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Some physical chemical and histological characteristics of ripening bananas Charles, Ronald John 1972

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SOME PHYSICAL CHEMICAL AND HISTOLOGICAL CHARACTERISTICS OF RIPENING BANANAS by RONALD JOHN CHARLES B.Sc.(Agric) U n i v e r s i t y of B r i t i s h Columbia 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF . THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department o f FOOD SCIENCE We accept t h i s t h e s i s as conforming to the requ i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1972. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Bri t ish Columbia, I agree that the Library shall make it freely available for reference andstudy. 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 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 SCIENCE The University of Br i t ish Columbia Vancouver 8, Canada Date September 15. 1972 i i ABSTRACT A s t u d y o f changes i n bananas during r i p e n i n g at 16 ± 1°C and 25 ± 1°C i s d e s c r i b e d . P e e l c o l o r was e v a l u -a t e d s u b j e c t i v e l y and by r e f l e c t a n c e s p e c t r o p h o t o m e t r y ; T h e o l o g i c a l p r o p e r t i e s by p a r a l l e l p l a t e c o m p r e s s i o n and v i s c o m e t r y ; s e l e c t e d c h e m i c a l p r o p e r t i e s by a p p r o p r i a t e t e s t s and h i s t o c h e m i c a l and h i s t o l o g i c a l p r o p e r t i e s by l i g h t m i c r o s c o p y . The r a t e o f p e e l c o l o r change a t t h e h i g h e r t e m p e r a t u r e was r o u g h l y t w i c e t h a t a t the l o w e r . H i g h e r t e m p e r a t u r e - r i p e n e d f r u i t s d i d n o t d e v e l o p a f u l l y e l l o w c o l o r due t o c h l o r o p h y l l r e t e n t i o n i n t h e p e e l . A l s o p u l p -t o - p e e l r a t i o f o r such f r u i t s t e n d e d t o be l o w e r t h a n t h a t o f f r u i t s r i p e n e d at t h e l o w e r t e m p e r a t u r e . The p u l p o f h i g h t e m p e r a t u r e - r i p e n e d f r u i t s became p r o g r e s s i v e l y s o f t e r and was r e f l e c t e d by a l i n e a r i n c r e a s e o f d e f o r m a t i o n u n d e r 1 kg f o r c e . F o r a g i v e n p e e l c o l o r i n d e x , maximum f o r c e and l i n e a r l i m i t o f the t i s s u e as w e l l as a power-law c o n s i s t e n c y c o e f f i c i e n t o f t h e p u r e e were g e n e r a l l y l o w e r d u r i n g r i p e n i n g at t h e h i g h e r t e m p e r a -t u r e . R e d u c i n g s u g a r s i n c r e a s e d l i n e a r l y t h r o u g h o u t r i p e n -i n g a t the h i g h e r t e m p e r a t u r e w h i l e at the l o w e r t e m p e r a t u r e t h e r e d u c i n g s u g a r c o n t e n t was e s s e n t i a l l y c o n s t a n t beyond c o l o r i n d e x 6 . On t h e b a s i s o f p e e l c o l o r i n d e x , t o t a l i i i s u g a r and m o i s t u r e c o n t e n t were h i g h e r w h i l e s t a r c h and AIS l e v e l s were l o w e r i n f r u i t s r i p e n e d at t h e h i g h e r t e m p e r a -t u r e . R i p e n i n g t e m p e r a t u r e t h e r e f o r e i n f l u e n c e s t h e r e l a t i o n s o f c o l o r i n d e x to m e c h a n i c a l and c h e m i c a l p r o p e r t i e s . R i p e n i n g was c h a r a c t e r i z e d by a g r a d u a l l o s s o f r i g i d i t y as w e l l as an a p p a r e n t t h i c k e n i n g o f the c e l l w a l l i n o v e r - r i p e p u l p t i s s u e . T a n n i n s d e c r e a s e d d u r i n g r i p e n i n g b u t d i d not d i s a p p e a r c o m p l e t e l y . E s t e r i f i e d p e c t i n s were no t d e t e c t e d i n h a r d g r e e n f r u i t ; however, s u b s t a n