 14 the p r o d u c t i o n of o r g a n i c components. The i n c l u s i o n of CO 2 i n the atmosphere has l e d to the o b s e r v a t i o n of r a d i o a c t i v i t y 14 i n c i t r i c , m a l i c , and o x a l i c a c i d s . I t appears t h a t the CO 2 e n t e r s the Krebs c y c l e p r i m a r i l y through the c a r b o x y l a t i o n of 35 p y r u v a t e and i s I n c o r p o r a t e d i n t o the a forement ioned In termed ia te s ( Z e m l l a n u k h i n and Ivanov , 1978) . 2 . 5 . 3 . 2 ORGANIC ACIDS ANALYSIS In t h i s s t u d y , i o n moderated p a r t i t i o n chromatography (IMPC) was used to determine the o r g a n i c a c i d p r o f i l e s of c h e r r y e x t r a c t s . T h i s method was chosen as i t o f f e r e d s u p e r i o r s e p a r a t i o n and r e s o l u t i o n to a l t e r n a t i v e methods of chromatography, such as r e v e r s e d - p h a s e l i q u i d chromatography. In a d d i t i o n , the use of a weakly a c i d i c mobi le phase f a c i l i t a t e d p r e p a r a t i o n and a n a l y s e s were r a p i d and r e p r o d u c i b l e . IMPC was o r i g i n a l l y deve loped as a means of s e p a r a t i n g i o n i c and n o n - i o n i c m a t e r i a l s u s i n g ion exchange r e s i n s (Wheaton and Bauman, 1953a); however, o r d i n a r i l y , no i o n exchange a c t u a l l y o c c u r s (Harlow and Morman, 1964) . The b a s i c t h e o r y beh ind IMPC i s d i s c u s s e d below. The r e s i n bed w i t h i n the column i s c o n s i d e r e d to e x i s t of t h r e e p a r t s : the s o l i d r e s i n m a t r i x ; the o c c l u d e d l i q u i d volume h e l d w i t h i n the beads of the r e s i n ; and the l i q u i d volume between the r e s i n p a r t i c l e s (the i n t e r s t i t i a l volume) (Harlow and Morman, 1964) . When an ion exchange r e s i n i s p l a c e d i n a d i l u t e s o l u t i o n of an e l e c t r o l y t e , the c o n c e n t r a t i o n of the e l e c t r o l y t e w i l l be lower i n the aqueous p o r t i o n of the r e s i n phase than i n the i n t e r s t i t i a l volume 36 (Wheaton and Bauman, 1953b) . T h i s i s because the e l e c t r o l y t e s o l u t i o n w i t h i n the beads i s c o n t a i n e d i n a hydrocarbon m a t r i x and c o n t a i n s a h i g h c o n c e n t r a t i o n of i o n i c g r o u p s . The r e s i n network f u n c t i o n s as a boundary or semi-permeable membrane between two l i q u i d phases , and due to the Donnan membrane e f f e c t , h i g h l y i o n i z e d m a t e r i a l s , such as s t r o n g m i n e r a l a c i d s , are e x c l u d e d from the i n t e r i o r of the r e s i n beads . Such compounds pass through the column u n r e t a i n e d , emerging i n the s o l v e n t f r o n t (Harlow and Morman, 1964) . The Donnan membrane t h e o r y , as a p p l i e d to e l e c t r o l y t e b e h a v i o u r , Impl i e s t h a t non-I o n i c m a t e r i a l s , such as o r g a n i c a c i d s , would occur i n e q u a l c o n c e n t r a t i o n s i n the aqueous p o r t i o n o f the r e s i n and i n the i n t e r s t i t i a l volume (Wheaton and Bauman, 1953b). N o n - i o n i c m a t e r i a l s , t h e r e f o r e , are a b l e to en ter the r e 3 l n p a r t i c l e s , and emerge a f t e r the I o n i c s p e c i e s have been e l u t e d (Harlow and Morman, 1964) . A l l n o n - i o n i c s p e c i e s do not e l u t e as a s i n g l e peak under the u s u a l c o n d i t i o n s of IMPC s i n c e t h e r e a r e d i f f e r e n c e s i n the t e n d e n c i e s of v a r i o u s n o n - i o n i c s o l u t e s to be r e t a i n e d by the r e s i n phase . T h i s p a r t i t i o n i n g e f f e c t a r i s e s due to p o l a r a t t r a c t i o n s between f u n c t i o n a l groups and t o Van der Waal ' s f o r c e s between the n o n - i o n i c compounds and the hydrocarbon p o r t i o n of the r e s i n . These d i f f e r e n c e s are i n f l u e n c e d by the n a t u r e of the s o l u t e and the c h a r a c t e r i s t i c s of the r e s i n used (Harlow and Morman, 1964) and the t emperature of o p e r a t i o n (Wheaton and Bauman, 1953a) . Higher temperatures 37 favour b e t t e r s e p a r a t i o n s , as the number of p l a t e s on the a n a l y t i c a l column n o r m a l l y i n c r e a s e s w i t h i n c r e a s i n g column temperature ( P e c i n a e j t a l . . , 1984) . A l t h o u g h s e v e r a l v a r i a b l e s c o n t r i b u t e to the s e p a r a t i o n of o r g a n i c a c i d s u s i n g IMPC, the o v e r r i d i n g f a c t o r i s the pKa of the i n d i v i d u a l a c i d s . I f a l l o p e r a t i o n a l parameters are h e l d c o n s t a n t , the s t r o n g e r a c i d s w i l l e l u t e f i r s t ( T u r k e l s o n and R i c h a r d s , 1978) . In the case of l i n e a r a c i d s , r e t e n t i o n t imes g e n e r a l l y i n c r e a s e w i t h i n c r e a s i n g c h a i n l e n g t h , due to a r e v e r s e d phase mechanism. Other f a c t o r s I n f l u e n c i n g the r e t e n t i o n t imes of compounds Inc lude the p o s i t i o n of f u n c t i o n a l g r o u p s , and the o c c u r r e n c e of branch p o i n t s i n the c h a i n . Compounds c o n t a i n i n g a t e r m i n a l f u n c t i o n a l group a r e more r e t a r d e d than t h e i r s econdary or t e r t i a r y i s o m e r s , w h i l e b r a n c h e d - c h a i n compounds have s h o r t e r r e t e n t i o n t imes than t h e i r c o r r e s p o n d i n g s t r a i g h t - c h a i n i s o m e r s . A l s o , i n c r e a s i n g the number of i d e n t i a l f u n c t i o n a l groups i n a g i v e n compound w i l l decrease the r e t e n t i o n t i m e . Thus , a d l - or t r i c a r b o x y l i c a c i d would have a s h o r t e r r e t e n t i o n time than a m o n o c a r b o x y l i c a c i d of the same c h a i n l e n g t h (Pec ina et a l . , 1984) . S e p a r a t i o n of o r g a n i c a c i d s u s i n g IMPC can be c o n t r o l l e d by v a r y i n g the c o m p o s i t i o n of the e l u a n t ( B i o - R a d L a b s , 1988) . P e c i n a e_t a l . (1984) i n d i c a t e d t h a t v a r i a t i o n l n the pH i n the range of pH 1 . 8 - 2 . 3 had l i t t l e i n f l u e n c e on the r e t e n t i o n t imes of most s u b s t a n c e s . The c o m p o s i t i o n of the mobi l e phase may a l s o be a l t e r e d t h r o u g h the a d d i t i o n of an o r g a n i c m o d i f i e r , 38 such as a c e t o n i t r i l e , which s e r v e s to decrease the a d s o r p t i o n o£ o r g a n i c compounds to the column m a t r i x ( B i o - R a d L a b s , 1988) . While s e p a r a t i o n of o r g a n i c a c i d s i s a c h i e v a b l e u s i n g o n l y d e i o n i z e d water as the e l u a n t , the use of a d i l u t e m i n e r a l a c i d mobi le phase h o l d s two d i s t i n c t advantages . F i r s t l y , the use of a s l i g h t l y a c i d i c e l u a n t c o n t i n u o u s l y r e g e n e r a t e s the r e s i n H+ form d u r i n g o p e r a t i o n , e l i m i n a t i n g the need for r e s i n r e g e n e r a t i o n ( P i c h a , 1985; T u r k e l s o n and R i c h a r d s , 1978) . S e c o n d l y , the use of a d i l u t e m i n e r a l a c i d as e l u a n t suppres se s the i o n i z a t i o n of s t r o n g to modera te ly s t r o n g o r g a n i c a c i d s , e n a b l i n g them to p a r t i t i o n i n t o the r e s i n phase . The net r e s u l t i s i n c r e a s e d r e t e n t i o n t imes and Improved s e p a r a t i o n of s t r o n g a c i d s ( T u r k e l s o n and R i c h a r d s , 1978) . R e s o l u t i o n may a l s o be enhanced through m a n i p u l a t i o n of the column t e m p e r a t u r e , as the number of p l a t e s on the a n a l y t i c a l column g e n e r a l l y Increases w i t h I n c r e a s i n g t e m p e r a t u r e . Higher column temperatures may a l s o change the r e t e n t i o n t imes of s o l u t e s by d e c r e a s i n g a d s o r p t i o n , which may a l l o w for b e t t e r r e s o l u t i o n (Wheaton and Bauman, 1953b; P e c i n a et a l . , 1984) . O p e r a t i o n of the system a t e l e v a t e d temperatures a l s o hastens the passage of s o l u t e s through the co lumn, t h e r e b y d e c r e a s i n g r e t e n t i o n t imes and o v e r a l l a n a l y s i s t i m e . C o n t r o l of column f low r a t e i s a t h i r d means of o p t i m i z i n g a n a l y s i s ( P e c i n a et a l . , 1984). S e p a r a t i o n s are Improved a t h i g h temperatures u s i n g a low f low r a t e due to b e t t e r e s t a b l i s h m e n t of e q u i l i b r i u m between the phases (Wheaton and Bauman, 1953a) . 39 3. MATERIALS AND METHODS 3.1 INTRODUCTION The methods and m a t e r i a l s s e c t i o n i s comprised of four main s e c t i o n s , namely c h e r r y p a c k a g i n g , c h e m i c a l a n a l y s e s , p h y s i c a l a n a l y s e s , and s e n s o r y a n a l y s i s of the s t o r e d f r u i t . The methods used i n each of these s e c t i o n s are d i s c u s s e d below. 3.2 CHERRY PACKAGING C h e r r y f r u i t w i t h stems (Prunus avium L . , c v . "Lambert") was h a r v e s t e d J u l y 7, 1987, a t Summerland, B . C . F r u i t was packed i n f i b r e b o a r d boxes ( c a . 44 kg/box) and t r a n s p o r t e d the next day by van to the Department of Food Sc i ence a t U . B . C . o F r u i t was put d i r e c t l y i n t o a 1+0.5 C s torage f a c i l i t y and h e l d o v e r n i g h t u n t i l the f r u i t was packaged on the f o l l o w i n g d a y . c h e r r i e s w i t h stems were v i s u a l l y s o r t e d on the b a s i s of c o l o u r (mahogany f r u i t w i t h b r i g h t green s t ems) , absence of s u r f a c e a b r a s i o n , s p l i t s , p i t t i n g , and s o f t n e s s . The c h e r r i e s used i n t h i s s t u d y were of e x c e p t i o n a l l y h i g h q u a l i t y Four d i f f e r e n t p o l y m e r i c p l a s t i c f i l m s were used f o r the f a b r i c a t i o n of e x p e r i m e n t a l bags wi th d imens ions of a p p r o x i m a t e l y 19 x 14 cm, p r o v i d i n g a s u r f a c e a r e a f o r gas 2 exchange of a p p r o x i m a t e l y 530 cm . The volume of gas w i t h i n the 3 bags was e s t i m a t e d to be 700 cm . P o l y e t h y l e n e f i l m s (Dupont Canada) w i t h v a r i o u s t h i c k n e s s e s (3 m i l to 6 m i l ) v a r i e d i n t h e i r p e r m e a b i l i t i e s to gases from a low b a r r i e r (LB) f i l m of r e l a t i v e l y h i g h p e r m e a b i l i t y to a medium-high b a r r i e r (MHB) 40 f i l m . A p o l y e t h y l e n e - e t h y l v i n y l a l c o h o l l aminate f i l m , d e s i g n a t e d as the h i g h b a r r i e r (HB) f i l m was a l s o u s e d . T h i s HB f i l m was e s s e n t i a l l y impermeable a t the s t o r a g e temperature used i n t h i s s t u d y (Table 3 . 1 ) . C h e r r i e s i n supermarket p l a s t i c produce bags , donated by Canada Safeway, s e r v e d as the c o n t r o l t r e a t m e n t . A p p r o x i m a t e l y 300 g of c h e r r i e s were packaged i n e x p e r i m e n t a l and c o n t r o l p l a s t i c bags . The e x p e r i m e n t a l bags were evacuated and the t e s t gas was I n j e c t e d and the bag was s e a l e d by a PacVac S . S . Impulse S e a l e r (Model #PVS18, Packag ing A i d s C o r p o r a t i o n , San F r a n c i s c o , C A ) . The t e s t gas In t h i s s t u d y was a i r ( a p p r o x i m a t e l y 0.03% carbon d i o x i d e , 21% oxygen, and 78% n i t r o g e n ) , so atmospheres around the c h e r r i e s were s e l f - m o d i f i e d through r e s p i r a t i o n p r o c e s s e s . Two r e p l i c a t e s per t rea tment were packaged i n t h i s manner, and r e t u r n e d to o s t o r a g e a t 1+0.5 C . The s t o r a g e t ime f o r a l l t rea tments was e i g h t weeks. Those samples which were not a n a l y z e d immedia te ly were packaged i n the HB f i l m bags (150 g/bag) under a b l a n k e t of o n i t r o g e n , and h e l d a t -18 C u n t i l a n a l y s e s were p e r f o r m e d . 3.3 PACKAGE HEADSPACE ANALYSIS The c o m p o s i t i o n of the headspace gases of a l l packages was de termined by a gas chromatograph ic ( G O method u s i n g a Shimadzu GC-9A gas chroraatograph (Shlmadzu C o r p o r a t i o n , K y o t o , 41 T a b l e 3.1 P r o p e r t i e s o f t h e P a c k a g i n g F i l m s F i l m Type T r a n s m i s s i o n R a t e s N i t r o g e n Oxygen Carbon D i o x i d e M.V.T.R. Low B a r r i e r Medium-Low B a r r i e r Medium-High B a r r i e r H i g h B a r r i e r 40 30 20 0.02 147 110 73 0.1 733 550 367 0.3 0.4 0 . 3 0.2 0.3 e x p r e s s e d as cm 3/100 i n 2 / 2 4 hr/atm at 23°C M o i s t u r e Vapour T r a n s m i s s i o n R a t e , g/100 i n ^ / 2 4 hr a t 95% R e l a t i v e H u m i d i t y 42 Japan) equipped w i t h a 100/120 C a r b o s i e v e S - I I column ( S u p e l c o , O a k v i l l e , O N . ) . A temperature g r a d i e n t e l u t l o n p a t t e r n was o employed; the temperature was programmed to h o l d a t 35 C for 7 o min , then Increased a t a r a t e of 32 C/min to a maximum of o 225 C . A one mL sample of gas was withdrawn from the headspace of each package (two packages per t rea tment ) and i n j e c t e d i n t o o a h e l i u m c a r r i e r s t ream (30 mL/min) a t 30 C . A f t e r e l u t l o n of oxygen and n i t r o g e n (at c a . 6 m i n ) , the column temperature was o i n c r e a s e d to 225 C t o a l l o w f o r e l u t l o n o f c a r b o n d i o x i d e a t o a p p r o x i m a t e l y 13.5 m i n . The column was c o o l e d to 30 C p r i o r to subsequent i n j e c t i o n s . A sample chromatogram Is Inc luded as F i g u r e 3 . 1 . Gases were d e t e c t e d by a t h e r m a l c o n d u c t i v i t y d e t e c t o r , and I d e n t i f i e d by r e t e n t i o n t i m e . Q u a n t i t a t i v e a n a l y s i s was performed by a Shimadzu Chromatopac C-R3A i n t e g r a t o r (Shimadzu C o r p o r a t i o n , K y o t o , J a p a n ) . 3.4 MOLD DEVELOPMENT DURING STORAGE A l l t rea tments were v i s u a l l y examined weekly for the presence of mo ld . At each s t o r a g e t i m e , f i v e bags per t rea tment were randomly removed from s t o r a g e , and the f r u i t w i t h i n each bag i n d i v i d u a l l y examined f o r m y c e l i a l growth . The number of moldy f r u i t was counted and c a l c u l a t e d as a percentage of the t o t a l number of f r u i t i n each bag . The 43 2 I 1 o UJ ~3 r 0 3 JL 1 — 12 ( M I N U T E S ) R E T E N T I O N 8 T I M E 14 F i g u r e 3 .1 Sample Gas Chromatogram of C h e r r y Package Headspace Peak I d e n t i f i c a t i o n : l=Oxygen; 2=Nitrogen; 3=Carbon D i o x i d e 44 v a l u e s for each of the f i v e bags were averaged to g ive a mean v a l u e f o r the t r e a t m e n t . 3 .5 FRUIT WEIGHT CHANGES DURING STORAGE The weight of each bag of c h e r r i e s was r e c o r d e d p r i o r to be ing put i n t o c o l d s t o r a g e . At each 7-day s t o r a g e i n t e r v a l , t e n bags were r e t r i e v e d from s t o r a g e and r e - w e l g h e d . Changes i n f r u i t we igh t , as % g a i n or l o s s , were c a l c u l a t e d as f o l l o w s : % weight change = (Wl - W2) X 100% WT where wl = t o t a l i n i t i a l weight of a l l bags; and W2 = t o t a l f i n a l weight of a l l bags . 3.6 PHYSICAL ANALYSES 3 . 6 . 1 OBJECTIVE EVALUATION OF CHERRY TEXTURE The t e x t u r e of I n d i v i d u a l c h e r r y f r u i t was de termined a c c o r d i n g to a m o d i f i e d method of L i d s t e r e_t a l . (1978) u s i n g an I n s t r o n U n i v e r s a l T e s t i n g Machine equipped w i t h a 20 kg l o a d c e l l . The t e s t c o n s i s t e d of measuring the f o r c e r e q u i r e d t o deform a c h e r r y by a 11-mm diameter s t a i n l e s s s t e e l probe moving downward a t a c o n s t a n t speed . Each c h e r r y was p o s i t i o n e d w i t h the stem a x i s a t r i g h t ang le s to the d i r e c t i o n 45 of f o r c e a p p l i c a t i o n . Each c h e r r y was h e l d in p l a c e manua l ly u n t i l the p o i n t of f i r s t c o n t a c t of the probe w i t h the s u r f a c e of the c h e r r y . The f o r c e t r a n s d u c e r and s t r i p c h a r t r e c o r d e r were a d j u s t e d to p r o v i d e a f u l l - s c a l e s e n s i t i v i t y of 2 k g . A c r o s s - h e a d speed of 1.0 cm/mln was used . F o r c e - d e f o r m a t i o n c u r v e s f o r i n d i v i d u a l c h e r r i e s , such as t h a t shown i n F i g u r e 3 . 2 , were g e n e r a t e d . F r u i t f i rmness was d e f i n e d as the maximum s l o p e (N/m) of the f o r c e - d e f o r m a t i o n c u r v e . F r u i t b i o y i e l d va lue (N) i s d e f i n e d as the maximum f o r c e r e q u i r e d to r u p t u r e the t i s s u e , a t which p o i n t the f o r c e decreases a b r u p t l y . De format ion (mm) was the d i s t a n c e of probe t r a v e l from the i n i t i a l p o i n t of c o n t a c t w i t h the s u r f a c e of the c h e r r y to the b i o y i e l d p o i n t . T e x t u r e e v a l u a t i o n s were conducted on r e p l i c a t e samples o of f r u i t t h a t had been a l l o w e d to warm to about 21 C . The f r u i t f i r m n e s s , b i o y i e l d , and d e f o r m a t i o n v a l u e s f o r 20 c h e r r i e s were averaged to p r o v i d e the t e x t u r a l a t t r i b u t e s f o r a s i n g l e t rea tment or c o n t r o l sample . T e x t u r a l a n a l y s i s was c a r r i e d out i n d u p l i c a t e f o r each r e p l i c a t e of each t r e a t m e n t . 3 . 6 . 2 CHERRY FRUIT SURFACE COLOUR C h e r r y s u r f a c e c o l o u r was e v a l u a t e d by u s i n g a HunterLab o o LabScan II 0 /45 S p e c t r o c o l o r i m e t e r (Hunter A s s o c i a t e s L a b o r a t o r y , I n c . , R e s t o n , VA) . The o p t i c a l head was i n t e r f a c e d 46 F i g u r e 3.2 T y p i c a l F o r c e - D e f o r m a t i o n Curve for an I n d i v i d u a l C h e r r y F r u i t 47 w i t h an IBM XT p e r s o n a l computer . I n d i v i d u a l c h e r r i e s were p l a c e d over an a p e r t u r e w i t h a 6.35 mm d i a m e t e r . A l l r e a d i n g s were made u s i n g i l l u m i n a n t D65. Each c h e r r y f r u i t was p r e s e n t e d w i t h i t s stem a x i s s i t u a t e d h o r i z o n t a l l y and was r o t a t e d about i t s a x i s to o b t a i n f o u r r e a d i n g s per f r u i t . T h u s , f o r each sample , about 40 r e a d i n g s were o b t a i n e d . Twenty f r u i t were a n a l y z e d for each of two r e p l i c a t e s , w i t h average Hunter L , a , and b r e a d i n g s b e i n g g e n e r a t e d . 3.7 CHEMICAL ANALYSES 3 . 7 . 1 CHERRY JUICE EXTRACTION For p e r c e n t t i t r a t a b l e a c i d i t y ( T A ) , pH, p e r c e n t s o l u b l e s o l i d s (SS) and t o t a l p h e n o l i c s d e t e r m i n a t i o n s , j u i c e was f i r s t o b t a i n e d from the c h e r r y f r u i t as f o l l o w s : A p p r o x i m a t e l y 100 g of p i t t e d c h e r r i e s ( e d i b l e t i s s u e o n l y ) were macerated i n a b l ender f o r one min and c e n t r i f u g e d o a t 13,200 x g f o r 15 min a t about 10 C . The j u i c e was decanted and f i l t e r e d through Whatman No. 4 p a p e r . 3 . 7 . 1 . 1 DETERMINATION OF CHERRY pH The pH of a l l samples was de termined on u n d i l u t e d j u i c e u s i n g - a F i s h e r Accumet Model 230 p H / i o n meter . A n a l y s i s was done i n d u p l i c a t e . 48 3 . 7 . 1 . 2 PERCENT SOLUBLE SOLIDS DETERMINATION P e r c e n t s o l u b l e s o l i d s were determined on d u p l i c a t e j u i c e samples u s i n g a Bausch and Lomb r e f r a c t o m e t e r (Bausch and Lomb, R o c h e s t e r , N Y ) . A l l v a l u e s were c o r r e c t e d to the o s t a n d a r d temperature of 20 C . 3 . 7 . 1 . 3 PERCENT TITRATABLE ACIDITY DETERMINATION T o t a l t i t r a t a b l e a c i d i t y (TA) was de termined on d u p l i c a t e samples of c h e r r y j u i c e a c c o r d i n g to the method of Amerine and Ough (1974) . Ten mL of j u i c e was d i l u t e d to 100 mL w i t h d i s t i l l e d water and t i t r a t e d to an endpo in t of pH 8.1 u s i n g a F i s h e r Accumet Model 230 p H / l o n meter w i th a s t a n d a r d 0.1N NaOH s o l u t i o n . P e r c e n t TA was c a l c u l a t e d as m a l i c a c i d , the p r i n c i p a l o r g a n i c a c i d i n sweet c h e r r i e s , a c c o r d i n g to the f o l l o w i n g f o r m u l a : %TA = e q u i v a l e n t weight of a c i d X n o r m a l i t y of NaOH X t i t r e 100 ( E q u i v a l e n t weight of m a l i c a c i d = 67.0 g) 3 . 