t i a l amounts a p p e a r e d at p e e l c o l o r i n d e x 3, t h e n d e c r e a s e d s t e a d i l y d u r i n g r i p e n i n g . P e e l c o l o r was the b e s t o v e r a l l i n d e x o f s t a g e o f r i p e n e s s f o r b o t h r i p e n i n g t e m p e r a t u r e s . A l t h o u g h r h e o l o g i c a l and c h e m i c a l p r o p e r t i e s at a g i v e n c o l o r i n d e x d i f f e r e d f o r t h e two r i p e n i n g t e m p e r a t u r e s , t h e s e i n t e r -c o r r e l a t i o n s r e m a i n e d h i g h e r (P < 0.01). I t i s recommended, t h a t r i p e n i n g t e m p e r a t u r e s be t a k e n i n t o a c c o u n t when the c o l o r i n d e x c h a r t i s u s e d t o e s t i m a t e the s t a g e o f r i p e n e s s o f b an an as . iv TABLE OF CONTENTS PAGE LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS x INTRODUCTION 1 LITERATURE REVIEW 4 Banana Ripening 4 Commercial methods 4 Factors which a f f e c t r i p e n i n g 4 Temperature 4 Humidity 6 Ethylene 6 Changes Associated with Ripening 8 Color 8 Texture 9 Carbohydrates 12 A c i d i t y 13 Moisture ' 13 Anatomy and H i s t o l o g y 14 EXPERIMENTAL METHODS 17 Sampling Procedures 17 M a t e r i a l s 17 Ripening 17 Sampling 18 V PAGE EXPERIMENTAL METHODS (Continued) P h y s i c a l P r o p e r t i e s 18 Length 18 Pulp-to-peel r a t i o 18 Color 18 Rhe o l o g i c a l P r o p e r t i e s 19 . Force-deformation behavior 19 Flow behavior 20 Chemical P r o p e r t i e s 23 Moisture 23 pH 23 Alco h o l i n s o l u b l e s o l i d s 23 Reducing sugars 24 Total,sugars 25 Starch 25 T i t r a b l e a c i d i t y 26 Histochemical P r o p e r t i e s 26 Starch 27 E s t e r i f i e d p e c t i n s 27 Tannins 27 H i s t o l o g i c a l P r o p e r t i e s «' 28 Sample p r e p a r a t i o n 28 Se c t i o n i n g and s t a i n i n g - 29 RESULTS AND DISCUSSION 31 Changes During Ripening 31 v i PAGE RESULTS AND DISCUSSION (Continued) P h y s i c a l p r o p e r t i e s 31 F r u i t s i z e 31 Pulp-to-peel r a t i o 31 Color 34 Rhe o l o g i c a l p r o p e r t i e s 34 Force-deformation behavior 34 Flow behavior 37 Chemical p r o p e r t i e s 40 Moisture 40 A c i d i t y 40 Al c o h o l i n s o l u b l e s o l i d s „ 40 Sugars 42 Starch 42 Histochemical p r o p e r t i e s 47 H i s t o l o g i c a l p r o p e r t i e s 49 E f f e c t of Ripening Temperature 51 P h y s i c a l p r o p e r t i e s 52 Rhe o l o g i c a l p r o p e r t i e s 52 Chemcial p r o p e r t i e s 54 R e l a t i o n s h i p s Among P r o p e r t i e s 58 CONCLUSIONS 64 LITERATURE CITED 66 v i i LIST OF TABLES TABLE PAGE Simple c o r r e l a t i o n s among s i z e c h a r a c t e r i s t i c s of bananas (pooled data, n = 195) 31 Means, standard d e v i a t i o n s and t - t e s t r e s u l t s f o r s i z e c h a r a c t e r i s t i c s of bananas 32 Simple c o r r e l a t i o n s among s e l e c t e d p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s of bananas ripened at 16 + 1°C. (n = 110). 59 Simple c o r r e l a t i o n s among s e l e c t e d p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s of bananas ripened at 25 + 1°C. (n = 85) 60 Simple c o r r e l a t i o n s among s e l e c t e d p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s of r i p e n i n g bananas. (Pooled data, n = 195). 61 v i i i LIST OF FIGURES FIGURE PAGE 1 Biochemical changes i n bananas during r i p e n i n g (Simmonds 1966) 10 2 T y p i c a l force-deformation curve f o r banana pulp t i s s u e 21 3 Changes i n pu l p - t o - p e e l r a t i o of bananas during r i p e n i n g 33 4 Changes i n c o l o r index of bananas during r i p e n i n g 35 5 Reflectance curves f o r the peel of bananas ripened at 16 i 1 C 36 6 Reflectance curves f o r the peel of bananas ripened at 25 ± 1°C 36 7 Changes i n l i n e a r l i m i t of banana pulp t i s s u e during r i p e n i n g 38 8 Changes i n consistency c o e f f i c i e n t of banana puree during r i p e n i n g 39 9 Changes i n moisture content of banana pulp during r i p e n i n g 41 10 Changes i n AIS content of banana pulp during r i p e n i n g 43 11. Changes i n t o t a l sugar content of banana pulp during r i p e n i n g 44 12 Changes i n reducing sugar content of banana pulp during r i p e n i n g . 45 13 Changes i n s t a r c h content of banana pulp during r i p e n i n g 46 14 Sections of banana pulp t i s s u e showing tannin d i s t r i b u t i o n , 48 15 Photomicrographs of banana pulp t i s s u e during r i p e n i n g at 16 ± 1°C (X 320) 50 16 E f f e c t of r i p e n i n g temperature on pulp-to-peel r a t i o of bananas 53 ix E f f e c t o f r i p e n i n g t e m p e r a t u r e on d e f o r m a t i o n o f b a n a n a . p u l p t i s s u e u n d e r 1 kg f o r c e E f f e c t o f r i p e n i n g t e m p e r a t u r e on t o t a l s u g a r c o n t e n t o f b a n a n a p u l p t i s s u e X ACKNOWLEDGEMENTS The author wishes to express h i s a p p r e c i a t i o n f o r a s s i s t a n c e by Dr. M.A. Tung, Food Science Department, who d i r e c t e d t h i s research p r o j e c t . A p p r e c i a t i o n i s also extended to Dr. W.D. Powrie, and Dr. J.F. Richards, Food Science Department; Dr. E.O. Nyborg, A g r i c u l t u r a l Engineering Department and Dr. P.A. J o l l i f f e , Plant Science Department f o r t h e i r a s s i s t a n c e as members of the research committee. The w r i t e r i s g r a t e f u l f o r the use of a Rotary Microtome i n the Plant Science Department. This research was financed, i n p a r t , by the Canadian I n t e r n a t i o n a l Development Agency. 1. INTRODUCTION Bananas are grown e x c l u s i v e l y i n the t r o p i c s but they are consumed i n p r a c t i c a l l y every country. In a d d i t i o n to being a major item of i n t e r n a t i o n a l t r a d e , the banana i s the most important t r o p i c a l f r u i t on the world market. Arthur et aj_. (1968) st a t e d that without doubt the banana i s the world's most widely consumed f r u i t . In 1969, t o t a l banana exports amounted to 5.93 m i l l i o n tons (FAO 1971). This exceeded the amount of c i t r u s f r u i t s and apples traded during the same year, l e a v i n g the banana as the most important f r e s h f r u i t i n i n t e r n a t i o n a l trade. P r e l i m i n a r y FAO estimates i n d i c a t e that 199,000 tons of bananas were imported i n t o Canada i n 1970. For the period commencing January 1969 to January 1972, the t o t a l import of bananas i n t o Canada was valued at $7.11 m i l l i o n , ( S t a t i s t i c s Canada 1972). In B r i t i s h Columbia, bananas account f o r a s u b s t a n t i a l amount of a l l imported f r e s h f r u i t . Banana imports through B.C. customs i n 1970 amounted to 28.3 m i l l i o n tons, (B.C. Dept. Ind. Dev. Trade $ Comm. 1971). Bananas are marketed throughout the year, but because of t h e i r p e r i s h a b l e nature, prolonged storage i s not p o s s i b l e . Weekly shipments of green bananas ensure a continuous supply of f r e s h f r u i t -at r e t a i l o u t l e t s . However, f l u c t u a t i o n s i n supply and demand make i t necessary f o r commercial r i p e n i n g establishments to adopt various r i p e n i n g schedules i n order to meet the market requirements. 