7 . 1 . 4 PERCENT SOLUBLE SOLIDS/PERCENT TITRATABLE ACIDITY RATIO (SS /TA RATIO) The S S / T A r a t i o f o r the f r u i t from each t rea tment was computed by d i v i d i n g the % s o l u b l e s o l i d s va lue by the va lue 49 o b t a i n e d for % t i t r a t a b l e a c i d i t y . 3 . 7 . 1 . 5 PHENOLIC CONTENT OF CHERRIES The t o t a l p h e n o l i c c o n t e n t of c h e r r y samples was determined as g a l l i c a c i d (mg g a l l i c a c i d / 1 0 0 0 mL j u i c e ) , a c c o r d i n g to the method of Amerine and Ough (1974). Samples of j u i c e were d i l u t e d 1:10 ( v / v ) w i t h d i s t i l l e d water . One mL of each d i l u t e d j u i c e s o l u t i o n was p i p e t t e d Into a 100 mL v o l u m e t r i c f l a s k , to which 60 mL of d i s t i l l e d water and 5.0 mL of F o l i n - C i o c a l t e a u (FC) reagent (BDH c h e m i c a l s , T o r o n t o , ON) were added and mixed . Between 30 sec and 8 min a f t e r the a d d i t i o n of the FC r e a g e n t , 15 mL of 20% sodium carbonate were added and mixed , and the c o n t e n t s brought to the 100 mL mark w i t h d i s t i l l e d water . A f t e r h o l d i n g each s o l u t i o n for 2 hr a t o about 22 C , the absorbance was read a t 765 nm a g a i n s t a reagent blank c o n t a i n i n g no added phenol u s i n g a Shlmadzu UV-160 UV-V l s i b l e R e c o r d i n g spec trophotometer (Shlmadzu C o r p o r a t i o n , K y o t o , J a p a n ) . The p h e n o l i c c o n t e n t of each s o l u t i o n was de termined w i t h the a i d of a s t a n d a r d absorbance curve f o r g a l l i c a c i d . 3 . 7 . 2 TOTAL ANTHOCYANINS ANALYSIS T o t a l a n t h o c y a n i n c o n t e n t s (TAcy) of the c h e r r i e s were de termined on r e p l i c a t e samples a c c o r d i n g to the method of F u l e k i and F r a n c i s (1968b) . T h i s method was chosen over the 50 s i m p l e r s i n g l e pH d e t e r m i n a t i o n of TAcy ( F u l e k i and F r a n c i s , 1968a) as i t takes i n t o account the o n - g o i n g a n t h o c y a n i n d e g r a d a t i o n i n the c a l c u l a t i o n of TAcy v a l u e s . As d i f f e r e n t MAP c o n d i t i o n s were expected to a f f e c t the e x t e n t of Acy d e g r a d a t i o n , the pH d i f f e r e n t i a l method was deemed s u p e r i o r for the purposes of t h i s s t u d y . 3 . 7 . 2 . 1 EXTRACTION PROCEDURE One hundred g of p i t t e d , p r e v i o u s l y - f r o z e n c h e r r i e s were macerated w i t h 100 mL of e x t r a c t i n g s o l v e n t for one min a t maximum speed i n an o s t e r l z e r b l e n d e r . The e x t r a c t i n g s o l v e n t was made up of a mix ture of a 95% e t h a n o l s o l u t i o n and 1.5N HCl s o l u t i o n (85 :15 ) . The homogenate was q u a n t i t a t i v e l y t r a n s f e r r e d to a 400 mL b e a k e r , u s i n g a p p r o x i m a t e l y 50 mL of e x t r a c t i n g s o l v e n t f o r the t r a n s f e r . The beaker was covered w i t h p a r a f i l m o and s t o r e d a t about 4 C f o r about 16 h r . Each homogenate was q u a n t i t a t i v e l y t r a n f e r r e d to c e n t r i f u g e tubes ( u s i n g e x t r a c t i n g s o l v e n t f o r the t r a n s f e r ) and c e n t r i f u g e d a t 10400 x g for 15 o min a t about 0 C . Combined c e n t r 1 f u g a t e s were then t r a n s f e r r e d to a f o u r - i n c h Buchner f u n n e l which had been f i t t e d w i t h No. 1 Whatman f i l t e r paper o v e r l a i d w i t h C e l i t e A n a l y t i c a l F i l t e r A i d (Sigma Chemica l C o . , S t . L o u i s , MO), and f i l t e r e d by s u c t i o n . The pomace was broken up and washed s u c c e s s i v e l y w i t h 100 mL a l i q u o t s of e x t r a c t i n g s o l v e n t . T h i s proces s was c o n t i n u e d u n t i l o n l y a l i g h t brown pomace remained on the f i l t e r bed , and 51 a p p r o x i m a t e l y 450 mL of f i l t r a t e had been c o l l e c t e d . The e x t r a c t was q u a n t i t a t i v e l y t r a n s f e r r e d to a 500-mL v o l u m e t r i c f l a s k and made up to volume u s i n g e x t r a c t i n g s o l v e n t . F l a s k s o were s t o p p e r e d and s t o r e d i n the dark a t about 22 C f o r 3 h r . Ten mL a l i q u o t s of e x t r a c t s were p i p e t t e d i n t o 250- and 50-mL v o l u m e t r i c f l a s k s and d i l u t e d to volume w i t h pH 1.0 and pH 4.5 b u f f e r s , r e s p e c t i v e l y . The pH 1.0 b u f f e r was p r e p a r e d by mix ing 0.2N K C l and 0.2N HCl s o l u t i o n s (25:67) and d i l u t i n g w i t h w a t e r . The pH 4.5 b u f f e r was a 100:60:90 m i x t u r e of IN sodium a c e t a t e - l N H C l - w a t e r . F o l l o w i n g d i l u t i o n w i t h b u f f e r s , e x t r a c t s were s t o r e d l n the dark a t room temperature for 2 hr to a l l o w f o r e q u i l i b r a t i o n . The absorbance of a l l samples was read a t 510 nm i n a Shlmadzu V i s i b l e R e c o r d i n g Spectrophotometer UV-160 (Shlmadzu C o r p o r a t i o n , K y o t o , Japan) a g a i n s t d i s t i l l e d water . 3 . 7 . 2 . 2 CALCULATIONS The absorbance v a l u e s f o r d i l u t e d pH 1.0 and pH 4.5 samples a t 510 nm were used to c a l c u l a t e v a l u e s f o r the TAcy c o n t e n t by both the s i n g l e pH and pH d i f f e r e n t i a l methods ( F u l e k i and F r a n c i s , 1968b). The c a l c u l a t i o n s are summarized below. C a l c u l a t i o n of T o t a l A n t h o c y a n i n Content (pH D i f f e r e n t i a l Method) The t o t a l absorbance f o r 100 g of c h e r r i e s a t pH 1.0 and 52 pH 4.5 was c a c u l a t e d u s i n g the f o l l o w i n g e q u a t i o n : TOTAL ABSORBANCE = ABSORBANCE X DV x V F X TEV CW where t o t a l absorbance = the absorbance r e a d i n g on the d i l u t e d sample (1 cm c e l l ) DV = D i l u t e d Volume or volume i n mL of the d i l u t e d sample p r e p a r e d f o r the O . D . measurement VF = Volume F a c t o r which c o r r e c t s f o r the d i f f e r e n c e between the O r i g i n a l Volume ( 0 V ) r u s u a l l y 100 mL, f o r which the c a l c u l a t i o n i s made and t h a t of the sample volume (SV) or the volume of the e x t r a c t used l n p r e p a r i n g the sample f o r the absorbancy measurement. VF = OV/SV = 100/SV The r e s u l t s were c o n v e r t e d to t o t a l absorbance /100 g c h e r r i e s by m u l t i p l y i n g the above r e s u l t by the f a c t o r TEV/CW, where TEV = t o t a l e x t r a c t i o n volume (500 mL) and CW = c h e r r y weight (100 g ) . The d i f f e r e n c e i n t o t a l absorbance between c h e r r y e x t r a c t a t pH 1.0 and pH 4.5 ( A a b s o r b a n c e ) was c a l c u l a t e d as f o l l o w s : absorbance = t o t a l absorbance - t o t a l absorbance (pH 1. o) C pH 4 . 5) 53 U s i n g the pH d i f f e r e n t i a l method, the TAcy c o n t e n t , i n mg, f o r 100 q of c h e r r i e s was c a l c u l a t e d from the absorbance 1% va lue w i t h the a i d of the a v A E 510 va lue for c y a n i d i n - 3 -1 cm g a l a c t o s i d e ( c y - 3 - g a l ) de termined by F u l e k i and F r a n c i s (1968b). Whi le the major a n t h o c y a n i n pigment i n c h e r r i e s i s r e p o r t e d l y c y a n i d i n - 3 - r u t i n o s i d e ( W r o l s t a d , 1976), no e x t i n c t i o n c o e f f i c i e n t for t h i s pigment was a v a i l a b l e i n the l i t e r a t u r e . S i n c e e x t i n c t i o n c o e f f i c i e n t s v a r y o n l y s l i g h t l y among a n t h o c y a n i n pigments ( W r o l s t a d , 1976), and r e s u l t s are to be used f o r compar i son o n l y , the use of the e x t i n c t i o n c o e f f i c i e n t f o r c y - 3 - g a l was j u s t i f i e d . R e s u l t s , however, are r e p o r t e d i n terras o f t h i s p igment . TAcy (mg/100 g) = absorbance = absorbance 76.5 -f-10 / 1% \ (avAE 5101\ 1 cm / C a l c u l a t i o n o f T o t a l A n t h o c y a n i n Content ( S i n g l e pH Method) The c a l c u l a t i o n of TAcy a t pH 1.0 i s the b a s i s of the s i n g l e pH method. U s i n g the t o t a l absorbance a t pH 1.0 as c a l c u l a t e d above , the TAcy i s c a l c u l a t e d as f o l l o w s : TAcy (mg/100 g) = t o t a l absorbance = t o t a l absorbance 1% \ / 87.3 avA E 510 1 cm 1/10 1 A g a i n , the e x t i n c t i o n c o e f f i c i e n t for c y - 3 - g a l a t pH 4.5 was used i n the c a l c u l a t i o n s . R e s u l t s were expressed as mg c y -3 - g a l / 1 0 0 g c h e r r i e s . 54 3 . 7 . 3 ORGANIC ACIDS ANALYSIS The o r g a n i c a c i d c o n t e n t s of the s t o r e d c h e r r y f r u i t were de termined by h i g h performance l i q u i d chromatography (HPLC) u s i n g the method of Reyes et. a l . (1982), w i t h some minor m o d i f i c a t i o n s . 3 . 7 . 3 . 1 SAMPLE PREPARATION One hundred g of p i t t e d , f r o z e n f r u i t were heated to b o i l i n g i n a beaker i n a microwave oven, and then h e l d f o r 30 sec l n a b o i l i n g water bath and c o o l e d immediate ly by immersion i n an i c e b a t h . The h e a t i n g s t e p s e r v e d to i n a c t i v a t e any enzyme systems which might have mediated changes i n the o r g a n i c a c i d p r o f i l e s o f samples d u r i n g the p r e p a r a t i o n s t e p . The weight l o s s i n c u r r e d through h e a t i n g was c o r r e c t e d f o r by the a d d i t i o n of d e i o n i z e d water . The f r u i t was homogenized f o r one min i n an O s t e r i z e r b l e n d e r . Ten g of homogenate were t r a n s f e r r e d to a p l a s t i c c e n t r i f u g e t u b e , to which 40 mL of 95% e t h a n o l was added . The c o n t e n t s were s u b j e c t e d to u l t r a s o n i c treatment f o r 3 min u s i n g a Tekmar S o n i c D i s r u p t e r (Tekmar Company, C i n c i n n a t i , OH) equipped w i t h a m i c r o t i p ( s e t t i n g 4, 50% d u t y c y c l e ) . T h i s s t e p e f f e c t e d d i s r u p t i o n of c e l l s for the r e l e a s e of o r g a n i c a c i d s , g e n e r a l l y c o n t a i n e d i n s u b - c e l l u l a r v a c u o l e s ( H a a r d , 1976) . The c e n t r i f u g e tube was covered wi th PVC wrap and o p l a c e d i n a r e f r i g e r a t o r a t 4 c for 1 h r . Tubes were not 55 a g i t a t e d d u r i n g r e f r i g e r a t e d s t o r a g e . The r e f r i g e r a t e d samples were f i l t e r e d by s u c t i o n through a 10 g pad of h y d r a t e d p o l y v i n y l - p o l y p y r r o l l d o n e (PVPP) (Sigma C h e m i c a l C o . , S t . L o u i s , MO) on a 5-cm d iameter Whatman No. 1 paper to d e c o l o u r i z e the e x t r a c t . The PVPP and sample r e s i d u e were r i n s e d t h r e e t imes w i t h 25 mL a l l q u o t s of 80% e t h a n o l . The f i l t r a t e and washings were c o l l e c t e d and c o n c e n t r a t e d under vacuum i n a r o t a r y e v a p o r a t o r (Buchi o Rotavapor 110, Brinkman I n s t r u m e n t s , Westbury, NY) a t 35 C to a f i n a l volume of c a . 5 mL. The c o n c e n t r a t e was p e r c o l a t e d through a p p r o x i m a t e l y 10 mL of c a t i o n exchange r e s i n , H+ form (Dowex 50w-x4, 100-200 mesh, BioRad L a b o r a t o r i e s , Richmond, CA) and r i n s e d w i t h d e i o n i z e d water to b r i n g the f i n a l volume of to 100 mL. o A l i q u o t s were c e n t r i f u g e d a t 23,500 X g for 30 min a t 0 C to c l a r i f y . Samples were f i l t e r e d through a 0.45 um membrane f i l t e r d i s k composed of mixed e s t e r s of c e l l u l o s e ( M l l l i p o r e C o r p o r a t i o n , B e d f o r d , MA) p r i o r to i n j e c t i o n i n t o the HPLC sys tem. 3 . 7 . 3 . 2 PREPARATION OF STANDARDS Standards of the f o l l o w i n g a c i d s were p r e p a r e d for use i n i d e n t i f i c a t i o n and q u a n t i t a t i o n of components i n c h e r r y samples : L - ( - ) m a l i c a c i d (Eastman Kodak C o . , R o c h e s t e r , NY) ; ( - ) - s h i k l m i c a c i d , ( - ) - q u i n i c a c i d and s u c c i n i c a c i d (Sigma 56 Chemica l C o . , S t . L o u i s , MO); c i t r i c a c i d (Matheson Coleman and B e l l M a n u f a c t u r i n g C h e m i s t s , Norwood, OH); t a r t a r i c a c i d ( M a l l i n c k r o d t Chemica l Works, S t . L o u i s , MO); f o r m i c a c i d and o x a l i c a c i d (BDH c h e m i c a l s L t d . , P o o l e , E n g l a n d ) . S tandards of o r g a n i c a c i d s were p r e p a r e d i n d i v i d u a l l y i n d e i o n i z e d water , f i l t e r e d through a 0.45 um mixed c e l l u l o s e e s t e r membrane f i l t e r ( M i l l i p o r e C o r p o r a t i o n , B e d f o r d , MA) and chromatographed s e p a r a t e l y i n o r d e r to determine the r e t e n t i o n t ime for each a c i d . The a c i d s were then combined to form a mixture of s t a n d a r d s ( F i g u r e 3 . 3 ) . D i l u t i o n s were performed to generate a wide range of c o n c e n t r a t i o n s . S tandard c u r v e s f o r each of the a c i d s were produced by p l o t t i n g peak a r e a a g a i n s t c o n c e n t r a t i o n (Appendix A ) . E x c e l l e n t l i n e a r responses were observed over a wide c o n c e n t r a t i o n r a n g e . 3 . 7 . 3 . 3 HPLC INSTRUMENTATION Chromatography was performed on an Aminex HPX-87H O r g a n i c A c i d s column (300 x 7.8 mm) p r o t e c t e d by an Aminex-85H guard c a r t r i d g e (40 x 4.6 mm) ( B l o - R a d L a b o r a t o r i e s , Richmond, C A ) . The a n a l y t i c a l column was c o n t a i n e d i n a g l a s s w a t e r -j a c k e t e d co lumn, through which water was c i r c u l a t e d by means o f a c i r c u l a t i n g t e m p e r a t u r e - c o n t r o l l e d water bath (Haake, B e r l i n , W. Germany) . Column temperature was moni tored u s i n g a F l u k e 77 M u l t i m e t e r (John F l u k e Mfg . C o . I n c . , E v e r e t t , WA). HPLC 57 equipment was comprised of a s p e c t r a - P h y s i c s 8100 S o l v e n t D e l i v e r y System, and a S p e c t r a - P h y s i c s Model 770 S p e c t r o p h o t o m e t r i c d e t e c t o r ( S p e c t r a - P h y s i c s , Santa C l a r a , C A ) . P l o t t i n g and i n t e g r a t i o n of e l u t i n g peaks was performed by a S p e c t r a - P h y s i c s 4100 computing i n t e g r a t o r , s e t a t a t t e n t u a t l o n 1 and a c h a r t speed of 1 cm/mln. The mobi le phase was 0.01N s u l p h u r i c a c i d p r e p a r e d by d i l u t i n g reagent grade s u l p h u r i c a c i d wi th d e i o n i z e d water . The mobi le phase was f i l t e r e d through a M l l l i p o r e 0.45 um mixed c e l l u l o s e e s t e r membrane f i l t e r , and c o n t i n u o u s l y degassed throughout the a n a l y s i s u s i n g a f i n e s t ream of h e l i u m gas . Column temperature was m a i n t a i n e d o a t 60 C . E l u a n t f l ow r a t e was 0.6 mL/min , and a c i d f r a c t i o n s were d e t e c t e d a t 210 nm, wi th the d e t e c t o r s e t a t 0.04 absorbance u n i t s f o r f u l l - s c a l e d e f l e c t i o n . A 20-uL sample loop a s s i s t e d i n o b t a i n i n g c o n s i s t e n t sample i n j e c t i o n vo lumes . Q u a n t i f i c a t i o n was a c h i e v e d u s i n g s t a n d a r d c u r v e s (peak a r e a v e r s u s c o n c e n t r a t i o n s ) f o r o r g a n i c a c i d s t a n d a r d s . I n d i v i d u a l a c i d s were i d e n t i f i e d by t h e i r r e t e n t i o n t i m e s . 3.8 SENSORY EVALUATION Sensory a n a l y s i s was conducted on a weekly b a s i s f o r the e n t i r e e i g h t week s t o r a g e p e r i o d , i n c l u d i n g an I n i t i a l s e s s i o n to determine z e r o - t i m e v a l u e s f o r the f r e s h f r u i t . A s i x -member p a n e l c o n s i s t i n g of persons from o u t s i d e the U n i v e r s i t y community was employed. These persons were s e l e c t e d on the 58 6 I 4 I L U r -0 2 ~T~ 4 "fs 8 S E" RETENTION TIME (MINUTES) 14 16 18 F i g u r e 3.3 HPLC Chromatogram of O r g a n i c A c i d S tandards Peak I d e n t i f i c a t i o n : S=solvent peak; l = o x a l i c a c i d ; 2 = c i t r i c a c i d ; 3= t a r t a r i c a c i d ; 4=malic a c i d ; 5=quinic a c i d ; 6= s u c c l n i c a c i d ; 7=acet ic a c i d 59 b a s i s of t h e i r r e s u l t s from a t r i a n g l e d i f f e r e n c e t e s t t h a t was conducted e a r l i e r i n another s t u d y (Powrie e t a l . , 1987) . The p a n e l i s t s were b r i e f e d on the a t t r i b u t e s under e v a l u a t i o n i n t h i s s t u d y , and were made f a m i l i a r w i t h e a t i n g and d r i n k i n g r e s t r i c t i o n s p r i o r to s e n s o r y e v a l u a t i o n s e s s i o n s . For each s e n s o r y e v a l u a t i o n s e s s i o n , two bags per t reatment were removed from c o l d s t o r a g e a p p r o x i m a t e l y 30 min p r i o r to a n a l y s i s . G e n e r a l l y , f i v e c h e r r i e s were p r e s e n t e d per t reatment per s e s s i o n , n e c e s s i t a t i n g two s e s s i o n s per d a y . Two r e p l i c a t e s were p r e s e n t e d a t two d i f f e r e n t s i t t i n g s i n one d a y . P a n e l i s t s were a l l o w e d to r e l a x f o r about 30 min between s e s s i o n s , and were i n s t r u c t e d to r e f r a i n from e a t i n g , d r i n k i n g , or smoking . The e v a l u a t i o n form (Appendix B) c o n t a i n e d n ine a t t r i b u t e s which were to be judged . These i n c l u d e d f i rmness In f i n g e r s , c o l o u r , o v e r a l l appearance , t e x t u r e ( through chewing) , aroma i n mouth, sweetness , b i t t e r n e s s , o f f - f l a v o u r , and o v e r a l l a c c e p t a n c e . Each a t t r i b u t e was ranked on a f i v e - p o i n t s c a l e , on which 5 was g e n e r a l l y h i g h l y a c c e p t a b l e , and 1 was u n a c c e p t a b l e . The d i v i d i n g l i n e a t the m i d p o i n t between a c c e p t a b l e and u n a c c e p t a b l e s c o r e s was a r b i t r a r i l y s e t a t a v a l u e of 2 . 5 . 3.9 STATISTICAL ANALYSIS Most of the d a t a c o l l e c t e d i n t h i s s t u d y (except s e n s o r y 60 a n a l y s i s da ta ) was s u b j e c t e d to a n a l y s i s of v a r i a n c e (ANOVA). A l l s t a t i s t i c s were computed wi th SPSSx ( S t a t i s t i c a l Package f o r S o c i a l S c i e n c e s ) . In i n s t a n c e s where d a t a a t e i g h t weeks of s t o r a g e was m i s s i n g for a p a r t i c u l a r packag ing t r e a t m e n t , d a t a s e t s were t r u n c a t e d a t s i x weeks of s t o r a g e and the s t a t i s t i c a l a n a l y s i s performed on the r e s u l t i n g d a t a s e t . Where ANOVA r e s u l t s i n d i c a t e d a s i g n i f i c a n t e f f e c t o f package a n d / o r t ime on the f a c t o r under i n v e s t i g a t i o n , Duncan's M u l t i p l e Range t e s t was used to determine where these d i f f e r e n c e s l a y . Only Duncan's M u l t i p l e Range t e s t was used f o r a n a l y s i s of s e n s o r y a n a l y s i s d a t a s i n c e the e l i m i n a t i o n o f c e r t a i n t rea tments a t v a r i o u s t ime p o i n t s i n the s t o r a g e s t u d y generated an incomple te d a t a s e t , p r o h i b i t i n g the e f f e c t i v e use of ANOVA. The o r g a n i c a c i d s d a t a s e t (as de termined by HPLC) p r e s e n t e d a s p e c i a l c a s e . Due to m i s s i n g v a l u e s for the MLB t r e a t m e n t , the ANOVA was performed on the e ight -week d a t a s e t , w i t h the e l i m i n a t i o n of the MLB d a t a . Duncan's M u l t i p l e Range t e s t was used for the a n a l y s i s of a l l t r e a t m e n t s . 6 1 4. RESULTS AND DISCUSSION 4.1 EFFECT OF STORAGE TIME AND PACKAGE ON PACKAGE HEADSPACE COMPOSITION The packag ing f i l m s used i n t h i s s t u d y were found to i n f l u e n c e d both the c a r b o n d i o x i d e and oxygen l e v e l s i n the packages of c h e r r i e s a t v a r i o u s s torage t imes ( F i g u r e s 4.1 and 4 .2; T a b l e s 4.1 and 4 . 2 ) . A f t e r one to two weeks of s t o r a g e a t o 1 C , the c h e r r i e s were r e s p i r i n g a t about the same r a t e as the r a t e of oxygen t r a n s p o r t i n t o the packages and thus wi th a s t a t e of e q u i l i b r i u m , a t m o s p h e r i c c o m p o s i t i o n d i d not change a p p r e c i a b l y t h e r e a f t e r up to four weeks. Carbon d i o x i d e l e v e l s remained lowest over the four-week s torage p e r i o d i n the c o n t r o l packages , wh i l e atmospheres w i t h i n the HB f i l m packages e x h i b i t e d the h i g h e s t c a r b o n d i o x i d e l e v e l s . Carbon d i o x i d e l e v e l s Increased i n the packages as f i l m p e r m e a b i l i t y i n c r e a s e d Oxygen l e v e l s d e c r e a s e d markedly d u r i n g the f i r s t week of s t o r a g e i n a l l packages except the c o n t r o l . S i n c e the HB f i l m had v e r y low t r a n s m i s s i o n r a t e s f o r carbon d i o x i d e , oxygen, and n i t r o g e n , the packages can be c o n s i d e r e d e s s e n t i a l l y c l o s e d sys tems . Hence, changes i n the component gases o f the atmosphere in these packages are a t t r i b u t a b l e a lmost s o l e l y to c h e r r y r e s p i r a t i o n , as opposed to gas t r a n s m i s s i o n through the f i l m . Oxygen d e p l e t i o n and carbon d i o x i d e a c c u m u l a t i o n i n s e a l e d packages of f r u i t was a consequence of c o n t i n u e d 62 r e s p i r a t i o n by the c h e r r i e s . R e s p i r a t i o n , under a e r o b i c c o n d i t i o n s , i n v o l v e s o x i d a t i o n of s u b s t r a t e s (most commonly c a r b o h y d r a t e s ) , w i t h the p r o d u c t i o n of c a r b o n d i o x i d e , water , and energy a c c o r d i n g to the f o l l o w i n g e q u a t i o n : c H O + 6 0 ^ 6 CO + 6 H O + energy 6 12 6 2 2 2 While g l u c o s e i s the p r e f e r r e d s t a r t i n g compound, a c i d s and o ther c e l l m e t a b o l i t e s may a l s o p a r t i c i p a t e i n the p r o c e s s of r e s p i r a t i o n . A c c o r d i n g to the above e q u a t i o n , the l e v e l s of oxygen s u r r o u n d i n g a g i v e n r e s p i r i n g commodity w i l l I n f l u e n c e the r a t e a t which the r e a c t i o n p r o c e e d s . A d d i t i o n a l l y , due t o the laws of mass a c t i o n , i n c r e a s e s i n c a r b o n d i o x i d e w i l l I n f l u e n c e the r e a c t i o n by c a u s i n g a r e d u c t i o n i n r e s p i r a t i o n r a t e s . In the i n i t i a l s t e p s of r e s p i r a t i o n , both a e r o b i c and a n a e r o b i c pathways i n v o l v e g l u c o s e c a t a b o l i s m i n a s e r i e s of r e a c t i o n s c o l l e c t i v e l y r e f e r r e d to as g l y c o l y s i s , w i th the net f o r m a t i o n of two m o l e c u l e s of pyruvate per molecu le of g l u c o s e . Up to the s tage of p y r u v a t e f o r m a t i o n , a n a e r o b i c and a e r o b i c r e s p i r a t i o n proceed i n an i d e n t i c a l manner ( R i c h t e r , 1978) . The f a t e of p y r u v a t e depends p r i m a r i l y on the a v a i l a b i l i t y of oxygen. Under a e r o b i c c o n d i t i o n s , p y r u v a t e i s f i r s t o x i d i z e d to A c e t y l - C o A (and carbon d i o x i d e ) , which e n t e r s Into the a e r o b i c r e s p i r a t i o n pathway, the Krebs c y c l e . The Krebs c y c l e p r o v i d e s a means of c o m p l e t e l y o x i d i z i n g p y r u v a t e to carbon d i o x i d e and water , v i a the f o r m a t i o n of s e v e r a l 63 7 0 TREATMENT STORAGE TIME (WEEKS) F i g u r e 4.1 Changes i n Carbon D i o x i d e C o n c e n t r a t i o n s In F i l m Packages C o n t a i n i n g C h e r r i e s D u r i n g Storage a t 1 ° C 64 T a b l e 4.1 Carbon D i o x i d e l e v e l s (%) i n C h e r r y Packages D u r i n g S t o r a g e at 1°C S t o r a g e T r e a t m e n t Time — — (Weeks) C o n t r o l LB MLB MHB HB 0. 0 0 ± 0 . 0 0 -a 0 . 0 0 ± 0 . 0 0 -a 0 . 0 0 ± 0 . 0 0 -a 0 . 0 0 ± 0 . 0 0 -a 0 . 0 0 ± 0 . 0 0 -a 3 4 4.20±2.29-1.87+0.17 2.22±0.35 2.57±0.26 ab a ab a ab 1.30+1.83-a 7.50+0.59£ b 7.14±0.25r b 6.99+0.05^ b 9.56±0.13£ b 13.67+1.39 cd 15.02±1.10-12.33 + 0 . 33-1 3 . 0 6 ± 1 . 7 8 £ b 21.1212.28^-d 2 5 . 2 3±0.7 8 ™ d 29.30+2.70^ d 33 . 45±1.47-43.62+2.07-e 5 8 . 4 7 ± 0 . 9 7 -e 5 6 . 7 7 ± 0 ^ 7 1 -e Data r e p r e s e n t the mean v a l u e + s t a n d a r d d e v i a t i o n of the mean (n=2). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t of the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t ( p ^ 0 . 0 5 ) . LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r 2 4 TREATMENT F i g u r e 4.2 Changes i n Oxygen C o n c e n t r a t i o n s i n F i l m Packages C o n t a i n i n g C h e r r i e s D u r i n g Storage a t 1 ° C 66 T a b l e 4.2 Oxygen L e v e l s (%) i n C h e r r y Packages D u r i n g S t o r a g e at 1°C S t o r a g e T r e a t m e n t Time (Weeks) C o n t r o l LB MLB MHB HB 0 2 0 . 9 0 1 0 . 0 0 -a 2 0 . 9 0 + 0 . 0 0 -a 2 0 . 9 0 + 0 . 0 0 -a 2 0 . 9 0 + 0 . 0 0 -a 20 . 90 + 0 . 0 0 -a 1 1 3 . 3 5 ± 3 . 8 2 ~ a 9.42 * 0 . 1 3 -a 1 . 9 6 ± 2 . 7 7 ^ D 0 . 0 0 ± 0 . 0 0 ^ D 0 . 0 0 ± 0 . 2 1 5 . 4 7 ± 0 . 9 0 -a o . o o + o . o o r D 1 . 3 1 + 0 . 0 0 -c 1 . 3 6 ± 0 . 1 4 -c 0 . o o l o . o o * 3 1 4 . 1 2 + 1 . 9 3 -a o . o o + o . o o r D o . o o + o . o o £ D 0.00+0.OO^ D 0 . 00 + 0 . OO^ 4 1 5 . 0 4 ± 0 . 7 6 -a 1 . 2 5 ± 1 . 7 7 £ b 0 . 6 3 ± 0 . 8 8 r D 0 . 0 0 ± 0 . 0 0 -D 0 . 4 5 ± 0 . x D a t a r e p r e s e n t the mean v a l u e t s t a n d a r d d e v i a t i o n of the mean (n=2). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t o f s t o r a g e t ime w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan' s m u l t i p l e r a n g e t e s t of the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0 . 0 5 ) . LB = Low B a r r i e r ; MLB = Med ium-Low B a r r i e r , - MHB = Med ium-High B a r r i e r ; HB = High B a r r i e r i n t e r m e d i a t e , weakly a c i d i c compounds, a l o n g w i t h the p r o d u c t i o n of ATP ( F i g u r e 4 . 3 ) . In the f i n a l s tage of a e r o b i c r e s p i r a t i o n , e l e c t r o n s are t r a n s f e r r e d through the e l e c t r o n t r a n s p o r t c h a i n to oxygen, the u l t i m a t e e l e c t r o n a c c e p t o r . The low p e r m e a b i l i t y to oxygen of the HB f i l m l i m i t e d i t s d i f f u s i o n i n t o the s t o r a g e bags from the e x t e r n a l a i r . Oxygen consumed through the course of r e s p i r a t i o n c o u l d not be r e p l e n i s h e d . T h i s r e s u l t e d i n r a p i d d e p l e t i o n of oxygen from the atmospheres w i t h i n the HB f i l m bags . I t appears t h a t w i t h i n one week of s t o r a g e , the oxygen l e v e l i n the atmosphere became l i m i t i n g , c a u s i n g a s h i f t t o a n a e r o b i c r e s p i r a t i o n . A n a e r o b i c r e s p i r a t i o n begins wi th the f o r m a t i o n of p y r u v a t e , which i s d e c a r b o x y l a t e d to a c e t a l d e h y d e . Ace ta ldehyde a c t s as the e l e c t r o n a c c e p t o r i n the r e g e n e r a t i o n of NAD from NADH, and e t h a n o l becomes the u l t i m a t e e n d - p r o d u c t : C H O + 2P1 + 2 ADP—> 2 C H O H + 2 C O + 2 H O + 2 ATP 6 12 6 2 5 2 2 Some p l a n t t i s s u e s produce no e t h a n o l under a n a e r o b i c c o n d i t i o n s , w h i l e i n o t h e r s , the amount does not e q u a l the amount of hexose c a t a b o l i z e d . I n s t e a d , o r g a n i c a c i d s , such as l a c t i c , o x a l i c , t a r t a r i c , m a l i c , and c i t r i c , may accumulate ( R i c h t e r , 1978) . The c o n t i n u o u s i n c r e a s e of c a r b o n d i o x i d e i n the HB f i l m packages over t ime i n d i c a t e d t h a t c h e r r i e s must have s w i t c h e d to a n a e r o b i c r e s p i r a t i o n . T h i s would be accompanied by e t h a n o l a n d / o r a c e t a l d e h y d e a c c u m u l a t i o n , which c o u l d l ead to 68 Glycogen k * P 2-Phosphoglucose Glucose Phosphodihydroxyacetone • Glucose-6-phosphate \ Fructose-6-phosphate \ Fructose-1,6-diphosphate -^3-Phosphoglyceraldehyde H , 0 1,3-Diphosphoglycerate 3-Phosphoglycerate , i a j (aerobic) 2-Phosphoglycerate § | ^ D P N + \ 5 jSkDPNH Phosphoenolpyruvate Flavoproteins t Pyridine nucleotides Fatty Acids Alanine Leucine Phenylalanine Tyrosine Aspartate Valine Isoleucine Methionine Threonine V ^ - * - O X A L A C E T A T E \ X l - M A L A T E / F U M A R A T E \ S U C C I N A T E K R E B S C Y C L E CITRATE \ o-ISOCITRATE I a-KETOGLUTARATE -SUCCINYL-C O E N Z Y M E A Glutamate N H 3 H 2 0 + ATP Glutamine ->• Propionylcoenzyme A ATP = Adenosine triphosphate A D P = Adenosine diphosphate CoA = Coenzyme A DPN = Diphosphopyridine nucleotide DPNH = Reduced form of same P = Inorganic phosphate F i g u r e 4 . 3 . The Krebs C y c l e and Some A s s o c i a t e d Pathways (Gardner , 1966) 69 p h y s i o l o g i c a l breakdown of the t i s s u e s . The c o n t r o l package f i l m e x h i b i t e d h i g h p e r m e a b i l i t y to both carbon d i o x i d e and oxygen, r e s u l t i n g i n l i t t l e atmosphere m o d i f i c a t i o n over the s t o r a g e p e r i o d . T h u s , r e s p i r a t i o n proceeded a e r o b i c a l l y f o r the e n t i r e s t o r a g e p e r i o d . The r a t e of r e s p i r a t i o n can be assumed to have been i n f l u e n c e d o n l y by temperature and any e f f e c t s of i n c r e a s e d r i p e n i n g or s enescence . D i f f u s i o n of gases a c r o s s the packag ing f i l m , i n a d d i t i o n to c o n t i n u e d f r u i t r e s p i r a t i o n , i n f l u e n c e d the a tmospher i c c o m p o s i t i o n w i t h i n the packages made from f i l m s of i n t e r m e d i a t e p e r m e a b i l i t y to g a s e s . LB f i l m was most e f f e c t i v e l n r e d u c i n g the r e s p i r a t i o n r a t e of the c h e r r i e s i n t h i s s t u d y . In a d d i t i o n , t h i s f i l m a l l o w e d f o r the most r a p i d e s t a b l i s h m e n t of e q u i l i b r i u m of gases between the i n t e r i o r of the package and the e x t e r n a l a tmosphere , as demonstrated by the v e r y l i m i t e d f l u c t u a t i o n i n a tmospher i c c a r b o n d i o x i d e l e v e l s a f t e r one week of s t o r a g e . The MLB and MHB packages d i s p l a y e d a r a p i d i n c r e a s e i n c a r b o n d i o x i d e c o n c e n t r a t i o n d u r i n g the f i r s t week of s t o r a g e , but g e n e r a l l y c o n t i n u e d to i n c r e a s e t h e r e a f t e r . The d i f f e r e n c e s i n the u l t i m a t e amounts of carbon d i o x i d e which accumulated l n the L B , MLB, and MHB f i l m packages over t ime r e f l e c t the v a r y i n g degrees of p e r m e a b i l i t i e s to c a r b o n d i o x i d e (as w e l l as oxygen) . As carbon d i o x i d e accumulates d u r i n g p r o d u c t r e s p i r a t i o n , a c o n c e n t r a t i o n 70 g r a d i e n t i s e s t a b l i s h e d between the i n t e r i o r o £ the package and the e x t e r n a l a tmosphere . The r a t e of carbon d i o x i d e d i f f u s i o n out of the package i s dependent on a number of f a c t o r s , i n c l u d i n g the s i z e of the c o n c e n t r a t i o n g r a d i e n t and f i l m p e r m e a b i l i t y . The i n h e r e n t r a t e of product r e s p i r a t i o n i s a l s o a d e t e r m i n a n t . The g r e a t e r the p e r m e a b i l i t y of the p a c k a g i n g m a t e r i a l t o c a r b o n d i o x i d e , the more r a p i d w i l l i t s d i f f u s i o n from the package be . T h u s , i t can be s a i d t h a t the LB packages p r o v i d e d for r a p i d exchange of carbon d i o x i d e w i t h the s u r r o u n d i n g atmosphere . S ince a f t e r two weeks of s t o r a g e no s i g n i f i c a n t i n c r e a s e i n carbon d i o x i d e l e v e l s i n the LB packages was n o t e d , i t appears t h a t an e q u i l i b r i u m was e s t a b l i s h e d i n which the r e s p i r a t i o n r a t e e q u a l l e d the r a t e of gas t r a n s m i s s i o n through the package f i l m . The p e r m e a b i l i t y of the MLB and MHB f i l m s to carbon d i o x i d e was s u f f i c i e n t l y low so as to r e s u l t i n a net i n c r e a s e i n carbon d i o x i d e l e v e l s i n the packages u n t i l about two weeks of s t o r a g e . A s i m i l a r s i t u a t i o n o c c u r r e d i n the case of oxygen d e p l e t i o n from the package headspace d u r i n g r e s p i r a t i o n . S i n c e , i n t h e o r y , one molecu le of carbon d i o x i d e i s genera ted per molecu le o f oxygen consumed d u r i n g a e r o b i c r e s p i r a t i o n v i a sugar o x i d a t i o n , i t would be expec ted t h a t the f a l l i n oxygen l e v e l s w i t h i n packages would f o l l o w s i m i l a r t r e n d s to those observed f o r the i n c r e a s e s i n c a r b o n d i o x i d e . However, oxygen d e p l e t i o n was observed to occur much more r a p i d l y . The reasons f o r t h i s are t w o - f o l d . F i r s t l y , f i l m s g e n e r a l l y e x h i b i t 71 p e r m e a b i l i t i e s to oxygen t h a t are four to s i x t imes lower than those for c a r b o n d i o x i d e . With c o n t i n u e d d e p l e t i o n of oxygen through r e s p i r a t i o n i n the packages , an oxygen c o n c e n t r a t i o n g r a d i e n t i s s e t up between the i n s i d e and o u t s i d e of the package which f a v o u r s the d i f f u s i o n of oxygen i n t o the package headspace . However, wh i l e carbon d i o x i d e Is a b l e to d i f f u s e out of the package , the l i m i t e d p e r m e a b i l i t y t o oxygen r e s u l t s i n i t s c o n t i n u e d d e p l e t i o n , w i t h a tendency toward a n a e r o b l o s i s i f the package i s v e r y impermeable t o oxygen. The second reason for the d r a m a t i c d e c l i n e l n oxygen l e v e l s r e l a t i v e to c a r b o n d i o x i d e content i n the i n t e r n a l atmospheres i s t h a t the r e s p i r a t o r y q u o t i e n t (RQ), d e f i n e d as the r a t i o of the amount of c a r b o n d i o x i d e produced to the amount of oxygen consumed, changes w i th v a r i o u s s u b s t r a t e s of o x i d a t i v e m e t a b o l i s m . The RQ i s a p p r o x i m a t e l y 1.0 when sugars s erve as r e s p i r a t o r y s u b s t r a t e s ; i t r i s e s to v a l u e s above 1.0 when o r g a n i c a c i d s s erve as s u b s t r a t e s ( H a a r d , 1976) . C a t a b o l i s m of o r g a n i c a c i d s generates more carbon d i o x i d e than the amount of oxygen consumed ( R i c h t e r , 1978) . 4.2 MOLD DEVELOPMENT IN CHERRIES DURING MAP STORAGE The m o d i f i e d atmospheres around c h e r r i e s i n e x p e r i m e n t a l packages s u p p r e s s e d mold growth for the d u r a t i o n of the s t o r a g e s t u d y , whereas mold growth commenced i n the c o n t r o l packages of c h e r r i e s some time a f t e r f i v e weeks of s t o r a g e , and Increased a t a r a p i d r a t e t h e r e a f t e r . At the end of e i g h t weeks of 72 s t o r a g e , a lmos t 80% of the f r u i t i n the c o n t r o l group was v i s i b l y I n f e c t e d . Mold i n h i b i t i o n under MA s t o r a g e c o n d i t i o n s was not s u r p r i s i n g , i n t h a t the presence of h i g h c a r b o n d i o x i d e and low oxygen l e v e l s i n the atmosphere , coup led w i t h a low s t o r a g e t e m p e r a t u r e , tended to prevent the development of mold . Most types of mold a r e i n h i b i t e d by l e v e l s of c a r b o n d i o x i d e r a n g i n g from 5 to 50%, w i t h the degree of i n h i b i t i o n i n c r e a s i n g a lmost l i n e a r l y i n t h i s r e g i o n . The degree of i n h i b i t i o n i s dependent on the food and the type of m i c r o f l o r a i n v o l v e d ( C l a r k e and T a k a c s , 1980) . A l t h o u g h low oxygen t e n s i o n s can r e s u l t i n s u p p r e s s i o n of mold growth , the e f f e c t i s more s p e c i e s -dependent than t h a t of h i g h carbon d i o x i d e l e v e l s ( U l r i c h , 1975). E l - K a z z a z e t a l . (1983) s t u d i e d the e f f e c t s of d i f f e r e n t atmospheres on r o t t i n g of s t r a w b e r r i e s by B o t r y t i s  c i n e r e a . They found t h a t under 21% oxygen and 10% carbon d i o x i d e , or 2.3% oxygen and 10% carbon d i o x i d e , development of B o t r y t i s g r a y mold l e s i o n s on s t r a w b e r r y f r u i t s was suppressed d u r i n g s t o r a g e . W i t h i n one week of s t o r a g e i n t h i s s t u d y , carbon d i o x i d e l e v e l s i n package atmospheres had i n c r e a s e d to a p p r o x i m a t e l y 10% or h i g h e r i n the MLB, MHB, and HB packages , w h i l e oxygen l e v e l s had d e c r e a s e d d r a m a t i c a l l y to a p p r o x i m a t e l y 1% or lower i n the same packages . L e v e l s of carbon d i o x i d e i n the LB package c l i m b e d to above 7% a f t e r two weeks o f s t o r a g e , and hovered t h e r e f o r the d u r a t i o n of the s t o r a g e p e r i o d . These l e v e l s of gases ( p a r t i c u l a r l y carbon d i o x i d e ) a r e w i t h i n the ranges quoted i n the l i t e r a t u r e for e f f e c t i v e p r e v e n t i o n of mold deve lopment . In c o n t r o l packages , however, c a r b o n d i o x i d e t e n s i o n s were m a i n t a i n e d a t a l e v e l o n l y s l i g h t l y h igher than t h a t l n a i r , w i t h oxygen l e v e l s d e c r e a s i n g o n l y s l i g h t l y . The ready a v a i l a b i l i t y of oxygen, and the lack of i n h i b i t o r y l e v e l s of carbon d i o x i d e a l l o w e d r a p i d mold p r o l i f e r a t i o n . 4.3 CHERRY WEIGHT LOSS DURING STORAGE Changes l n the weights of c h e r r y f r u i t throughout the s t o r a g e p e r i o d are shown i n T a b l e 4 . 3 . Whi le t h e r e were d i f f e r e n c e s i n the r a t e and ex tent of weight l o s s i n the v a r i o u s t r e a t m e n t s , i t must be noted t h a t weight l o s s remained below 1%, r e g a r d l e s s of the packag ing t r e a t m e n t . One o f the b e n e f i t s o f employing MAP for f r u i t s t o r a g e i s the c o n t r i b u t i o n of the packag ing m a t e r i a l t o the maintenance of h i g h r e l a t i v e h u m i d i t i e s w i t h i n the package to m i t i g a t e m o i s t u r e l o s s from the f r u i t . The r a t e of m o i s t u r e l o s s from the package i s de termined by the m o i s t u r e vapour t r a n s m i s s i o n r a t e (MVTR) o f the f i l m . Lower MVTR v a l u e s a l l o w for h i g h e r r e l a t i v e h u m i d i t i e s w i t h i n the package . The MVTR v a l u e s of the t e s t f i l m s i n t h i s s t u d y are p r e s e n t e d i n T a b l e 3 . 1 . In t h i s s t u d y , c h e r r i e s packaged i n HB f i l m , w i t h a low MVTR v a l u e , d i s p l a y e d the l e a s t weight l o s s throughout the s t o r a g e p e r i o d . With i n c r e a s i n g MVTR v a l u e s f o r the c o n t r o l and LB packages , weight l o s s e s from the f r u i t were observed to 74 T a b l e 4.3 P e r c e n t Weight L o s s i n C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s S t o r a g e T r e a t m e n t ' Time (Weeks) C o n t r o l LB MLB MHB HB 1 0.05+0.02-a o.oo+o.oor D 0.03+0.02-0 0.01±0.02£ b 0.00±0. 2 0 . 1 1 * 0 . 0 2 — a 0.06±0.03^ D O . H l O . 0 3 -a 0.0910.03-ac 0.0710. 0 2 f c 3 0.1310.10-. ab 0.0710.05-ac 0.1110.07-. ab 0.1510.04§ b 0.0310. 0 3 ^ c 4 0.14±0.02-a 0.0710.04^ b 0.10±0.10-. ab 0.2810.03-c 0.0610. 02§ b 5 0.27*0.05-a 0.30+0.07-a 0.21±0.10§ b 0.49±0.06-c 0.16±0. < 6 0.40+0.17-a 0.3210.04^ b 0.3010.07^ b 0.6010.03-c 0.1510. 7 0.39±0.02-a 0.2410.04c b 0.5410.11-c 0.7310.03# d 0.1210. e 8 0.54±0.10-a 0.35±0.04| b 0.6510.08-c 0.84±0.03^ d 0.1410. 0 2 ^ e D a t a r e p r e s e n t t h e mean ± s t a n d a r d d e v i a t i o n of t h e mean ( n = 1 0 ) . The u p p e r l e t t e r i n d i c a t e s t h e r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t o f t h e e f f e c t s o f s t o r a g e t i m e w h i l e t h e l o w e r l e t t e r i n d i c a t e s t h e r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t o f t h e e f f e c t o f p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group o r t i m e s e r i e s t h a t s h a r e t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t ( p > 0 . 0 5 ) . "LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ) MHB=Medium-High B a r r i e r ; HB=High B a r r i e r i n c r e a s e . Seemingly anomalous r a t e s of weight change were observed f o r the c h e r r i e s i n the MHB and MLB f i l m bags , w i t h these t rea tments d i s p l a y i n g the g r e a t e s t weight l o s s e s a t the end of the s t o r a g e p e r i o d of a l l of the t r e a t m e n t s . The c o m b i n a t i o n of r e s p i r i n g c h e r r i e s w i t h low temperature s t o r a g e may have r e s u l t e d i n some water c o n d e n s a t i o n on the i n s i d e of the f i l m . I t Is known t h a t mo i s ture c o n d e n s a t i o n on f i l m s a d v e r s e l y a f f e c t s t h e i r p e r m e a b i l i t y (Day, 1988) . M o i s t u r e a c c u m u l a t i o n on the i n n e r s u r f a c e of the f i l m may have f a c i l i t a t e d the escape of water from the packages , d e s p i t e t h e i r apparent lower MVTR v a l u e s , r e s u l t i n g i n g r e a t e r weight l o s s e s . 