2. The r i p e n i n g period can be v a r i e d from 4 to 10 days ( S e e l i g 1969). The p r i n c i p a l f a c t o r s used i n the r e g u l a t i o n of r i p e n i n g are temperature, humidity, v e n t i l a t i o n and ethylene gas. Two of those f a c t o r s -- temperature and ethylene -- are perhaps the most important. Most commercial rip e n e r s use ethylene to s t i m u l a t e or " t r i g g e r " the r i p e n i n g process while the rate of r i p e n i n g i s c o n t r o l l e d by tempera-ture r e g u l a t i o n . F r u i t q u a l i t y i s known to be a f f e c t e d by storage and r i p e n i n g temperatures (Simmonds 1966). Prolonged exposure to high temperatures during r i p e n i n g may lead to " b o i l e d " f r u i t , while low temperatures give r i s e to c h i l l i n g i n j u r y ( H a l l 1967): Under normal commercial c o n d i t i o n s , such forms of i n j u r y r a r e l y occur. However, there have been se v e r a l reports ( H a l l 1967 ; D a l a i e_t a_l_. 1969; Sanchez Nieva e_t a_l_. 1969; Murata 1970) of d i f f e r e n c e s i n f r u i t q u a l i t y , obtained w i t h i n the range of normal r i p e n i n g procedures. Many of the stud i e s i n v o l v i n g bananas ripened under d i f f e r e n t c o n d i t i o n s , have focussed on major chemical c o n s t i t u e n t s and used panel e v a l u a t i o n of q u a l i t y . The changes i n p h y s i c a l p r o p e r t i e s of the f r u i t have been considered l a r g e l y i n d e s c r i p t i v e , terms, although t h e i r importance i n f r u i t q u a l i t y i s recognized ( S e e l i g 1969). This study was undertaken to i n v e s t i g a t e some p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s of the banana d u r i n g r i p e n i n g . A study was a l s o made of the h i s t o c h e m i c a l and h i s t o l o g i c a l changes i n the r i p e n i n g f r u i t , u s ing l i g h t microscopy. The o v e r a l l aim was to o b t a i n a b e t t e r under-standing' of the r e l a t i o n s h i p s among the major chemical and r h e o l o g i c a l p r o p e r t i e s of the r i p e n i n g f r u i t and t h e i r dependency upon the temperature of r i p e n i n g . 4 . LITERATURE REVIEW Banana Ripening Commercial methods The c o n t r o l l e d r i p e n i n g of bananas i s c a r r i e d out by various methods. In temperate c o u n t r i e s , r i p e n i n g i s c a r r i e d out i n s p e c i a l l y constructed r i p e n i n g rooms i n which temperature, humidity and a i r c i r c u l a t i o n are c a r e f u l l y c o n t r o l l e d . Modern r i p e n i n g methods have been reviewed by vonLoesecke (1950), Haarer (1964) and Simmonds (1966). S e e l i g (1969) reviewed the requirements f o r r i p e n i n g rooms with p a r t i c u l a r reference to those adapted f o r boxed f r u i t . The major companies i n v o l v e d i n the banana trade provide customers with r i p e n i n g recommendations which allow the r i p e n i n g p e r i o d to be v a r i e d from 4 to 8 days (United F r u i t Sales Corp. 1970; Standard F r u i t and Steamship Co. 1964). Factors which a f f e c t r i p e n i n g . Temperature: During r i p e n i n g , bananas produce a considerable amount of heat as a r e s u l t of r e s p i r a t o r y a c t i v i t y . The amount of heat given o f f by green bananas at 54°F (12.2°C) i s approximately 140 Btu/ton hr (USDA 1954). Simmonds (1966) c a l c u l a t e d the heat production of p r e c l i m a c t e r i c f r u i t at 53°F (I1.7°C) to be approximately 150 Btu/ton hr. At 68°F (20°C) heat production increases from 348 Btu/ton hr at p r e c l i m a c t e r i c to 386 Btu/ton hr during the c l i m a c t e r i c (USDA 1954). These c a l c u l a t i o n s are based on the amount of carbon dioxide evolved. To obtain a r i p e f r u i t of e x c e l l e n t q u a l i t y the pulp temperature should be kept between 58°F (14.3°C) and 64°F (17.6°C) depending on the rate of r i p e n i n g d e s i r e d (United F r u i t Sales Corp. 1970). The maintenance of con-stant