4.4 EFFECT OF STORAGE TIME AND PACKAGE ON CHERRY TEXTURE AS DETERMINED WITH THE INSTRON c h e r r y t e x t u r e was measured o b j e c t i v e l y u s i n g the I n s t r o n t ex turometer as d e s c r i b e d i n S e c t i o n 3 . 6 . 1 . The t e c h n i q u e used measured the f o r c e - d e f o r m a t i o n behav iour of f r u i t s u b j e c t e d to a c o n s t a n t r a t e of l o a d i n g , which e l i m i n a t e s the p o s s i b i l i t y of e r r o r due to v a r i a b l e l o a d i n g r a t e s , p r o v i d i n g more a c c u r a t e i n f o r m a t i o n on the t e x t u r a l p r o p e r t i e s of the f r u i t ( L i d s t e r e t a l . , 1978) . The f o r c e - d e f o r m a t i o n c u r v e s g e n e r a t e d f o r I n d i v i d u a l c h e r r i e s were used f o r the c a l c u l a t i o n of t h r e e p a r a m e t e r s , namely b i o y i e l d , d e f o r m a t i o n , and f r u i t f i r m n e s s . L i d s t e r e t a l . (1978) i n d i c a t e d t h a t the f r u i t f i rmness v a l u e may p r o v i d e the most u s e f u l index of 76 c h e r r y f r u i t t e x t u r e . Those r e s e a r c h e r s a l s o suggested t h a t the f o r c e a p p l i e d to the c h e r r y a t the b i o y i e l d p o i n t may be an index of f o r c e - d e f o r m a t i o n behav iour of the f r u i t s u b j e c t e d to a c o n s t a n t r a t e of l o a d i n g . The b i o y i e l d va lue I n d i c a t e s the p o i n t a t which t i s s u e s t a r t s to r u p t u r e . O b j e c t i v e t e s t s which measure the f o r c e r e q u i r e d to compress the f r u i t a r e u s e f u l , s i n c e consumers i n i t i a l l y judge the r i p e n e s s and q u a l i t y of f r u i t s by p r e s s i n g them w i t h t h e i r f i n g e r s (Matz , 1962) . G e n e r a l l y , c h e r r y b i o y i e l d v a l u e s ( F i g u r e 4.4) and the f i rmness (maximal s l o p e of the f o r c e - d e f o r m a t i o n c u r v e , F i g u r e 4.5) v a r i e d w i t h s t o r a g e t i m e . S t a t i s t i c a l a n a l y s i s of the r e s u l t s r e v e a l e d t h a t b i o y i e l d and f i rmness v a l u e s v a r i e d s i g n i f i c a n t l y (p<0.05) w i t h both t ime and package f i l m type ( T a b l e s 4.4 and 4 . 5 ) . C h e r r i e s i n the HB f i l m packages underwent e x t e n s i v e s o f t e n i n g between the second and f o u r t h weeks of s t o r a g e as shown by the decrease i n f i rmness v a l u e s . F irmness v a l u e s of c h e r r i e s a t the s i x t h and e i g h t h weeks of s t o r a g e were s i m i l a r to those a t the f o u r t h week. S i m i l a r t r e n d s were a l s o observed i n s e n s o r y a n a l y s i s , where "Firmness" and "Texture" s c o r e s d e c r e a s e d r a p i d l y a f t e r two weeks of s t o r a g e ( S e c t i o n 4 . 1 0 ) . F i rmness v a l u e s of c h e r r i e s In packages of MLB and MHB i n c r e a s e d d u r i n g the f i r s t two weeks of s t o r a g e , and then a drop a t the four-week p e r i o d . S u b s e q u e n t l y , f i rmness v a l u e s of these c h e r r i e s i n c r e a s e d f u r t h e r a t s i x and e i g h t weeks. R e s u l t s of the c o n t r o l - a n d LB-packaged c h e r r i e s were not 77 T R E A T M E N T 0 2 4 6 8 S T O R A G E TIME (WEEKS) F i g u r e 4.4 Chanqes i n C h e r r y B i o y i e l d Va lues D u r i n g Storage a t 1 ° C (Data r e p r e s e n t the means + s t a n d a r d d e v i a t i o n of the mean) 78 T a b l e 4.4 B i o y i e l d V a l u e s (N) of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s S t o r a g e Time (Weeks) C o n t r o l LB Treatment' MLB MHB HB 0 9.4*2.1-a 9.4±2.1-a 9.4±2.1-.a 9.412.1-a 9.412.1-a 2 • 1 1 . 6 ± 2 . 8 -a 9.9 + 3 . 1 ^ ab 10. 6±2 . 5-. ab 1 1 . 0 ± 2 . 5 - -a 9 . 0 ± 1 . 3 | 4 11.6+2.9^ a 1 1 . 3 ± 3 . 0 -a 8.9*1.7*-b 1 1 . 6 ± 2 . 3 -a 9 . 3 ± 1 . 4 ^ b 6 14.6±2. 1 -a 1 4 . 2 ± 2 . 5 -ac 1 3 . 5 ± 2 . 0 -ac 1 6 . 5 ± 2 . 6 ^ b 1 2 . 9 ± 2 . 8 -c 8 1 8 . 5 ± 4 . 3 -a N.A. 17.713.1-a 19.614.0-a 15.013.6^ b Data r e p r e s e n t t h e mean v a l u e 1 s t a n d a r d d e v i a t i o n o f t h e mean (n=20). The u p p e r l e t t e r i n d i c a t e s the r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t of t h e e f f e c t s of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group o r time s e r i e s t h a t s h a r e the same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t (p> 0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A.=Not A v a i l a b l e T R E A T M E N T S T O R A G E T I M E ( W E E K S ) i g u r e 4 . 5 . Changes i n C h e r r y F irmness Va lues D u r i n g Storage a t 1 ° C . Data r e p r e s e n t the means + s t a n d a r d d e v i a t i o n of the mean) T a b l e 4 . 5 F i r m n e s s V a l u e s ( N / m ) o f C h e r r i e s U n d e r V a r i o u s P a c k a g i n g C o n d i t i o n s ^ 2 S t o r a g e T r e a t m e n t Time (Weeks) C o n t r o l LB MLB MHB HB 2157± 245-a 2578± 8 7 3 — a 2284± 745-ab 2990± 716-ab 3 0 2 9 ± 1 1 0 8 -a 2157± 245-a 2245± 755-a 2 5 5 9 ± 1 0 2 9 -a 3127± 686-a N. A. 2157± 245-a 2647± 618-1951± 647 2657+ 461 be b 3569± 814-a 2157+ 245-a 2 676± 755 be 2314± 549-^ ab 2882X 725-ab 3412± 843-a 2157± 245-a 2186± 412-a 1549± 382 1598± 441 1784± 794 Data r e p r e s e n t the mean v a l u e ± s t a n d a r d d e v i a t i o n o f t h e mean (n=20). The upper l e t t e r i n d i c a t e s t h e r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t s o f s t o r a g e time w h i l e t h e l o w e r l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t o f p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group o r t i m e s e r i e s t h a t s h a r e t h e same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t ( p ^ 0 . 0 5 ) . LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A.=Not A v a i l a b l e s i g n i f i c a n t l y d i f f e r e n t (p>0.05) for the f i r s t four weeks but the v a l u e s a t a s t o r a g e time of s i x weeks were h i g h e r . Perhaps p e c t i c subs tances were demethylated d u r i n g the i n i t i a l p a r t of the s t o r a g e p e r i o d and l a t e r was f o l l o w e d by the c r o s s - l i n k i n g of p e c t i c polymers w i th d i v a l e n t c a t i o n s , r e s u l t i n g i n i n c r e a s e d f i r m n e s s v a l u e s . C h e r r y b i o y i e l d v a l u e s r e p r e s e n t the amount of f o r c e r e q u i r e d to r u p t u r e c h e r r y t i s s u e . These v a l u e s i n c r e a s e d throughout the s t o r a g e p e r i o d for c h e r r i e s i n a l l of the e x p e r i m e n t a l f i l m packages and the c o n t r o l packages . A d e f o r m a t i o n v a l u e i n d i c a t e s the amount of c o m p r e s s i o n (mm) t h a t a c h e r r y can endure u n t i l the p o i n t of s k i n r u p t u r e and t i s s u e c o l l a p s e . The g r e a t e r the e l a s t i c i t y of the s k i n , the g r e a t e r the d e f o r m a t i o n v a l u e . S o f t f r u i t may have s k i n wi th g r e a t e r e l a s t i c i t y and parenchyma t i s s u e w i t h a l o s s of i n t e r c e l l u l a r c o h e s i o n . C h e r r i e s i n the HB f i l m packages had the h i g h e s t d e f o r m a t i o n v a l u e s o f a l l c h e r r i e s i n e x p e r i m e n t a l packages ( F i g u r e 4 . 6 ; T a b l e 4 . 5 ) . Whi le the l o s s of m o i s t u r e from f r u i t r e s u l t s i n a l o s s of t u r g o r p r e s s u r e and t e x t u r a l q u a l i t y of f r u i t (Powr ie , 1988) , the e f f e c t s of water l o s s on c h e r r y t e x t u r e i n t h i s s t u d y can be i g n o r e d , as water l o s s was m a i n t a i n e d below 1% i n a l l t r e a t m e n t s ( S e c t i o n 4 . 3 ) . Chen e t aj^. (19 81) found t h a t the f i rmness of * B i n g ' sweet c h e r r i e s i n c r e a s e d d u r i n g s torage under low oxygen t e n s i o n s , but t h a t lower s t o r a g e temperatures enhanced f r u i t 82 F i g u r e 4 . 6 . Changes l n C h e r r y Deformat ion Va lues D u r i n g S torage a t l ° c (Data r e p r e s e n t the mean + s t a n d a r d d e v i a t i o n of the mean) 83 T a b l e 4.6 D e f o r m a t i o n V a l u e s (mm) of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s 1 S t o r a g e T r e a t m e n t Time (Weeks) C o n t r o l LB MLB MHB HB 0 6.3+1.2-a 6.3±1.2-a 6.3±1.2-a 6.3±1.2-a 6 . 3 ± 1 . 2 -a 2 6. 7 ± 1 . 1 — a 6 . 7 ± 1 . 3 — a 6 . 3 ± 1 . 4 -a 6.7±1.1-a 5.9+1.0-a 4 8.4±1.6-. ab 7.8±1.9-a 7 . 9 ± 1 . 3 -a 8.6±1.2- v ab 9.1±l.lJ b 6 7.2±1.3-a 7.5+1.2^ a 8 . 4 ± 1 . 3 ^ b 8.7±1.2^ b 10.2+1.2-c 8 8.2±1.2-a N.A. 7.6+1.4-a 7.8+1.3-a 10.5+1.7^ b Data r e p r e s e n t t h e mean v a l u e + s t a n d a r d d e v i a t i o n o f t h e mean (n=20). The u p p e r l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t o f t h e e f f e c t o f s t o r a g e t i m e w h i l the l o w e r l e t t e r i n d i c a t e s t h e r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t o f t h e e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or t i m e s e r i e s t h a t s h a r e t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( p ^ 0 . 0 5 ) . LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A.=Not A v a i l a b l e f i rmness independent of c o n t r o l l e d atmosphere c o n d i t i o n s . The r e h a r d e n i n g phenomenon of c h e r r i e s may be s i m i l a r to t h a t observed i n peaches s t o r e d a t low t e m p e r a t u r e s , which may be due to the g e l l i n g behav iour of the w a t e r - s o l u b l e p e c t i n f r a c t i o n (Werner and F r e n k e l , 1978) . Those r e s e a r c h e r s suggested t h a t changes i n temperature a f f e c t the behav iour of p e c t i c s u b s t a n c e s , and p r o b a b l y o ther c e l l w a l l c o n s t i t u e n t s ( e . g . , p o l y s a c c h a r i d e s ) , as low temperatures promote t h i c k e n i n g of these compounds. P a t t e r s o n (1981) found t h a t a t m o s p h e r i c c o n d i t i o n s I n f l u e n c e the t e x t u r a l c h a r a c t e r i s t i c s of c h e r r i e s . I t was shown t h a t CA c h e r r i e s r e t a i n e d a f i r m e r t e x t u r e over an extended s t o r a g e p e r i o d as compared to c o n v e n t i o n a l l y s t o r e d f r u i t . Oxygen l e v e l s of l e s s than 10% appeared to a c c e l e r a t e s o f t e n i n g , w h i l e 20% carbon d i o x i d e promoted the g r e a t e r r e t e n t i o n of c h e r r y f i rmness as compared to c h e r r i e s i n a 1% carbon d i o x i d e atmosphere a t the same s t o r a g e t e m p e r a t u r e . The e f f e c t s of CAS on c h e r r y t e x t u r e may a l s o be due to an i n f l u e n c e of the atmosphere on p e c t i c enzymes. I t has been shown t h a t the s t o r a g e of mature -green tomato f r u i t i n an atmosphere of 5% oxygen and 5% carbon d i o x i d e d e l a y s the s y n t h e s i s of p o l y g a l a c t u r o n a s e , a key enzyme i n f r u i t s o f t e n i n g (Goodenough e_t § _ 1 . , 1982) . I t was suggested t h a t CA c o n d i t i o n s prevent the <te novo s y n t h e s i s of p o l y g a l a c t u r o n a s e , as opposed to s i m p l y r e g u l a t i n g i t s a c t i v i t y . CA c o n d i t i o n s may p r e v e n t the t r a n s c r i p t i o n o f preformed messenger RNA to enzyme p r o t e i n (Goodenough, 1982) . The f a i l u r e of p e c t i c enzymes to be produced or to be o p e r a t i v e i n c h e r r i e s might account for the 85 observed r e t e n t i o n of c h e r r y f i rmness i n t h i s s t u d y . 4 .5 EFFECT OF STORAGE TIME AND PACKAGE ON CHERRY SURFACE COLOUR (REFLECTANCE MEASUREMENTS) C o l o u r , a v e r y important q u a l i t y a t t r i b u t e of a l l f o o d s , p l a y s a key r o l e i n food a c c e p t a b i l i t y . The c o l o u r of a food may be an i n d i c a t o r of c h e m i c a l changes t h a t may have o c c u r r e d i n a food (deMan, 1982) , and changes i n c o l o u r are f r e q u e n t l y c o r r e l a t e d w i t h r i p e n i n g ; t h e r e f o r e , c o l o u r can o f t e n be a u s e f u l index of m a t u r i t y ( F u l e k l , 1970) . S u r f a c e c o l o u r of f r u i t s and v e g e t a b l e s i s g e n e r a l l y a s ses sed u s i n g r e f l e c t a n c e measurements. One of the most common systems employed i s the Hunter L , a , b sys tem, which uses c o l o u r s c a l e s based on the o p p o n e n t - c o l o u r t h e o r y of c o l o u r v i s i o n . In t h i s sys tem, as i n the b r a i n , red responses are compared w i t h green to g i v e a r e d - t o - g r e e n c o l o u r d i m e n s i o n , d e s i g n a t e d as the a v a l u e . S i m i l a r l y , the green response i s compared w i t h b lue to generate a y e l l o w - t o - b l u e c o l o u r d i m e n s i o n , q u a n t i t a t e d i n the b v a l u e of the Hunter sys tem. L i s a measure of l i g h t n e s s and i s a n o n - l i n e a r s c a l e on which L v a l u e s of z e r o and 100 r e p r e s e n t b l a c k and w h i t e , r e s p e c t i v e l y ( F i g u r e 4.7) (deMan, 1982) . In the case of c h e r r i e s , changes might be expected i n both the Hunter a and b v a l u e s w i t h r i p e n i n g and senescence . Increase s i n the p o s i t i v e a v a l u e r e f l e c t an i n c r e a s e i n r e d n e s s , wh i l e an i n c r e a s i n g b v a l u e i n the nega t ive r e g i o n s 86 F i g u r e 4.7 The Hunter L , a , b C o l o u r S o l i d (deMan, 1982) 87 would i n d i c a t e a l o s s of b lue c o l o u r . D e c r e a s i n g L v a l u e s would r e f l e c t an o v e r a l l d a r k e n i n g of the s u r f a c e of the f r u i t , which might be a t t r i b u t a b l e t o changes i n the c h e m i c a l components of the f r u i t , such as o x i d a t i v e changes l e a d i n g to browning . Low L v a l u e s a l s o i n d i c a t e i n t e n s e l y c o l o u r e d f r u i t s ( P o l e s e l l o and B o n z i n i , 1977) . The L , b , and a v a l u e s f o r c h e r r i e s d u r i n g MAP s t o r a g e are p r e s e n t e d i n F i g u r e s 4 .8 , 4 . 9 , and 4 .10 , r e s p e c t i v e l y . S t a t i s t i c a l a n a l y s i s of the r e s u l t s i s i n c l u d e d i n T a b l e s 4.7 to 4 . 9 . The L v a l u e s of the c h e r r i e s were found to v a r y w i d e l y over the e n t i r e s t o r a g e p e r i o d , w i t h no w e l l - d e f i n e d t r e n d b e i n g e v i d e n t . For the most p a r t , v a l u e s d i d not v a r y s i g n i f i c a n t l y w i t h time (p > 0 . 0 5 ) . However, the L v a l u e s o f c h e r r i e s i n the c o n t r o l packages were lower a t the end of the s t o r a g e p e r i o d than a t the b e g i n n i n g . Moreover , a t s t o r a g e p e r i o d s from f i v e to e i g h t weeks, the L v a l u e s of c h e r r i e s i n the e x p e r i m e n t a l packages were h i g h e r than those i n the c o n t r o l packages . The lower l i g h t n e s s of the c o n t r o l c h e r r i e s may have been due to the f o r m a t i o n of brown pigments through p o l y m e r i z a t i o n of p h e n o l s . I t i s known t h a t a n t h o c y a n i n d e s t r u c t i o n o c c u r s r a p i d l y i n the presence of a i r (Von E l b e , 1986; Adams, 1973) . T h i s i s p a r t i c u l a r l y t r u e i n the presence of a s c o r b i c a c i d , where an i n t e r a c t i o n o c c u r s between the a n t h o c y a n i n s and a s c o r b i c a c i d , l e a d i n g to a l o s s of both compounds ( C l y d e s d a l e and F r a n c i s , 1976) . The d e s t r u c t i o n o f a n t h o c y a n i n s w i l l be more c o m p l e t e l y d i s c u s s e d i n S e c t i o n 4 . 7 . 88 I t may be, t h e n , t h a t i n the a e r o b i c atmosphere w i t h i n the c o n t r o l packages t h a t a n t h o c y a n i n s and a s c o r b i c a c i d breakdown, w i t h a concomi tant f o r m a t i o n of brown d e g r a d a t i o n p r o d u c t s , l e d to a p r o g r e s s i v e d a r k e n i n g of the f r u i t s u r f a c e . I t appears t h a t the low oxygen l e v e l s i n MAP packages i n h i b i t e d the breakdown of a n t h o c y a n i n s to the ex ten t t h a t i t was not e v i d e n t on the s u r f a c e of the f r u i t . The f a t e of a n t h o c y a n i n s can be important in i n f l u e n c i n g L v a l u e s , as the L v a l u e of a n t h o c y a n i n s o l u t i o n s has been shown to be i n f l u e n c e d by pH and the type and q u a n t i t y of a n t h o c y a n i n s presen t (Van Buren e t a l . , 1974) . As w i l l be d i s c u s s e d i n S e c t i o n 4 . 6 . 1 , MAP t rea tment s a l s o a f f o r d e d b e t t e r r e t e n t i o n of pH v a l u e s i n the r e g i o n observed for f r e s h f r u i t , which would a i d i n s t a b i l i z i n g the p igments . As shown i n F i g u r e 4 . 9 , Hunter b v a l u e s of c h e r r i e s i n the c o n t r o l and HB f i l m packages d e c r e a s e d over the e ight-week s t o r a g e p e r i o d . Thus , the c h e r r y s u r f a c e l o s t y e l l o w n e s s and tended toward b l u e . The Hunter a va lues of c h e r r i e s i n the c o n t r o l and HB f i l m packages d e c l i n e d d u r i n g s t o r a g e for e i g h t weeks w i t h the i n d i c a t i o n of red c o l o u r l o s s ( F i g u r e 4 . 1 0 ) . S i m i l a r r e s u l t s f o r f r o z e n c h e r r i e s were r e p o r t e d by P o l e s e l l o and B o n z i n i (1977) , who i n d i c a t e d t h a t t h e r e was a s h i f t toward p u r p l e - r e d c o l o u r a t the end of the s t o r a g e p e r i o d . S i m i l a r changes have been observed d u r i n g the r i p e n i n g of Saskatoon b e r r i e s , which underwent a c o l o u r change from r e d to p u r p l e - r e d (Green and Mazza , 1986) . 89 2 3 4 5 6 7 STORAGE TIME (WEEKS) F i g u r e 4.8 Changes i n Hunter L Va lues of C h e r r i e s D u r i n g S torage a t 1° C 90 T a b l e 4.7 Hunter L Values of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s S t o r a g e Treatment^ Time — • (Weeks) C o n t r o l LB MLB MHB HB 0 12.0*0.5-a 12.0*0.5-a 1 2 . 0 * 0 . 5 — a 12 . 0 * 0 . 5 ^ a 12 + 0*0.5-^ a 1 12.1*0.7-a 12.2*0.7-a 1 2 . 1 * 0 . 5 ^ a 12. 8 * 0 . 6 ^ a 12 . 8*0.2^ a 2 11.8*1.1-a 12.2*0.8-a 1 2 . 7 * 1 . 0 ^ a 12 . 7 * 0 . 6 ^ a 12 . 6 * 0 . 8 ^ a 3 11.9+0.6-a 11.6+0.5^ a 11.5+0.6-a 12 . 9 + 0 . 8 ^ b 12 . 3 ± 0 ' 3 a T 4 10.9* 0 . 4 — a 11.0*0.3-a 1 2 . 2 * 1 . 4 ^ b 11. 7 * 0 . 5 ^ ab 12 . 2 * 0 . 2 ^ b 5 1 0 . 4 * 0 . 5 — a 12.4*0.9^ D 11.5*0.9-^ ab 11. 9 * 0 . 7 ^ b 12 . 5 * 0 . 7 ^ b 6 1 1 . 4 * 0 . 5 ^ a 11.9±0.3- v ab 1 2 . 0 * 0 . 8 ^ ab 13. 6*1.5^ c 12 . 9*0.2§ b c 7 10.2±0.8-a N.A. 13.2*0.7^ b 13. 0±2.l££ b 12 . 8 ± 0 . 6 ^ b 8 10 . 6 * 0 . 3 — a N.A. 1 2 . 5 * 1 . 0 ^ 11. 2*1.1^ a 12 . 6 * 0 . 5 ^ b Data r e p r e s e n t the mean * s t a n d a r d d e v i a t i o n of the mean (n=4). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e The changes observed i n the Hunter a and b v a l u e s w i t h time i n the c h e r r i e s s t o r e d under MAP c o n d i t i o n s can be e x p l a i n e d independent of each o ther through examinat ion of the pigments p r e s e n t i n c h e r r y f r u i t . C h e r r i e s c o n t a i n r e l a t i v e l y h i g h l e v e l s of c a r o t e n o i d pigments ( G a l l e r and MacKlnney , 1965), which a r e a group of m a i n l y l i p i d - s o l u b l e , h i g h l y u n s a t u r a t e d compounds. The h i g h degree of u n s a t u r a t i o n r e n d e r s c a r o t e n o i d s s u s c e p t i b l e to o x i d a t i o n . S i n c e the pigments may a u t o x i d i z e w i th a tmospher i c oxygen ( F r a n c i s and C l y d e s d a l e , 1976), the lower l e v e l s of oxygen under MAP c o n d i t i o n s shou ld i n f l u e n c e c a r o t e n o i d s t a b i l i t y . I t has been demonstrated t h a t the l o s s of c a r o t e n e i n s t o r e d c a r r o t s i s i n h i b i t e d under low oxygen t e n s i o n s ( B u r t o n , 1974) . T h i s i s l i k e l y due to the i n h i b i t i o n of o x i d a t i v e enzyme proces se s i n such atmospheres ( B u r t o n , 1982) . As p r e v i o u s l y i n d i c a t e d , the b v a l u e s showed a downward t r e n d over the s t o r a g e p e r i o d i n a l l packaging t r e a t m e n t s . F r u i t i n the c o n t r o l packages d i s p l a y e d s i g n i f i c a n t l y lower b v a l u e s ( l e s s y e l l o w ) a t the end of s t o r a g e , due to the h i g h l e v e l s of oxygen e x i s t i n g i n the packages throughout the s t u d y . The h i g h l e v e l of oxygen i n the c o n t r o l packages undoubted ly p e r m i t t e d the o x i d a t i o n of c a r o t e n o i d s (among o ther components) i n c h e r r i e s r e s u l t i n g i n a l o s s of y e l l o w c o l o u r . D u r i n g the e x t r a c t i o n s t e p i n p r e p a r a t i o n for HPLC a n a l y s i s of o r g a n i c a c i d s ( S e c t i o n 3 . 7 . 3 . 1 ) , a l a r g e y e l l o w p e l l e t was noted w i t h e x t r a c t a n t s from low-oxygen MA packages a f t e r c e n t r i f u g a t i o n . 92 H TREATMENT O CONTROL • LB A MLB 0 MHB * HB 0 1 2 3 4 5 6 7 STORAGE TIME (WEEKS) 8 F i g u r e 4.9 Changes i n Hunter b Values of C h e r r i e s D u r i n g Storage a t 1 ° C 93 T a b l e 4.8 Hunter b Values of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s Storage Treatment^ Time : : (Weeks) C o n t r o l LB MLB MHB HB 0 4.2±0.2-a 4.2±0.2-a 4 . 2 * 0 . 2 ^ a 4. 2*0.2-^ a 4.2+0.2-a 1 3.7±0.4-^ a 3 > 8 ± 0 . 3 ^ a 3 . 8 ± 0 . 1 ^ a 4. 4 + 0 . 2 ^ b 4.0±0.2-a 2 3.9+0.7^ a 3.7+0.3^ a 3.9+0.8^ a 4. 1 + 0 . 3 ^ a 4.0±0.7-a 3 3.5+0.5^ a 3 . 8 ± 0 . 4 ~ ab b 4. 8 ± 0 . 9 - v ab 4 . 0 ± 0 . 8 - v ab 4 3.3 + 0 . 3 ^ a 3.4+0.3^ a 4.4+0.8^ b 4. 0+0.6-^ ab 3.9+0.5- K ab 5 2 . 7 ± 0 . 3 ^ a 4.2*0.5^ D 3 . 7 * 0 . 6 ^ b 3 . 9 ± 0 . 7 ^ b 3 . 5 * 0 . 4 ^ b 6 2.4+0.6^ a 3.3±0.2- v ab 3 . 3 ± 0 . 7 - K ab 4. 1 + 1 . 3 ^ b 3 . 5 ± 0 . 5 ^ ab 7 2.3±0.4-a N. A. 4.9±0.7^ be 4. 3 ± 1 . 4 ^ c 3.010.8-^ ab 8 2.3*0.3-a N. A. 4 . 4 * 0 . 8 ^ b 3 . 0*0.9^ a 2.8*0.5-a Data r e p r e s e n t the mean i s t a n d a r d d e v i a t i o n of the mean (n=4). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of pac k a g i n g m a t e r i a l . R e s u l t s w i t h i n a treatment group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e T h i s p e l l e t was assumed to be compri sed m a i n l y o £ c a r o t e n o l d s and other w a t e r - i n s o l u b l e c e l l components. The redness of c h e r r y f r u i t s i s a t t r i b u t a b l e to the a n t h o c y a n i n pigments p r e s e n t both i n the s k i n and f l e s h a t the time of h a r v e s t . Anthocyan ins are h i g h l y u n s t a b l e compounds, and t h e i r c o l o u r i s h i g h l y dependent on pH. In a d d i t i o n , a n t h o c y a n i n s r e a d i l y undergo o x i d a t i o n i n the presence of a tmospher i c oxygen. Whi le i t has been e s t a b l i s h e d t h a t changes i n c h e r r y a n t h o c y a n i n s occur p r e d o m i n a n t l y in the f l e s h ( P o l e s e l l o and B o n z i n i , 1977) , i t i s q u i t e p r o b a b l e t h a t some a l t e r a t i o n i n t h e i r s t r u c t u r e or d i s t r i b u t i o n a l s o occurs i n the s k i n , and i s r e f l e c t e d i n the Hunter a v a l u e . Hunter a v a l u e s d e c r e a s e d i n a l l t reatments i n t h i s s t u d y , w i t h v a l u e s b e i n g s i g n i f i c a n t l y lower a t the end of the s t o r a g e p e r i o d f o r the c o n t r o l , L B , and HB f i l m s , r e f l e c t i n g a g r e a t e r l o s s of r e d c o l o u r ( F i g u r e 4 .10; T a b l e 4 . 9 ) . C o n v e r s e l y , a v a l u e s for the MLB and MHB f i l m f r u i t were not s i g n i f i c a n t l y d i f f e r e n t (p > 0.05) a t the end of e i g h t weeks s t o r a g e , a l t h o u g h they were s i g n i f i c a n t l y d i f f e r e n t (p <0.05) from each o t h e r . The l o s s of r e d c o l o u r l n the c o n t r o l and LB packages was l i k e l y due to changes l n the a n t h o c y a n i n s . In the HB-packaged c h e r r i e s some a n t h o c y a n i n d e g r a d a t i o n may have o c c u r r e d . The l o s s of redness from HB-package f r u i t was l i k e l y due to a n t h o c y a n i n p o l y m e r i z a t i o n accompanying the p h y s i o l o g i c a l breakdown of the f r u i t t i s s u e . F u l e k i (1970) measured the c o l o u r of t a r t c h e r r i e s u s i n g 95 22 20H * HB T 1 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 STORAGE TIME (WEEKS) F i g u r e 4.10 Changes i n Hunter a Va lues of C h e r r i e s D u r i n g S torage a t 1° C 96 T a b l e 4,9 Hunter a Values of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s ^ S t o r a g e Treatment^ Time — — — — • (Weeks) C o n t r o l LB MLB MHB HB 0 17.6*0.9- 17.6*0.9- 17.6*0.9^2- 1 7 . 6 * 0 . 9 — 17.6*0.9-a a a a a 1 1 5 . 5 * 1 . 1 — 16.2±1.0*jf£ 16.5+0.5-^ 18.2 + 0.7-^ 1 6 . 8 * 0 . 6 ^ a ab ab c b 2 ' 1 6 . 8 * 2 . 3 ^ 1 5 . 7 * 1 . 3 ^ . " 1 6 . 6 * 2 . 5 - ^ 1 7 . 3 * 0 . 9 ^ 1 7 . 1 * 2 . 3 ^ a a a a a 3 * 15.2*1.7- 1 6 . 3 * 1 . 3 ^ 1 7 . 0 * 1 . 3 ^ 19.3*2.6^ 1 6 . 5 * 2 . 4 ^ a ab b ab ab 4 1 4 . 5 * 1 . 0 ^ 1 4 . 7 * 1 . 0 ^ 1 8 . 4 * 2 . 6 ^ 1 6 . 9 * 1 . 8 ^ 1 6 . 1 * 1 . 6 ^ a a b ab ab 5 1 2 . 5 * 1 . 2 ^ 1 6 . 9 * 1 . 4 ^ 1 5 . 8 * 2 . 1 ^ 1 5 . 7 * 2 . 0 ^ 1 4 . 5 * 1 . 2 ^ a b b b b 6 11.7*2.1- 14.2*1.0-. 14.4*2.3-. 1 6 . 8 * 4 . 2 ^ 1 4 . 6 * 1 . 9 ^ a ab ab b ab 7 10.9*1.4- N.A. 19.3*2.3^ 1 7 . 0 * 4 . 4 ^ 12.2*2.4-a b b a 8 10.5*1.4- N.A. 1 7 . 6 * 2 . 3 ^ - 13.3*2.9- 12.0*1.6-a b a a '''Data r e p r e s e n t the mean * s t a n d a r d d e v i a t i o n of the mean (n=4). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p^O.05). 2 LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A.= Not A v a i l a b l e the Hunter system as an o b j e c t i v e method. The a r e a d i n g s were found to c o r r e l a t e bet w i t h the v i s u a l assessment . I f the a va lue i s c o n s i d e r e d to be the best measure of s u r f a c e c o l o u r , then i n t h i s s t u d y , the MLB and MHB f i l m s f o r packages would be best f o r the r e t e n t i o n of r e d s u r f a c e c o l o u r . 4.6 CHANGES IN pH, PERCENT TITRATABLE ACIDITY, PERCENT SOLUBLE SOLIDS, AND PERCENT SOLUBLE SOLIDS/PERCENT TITRATABLE ACIDITY RATIOS WITH STORAGE TIME 4 . 6 . 1 pH CHANGES The pH v a l u e s f o r the c h e r r i e s i n a l l t r ea tment s were observed to i n c r e a s e d u r i n g the s torage p e r i o d ( F i g u r e 4 .11; T a b l e 4 . 1 0 ) . R e s u l t s showed t h a t c h e r r i e s i n packages of a l l e x p e r i m e n t a l f i l m s and the c o n t r o l packages underwent a s i g n i f i c a n t i n c r e a s e (p < 0.05) l n pH v a l u e s over the e n t i r e s t o r a g e p e r i o d . O n l y the HB-packaged c h e r r i e s v a r i e d s i g n i f i c a n t l y (p < 0.05) from the o thers a t the end of e i g h t weeks. I t seems as though some mechanism was o p e r a t i v e i n the HB packages t h a t p r o h i b i t e d pH change. The h i g h e s t pH v a l u e s o b s e r v e d , i n the c o n t r o l , MHB, and MLB packages , were l e s s than the c r i t i c a l v a l u e of 4 .6 ; t h e r e f o r e , i t i s l i k e l y sa fe to assume t h a t even i f the atmospheres w i t h i n these packages became a n a e r o b i c , the growth of and t o x i n f o r m a t i o n by C l o s t r i d l u m b o t u l i n u m would pose no r i s k . In the HB f i l m packages , where c o n d i t i o n s were undoubted ly a n a e r o b i c , c h e r r i e s had pH v a l u e s w e l l below 4 .6 ; thus no p a t h o l o g i c a l r i s k i s e v i d e n t w i t h r e s p e c t to C . b o t u l i n u m . 98 4.6 3 4 5 6 7 STORAGE TIME (WEEKS) F i g u r e 4.11 Changes i n C h e r r y pH Values Dur ing Storage a t 1 C 99 T a b l e A.10 pH Values of C h e r r i e s Under V a r i o u s Packaging C o n d i t i o n s S t o r a g e ' Time (Weeks) C o n t r o l Treatment' LB MLB MHB HB 3.92*0.01- 3.92*0.01- 3.92*0.01-a 3.92*0.01-a 3.91*0.01-a 4.11+0.01-a 4. 24+0.12-a 4.18+0.05-a 4.14+0.04--a 4.23+0.06 be 4. 16i 0 . 0 9 -4.23+0.01 a be 4.19±0.00-a 4. 33±0.06 cd 4.16±0.06-a 4. 23+0. 03-a 4 . 2 0 ± 0 . 0 4 £ a 4.25±0.04-. abc 4.19±0.02-a 4.20+0.02-a 4.21+0.01^ a 4. 31*0.01-. ab 4.11±0.01-a 4.18+0.01-a 4.17+0.05^ a 4.20*0.01-4.12±0.01-4.22+0.03 be 4. 1 9 ± 0 . 0 8 — a 4 . 23*0.01— bc 4 .44*0 . 0 5 — a 4.27+0.02^ b 4.28 + 0.05^-b 4.27+0.04^ b 4.12+0.01-c 4.53±0.07-a N. A. 4.40±0.0 5- v ab 4.45*0.02- v ab 4.28±0.09r b 4.48*0.10-a N. A, 4.42+0.01- 4.50+0.04-a 4.24+0.04 be 1 Data r e p r e s e n t the mean * s t a n d a r d d e v i a t i o n of the mean (n=2). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group c r time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). "LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e The i n c r e a s e i n pH i s a commonly observed phenomenon d u r i n g r i p e n i n g due to d e c r e a s e s i n the amounts of the v a r i o u s o r g a n i c a c i d s because of the c o n t i n u e d metabol i sm of l i m i t e d energy sources w i t h i n the h a r v e s t e d f r u i t ( U l r i c h , 1970) . The p r i n c i p a l e f f e c t of MAP i s to reduce the r a t e of metabo l i sm; t h i s i s r e f l e c t e d i n an a l t e r a t i o n i n the r a t e and ex ten t of change of pH v a l u e s . In t h i s s t u d y , c h e r r i e s i n the LB and HB f i l m packages d i s p l a y e d the s lowest r a t e of change of pH, and m a i n t a i n e d the lowest pH v a l u e s a t the end of t h e i r r e s p e c t i v e s t o r a g e p e r i o d s . T h e r e f o r e , the c o n d i t i o n s w i t h i n these packages can be c o n s i d e r e d to be p r e f e r a b l e to those i n the o ther t rea tments w i t h r e s p e c t to maintenance of " f r e s h " pH v a l u e s . I t must be r e - s t a t e d , though , t h a t the HB f r u i t was judged to be u n a c c e p t a b l e e a r l y i n the s t o r a g e p e r i o d , i n d i c a t i n g the u n s u i t a b i l i t y of t h i s packag ing regime r e g a r d l e s s of i t s e f f e c t s on f r u i t pH v a l u e s . 4 . 6 . 2 PERCENT TITRATABLE ACIDITY The p e r c e n t t i t r a t a b l e a c i d i t y (TA) v a l u e s of c h e r r i e s decreased f o r i n a l l of the packag ing systems i n c l u d i n g the c o n t r o l packages d u r i n g s t o r a g e , w i t h the change g e n e r a l l y b e i n g m i r r o r e d by the r i s e i n pH ( F i g u r e 4 . 1 2 ) . TA v a l u e s were found to v a r y s i g n i f i c a n t l y (p < 0.05) w i th both time and package f i l m type (Tab le 4 . 1 1 ) . 101 TREATMENT O CONTROL • LB 0.3 -\ 1— 1 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 STORAGE TIME (WEEKS) F i g u r e 4 .12 . Changes In P e r c e n t T i t r a t a b l e A c i d i t y L e v e l s i n (as M a l i c A c i d ) C h e r r i e s Dur ing Storage a t 1 ° C 102 T a b l e 4.11 Pe r c e n t T i t r a t a b l e A c i d i t y L e v e l s (as M a l i c A c i d ) of C h e r r i e s Under V a r i o u s Packaging C o n d i t i o n s ! S t o r a g e T r e a t m e n t 2 Time . . (Weeks) C o n t r o l LB MLB MHB HB 0.71±0.02- 0. 71±0.02-a 0.71±0.02-a 0. 71±0.02- 0.71±0.02-a 0.62±0.04-,_ ab 0.69±0.01-a 0.62±0.04 ab 0.56±0.05t 0. 6 4 ± 0 . 0 2 ~ ab 0.56±0.00-a 0.56+0.00- 0.54+0.00r b 0. 57 + 0. 0 0 — a be 0. 60 + 0 . 0 0 — c 0.57±0.02-a 0.60±0.06-a 0.53+0.00-a 0.62±0.02-a 0.55±0.06-a o 0.56±0.01-a 0.58+0.02-a 0.53+0.02-a 0.55+0.02-a 0.58 + 0 . 0 7 — 0.50±0.03-a 0.59±0.02-c 0.52±0.03^r ab 0.54±0.01- v abc 0.57±0.03^-bc 0.49*0.03 0.44±0.02 de a ef 0.57+0.05^ be N.A. 0. 50+0. 0 0 ^ ab 0. 52+0 . 0 5 ^ b 0.51±0.03- v abc 0.53+0.01^ b 0.59 + 0.01 — c 0. 60 + 0. 00 — c 0.43*0.00-a N.A. 0.46+0.01-a 0.44+0.02-a 0.57+0.OO^-b Data r e p r e s e n t the mean * s t a n d a r d d e v i a t i o n of the mean (n=2)i The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a tr e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.O5). "LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e Percent TA i s de termined by a l k a l i t i t r a t i o n w i t h the o b j e c t i v e b e i n g to measure the t o t a l n e u t r a l i z a t i o n of a l l a c i d i c groups i n c l u d i n g p h e n o l s , amino a c i d s , and o ther c o n s t i t u e n t s a b l e to combine w i t h the t i t r a n t ( U l r i c h , 1970) . T h e r e f o r e , TA v a l u e s may r e f l e c t changes In any of a number of c o n s t i t u e n t s of f r u i t s . T i t r a t a b l e a c i d i t y v a l u e s decreased most d r a m a t i c a l l y i n the c o n t r o l , MLB, and MHB f i l m packages , w i th a l l of these treatments e x h i b i t i n g comparable l e v e l s of a c i d i t y a t the end of the e ight -week s t o r a g e s t u d y . These TA v a l u e s were found to be s i g n i f i c a n t l y d i f f e r e n t (p < 0.05) from i n i t i a l TA v a l u e s for these f i l m packages , w h i l e no s i g n i f i c a n t d i f f e r e n c e e x i s t e d among the f i l m packages (p > 0 . 0 5 ) . As was observed for pH v a l u e s , c h e r r i e s i n the LB and HB packages f r u i t d i s p l a y e d the lowest r a t e of change , and a t t a i n e d comparable l e v e l s of a c i d i t y a t the end of t h e i r r e s p e c t i v e s t o r a g e p e r i o d s . i n the case of the LB f i l m , the s low decrease i n TA v a l u e s over the e n t i r e e ight -week s t o r a g e p e r i o d was l i k e l y due to the marked r e d u c t i o n i n the r a t e of r e s p i r a t i o n , and thus to a s lower u t i l i z a t i o n of o r g a n i c a c i d s as o x i d a t i v e s u b s t r a t e s . The s low r a t e of d e c l i n e of TA v a l u e s i n the HB f i l m c h e r r i e s may have been due to the h y d r o l y s i s of some p r o t e l n a c e o u s components, r e l e a s i n g f r e e amino a c i d s Into the medium, which would be accounted for i n €he TA v a l u e . The TA v a l u e s of f r u i t s n o r m a l l y decrease p o s t - h a r v e s t ( U l r i c h , 1970) . T h i s i s due to the metabol i sm of o r g a n i c a c i d s through a e r o b i c r e s p i r a t i o n . 104 While TA may be a u s e f u l index of m a t u r i t y or serve as o b j e c t i v e i n f o r m a t i o n r e l a t i n g to f l a v o u r , U l r i c h (1970) i n d i c a t e d t h a t from a p h y s i o l o g i c a l v i e w p o i n t , TA f i g u r e s may be of l i t t l e use , s i n c e a n i o n s are a l s o i n v o l v e d i n metabo l i sm. F u r t h e r m o r e , some a c i d s are v e r y important i n metabo l i sm, d e s p i t e t h e i r low c o n c e n t r a t i o n ; t h e r e f o r e , I t i s more i n f o r m a t i v e to determine the amount of i n d i v i d u a l a c i d s p r e s e n t . T h u s , whi l e the type of packag ing m a t e r i a l o b v i o u s l y i n f l u e n c e d the r a t e of a c i d i t y d e c l i n e of the c h e r r i e s d u r i n g s t o r a g e , the o r g a n i c a c i d s p r o f i l e s shed more l i g h t on what may a c t u a l l y be o c c u r r i n g a t the c e l l u l a r l e v e l as a r e s u l t of i n t e r n a l atmosphere m o d i f i c a t i o n . T h i s w i l l be d i s c u s s e d i n d e t a i l i n S e c t i o n 4 . 9 . 4 . 6 . 3 PERCENT SOLUBLE SOLIDS S t a t i s t i c a l a n a l y s i s of p e r c e n t s o l u b l e s o l i d s (SS) d a t a for s t o r e d c h e r r i e s r e v e a l e d t h a t SS l e v e l s v a r i e d s i g n i f i c a n t l y w i t h both t ime and package type (p < 0.05) (Table 4 . 1 2 ) . R e s u l t s are p r e s e n t e d g r a p h i c a l l y i n F i g u r e 4,13 and show a s i g n i f i c a n t l o s s of SS i n c h e r r i e s i n e x p e r i m e n t a l f i l m packages and c o n t r o l packages d u r i n g the f i r s t two to four weeks of s t o r a g e . These r e s u l t s may be accounted f o r by the breakdown of sugars and a c i d s i n the r e s p i r a t i o n p r o c e s s . As s t o r a g e t ime p r o g r e s s e d , the SS i n c r e a s e d to a l e v e l c l o s e to the i n i t i a l v a l u e of the u n s t o r e d c h e r r i e s a t about 20%. P r e c u r s o r s of sugars such as s t a r c h and p e c t i n s were p r o b a b l y h y d r o l y z e d e n z y m a t i c a l l y to produce more s o l u b l e s o l i d s . 105 24 23 H 22 H 14H 13 TREATMENT O CONTROL • LB A MLB 0 MHB * HB 12 0 T 2 3 4 5 ~6 7 STORAGE TIME (WEEKS) 8 F i g u r e 4.13 Changes i n P e r c e n t S o l u b l e S o l i d s L e v e l s of C h e r r i e s D u r i n g Storage a t l ^ C 106 T a b l e 4.12 P e r c e n t S o l u b l e S o l i d s L e v e l s of C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s ^ Storage T r e a t m e n t 2 Time (Weeks) C o n t r o l LB MLB MHB HB 19.93±0.06 & 19.93±0.06-^ a a 19.93+0.06-a 19.93±0.06-a 19.93±0.06 ab 20.45±0.86-a 18.99±0.57 bed 17.49±1.20-a 17.67+0.18 de 18.22±0.60 ab 17.7 7+0.6 7-ab 18.14+2.12— a ah 18.67*0.18— 19.22*0.74*. 18.29±0.00 16.64±0.07 ab ab abc be 15.77±0.74-a 18.97±0.39-ab 16.89+0.00^ b 19.37+0.53-a 18.53±0.83-a 20.45±0.29-a 19.22±0.81 18.02+0.67 ab c ab c 1 7 . 7 2 ± 2 . 5 1 — -a 17 . 39+0 . 00-. ab 18.19 + 0 . 0 7 ^ — abc 20.63+0.46-c 20. 05 + 1. 4 2 — 16.39±1.63 17.22+0.88 a be be 18.82±0.11 19.04+0.92 be ab 16.47±0.18-16.14+0.78-c 17.51±0.67- v ab N. A. 17.33+0.21— a 19.16±0.88^ b 1 6 . 3 8 ± 0 . 5 7 -a 19.22±0.39 abc N. A. 16.92+0 . 5 3 ^ b 18.75±0.30-a 18.22+0.67 abc ab Data r e p r e s e n t the mean ± s t a n d a r d d e v i a t i o n of the mean (n=2). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of pa c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a tr e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t ( p ^ 0 . 0 5 ) . "LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e P r o d u c t i o n of amino a c i d s from p r o t e i n s may a l s o have been i n v o l v e d i n the SS r i s e . 4 .6 .4 CHANGES IN PERCENT SOLUBLE SOLIDS/PERCENT TITRATABLE ACIDITY (SS/TA)RATIOS The t a s t e i n t e r r e l a t i o n between sugars and a c i d s can be e v a l u a t e d o b j e c t i v e l y by the S S / T A r a t i o . In t h i s s t u d y , S S / T A r a t i o s g e n e r a l l y Increased w i t h s t o r a g e time ( F i g u r e 4 . 1 4 ) , w i th changes b e i n g s t a t i s t i c a l l y s i g n i f i c a n t w i t h r e s p e c t to both s t o r a g e t ime and packag ing treatment (p < 0.05) (Table 4 . 1 3 ) . T h u s , the sweetness of the c h e r r i e s s h o u l d i n c r e a s e as s torage t ime p r o g r e s s e s . Duncan's m u l t i l p l e range t e s t i n d i c a t e d t h a t the S S / T A r a t i o s were s i g n i f i c a n t l y d i f f e r e n t from i n i t i a l v a l u e s a t the end of the s t o r a g e p e r i o d (p < 0 . 0 5 ) . At s i x weeks of s t o r a g e , no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e (p > 0.05) e x i s t e d among the c h e r r i e s i n the v a r i o u s f i l m packages; however, a t e i g h t weeks, the c h e r r i e s i n the MLB and HB packages d i s p l a y e d s i g n i f i c a n t l y lower v a l u e s than those determined for f r u i t i n the c o n t r o l and MHB packages . G e n e r a l l y , S S / T A r a t i o s i n c r e a s e w i th f r u i t m a t u r i t y as demonstrated w i t h Saskatoon b e r r i e s (Green and Mazza , 1986) and b l u e b e r r i e s (Woodruff e_t a l . . , 1960) . T h e r e f o r e , the more r a p i d the r a t e of i n c r e a s e of S"S/TA r a t i o s , the more q u i c k l y the f r u i t i s r i p e n i n g and t e n d i n g towards senescence . 108 50 TREATMENT " O CONTROL • LB 25-20 H 1 1 1 1 1 1 j 0 1 2 3 4 5 6 7 6 STORAGE TIME (WEEKS) F i g u r e 4.14 Changes l n P e r c e n t S o l u b l e S o l i d s / P e r c e n t T i t r a t a b l e A c i d i t y R a t i o s of C h e r r i e s D u r i n g Storage a t l ° c 109 T a b l e 4.13 P e r c e n t T i t r a t a b l e A c i d i t y / P e r c e n t S o l u b l e S o l i d s R a t i o s of C h e r r i e s Under V a r i o u s Packaging C o n d i t i o n s ^ Storage Time (Weeks) C o n t r o l T r e a t m e n t 2 LB MLB MHB HB 28.1±0.7-a 3 2 . 8 ± 0 . 6 — a 28.1±0.7-2 6 . A i l . 5 $ b 28.1+0 31.1+1 a 1 a b c ab 2 8 . 1 ± 0 . 7 -a 34.2±3.9 bed 2 8 . 1 ± 0 . 7 — a 3 1 . 9 ± 0 . 4 -a 3 4 . 0 ± 0 . 8 — a 3 1 . 8 + l . l r be 30.9±3.4 31.6±0.1 ab a ab ab 34. 7X1. 8 — a 37.3 + 2 . 1 ^ 39.6±3 . 2 30.3±0.3 32.5±1.2 be a cd ab 35.2±2.0-35.1±0.6-44.3±0. 7-a N.A, N.A. 33.8±0.1 31.5±0, 29.7+2. 31.5±1, 34.7±1. 33.6±3, 36.7±1. bed ab ^abc a , ab *b" . abc 'aT" , £1 a .bed 29.8±0.3 31.5±1.9 33.5+0.3 ab c abc a bed 4 35.0+1.1^4 3 7 . l i 0 . 2 -36.4+2.3-a 4 3 . 1 ± 2 . 7 -a 3 2 . 2 ± 1 . 2 - v ab 3 3 . 1 ± 2 . 1 -a 30.7 + 0 . 7 ^ ab 28.7 + 1.0^-2 7.6±1,8-27.4±0.8^ b 32.0±1.4t Data r e p r e s e n t the mean ± s t a n d a r d d e v i a t i o n of the mean (n=2). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t o f s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). 'LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e The HB-packaged c h e r r i e s e x h i b i t e d an o v e r a l l d e c l i n e i n S S / T A r a t i o . T h i s was due to an i n c r e a s e i n the r a t e of sugar d e c l i n e as compared to the r a t e of change i n T A . As p r e v i o u s l y d i s c u s s e d , HB-packaged f r u i t d i s p l a y e d l i t t l e change In T A , wh i l e SS l e v e l s c o n t i n u e d to d e c l i n e up to 7 weeks of s t o r a g e . T h i s d e c l i n e may have been due to a change i n the p a t t e r n of r e s p i r a t o r y metabo l i sm under a n a e r o b i c c o n d i t i o n s . In the a n a e r o b i c environment w i t h i n HB packages , the r a t e of r e s p i r a t i o n of the c h e r r i e s must have i n c r e a s e d , l e a d i n g to a more r a p i d d e p l e t i o n of s u g a r s . A n a e r o b i c r e s p i r a t i o n r e s u l t s i n a c e t a l d e h y d e (and u l t i m a t e l y e t h a n o l ) p r o d u c t i o n ; t h u s , o r g a n i c a c i d s are not generated through the Krebs c y c l e , r e s u l t i n g i n l i t t l e change i n a c i d s i f they themselves do not serve as s u b s t r a t e s . 4.7 EFFECT OF STORAGE TIME AND PACKAGE ON TOTAL ANTHOCYANIN CONTENT OF CHERRIES C o l o u r changes i n the c h e r r y f r u i t d u r i n g MAP s t o r a g e were moni tored by d e t e r m i n a t i o n of the t o t a l a n t h o c y a n i n s (TAcy) c o n t e n t , as w e l l as measurement of Hunter L , / a , and b v a l u e s , as p r e v i o u s l y d i s c u s s e d . As was p o i n t e d out e a r l i e r , I t Is n e c e s s a r y to use both s u r f a c e measurement of c o l o u r and TAcy v a l u e s In order to g a i n a b e t t e r u n d e r s t a n d i n g of how and why c h e r r y c o l o u r changes 6ver t ime i n s t o r a g e . The s t a b i l i t y of a n t h o c y a n l n s i n f r u i t i s dependent upon a number of f a c t o r s , i n c l u d i n g t e m p e r a t u r e , l i g h t , pH, and the presence of oxygen, a s c o r b i c a c i d , and sugar d e g r a d a t i o n 111 p r o d u c t s such as f u r f u r a l and 5 - h y d r o x y m e t h y l f u r f u r a l (Adams, 1973) . S ince temperature and l i g h t were main ta ined c o n s t a n t throughout the s t u d y , and were i d e n t i c a l . f o r a l l t r e a t m e n t s , they may be d i s m i s s e d from f u r t h e r d i s c u s s i o n . In the p r e s e n t s t u d y , the pH l e v e l s of the f r u i t and the oxygen l e v e l s i n the atmospheres w i t h i n packages l i k e l y e x e r t e d the s t r o n g e s t i n f l u e n c e on changes i n TAcy v a l u e s , s i n c e both pH and oxygen l e v e l s were found to v a r y w i t h packag ing reg ime . Whi le TAcy v a l u e s were observed to v a r y s i g n i f i c a n t l y wi th time and package (p < 0.05) (Tab le 4 . 1 4 ) , d i s t i n c t d i f f e r e n c e s i n the amount of v a r i a t i o n r e s u l t e d wi th d i f f e r e n t packag ing m a t e r i a l s ( F i g u r e 4 . 1 5 ) . L e v e l s of Acy i n c r e a s e d most d r a m a t i c a l l y i n the c o n t r o l f r u i t , w i th t h i s i n c r e a s e be ing s i g n i f i c a n t l y g r e a t e r than t h a t observed i n the o ther package regimes (p < 0 . 0 5 ) . T h i s Is c o n s i s t e n t w i t h the t h e o r y tha t MAP suppresses Acy b i o s y n t h e s i s (Kader , 1986) . The LB packages brought about the s t a b i l i z a t i o n of TAcy l e v e l s i n c h e r r i e s , w i t h no s i g n i f i c a n t changes (p > 0.05) o c c u r r i n g throughout the s t o r a g e p e r i o d . The pH v a l u e s of c h e r r i e s i n the LB packages were observed to v a r y o n l y s l i g h t l y , which may have a c t e d to s t a b i l i z e the a n t h o c y a n l n s In the c h e r r i e s . In the r e m a i n i n g packag ing reg imes , TAcy l e v e l s of c h e r r i e s d e c r e a s e d up to s i x weeks, a f t e r which they Increased s h a r p l y . The decrease i n Tacy l e v e l s may have been due to a number of f a c t o r s , the most important be ing t h e i r d e s t a b i l i z a t i o n w i t h i n c r e a s i n g pH. 112 T R E A T M E N T S T O R A G E TIME (WEEKS) F i g u r e 4.15 Changes i n T o t a l Anthocyan ins Contents of C h e r r i e s D u r i n g Storage a t 1*C (Data r e p r e s e n t mean v a l u e + s t a n d a r d d e v i a t i o n of the mean) 113 T a b l e 4.14 T o t a l A n t h o c y a n i n C o n t e n t o f C h e r r i e s (mg C y a n i d i n - 3 - g a l a c t o s i d e / 1 0 0 g E d i b l e F r u i t ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s 1 S t o r a g e T r e a t m e n t Time — — — — — (Weeks) C o n t r o l LB MLB MHB HB 0 37.4± 3.8-a • ab 3 7.4+ 3 . 8 — a 37 . 4± „ ~ a 3 . 8-a 3 7.4± „ „ a 3 . 8-a 37 . 4± o r> a 3 . 8-a 2 36.4± 6.2-a 42.3+ 4.6-a 41.5 + 9 . 4 * a 38 . 3± 7.3* a 41 . 4± 4.5^ a 4 39.9± 6.2-a 38.8+ 1.4--a 32 . 4+ 8 . 9 ^ ab 34.3 + 6 - 2 fb 25 . 6 + 6 42.2+10.0-a 31.9± 7.4- u ab 22 . 5± be 17 . 8± 4.8* c 23 . 4± '•'So 8 6 3 . 0 ± 1 1 . 6 -a N.A. 3 7 . 0 ± 1 1 . 5 ^ b 47 . 9± 37 . 6± ' • 2 f Data r e p r e s e n t t h e mean v a l u e ± s t a n d a r d d e v i a t i o n of t h e mean (n=4). The u p p e r l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t o f t h e e f f e c t of s t o r a g e t i m e w h i l e t h e lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t o f p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e t h e same l e t t e r a re not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e Another p o s s i b l e e x p l a n a t i o n for the l o s s of Acy i n the MLB, MHB, and HB packages may be t h a t an Increased j p h y s i o l o g i c a l breakdown, induced by the h i g h l e v e l s of carbon d i o x i d e (Kader , 1986) may have o c c u r r e d d u r i n g s t o r a g e . S t r u c t u r a l changes c o u l d l e a d to more i n t i m a t e c o n t a c t of enzymes, such as p o l y p h e n o l o x i d a s e , w i th s u b s t r a t e s through d e c o m p a r t m e n t a l i z a t i o n . The presence of a p o l y p h e n o l o x i d a s e , or anthocyanase i n sweet c h e r r y was conf i rmed by P l f f e r i and C u l t r e r a (1974) who r e p o r t e d t h a t d e c o m p o s i t i o n of a n t h o c y a n i n s o c c u r r e d w i t h enzymes e x t r a c t e d from both the p e e l and p u l p of sweet c h e r r i e s . T h e r e f o r e , i n the HB f i l m packages , the l o s s of Acy may be due l a r g e l y to anthocyanase breakdown of c h e r r y a n t h o c y a n i n s . S ince p o l y p h e n o l o x i d a s e has a low a f f i n i t y f o r oxygen, i t may have been a c t i v e under even the severe a t m o s p h e r i c c o n d i t i o n s i n the HB packages . A second mechanism may have caused the decrease l n TAcy l e v e l s i n both the MHB and HB packages . With the decreased oxygen l e v e l s i n these packages , the f r u i t would have undoubted ly gone i n t o a n a e r o b i c r e s p i r a t i o n , r e s u l t i n g i n the p r o d u c t i o n of e t h a n o l and u l t i m a t e l y a c e t a l d e h y d e . I t was r e c e n t l y shown t h a t a c e t a l d e h y d e can r e a c t w i t h c a t e c h i n and a n t h o c y a n i n s , i n both Saskatoon b e r r y e x t r a c t s and model systems c o n t a i n i n g a s i n g l e a n t h o c y a n i n (Green and Mazza , 1988). Aqueous model systems c o n t a i n i n g a n t h o c y a n i n s t o r e d wi th both c a t e c h i n and a c e t a l d e h y d e d i s p l a y e d an i n t e n s i f i c a t i o n of c o l o u r which was a t t r i b u t e d to the f o r m a t i o n of h i g h l y c o l o u r e d i n t e r m e d i a t e s c o n t a i n i n g a n t h o c y a n i n and c a t e c h i n l i n k e d by CH CH b r i d g e s ( F i g u r e 4 . 1 6 ) . S i m i l a r l y , i n 3 Saskatoon b e r r y e x t r a c t s , the presence of a c e t a l d e h y d e l e a d to a n t h o c y a n i n c o l o u r i n t e n s i f i c a t i o n , wi th the r a t e and ex ten t of the i n t e n s i f i c a t i o n I n c r e a s i n g w i t h ace ta ldehyde c o n c e n t r a t i o n . A n a l y s i s of Hunter L , a , and b v a l u e s i n d i c a t e d a s h i f t i n the c o l o u r of b e r r y e x t r a c t s to a deeper , v i o l e t shade i n the presence of a c e t a l d e h y d e . I t i s q u i t e p o s s i b l e t h a t a s i m i l a r phenomenon o c c u r r e d i n the c h e r r y f r u i t i n the presen t exper iment . Sweet c h e r r y f r u i t c o n t a i n both the f l a v a n s ( + ) - c a t e c h i n and ( - ) - e p i c a t e c h i n (Van Buren , 1971) , the former of which c o u l d r e a c t w i th a n t h o c y a n i n s and o ther phenols i n the presence of a c e t a l d e h y d e i n the m o l e c u l a r c o n d e n s a t i o n r e a c t i o n d e s c r i b e d above . Assuming t h a t s u f f i c i e n t ace ta ldehyde had been p r o d u c e d , t h i s t h e o r y s e r v e s to e x p l a i n the l o s s of a n t h o c y a n i n s observed i n the HB and MHB samples over t i m e . The sudden i n c r e a s e i n TAcy l e v e l s a t e i g h t weeks of s torage i n the MLB, MHB, and HB packages i s d i f f i c u l t t o e x p l a i n . I t appears t h a t a f t e r r e a c h i n g a minimum l e v e l of a n t h o c y a n i n s , t h e r e was a renewed s y n t h e s i s of these compounds. T h i s i s not documented i n the l i t e r a t u r e , a l t h o u g h i t has been observed e m p i r i c a l l y by o ther r e s e a r c h e r s , who have noted t h a t c h e r r i e s under MAP s t o r a g e undergo a p r o g r e s s i v e r e d d e n i n g of the f l e s h (Powr ie , 1989) . I f t h i s i s r e p r e s e n t a t i v e of renewed a n t h o c y a n i n s y n t h e s i s , then t h i s i s a p o s s i b l e e x p l a n a t i o n f o r the a p p a r e n t l y anomalous r i s e i n TAcy l e v e l s a t the end of the s torage p e r i o d . 116 F i g u r e 4.16 R e a c t i o n of Ace ta ldehyde (I) w i t h C a t e c h i n ( I I ) and c y a n i d i n - 3 - g l u c o s i d e ( I I I ) . (Green and Mazza , 1988) 117 4.8 EFFECT OF STORAGE TIME AND PACKAGE ON THE TOTAL PHENOLIC CONTENT OF CHERRIES In the present study, the t o t a l phenols content (expressed as g a l l i c acid) ranged from 943.7 mg/L juice to 1490.8 mg/L juice (Figure 4 .17 , Table 4 . 1 5 ) . S t a t i s t i c a l analysis indicated that values varied s i g n i f i c a n t l y with package type and storage time (p < 0 . 0 5 ) . Control samples displayed an increase in t o t a l phenols over the storage period and leve l s were s i g n i f i c a n t l y higher (p < 0.05) at the end of the storage period than they were i n i t i a l l y . S i m i l a r l y , as was previously reported, anthocyanin levels did not vary extensively for the duration of storage. Values for t o t a l phenols content of cherries in the LB packages did not vary s i g n i f i c a n t l y (p > 0.05) throughout the storage period, while cherries in the MLB, MHB, and HB packages generally showed a decrease in t o t a l phenolics. Total phenols contents of cherries in the HB, MHB, and MLB packages changed s i g n i f i c a n t l y (p < 0.05) with storage time. With cherries in the MHB and MLB packages, values declined during the f i r s t s i x weeks, after which they Increased dramatically. Comparable losses were observed in the TAcy contents over the same time period. The loss of phenols in cherries within the MHB and MLB packages was l i k e l y due to a large extent to the loss of anthocyanlns, which are included in the t o t a l phenols measurement. As was explained in Section 4 . 7 , losses In anthocyanlns may be attributable to condensation 118 T R E A T M E N T S T O R A G E T I M E ( W E E K S ) F i g u r e 4.17 Changes i n T o t a l Phenols Contents of C h e r r i e s D u r i n g Storage a t 1 ° C (Data r e p r e s e n t the mean + s t a n d a r d d e v i a t i o n of the mean) 119 T a b l e 4.15 T o t a l P h e n o l i c C o n t e n t of C h e r r i e s (mg G a l l i c A c i d / 1 0 0 0 mL J u i c e ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s ^ S t o r a g e T r e a t m e n t Time (Weeks) C o n t r o l LB MLB MHB HB 0 1 2 4 0 . 5 ± 1 2 8 . 5 -a 1240. 5 ± 1 2 8 . 5 -a 1 2 4 0 . 5 ± 1 2 8 . 5^ a 1 2 4 0 . 5 ± 1 2 8 . 5^ a 1240.5± 128.5-a 2 1 3 0 4 . 5 ± 1 1 4 . 5 -a 1156. 7 ± 1 2 5 . 5 ^ b 1 1 8 0 . 9 ± 1 0 0 . .. ab 6 b ~ 1157.9*105. ab 8 b ~ 1 4 9 0 . 8 ± 1 0 0 . 5 -c 4 1231.3* 95.6-a 1170. 7 ± 1 6 2 . 3 - u ab 1090.4± 65. <* 1 0 7 8 . 7 ± 1 4 1 . 4 be 965.8± 52 . 8-c 6 1 4 3 2 . 6 ± 1 1 2 . 8 -a 1283. 9 ± 1 0 1 . 6 ^ b 993.7± 41. 2£ c 943.7± 59. 7^ c 940.2± 43 . 9-c 8 1427.9± 36.8-a 1275 . 4 ± 1 4 0 . 5 ^ b 1171.1± 91. 6 ^ c 1359.3* 68. ab 1128.8± 71.6^ c ^Data r e p r e s e n t the mean v a l u e ± s t a n d a r d d e v i a t i o n o f t h e mean (n=8). The upper l e t t e r i n d i c a t e s the r e s u l t s o f Duncan's m u l t i p l e range t e s t o f t h e e f f e c t o f s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e the same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( p >0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r w i t h c a t e c h i n i n the presence of a c e t a l d e h y d e , (Green and Mazza, 1988) . An i n t e r e s t i n g p a t t e r n was observed i n the HB-packaged c h e r r i e s , i n which t o t a l phenols d i s p l a y e d a l a r g e Increase d u r i n g the f i r s t two weeks of s t o r a g e , but l e v e l s d e c l i n e d d r a m a t i c a l l y a t the end of the s torage p e r i o d . Sensory a n a l y s i s of the HB-packaged c h e r r i e s i n d i c a t e d t h a t the q u a l i t y d i m i n i s h e d q u i t e r a p i d l y d u r i n g s t o r a g e . A d d i t i o n a l l y , the I n s t r o n t e x t u r e d a t a i n d i c a t e d a p r o g r e s s i v e s o f t e n i n g w i t h s torage t i m e . T h u s , i t i s l i k e l y the f r u i t underwent s t r u c t u r a l changes such as middle l a m e l l a breakdown and d e c o m p a r t m e n t a l i z a t i o n of enzymes, which may occur a f t e r p h y s i c a l b r u i s i n g . An i n c r e a s e i n p h e n o l i c s i n p l a n t t i s s u e s may occur when they are wounded or a t t a c k e d by i n s e c t s or d i s e a s e ( S i r i p h a n i c h and K a d e r , 1985) . The ensu ing decrease l n the t o t a l phenols c o n t e n t may have been due to a v a r i e t y of f a c t o r s , the most impor tant one be ing the l o s s of a n t h o c y a n i n s . There may a l s o have been c o n d e n s a t i o n of c a t e c h i n w i t h an thocyan ins i n the presence of ace ta ldehyde (Green and Mazza , 1988) . Were t h i s the c a s e , a l a r g e r decrease i n t o t a l phenols would be expected than i n the l e v e l s of a n t h o c y a n i n s , as f o r e v e r y c o n d e n s a t i o n r e a c t i o n , two p h e n o l i c compounds ( c a t e c h i n + a n t h o c y a n i n ) would be l o s t , r e s u l t i n g i n a more s i g n i f i c a n t decrease i n t o t a l phenols than i n T A c y , where o n l y one a n t h o c y a n i n molecu le would be l o s t i n the same r e a c t i o n . Another p o s s i b i l i t y i s t h a t phenols (as w e l l as a n t h o c y a n i n s ) may have been l o s t thr ough enzymat ic d e g r a d a t i o n by c h e r r y PPO ( P i f f e r i and C u l t r e r a , 1974) . As was the case w i t h i n T A c y , t o t a l p h e n o l i c l e v e l s i n a l l packaged c h e r r i e s Increased d r a m a t i c a l l y a f t e r d e c l i n i n g to a low at s i x weeks of s t o r a g e . I t appears t h a t t h e r e i s some mechanism o p e r a t i v e i n the c h e r r i e s w i t h i n the MLB, MHB, and HB packages t h a t causes a sudden Increase i n a n t h o c y a n l n s (and thus p h e n o l i c s ) a f t e r t h i s p o i n t i n s t o r a g e . T h i s may be a response to s t r e s s , a l t h o u g h t h e r e appears to be no documentat ion of i t i n the l i t e r a t u r e . i n the f i n a l a n a l y s i s , i t can be s t a t e d t h a t the LB f i l m packages p e r m i t t e d the r e t e n t i o n of p h e n o l i c s l e v e l s c l o s e to those observed i n f r e s h c h e r r i e s , s u g g e s t i n g t h a t t h i s i s the f i l m of c h o i c e w i t h r e s p e c t to p h e n o l i c r e t e n t i o n i n the c h e r r i e s . 4.9 EFFECT OF STORAGE TIME AND PACKAGE ON THE ORGANIC ACID PROFILES OF CHERRY FRUIT HPLC a n a l y s i s of c h e r r y e x t r a c t s was conducted f o r the i d e n t i f i c a t i o n and q u a n t i f i c a t i o n of o r g a n i c a c i d s . Three o r g a n i c a c i d s , namely m a l i c , s u c c i n i c , and q u i n l c , were i d e n t i f i e d . A f o u r t h peak, o c c u r r i n g a t an e l u t l o n time of a p p r o x i m a t e l y 14 m i n , was t e n t a t i v e l y i d e n t i f i e d as f o r m i c a c i d . A sample chromatogram i s i n c l u d e d as F i g u r e 4 .18 . M a l i c a c i d c o n c e n t r a t i o n s decreased i n c h e r r i e s i n a l l packag ing regimes over the e ight -week s t o r a g e time ( F i g u r e 4 . 1 9 ) . These d e c r e a s e s were observed to be s i g n i f i c a n t (p < 0.05) i n a l l but the LB f r u i t . The decrease i n m a l i c a c i d 122 s 1 3 4 i i i 1 1 1 1 1 1 0 2 4 6 8 10 12 14 16 RETENTION TIME (MINUTES) F i g u r e 4.18 T y p i c a l HPLC Chromatogram of O r g a n i c A c i d s l n C h e r r y E x t r a c t Peak I d e n t i f i c a t i o n : S=Solvent Peak; l = M a l i c A c i d ; Q u i n i c A c i d ; 3 = S u c c i n i c A c i d ; 4=Formic A c i d 123 T R E A T M E N T S T O R A G E T I M E ( W E E K S ) F i g u r e 4.19 Changes In M a l i c A c i d L e v e l s In C h e r r i e s D u r i n g Storage a t 1 ° C 124 T a b l e 4.16 M a l i c A c i d C o n t e n t of C h e r r i e s (mg/100 g E d i b l e F r u i t ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s - ^ S t o r a g e T r e a t m e n t Time (Weeks) C o n t r o l LB MLB MHB HB 0 154.7±10. 9^ a 154. 7 + 10. 9^ a 154.7+10.9-a 154. 7 + 10. 9 £ a 154. 7 + 10. 9^ a 2 141.8± 8. ab 148. 8 + 16. 7^ a 130.7+ 4.3r b 141. 9+ 9. 147 . 2+ 5. a 4 130.3± 4. ab 144. 5+ 1. 1 3 3 . 7 ± 1 0 . 7 -a 122 . 5± 5. 132 . 8± 5. 8^ a 8 125.7± 5. 4^ a 140 . 1± 7. •>! N.A . 125. 8± 7. a 137 . 8± 8. 1 b c b Data r e p r e s e n t t h e mean v a l u e + s t a n d a r d d e v i a t i o n o f t h e mean (n=4). The u p p e r l e t t e r i n d i c a t e s the r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t o f t h e e f f e c t o f s t o r a g e t i m e w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t o f p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( p >0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e l e v e l s i n the c o n t r o l f r u i t was l i k e l y due to u t i l i z a t i o n of the a c i d i n the ongoing r a p i d r e s p i r a t i o n under a e r o b i c c o n d i t i o n s . The maintenance of h igh l e v e l s of m a l i c a c i d i n c h e r r i e s packaged i n the LB f i l m was p r o b a b l y due to i n h i b i t i o n of the Krebs c y c l e under reduced oxygen l e v e l s . The MLB, MHB, and HB packaged c h e r r i e s underwent s i g n i f i c a n t d e c r e a s e s l n m a l i c a c i d l e v e l s (p < 0.05) (Table 4 . 1 6 ) . T h i s was i n d i r e c t c o n t r a d i c t i o n to the bulk of the l i t e r a t u r e which i n d i c a t e s t h a t m a l i c a c i d l e v e l s g e n e r a l l y do not d e c l i n e ( M e t l i k s k l i e t a l . , 1983) . However, Wankier e t a l . (1970) found t h a t the r a t e of malate d e g r a d a t i o n i n peaches and a p r i c o t s a c c e l e r a t e d w i t h i n c r e a s i n g carbon d i o x i d e i n the s torage atmosphere . T h i s o b s e r v a t i o n suggests an i n h i b i t i o n of s u c c i n i c dehydrogenase . Such an i n h i b i t i o n may have o c c u r r e d i n the c h e r r i e s i n the MLB and MHB packages . The decrease i n the m a l i c a c i d l e v e l s i n the HB c h e r r i e s may be a t t r i b u t e d to the v e r y h i g h l e v e l s of carbon d i o x i d e presen t i n the atmosphere . I t has been shown t h a t exposure of c o r n to s h o r t p e r i o d s of 100% carbon d i o x i d e l eads to an i n c r e a s e i n f o r m a t i o n of pyruvate and s u c c i n a t e , and a r e d u c t i o n i n the l e v e l s of m a l a t e . T h i s was a t t r i b u t e d to complete i n h i b i t i o n of the Krebs c y c l e , presumably through i n h i b i t i o n of some or a l l of the key enzymes i n v o l v e d ( Z e m l i a n u k l n and Ivanov, 1978) . S u c c i n i c a c i d l e v e l s a l s o decreased s i g n i f i c a n t l y (p < 0.05) i n a l l packaged c h e r r i e s except the HB-packaged c h e r r i e s 126 F i g u r e 4.20 Changes i n S u c c i n i c A c i d L e v e l s i n C h e r r i e s D u r i n g S torage a t 1 ° C (Data r e p r e s e n t the mean + s t a n d a r d d e v i a t i o n of the mean) 127 T a b l e 4.17 Succ i n i c A c i d C o n t e n t of C h e r r i e s (mg/100 E d i b l e F r u i t ) Under Var i o u s P a c k a g i n g ; C o n d i t i o n s ^ S t o r a g e T r e a t m e n t Time (Weeks ) C o n t r o l LB MLB MHB HB 0 4 1 . 5 ± 3 . 6 -a 41.5±3 a 4 1 . 5 ± 3 . 6 -a 4 1 . 5 ± 3 . 6 -a 4 1 . 5 ± 3 . 6^ a 2 3 6 . 4 ± 3 . 8 -a 36.5+4 . 1 ^ a 3 3 . 9 ± 1 . 7 -a 3 4 . 7 ± 1 . 7 -a 38 . 2 ± 4 . 5^ a 4 3 6 . 6 ± 2 . 0 -a 33.9±3 ab 3 2 . 0 ± 1 . 8 ^ b 34. 3 ± 1 . 2-. ab 2 8 . 9 ± 0 . 8* c 8 3 5 . 6 ± 1 . 4 -a 35.3±2 .9* a N.A. 3 5 . 8 ± 3 . 0 -a 41. 6 ± 2 . 3 f Data r e p r e s e n t the mean v a l u e I s t a n d a r d d e v i a t i o n of the mean (n=4). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r ange t e s t of the e f f e c t s of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05).. LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e ( F i g u r e 4 .20; T a b l e 4 . 1 7 ) . T h i s l a c k of change i n s u c c i n i c a c i d l e v e l s i n the HB c h e r r i e s may have been caused by the h i g h carbon d i o x i d e l e v e l s i n the package atmospheres , as d i s c u s s e d above. S u c c i n i c a c i d d e c r e a s e d to a p p r o x i m a t e l y the same l e v e l s i n c h e r r i e s i n the o ther f i l m packages a t the end of e i g h t weeks. Those l e v e l s were s i g n i f i c a n t l y lower (p < 0 .05) than those observed i n the HB-packaged c h e r r i e s . Once a g a i n , t h i s i s i n c o n s i s t e n t w i t h what has been r e p o r t e d i n the l i t e r a t u r e . The o n l y p l a u s i b l e e x p l a n a t i o n seems to be t h a t the u t i l i z a t i o n of s u c c i n i c a c i d i n c h e r r y metabol i sm d i f f e r s from t h a t f o r o ther f r u i t s . Q u i n i c a c i d l e v e l s g e n e r a l l y decreased to four weeks of s t o r a g e , a f t e r which they showed a sharp i n c r e a s e ( F i g u r e 4 .21 ; Tab le 4 . 1 8 ) . S ince q u i n i c a c i d does not p a r t i c i p a t e i n the Krebs c y c l e , i t i s u n l i k e l y t h a t these changes were due to changes i n the r e s p i r a t o r y metabo l i sm of the f r u i t . Q u i n i c a c i d d o e s , however, combine w i t h p h e n o l i c a c i d s , such as p - c o u m a r i c , c a f f e i c , and f e r u l i c ( H o l i e r and Herrmann, 1983). I f much of the q u i n i c a c i d i n c h e r r i e s Is presen t as an e s t e r of h y d r o x y c i n n a m i c a c i d s , decreases In the l e v e l s of p h e n o l i c s s h o u l d be r e l a t e d to decreases i n the l e v e l s of q u i n i c a c i d . As has been d i s c u s s e d , the t o t a l p h e n o l i c s content s of the c h e r r i e s f o l l o w e d s i m i l a r t r e n d s as have been d i s c u s s e d here for q u i n i c a c i d . Thus changes i n q u i n i c a c i d l e v e l s may be a s s o c i a t e d w i t h the d e c o m p o s i t i o n of p h e n o l i c compounds. 129 T R E A T M E N T 0 2 4 8 S T O R A G E T I M E ( W E E K S ) F i g u r e 4.21 Changes In Q u i n i c A c i d L e v e l s i n C h e r r i e s Dur ing S torage a t 1 ° C (Data r e p r e s e n t the mean + s t a n d a r d d e v i a t i o n of the mean) 130 T a b l e 4.18 Q u i n i c A c i d C o n t e n t o f C h e r r i e s (mg/100 g E d i b l e F r u i t ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s 1 2 S t o r a g e T r e a t m e n t Time •— (Weeks) C o n t r o l LB MLB MHB HB 0 3 3 . 9 ± 3 . 3 * a 33.9+3.3* a 33.9+3.3* a 33 . 9 + 3 . 3 * a 33.9+3.3* a 2 a h 3 0 . 4 ± 2 . 7 ~ ab 3 0 . 8 ± 4 . 5 * a 2 4 .1±1.6^ b a h 28 . 9±5 . 3~ ab 2 9 . 9 ± 4 . 7 * £ ab 4 22.6+1.6* ab 2 3 . 2 ± 2 . 6 - w ab 2 2 . 4 + 1 . l - u ab 23 . 5 ± 0 . 7 -a 2 0 . 8 ± 1 . 4 § b 8 2 8 . 4 ± 3 . 1 -a 2 9 . 9 ± 3 . 6 * a N.A. 2 2 . 3 ± 9 . 0 -a 2 8.8±1.4 -a Data r e p r e s e n t t h e mean v a l u e ± s t a n d a r d d e v i a t i o n o f the mean (n=4). The up p e r l e t t e r i n d i c a t e s the r e s u l t s o f Duncan's m u l t i p l e range t e s t o f t h e e f f e c t o f s t o r a g e time w h i l e t h e lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r a n g e t e s t o f t h e e f f e c t o f p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t ( p ^ 0 . 0 5 ) . LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e The most d r a m a t i c change i n o r g a n i c a c i d l e v e l s were observed for the a c i d t e n t a t i v e l y i d e n t i f e d as f o r m i c a c i d ( F i g u r e 4 .22; T a b l e 4 . 1 9 ) . S i g n i f i c a n t i n c r e a s e s (p<0.05) i n the l e v e l s of f o r m i c a c i d l n c h e r r i e s were observed d u r i n g s t o r a g e i n a l l packag ing r e g i m e s , except f o r those c h e r r i e s s t o r e d i n the LB f i l m . The l e v e l s of f o r m i c a c i d i n c r e a s e d w i t h d e c r e a s i n g f i l m p e r m e a b i l i t y , w i t h the HB f i l m - p a c k a g e d f r u i t d i s p l a y i n g s i g n i f i c a n t l y h i g h e r l e v e l s a t the end of e i g h t weeks of s t o r a g e than c h e r r i e s s t o r e d i n the o ther package t y p e s . I t seems as though the b i o s y n t h e s i s of t h i s a c i d i c component was t r i g g e r e d as the c o n c e n t r a t i o n of carbon d i o x i d e i n the atmosphere i n c r e a s e d , or as the l e v e l of oxygen f e l l . I f t h i s i s not f o r m i c a c i d , i t may be some o ther t o x i c m e t a b o l i t e . Whatever the compound, I t appears to be l i n k e d to c h e r r y d e t e r i o r a t i o n , as the h i g h e s t l e v e l s were observed i n the MHB and HB f r u i t , which a l s o underwent the most d e t e r i o r a t i o n or q u a l i t y l o s s over the s t o r a g e p e r i o d . 4.10 SENSORY ANALYSIS Sensory a n a l y s i s of the c h e r r y f r u i t w i t h i n packages of f i v e d i f f e r e n t f i l m types was conducted on a weekly b a s i s over the e ight-week s t o r a g e p e r i o d . Sensory a n a l y s i s of HB - p a c k a g e d c h e r r i e s was d i s c o n t i n u e d a f t e r four weeks, s i n c e the development of e x t e n s i v e o f f - f l a v o u r and s o f t e n i n g rendered the c h e r r i e s u n a c c e p t a b l e . S ince mold growth on many of the c o n t r o l packaged c h e r r i e s o c c u r r e d a f t e r f i v e weeks, s e n s o r y 132 F i g u r e 4.22 Changes i n Formic A c i d L e v e l s i n C h e r r i e s D u r i n g Storage a t 1 ° C 133 T a b l e 4.19 Formic A c i d C o n t e n t of C h e r r i e s (mg/100 g E d i b l e F r u i t ) Under V a r i o u s P a c k a g i n g C o n d i t i o n s 1 2 S t o r a g e T r e a t m e n t Time (Weeks) C o n t r o l LB MLB MHB HB 0 6.6±1.8-a 6.6*1.8* a 6.6+1.8* a 6.611.8* a 6.611.8* a 2 4 . 9 ± 1 . 0 * a 8.316.4* ab 9.1+2.0*^ ab 6.9+2.6* ab 12.315.4* b 4 10.1*1.4* a 8.0+1.4* a 10.3+2.1-a 1 3 . 5 l 0 . 5 r b 29.1+1.9-c 8 12.9*0.9* a 10.8+0.9* a N.A. 22.6+1.9* b 40.1+8.6* c Data r e p r e s e n t t h e mean v a l u e t s t a n d a r d d e v i a t i o n o f t h e mean (n=4). The u p p e r l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e r ange t e s t o f t h e e f f e c t o f s t o r a g e t i m e w h i l e the lower l e t t e r i n d i c a t e s t h e r e s u l t s o f Duncan's m u l t i p l e r a n g e t e s t o f the e f f e c t of p a c k a g i n g m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t s h a r e the same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e a n a l y s i s of these c h e r r i e s was d i s c o n t i n u e d a t t h a t t i m e . The u n a v a i l a b i l i t y of LB sample a f t e r s i x weeks of s torage prevented f u r t h e r s ensory a n a l y s i s a f t e r t h a t t i m e . As shown on the s e n s o r y e v a l u a t i o n s c o r e shee t (Appendix B ) , the o v e r a l l appearance a c c e p t a b i l i t y was p r i m a r i l y determined by two a t t r i b u t e s , namely c h e r r y c o l o u r and f r u i t f i rmness i n f i n g e r s . These q u a l i t y assessments are of paramount impor tance , i n consumers' i n i t i a l i m p r e s s i o n s of f r u i t q u a l i t y . F i n g e r f i rmness s c o r e s of c h e r r i e s were found to d i f f e r w i th each packag ing system throughout the e ight -week s t o r a g e p e r i o d ( F i g u r e 4 . 2 3 ) , C h e r r i e s i n the c o n t r o l , L B , and MLB packages were not s i g n i f i c a n t l y s o f t e r (p > 0.05) a t the end of t h e i r r e s p e c t i v e s t o r a g e p e r i o d s than they were a t zero s torage time (Table 4 . 2 0 ) . C h e r r i e s i n the MHB f i l m packages were r a t e d s i g n i f i c a n t l y l e s s f i r m (p < 0.05) a t the e i g h t week s torage t ime as compared to c h e r r i e s a t o ther s t o r a g e t i m e s . The f i rmness v a l u e f o r the c h e r r i e s l n the HB f i l m packages a t the four-week of s t o r a g e time were lower than those s t o r e d a t the p r e v i o u s s t o r a g e t i m e s . These changes i n f i rmness may be a t t r i b u t e d to the e f f e c t s of i n t e r n a l atmospheres of the v a r i o u s package regimes on f r u i t r e s p i r a t i o n . F irmness r e t e n t i o n i n the LB and MLB packaged c h e r r i e s was most l i k e l y due to a decrease l n the r e s p i r a t i o n r a t e and r e d u c t i o n of the r i p e n i n g p r o c e s s . P e c t i c enzymes, such as p o l y g a l a c t u r o n a s e , may have been i n o p e r a t i v e 1 3 5 4H O CJ GO 3 CO CO w S3 3 2 05 h—I o 2 3 4 5 6 *7 STORAGE TIME (WEEKS) T R E A T M E N T O C O N T R O L • L B A MLB 0 M H B * H B 8 F i g u r e 4.23 Changes i n Sensory F irmness Va lues for C h e r r i e s S t o r e d a t 1 ° C 136 Table 4.20 Sensory Firmness Scores for Cherries Under Various Packaging Conditions Storage Time (Weeks) Control LB Treatment' MLB MHB HB 4.50*0.15- 4.50*0.15-a 4.50*0.15— a 4.50*0.15— 4.50*0.15-4.58*0.15-a 4.83*0.11-a 4.75*0.13-a 4.67*0.14^ 4.67*0.14-4.50*0.19-a 4.75*0.13-a 4.67*0.14- 4.75*0.13-a 4.67*0.14-a 4.58*0.19-a 4.50*0.15-a 4.67*0.14-a 4.50*0.15 ab 4.17*0.17-a 4.33*0.14-a 4.00*0.25-a N.A. 4.58+0.15-a 4.50*0.26-a 4.50+0.15-a 4.33+0.14 4.08*0.19 4.42+0.26 ab a b a ab 4 . 3 3 ± 0 . 1 4 ^ a 4.17*0.11 be 4.33+0.19^ a 3.42*0.26^ b N.A. N.A. N.A. N.A. 4.42 + 0.15-^ a 4.33±0.19 abc N.A. N.A. N.A. 4.58+0.19 ab 3.83±0.27^ b N.A. Data represent the mean value ± standard error of the mean (n=12). The upper l e t t e r indicates the r e s u l t s of Duncan's multiple range test of the e f f e c t of storage time while the lower l e t t e r indicates the r e s u l t s of Duncan's multiple range test of the e f f e c t of packaging material. Results within a treatment group or time series that share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p 0.05). "LB=Low Barrier; MLB=Medium-Low Barrier; MHB=Medium-High B a r r i e r ; HB=High Ba r r i e r N.A. = Not Available under the p r e v a i l i n g a t m o s p h e r i c c o n d i t i o n s . S o f t e n i n g of f r u i t i n the MHB and HB packages may have been due to p h y s i o l o g i c a l breakdown i n the presence of I n c r e a s i n g l e v e l s of a c e t a l d e h y d e a n d / o r e t h a n o l which accumulated d u r i n g a n a e r o b i c r e s p i r a t i o n of the c h e r r i e s , wh i l e the r a p i d decrease l n t e x t u r e v a l u e s f o r the c o n t r o l group was due to normal senescence of the c h e r r i e s . V i s u a l c o l o u r of c h e r r i e s remained v e r y a c c e p t a b l e ( score > 4.5) l n a l l packaged f r u i t throughout the e n t i r e s torage p e r i o d (Table 4 . 2 1 ) . There was no s i g n i f i c a n t d i f f e r e n c e (p > 0.05) among t rea tments w i t h r e s p e c t to t h e i r e f f e c t s on s e n s o r y c o l o u r s c o r e s . C o l o u r s c o r e s g e n e r a l l y d e c r e a s e d , w i t h t h i s decrease b e i n g s i g n i f i c a n t i n the c o n t r o l , L B , and MHB packages a t the end of t h e i r s t o r a g e p e r i o d s . The MLB package a f f o r d e d s u p e r i o r c h e r r y c o l o u r r e t e n t i o n over the e n t i r e e i g h t weeks of s t o r a g e . Whi le c o l o u r s c o r e s d i d not change s i g n i f i c a n t l y (p > 0.05) for the HB f i l m f r u i t , i t must be r e i t e r a t e d t h a t f r u i t was e v a l u a t e d o n l y to four weeks of s t o r a g e . Decreases i n c o l o u r s c o r e s were l a r g e l y a t t r i b u t a b l e to changes l n the l e v e l s and forms of a n t h o c y a n i n s i n the f r u i t . As was d i s c u s s e d e a r l i e r , TAcy v a l u e s i n c r e a s e d d r a m a t i c a l l y i n the c o n t r o l packages . With the i n c r e a s e i n pH v a l u e s , the c h e r r i e s tended to a p p e a l more b l u e , and i n f a c t , t h i s was r e f l e c t e d i n the d e c r e a s i n g Hunter a and b v a l u e s . T h i s type of c o l o u r change may be u n a c c e p t a b l e to consumers , as i n d i c a t e d 138 Table 4.21 Sensory Colour Scores f o r C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s ^ S torage Time (Weeks) C o n t r o l Treatment^ LB MLB MHB HB 5.00±0.00-a 4.92+0.08 ab 5.00±0.00 4.92±0.08 a ab 5.00+0.00-5.0010.00-a 5 . 00+0 . 00-5.0010.00-a 5.00+0.00-a 5.0010.00-a 5.0010.00-a 5.0010.00- 5.0010.00- 5.00+0.00- 5.0010.00-a 5.00±0.00- 5.00+0.00-a 4.92+0.08-a 4.92+0.08-a 5.00+0.00-a CO CD 5.00±0.00-a 4.75±0.13-a N.A. N.A. 5.00+0.00-4 . 8 3 ± 0 . 1 1 ^ a 4.75+0.13-N. A . 5.00+0.00-a 4.75±0.13-4.83+0.11-a 4.83+0.11-a 4.92+0.08-4.75±0.13 a ab 4.83 + 0 . 1 1 — a 4.83 + 0 . 1 1 — 4.92+0.08-a N.A. N.A, N.A. N.A. N.A. 4.8310.11-a 4.58+0.15-a N.A, '•Data r e p r e s e n t the mean value t s t a n d a r d e r r o r of the mean (n = 12) . The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time wh i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a treatment group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). 2LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N .A . = Not A v a i l a b l e T a b l e 4.22 Sensory Appearance Scores f o r C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s Storage Time (Weeks) C o n t r o l Treatment' LB MLB MHB HB 5.00*0.00-a 5.00±0.00-a 5.00*0.00-a 5.00±0.00-a 5.00*0.00-a 4.92*0.08-a 4.92*0.08-a 5.00*0.00-a 5.00*0.00-a 5.00*0.00-5.00+0.00-a 5.00+0.00-a 5.00+0.00-a 5.00+0.00- 5.00+0.00-a 5.00±0.00-a 5.00*0.00-a 4.92*0.08-a 4.92±0.08-a 4.92*0.08-4.83*0.11 ab ab 4.75*0.18-. ab 5.00*0.00-a 4.58*0.23 ab ab 4.33*0.26^ b 4.67±0.14-a N.A. 4.75±0.13-a 4.33+0.28-a 4.50±0.15 4.75±0.13 a ab 4.67±0.14-a 4.83±0.11-a N.A. N.A, N.A. N.A. N. A . N.A. 4.75+0.13 ab 4.58+0.19-a 4.58±0.15 ab 4.17±0.32-a N.A. N.A. Data r e p r e s e n t the mean v a l u e * s t a n d a r d e r r o r of the mean (n=12). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a t r e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). "LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e by the s e n s o r y a n a l y s i s r e s u l t s o b t a i n e d i n t h i s s t u d y . The MLB package was r e s p o n s i b l e f o r s u p e r i o r c o l o u r r e t e n t i o n i n c h e r r i e s , as shown by the s m a l l change i n s e n s o r y c o l o u r s c o r e s and Hunter a and b v a l u e s over the s t o r a g e p e r i o d . O v e r a l l appearance s c o r e s a t the end of the s t o r a g e p e r i o d s ranged from modera te ly a c c e p t a b l e ( score 3.5 to 4.5) f o r L B , MHB, and HB f r u i t , to v e r y a c c e p t a b l e ( score 4 .5 or h i g h e r ) for the r e m a i n i n g packag ing regimes (Table 4 . 2 2 ) . S ince v i s u a l c o l o u r s c o r e s d i d not v a r y s i g n i f i c a n t l y between packaged c h e r r i e s , i t can be assumed t h a t v a r i a t i o n s i n f i rmness accounted l a r g e l y f o r the observed d i f f e r e n c e s i n o v e r a l l appearance a c c e p t a b i l i t y s c o r e s . T h i s i s s u p p o r t e d by the o b s e r v a t i o n t h a t the MHB and HB r e c e i v e d the lowest f i rmness s c o r e s , and a l s o r e c e i v e d lower o v e r a l l appearance r a t i n g s than the c h e r r i e s i n o ther packag ing r e g i m e s . O v e r a l l appearance s c o r e s d e c l i n e d most r a p i d l y for the HB f r u i t , w i th s cores be ing s i g n i f i c a n t l y lower (p < 0.05) than i n i t i a l s c o r e s a f t e r o n l y four weeks of s t o r a g e . w i th a l l o ther packag ing reg imes , c h e r r i e s were judged to have a s i g n i f i c a n t l y poorer appearance a t the end of the e ight-week s t o r a g e p e r i o d . While the o v e r a l l appearance s c o r e s f o r the MLB and MHB c h e r r i e s had decreased s i g n i f i c a n t l y (p < 0.05) a t the end of e i g h t weeks, they were not s i g n i f i c a n t l y d i f f e r e n t from each o ther (p > 0 . 0 5 ) . However, the MLB f r u i t r e t a i n e d a h i g h e r o v e r a l l appearance s c o r e a t the end of e i g h t weeks. 141 O v e r a l l f l a v o u r a c c e p t a b i l i t y was determined p r i n c i p a l l y by t e x t u r e i n the mouth, aroma, sweetness , b i t t e r n e s s , and the presence of o f f - f l a v o u r . S i g n i f i c a n t (p < 0.05) decreases i n the s c o r e s for a l l of the above a t t r i b u t e s were observed i n a l l t rea tments d u r i n g the s t o r a g e p e r i o d . Trends for t e x t u r e s c o r e s s i m i l a r to those of f i rmness s c o r e s were o b s e r v e d , w i t h v a l u e s g e n e r a l l y d e c l i n i n g d u r i n g s torage ( F i g u r e 4 . 2 4 ) . T e x t u r e s c o r e s , however, were always lower than those f o r f i r m n e s s , r e f l e c t i n g s t r u c t u r a l changes i n the f r u i t t h a t c o u l d not be d e t e c t e d through f i n g e r p r e s s u r e t e s t i n g of the c h e r r i e s (Tab le 4 . 2 3 ) . S u p e r i o r r e t e n t i o n of t e x t u r e , as de termined by m a s t i c a t i o n , was observed i n the L B -and MLB-packaged c h e r r i e s . With a decrease In the p e r m e a b i l i t y of the packag ing f i l m s , the r a t e of t e x t u r e s c o r e d e c l i n e I n c r e a s e d , w i t h the HB-packaged f r u i t undergo ing the g r e a t e s t amount of change . A f t e r t h r e e weeks of s t o r a g e , t e x t u r e s c o r e s for HB f r u i t became s i g n i f i c a n t l y d i f f e r e n t (p < 0.05) from the c h e r r i e s a t p r e v i o u s s t o r a g e t i m e s . The more r a p i d l o s s of t e x t u r e In the HB c h e r r i e s , and l i k e l y a l s o i n the MHB c h e r r i e s , was due to t i s s u e breakdown under a n a e r o b i c c o n d i t i o n s , perhaps due i n p a r t to an a c c u m u l a t i o n of t o x i c end p r o d u c t s . C h e r r i e s i n the LB and MLB packages d i d not d i s p l a y any s i g n i f i c a n t d e c r e a s e (p < 0.05) i n s e n s o r y t e x t u r e s c o r e s over the d u r a t i o n of the s t o r a g e s t u d y . Tex ture s c o r e s for the MLB and MHB packaged f r u i t were not s t a t i s t i c a l l y d i f f e r e n t from each o ther a t the end of e i g h t weeks of s t o r a g e ; however, 142 EH X! 2 -1-T R E A T M E N T O C O N T R O L • L B A MLB 0 MHB * H B 0 2 3 4 5 6 V STORAGE TIME (WEEKS) 8 F i g u r e 4.24 Changes In Sensory Tex ture Scores for C h e r r i e s D u r i n g S torage a t 1 ° C 143 Table 4.23 Sensory Texture Scores for Cherries under Various Packaging Conditions Storage Treatment Time (Weeks) Control LB MLB MHB HB 0 4.42*0.19-a 4. 42*0.19-a 4. 42±0.19^ a 4 . 42±0.19-a 4 . 42±0.19-a 1 4.58±0.15-a 4. 75±0.13-a 4. 6710.14-a 4. 5010.15-a 4 . 50±0.19-a 2 4.25*0.18-a 4. 25*0.22-a 4. 25*0 . 25-^ a 4. 25*0.18— a 4 . 25*0.13-a 3 4.25*0.22-a 4. 33*0.14-a 4. 58*0.15-a 4. 08*0. 2 6 ^ a 3 . 25*0.22^ b 4 4.25*0.13-a 4. 33*0.18-a 4. 25±0.18— a 4. 1 7 ± 0 . 1 7 - ^ a 2 . 92*0.23^ b 5 3.50*0.29-a 4. 25+0.28-a 3. 92+0.23-a 3 . 67+0. 2 2 — a N.A. 6 N.A. 4. 25*0.13-a 4. 33*0.19^ a 3 . 50*0.29§ b N.A. 7 N.A. N.A. 4 . 17 + 0. 2 1 — a 4 . 0 0 ± 0 . 1 7 ~ a N.A. 8 N.A. N.A. 4. 08+0.23— a 3. 58 + 0.36— a N.A. '"Data represent the mean value ± standard error of the mean (n= 12). The upper l e t t e r indicates the r e s u l t s of Duncan's multiple range test of the e f f e c t of storage time while the lower l e t t e r indicates the r e s u l t s of Duncan's multiple range test of the ef f e c t of packaging material. Results within a treatment group or time seri e s that share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low Barrier; MLB=Medium-Low Barrier; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not Available the MLB c h e r r i e s once a g a i n e x h i b i t e d s u p e r i o r r e t e n t i o n of t e x t u r e as ev idenced by the h i g h e r s c o r e . C o n t r o l packaged c h e r r i e s a l s o s o f t e n e d d u r i n g s t o r a g e ; t h i s s o f t e n i n g was l i k e l y a t t r i b u t a b l e to normal r e s p i r a t i o n and senescence of the f r u i t . Aroma s c o r e s d e c l i n e d g r a d u a l l y d u r i n g s t o r a g e , w i t h the most r a p i d d e c l i n e b e i n g e x h i b i t e d by the HB f i l m f r u i t (Table 4 . 2 4 ) . C o n t r o l - and LB-packaged c h e r r y aroma s c o r e s changed o n l y s l i g h t l y over t i m e , w i t h r e t e n t i o n of the "s trong" n a t u r a l c h e r r y odour ( score 3 .5 to 4.5) C o n v e r s e l y , c h e r r i e s i n the HB, MHB, and MLB f i l m packages possessed o n l y a s l i g h t aroma ( score 2.5 to 3.5) a t the end of t h e i r r e s p e c t i v e s t o r a g e p e r i o d s . In f a c t , c h e r r i e s l n the HB packages were judged to have o n l y a s l i g h t aroma a f t e r t h r e e weeks of s t o r a g e and were s i g n i f i c a n t l y d i f f e r e n t (p < 0.05) from the z e r o - s t o r a g e c h e r r i e s a f t e r o n l y f o u r weeks of s t o r a g e . O n l y the c o n t r o l and LB packages m i t i g a t e d changes i n aroma s c o r e s to the ex tent t h a t s c o r e s d i d not v a r y s i g n i f i c a n t l y (p > 0.05) a t the end of s torage from those g i v e n to the f r e s h f r u i t . No s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e (p > 0.05) among treatments was observed to four weeks of s t o r a g e . Whi le MLB- and MHB-packaged c h e r r i e s d i s p l a y e d s i g n i f i c a n t l y d i f f e r e n t s c o r e s , a t the end of e i g h t weeks, the two t rea tments were not found to be s t a t i s t i c a l l y d i f f e r e n t from each o t h e r ; With r e s p e c t to aroma, i t can be s a i d t h a t the LB f i l m was r e s p o n s i b l e for s u p e r i o r r e t e n t i o n of t h i s q u a l i t y a t t r i b u t e . 145 Table 4.24 Sensory Aroma Scores f o r C h e r r i e s Under V a r i o u s Packaging C o n d i t i o n s 1 S t o r a g e Treatment Time (Weeks) C o n t r o l LB MLB MHB HB 0 4.17±0. 24* a 4. 17±0. 24* a 4.17±0.24* a 4 . 17±0.24* a 4 . 17 + 0 . 2 4 — a 1 3.92±0. 2 6* a 4. 17±0. 30* a • 4.17±0.30* a 4 . 1710.27* a 4. 5 0 l 0 . 1 9 * a 2 3.67±0. 2 8* a 3. 67+0. 22* a 4.08+0.23* a 3 . 92+0.29— a 3 . 83 + 0 . 2 1 — a 3 3.50±0. 2 6* a 3. 92±0. 19* a ah 3 . 8 3 ± 0 . 3 0 — a 3. 75+0.28*** a 3. 58+0.29-a 4 3.42+0. 31^ a 3. 58+0. 31* a 3.42+0.31— a 3 . 6 7 ± 0 . 2 6 * * * a 2 . 75+0.28* a 5 3.50±0. 2 9* a 4. 00±0. 21* a 3 . 5 8 ± 0 . 3 4 — a 3 . 2510.37*** a N.A . 6 N.A. 4. 08±0. 2 9* a 3.6710.33— a 3 . 2510.30*** a N.A . 7 N.A . N.A . ah 3 . 83*0 . 3 0 — a 3 . h o 17±0. 2 7 — a N.A . 8 N.A . N.A . 2.92±0.34* a 2 . 92±0.34* a N.A . Data r e p r e s e n t the mean v a l u e + st a n d a r d e r r o r of the mean (n=12). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time wh i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a treatment group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e Sensory sweetness s c o r e s , as w e l l as s t a t i s t i c a l a n a l y s i s of the r e s u l t s , are i n c l u d e d as T a b l e 4 .25 . Scores f o r sweetness remained r e l a t i v e l y c o n s t a n t throughout s t o r a g e for the c o n t r o l and LB-packaged c h e r r i e s , w i t h s c o r e s r e m a i n i n g above 3.5 (moderate ly sweet) a t the end of the e ight -week s t o r a g e p e r i o d . Sweetness s c o r e s were r e l a t i v e l y c o n s t a n t f o r MLB f r u i t u n t i l the e i g h t h week of s t o r a g e , when the average s c o r e s l i p p e d Into the s l i g h t l y sweet range ( score 2.5 to 3 . 5 ) ; however, t h i s v a l u e was not s t a t i s t i c a l l y d i f f e r e n t (P > 0.05) from the va lue f o r c h e r r i e s a t z e r o - s t o r a g e t i m e . F r u i t h e l d i n the MHB and HB f i l m packages d i s p l a y e d a more r a p i d decrease i n sweetness s c o r e s over the s t o r a g e p e r i o d , w i th both groups a t the end of e i g h t weeks b e i n g judged to be o n l y s l i g h t l y sweet; however, these v a l u e s were not s i g n i f i c a n t l y d i f f e r e n t from zero s t o r a g e time v a l u e s or from each o t h e r . In summary, there appeared to be no d i f f e r e n c e between packag ing regimes on the r e t e n t i o n of sweetness i n c h e r r i e s . The observed l o s s of sweetness was undoubted ly due to a decrease i n sugars through c o n t i n u e d r e s p i r a t i o n ; i n f a c t , the % s o l u b l e s o l i d s v a l u e s were g e n e r a l l y lower a t the end of the s t o r a g e p e r i o d than those f o r the z e r o s t o r a g e f r u i t ( S e c t i o n 4 . 6 . 3 ) . B i t t e r n e s s s c o r e s for s t o r e d c h e r r i e s were c o n s i s t e n t l y above 4.0 (Tab le 4.26) B i t t e r n e s s s c o r e s d e c r e a s e d s l i g h t l y d u r i n g s t o r a g e for c h e r r i e s i n a l l package t y p e s , but a t four weeks of s t o r a g e , v a l u e s were not s i g n i f i c a n t l y d i f f e r e n t (p > 0.05) from the v a l u e s for c h e r r i e s a t zero s t o r a g e t i m e . At the end of e i g h t weeks of s t o r a g e , the MLB- and MHB-packaged 147 T a b l e 4.25 Sensory Sweetness Scores f o r C h e r r i e s Under V a r i o u s P a c k a g i n g C o n d i t i o n s S t o r a g e Treatment^ Time (Weeks) C o n t r o l LB MLB MHB HB 0 3.83±0.21* a 3.83±0.21* a 3.83 + 0 . 2 1 — a 3 . 83±0. 21** a 3 . 83+0.21** a 1 4.00+0.25* a 3.83±0.30* a 4.25+0.25* a 4 . 08±0. 31* a 4 . 17+0 . 34* a 2 3.83±0.27* a 4.00±0.33* a 4 . 0 0 ± 0 . 3 0 — a 3 . 75±0. 28** a 3 . 58±0. 34** a 3 * 3.58±0.29* a 4.00±0.28* a 4.00+0.30— a 3 . 67+0.33** a 3 . 08±0 . 29* a 4 3.67+0.28* a 3.67+0.33* a 3 . 33+0 . 3 6 — a 3 . 50+0. 2 9** a 2 . 92 + 0 . 38* a 5 3.58±0.29* a 3.83±0.32* a 3 . 7 5 ± 0 . 3 3 — a 3 . 00±0. 43** a N.A. 6 N.A . 4.00±0.33* a 3 . 7 5 ± 0 . 3 7 — a 3 . 50±0. 34** a N.A. 7 N.A . N.A. 3.83 + 0 . 3 4 — a 2 . 92+0. 34* a N.A. 8 N.A'. N. A . 3.08±0.38-a 2 . 92±0 . 47* a N.A. ''Data r e p r e s e n t the mean value + standard e r r o r of the mean (n= 12). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time w h i l e the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a treatment group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05) LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e c h e r r i e s r e c e i v e d s i g n i f i c a n t l y lower b i t t e r n e s s s c o r e s (p < 0.05) than those f o r the zero s torage time f r u i t , but the c h e r r i e s i n the v a r i o u s packag ing regimes were not judged to be s i g n i f i c a n t l y d i f f e r e n t from each other (p < 0 . 0 5 ) . In t h a t b i t t e r n e s s development was m i n i m a l , i t i s q u e s t i o n a b l e whether or not t h i s had a l a r g e i n f l u e n c e on the o v e r a l l a c c e p t a b i l i t y of the c h e r r i e s . Dramat ic d i f f e r e n c e s i n the response of c h e r r i e s to packag ing regimes were r e v e a l e d by the s c o r e s for o f f - f l a v o u r ( F i g u r e 4 . 2 5 ) . C o n t r o l and LB f r u i t were judged to have a b s o l u t e l y no o f f - f l a v o u r a t the end of t h e i r r e s p e c t i v e s t o r a g e s p e r i o d and d i d not d i s p l a y s i g n i f i c a n t l y lower v a l u e s for t h i s a t t r i b u t e a t the end of s torage (p > 0.05) (Tab le 4.27) O f f - f l a v o u r development was e v i d e n t i n the f r u i t i n the r e m a i n i n g package t y p e s , w i th the r a t e of development i n c r e a s i n g i n the o r d e r of MLB < MHB < HB. The s w i t c h to a n a e r o b i c r e s p i r a t i o n d u r i n g s t o r a g e of c h e r r i e s i n the HB and MHB packages , w i t h a concomitant i n c r e a s e i n the l e v e l s of a c e t a l d e h y d e , e t h a n o l , and o ther o r g a n i c v o l a t l l e s undoubted ly accounted l a r g e l y f o r the d e t e c t e d o f f - f l a v o u r . O f f - f l a v o u r remained n e g l i g i b l e In the MLB packages u n t i l a f t e r the s eventh week of s t o r a g e , a f t e r which f r u i t was judged to possess a s l i g h t o f f - f l a v o u r ( score 3.5 to 4 . 5 ) . The c h e r r i e s may have swi tched to a n a e r o b i c r e s p i r a t i o n a t t h i s p o i n t i n the s t o r a g e s t u d y , l e a d i n g to o f f - f l a v o u r development . 149 Table 4.26 Sensory Bitterness Scores for Cherries Under Various Packaging Conditions^ Storage Time (Weeks) Cotrol Treatment 2 LB MLB MHB HB 5.00*0.00-a 5.00*0.00-a 5.00*0.00-a 5.00*0.00- 5.00*0.00-a 5.00*0.00-a 5.00±0.00-a 5.00±0.00-a 5.00±0.00-a 5.00±0.00-a 5.00+0.00- 5.00±0.00-a 5.00±0.00-a 5.00±0.00-a 5.00±0.00-5.00*0.00-a 5.00±0.00- 5.00±0.00-a 4.92±0.08-a 4.75±0.18-a 4.83*0.11- 4.92*0.08-a 4.92*0.08-a 4.75*0.18-a 4.67*0.19-a 4.83+0.11-a 4.92±0,08-a 4.92±0.08-a 4.58+0.23 ab N.A. N.A. 4.92±0.08-a 4.83*0.11-a 4.67*0.22-a N.A. N.A. N.A. N.A. N.A. 4.92*0.08-4.42*0.29 4.67*0.19-a 4.08*0.36-a N.A. N.A. Data represent the mean value * standard error of the mean (n=12). The upper l e t t e r indicates the r e s u l t s of Duncan's multiple range test of the e f f e c t of storage time while the lower l e t t e r indicates the r e s u l t s of Duncan's multiple range t e s t of the e f f e c t of packaging material. Results within a treatment group or time s e r i e s that share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). 2LB=Low Barrier; MLB=Medium-Low Barrier; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not Available 2 3 4 5 6 V STORAGE TIME (WEEKS) F i g u r e 4.25 Changes i n Sensory O f f - F l a v o u r Scores for C h e r r i e s D u r i n g S torage a t 1 ° C 151 Table 4.27 Sensory Off-Flavour Scores for Cherries Under Various Packaging Conditions Storage Treatment en Time (Weeks ) Control LB MLB MHB HB 0 5.00±0.00-a 5. 00±0.00-a 5. 00+0.00-a 5. 00+0.00-a 5 .00+0.00-a 1 5.00±0.00-a 5. 00+0.00-a 4. 92±0.08-a 4. 83±0.11-a 4 .08±0.23^ b 2 . 5.00*0.00-a 4. 92+0.08-a 4. 9 2+0.0 8-a 4. 83+0.11-a 4 .08±0.15^ b 3 ' 4.8310.11-, ab 5. OOlO.00-a 4. 9210.08-a 4. 4210.19^-b 3 .4210.29-c 4 4.92l0.08-a 4 . 9210.08-a 4. 83l0.11-a 4. 4210. 2 3 — a 3 .3310.4o£ b 5 4.92±0.08-a 4. 67+0.14-a 4. 6710.26-a 3. 5810 . 3 8 ^ b N.A. 6 N. A . 4 . 8310.11— a 4. 67+0.19-a 3. be 5810. 3 1 ^ b N.A. 7 N.A. N.A. 4. 58±0.19-a 3. 42±0.40£ b N.A. 8 N.A. N.A. 3. 8310.37-a 3. 2510.45-a N.A. ''Data represent the mean value 1 standard error of the mean (n= 12). The upper l e t t e r indicates the r e s u l t s of Duncan's multiple range test of the e f f e c t of storage time while the lower l e t t e r indicates the r e s u l t s of Duncan's multiple range te s t of the e f f e c t of packaging material. Results within a treatment group or time seri e s that share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0.05). LB=Low Barrier; MLB=Medium-Low Barrier; MHB=Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not Available O v e r a l l a c c e p t a b i l i t y s c o r e s decreased w i t h d e c r e a s i n g f i l m p e r m e a b i l i t y , as d e p i c t e d i n F i g u r e 4 .26 . The most r a p i d d e c l i n e i n o v e r a l l a c c e p t a b i l i t y was observed i n the HB f r u i t (Tab le 4 . 2 8 ) , which was judged to be s l i g h t l y u n a c c e p t a b l e ( score below 2.5) a f t e r four weeks of s t o r a g e . S i m i l a r l y , MHB and MLB f r u i t showed a s i g n i f i c a n t d e c l i n e In t h e i r o v e r a l l a c c e p t a b i l i t y but both groups remained a c c e p t a b l e ( score 2.5 to 3.5) a t the end of s t o r a g e . Losses i n o v e r a l l f l a v o u r a c c e p t a b i l i t y i n c u r r e d by the MLB, L B , and c o n t r o l f r u i t o c c u r r e d more s l o w l y than i n the HB and MHB packages , which i s not s u r p r i s i n g c o n s i d e r i n g t h a t the f r u i t i n both of these groups g e n e r a l l y showed no s i g n i f i c a n t changes (p 0.05) i n any of the a t t r i b u t e s e v a l u a t e d . Decreases i n the o v e r a l l a c c e p t a b i l i t y s c o r e s of c o n t r o l f r u i t l i k e l y a r o s e due to the development of o f f - f l a v o u r s or s t a l e f l a v o u r s and the l o s s of t e x t u r e accompanying normal f r u i t s enescence . In terms of m a i n t a i n i n g " fre sh" q u a l i t y throughout an extended s t o r a g e p e r i o d , the c o n t r o l , MLB, and LB packages were s u p e r i o r to the r e m a i n i n g two packag ing reg imes , as a s se s sed through s e n s o r y a n a l y s i s . MLB and LB c h e r r i e s g e n e r a l l y e x h i b i t e d the l e a s t amount of change of a l l a t t r i b u t e s j u d g e d . However, i t must be noted t h a t c o n t r o l - p a c k a g e d c h e r r i e s were e l i m i n a t e d from s e n s o r y a n a l y s i s a f t e r f i v e weeks of s t o r a g e due to mold deve lopment , i n d i c a t i n g I t s u n s u i t a b i l i t y as a packag ing o p t i o n . 1 5 3 T R E A T M E N T O C O N T R O L • L B MLB 0 MHB * H B 2 3 4 5 6 V STORAGE TIME (WEEKS) 8 F i g u r e 4.26 Changes i n Sensory O v e r a l l A c c e p t a b i l i t y Scores f o r C h e r r i e s D u r i n g Storage a t 1 ° C 154 Table 4.28 Sensory Scores f o r O v e r a l l A c c e p t a b i l i t y of C h e r r i e s Under V a r i o u s Packaging C o n d i t i o n s ^ S torage T r e a t m e n t 2 Time (Weeks) C o n t r o l LB MLB MHB HB 0 4.92*0.08* a 4.92*0.08* a 4.92*0.08* a 4.92*0.08* a 4.92*0.08* a 1 4.58±0.19*£ ab 4 . 7 5 ± 0 . 1 3 — a 4.83±0.17* a 4.75±0.18* a 4.08±0.31* b 2 4.75+0.18— a 4.67+0.14*^ ab 4.75+0.18— a 4.58+0.26* ab 4.08+0.26* b 3 - 4.75*0.13** a 4.50±0.23*£ ab 4.58±0.15*£* ab 3.92*0.2 9** b 2.75*0.33-c 4 4 . 3 3 ± 0 . 1 4 — a 4.42+0.19** a 4. 00+0. 3 5 — a 4.25+0.25* a 2.33+0.36^ b 5 4.08+0.23* a 4.33+0.22* a 3.92+0.34* ab 3.00+0.46^* b N.A . 6 N.A. 4 . 4 2 ± 0 . 1 9 — a 4.17±0.21*** a 3.00±0.39^* b N.A . 7 N.A. N.A. 4.00*0. 3 3 — a 2.75*0.43* b N.A . 8 N.A. N.A. 3.08+0.36-a 2.58±0.47* a N.A.. '•Data r e p r e s e n t the mean value + standard e r r o r of the mean ( n=12). The upper l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of s t o r a g e time while the lower l e t t e r i n d i c a t e s the r e s u l t s of Duncan's m u l t i p l e range t e s t of the e f f e c t of packaging m a t e r i a l . R e s u l t s w i t h i n a tr e a t m e n t group or time s e r i e s t h a t share the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p>0 .05) . 2LB=Low B a r r i e r ; MLB=Medium-Low B a r r i e r ; MHB= Medium-High B a r r i e r ; HB=High B a r r i e r N.A. = Not A v a i l a b l e 5. CONCLUSIONS AND RECOMMENDATIONS 5.1 SUMMARY OF RESEARCH FINDINGS AND CONCLUSIONS The r e s u l t s of t h i s s t u d y showed tha t the h i g h b a r r i e r f i l m promoted the development of a n a e r o b i c c o n d i t i o n s w i t h i n the packages which r e s u l t e d l n s i g n i f i c a n t q u a l i t y l o s s e s l n the c h e r r i e s d u r i n g the s t o r a g e p e r i o d In p a r t i c u l a r , f r u i t became v e r y s o f t , and deve loped and o f f - o d o u r and o f f - f l a v o u r . T h i s f i l m i s thus of no use i n MAP a p p l i c a t i o n s . C h e r r i e s i n the c o n t r o l packages deve loped mold due to the h i g h oxygen and low carbon d i o x i d e l e v e l s p r e v a i l i n g i n the atmosphere , c o n f i r m i n g the u n s u i t a b l l i t y of t h i s s t o r a g e method for c h e r r i e s . A l l t e s t f i l m s were s u c c e s s f u l i n m a i n t a i n i n g atmospheres which were I n h i b i t o r y to molds . The MHB f i l m may not be u s e f u l f o r the MAP s t o r a g e of c h e r r i e s . Changes i n q u a l i t y a t t r i b u t e s i n c h e r r i e s s t o r e d l n these bags f o l l o w e d s i m i l a r t r e n d s as those observed f o r c h e r r i e s h e l d i n the HB f i l m bags; however, the r a t e of q u a l i t y d e t e r i o r a t i o n was s l i g h t l y suppressed i n the MHB bags as compared to t h a t i n the HB bags . The LB and MLB packag ing f i l m s g e n e r a l l y r e s u l t e d i n i n t e r n a l atmospheres t h a t favoured c h e r r y l o n g e v i t y . T h i s was shown through the maintenance of a number of q u a l i t y a t t r i b u t e s , i n c l u d i n g t e x t u r e and c o l o u r . F r u i t i n these packages g e n e r a l l y remained h i g h l y a c c e p t a b l e to s e n s o r y p a n e l i s t s throughout the s t o r a g e p e r i o d . The LB f i l m g e n e r a l l y performed b e t t e r than the MLB f i l m 156 i n promoting the g e n e r a t i o n of atmospheres f a v o u r a b l e to the maintenance of c h e r r y q u a l i t y . T h u s , t h i s f i l m was the most p r o m i s i n g of the f i l m s t e s t e d f o r a p p l i c a t i o n i n MAP c h e r r y s t o r a g e . 5.2 RECOMMENDATIONS FOR FURTHER RESEARCH F u r t h e r s t u d i e s s h o u l d be c a r r i e d out t o : 1. a s se s s the I n f l u e n c e of p r e t r e a t m e n t s on p r o l o n g i n g the s torage time of f r e s h MAP c h e r r i e s . P r e t r e a t m e n t s such as o exposure of the f r u i t to h i g h temperatures (around 38 C and low o temperatures (about -3 C for v a r i o u s p e r i o d s of t i m e , and exposure to h i g h c o n c e n t r a t i o n s (50 to 100%) of oxygen and carbon d i o x i d e s h o u l d be examined on the assumpt ion t h a t advantageous changes i n enzyme systems and i n biomembranes w i l l o c c u r . C h e m i c a l , p h y s i c a l , and s e n s o r y a n a l y s e s of p r e t r e a t e d MAP c h e r r i e s s h o u l d be conducted d u r i n g the s t o r a g e p e r i o d a t o o temperatures of 1 C and 5 C . 2. de termined the p h y s i c a l , c h e m i c a l , and s e n s o r y a t t r i b u t e s of MAP c h e r r i e s a f t e r they have been withdrawn from r e f r i g e r a t e d s t o r a g e a t two, f o u r , s i x , and e i g h t weeks, and o exposed to room temperature (about 20 C) f o r one, two and t h r e e d a y s . 3. examined the e f f e c t of s o a k i n g h a r v e s t e d f r e s h c h e r r i e s i n a c a l c i u m s a l t s o l u t i o n p r i o r to MAP of the f l e s h f i r m n e s s , s k i n e l a s t i c i t y , and i n h i b i t i o n of mold growth . 4. determine the i n f l u e n c e of h i g h c a r b o n d i o x i d e 157 l e v e l s around f r e s h c h e r r i e s on the enzyme systems i n the middle l a m e l l a , on the Krebs c y c l e enzymes, and on c h e r r y f i rmness d u r i n g r e f r i g e r a t e d s t o r a g e . 5. e v a l u a t e d the e f f e c t of the degree of m a t u r i t y of f r e s h h a r v e s t e d c h e r r i e s on the s t o r a b i l i t y under MAP c o n d i t i o n s . 158 REFERENCES Adams, J . 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In "P lant L i f e i n A n a e r o b i c E n v i r o n m e n t s , " D . D . Hook and R . M . M . Crawford ( E d . ) . Ann Arbor Sc i ence P u b l i s h e r s I n c . , Ann A r b o r , MI . A P P E N D I C E S Appendix A : S tandard Curves for O r g a n i c A c i d s i n Sweet Cherr i e s CONCENTRATION (mg/100 mL) 167 Appendix B : Sensory E v a l u a t i o n Form for Sweet C h e r r i e s 168 SENSORY EVALUATION SCORE SHEET - SWEET CHERRIES SAMPLE NUMBER: NAME: DATE: You have been presented with samples of sweet cherr ies. Please observe and taste each f r u i t included within each sample and rate according to the level of acceptab i l i ty of the character i s t i cs l i s t ed below. Feel free to make further comments on any of the character i s t i cs l i s t ed below, as well as any other general comments you may have. Please rinse between tast ing samples. I . FIRMNESS IN FINGERS I I . 5. very f irm 4. moderately firm 3. si ight ly f i rm 2. s l i g h t l y soft 1. very soft I I I . OVERALL APPEARANCE ACCEPTABILITY 5. very acceptable 4. moderately acceptable 3. acceptable 2. s l i g h t l y unacceptable 1. unacceptable CHERRY COLOUR 5. very acceptable 4. moderately acceptable 3. s l i g h t l y acceptable 2. s l i g h t l y poor 1. very poor IV. TEXTURE IN MOUTH 5. very firm 4. moderately f irm 3. s l i gh t l y firm 2. s l i gh t l y soft 1. very soft AROMA BY MOUTH VI. SWEETNESS 5. very strong 4. strong 3. moderately strong 2. s l i gh t 1. no aroma 5. very sweet 4. sweet 3. moderately sweet 2. s l i g h t l y sweet 1. not sweet VII. BITTERNESS 5. not b i t t e r 4. s i i g h t l y b i t t e r 3. moderately b i t t e r 2. b i t t e r 1. very b i t t e r IX. OVERALL FLAVOUR ACCEPTABILITY 5. very acceptable 4. moderately acceptable 3. acceptable 2. s l i g h t l y unacceptable 1. unacceptable VIII, (A) (B) OFF-FLAVOUR 5. absolutely none 4. very si ight 3. s l i gh t 2. moderately strong 1. strong OBJECTIONABLE? Yes No 169 

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