pulp temperatures requires that heat be withdrawn from the box at l e a s t as f a s t as i t i s produced by the f r u i t . The a i r temperature must be lower since the cardboard acts as an i n s u l a t o r . In order to maintain the pulp temperatures l i s t e d above, a i r temperatures between 52°F (11.1°C) and 58°F (14.3°C) are recommended (United F r u i t Sales Corp. 1964). At the c l i m a c t e r i c , pulp temperature tends to increase very r a p i d l y and room temperature i s u s u a l l y lowered to minimize the i n c r e a s e . A f t e r the f r u i t has "sprung" -- i . e . i n the post c l i m a c t e r i c p e r i o d -- the a i r temperature may again be r a i s e d g r a d u a l l y as heat e v o l u t i o n subsides. Changes i n a i r temperature r e s u l t i n a gradual change i n pulp temperature, and because of t h i s i t i s recommended that pulp temperatures be recorded at l e a s t twice a day (United F r u i t Sales Corp. 1970). Temperature a f f e c t s the rate of r i p e n i n g as w e l l as the q u a l i t y of r i p e f r u i t . The p r e c i s e e f f e c t s are d i f f i c u l t to evaluate because of i n t e r a c t i o n with f a c t o r s such as v e n t i l a t i o n , humidity and the p h y s i o l o g i c a l age of the f r u i t . Other f a c t o r s such as v a r i e t y , c o n d i t i o n s of production and p r e - r i p e n i n g storage may be of considerable s i g n i f i c a n c e . Humidity: The s k i n of a mature banana contains 2 a large number 480/cm ) of stomata and t r a n s p i r a t i o n i s very a c t i v e (Palmer 1971). Simmonds (1966) summarized the r e s u l t s of e a r l i e r research which showed that during r i p e n i n g t r a n s p i r a t i o n increases r a p i d l y at the c l i m a c t e r i c . This i s followed by a steady s t a t e i n which t r a n s p i r a t i o n i s higher than i n the p r e c l i m a c t e r i c stage. Increased water loss o c c u r r i n g at advanced r i p e n i n g i s r e l a t e d to fungal attack. The rate of t r a n s p i r a t i o n i s l a r g e l y dependent upon temperature and humidity. In order to ensure proper water r e l a t i o n s during r i p e n i n g a high r e l a t i v e humidity must be maintained. In g e n e r a l , r e l a t i v e humidity of 85 - 95% i s recommended at the beginning of r i p e n i n g . As the f r u i t "breaks" c o l o r the humidity i s reduced to 75 - 85%. Ethylene: vonLoesecke (1950) reviewed the develop ments which led to widespread use of ethylene i n banana r i p e n i n g . Since then other workers ( B i a l e et al_. 1954; Burg and Burg 1965) have examined the r e l a t i o n s h i p between endogenous ethylene and the r e s p i r a t o r y c l i m a c t e r i c . The r o l e of ethylene i n f r u i t r i p e n i n g has been r e c e n t l y analyzed by P r a t t and Goeschl (1969) and by McGlasson (1970) 7 . while Palmer (1971) has discussed the s i g n i f i c a n c e of ethylene i n commercial t r a n s p o r t and r i p e n i n g of bananas. The mechanism of ethylene a c t i o n i n f r u i t s i s s t i l l unresolved, despite extensive research. McGlasson (1970) observed that s e v e r a l hypotheses have been presented which attempt to e x p l a i n the a c t i o n of ethylene i n terms of i t s e f f e c t s on enzyme a c t i v i t i e s , i n t e r a c t i o n s with n u c l e i c acids and metallo-enzymes and e f f e c t s on l i p o -p r o t e i n membranes. These hypotheses can be supported adequately, but they f a i l to e s t a b l i s h the nature of the primary a c t i o n of ethylene i n f r u i t t i s s u e . B i a l e ejt a_l_. (1954) reported that ethylene was a by-product of r i p e n i n g . Burg and Burg (1965) have since found that p r e c 1 i m a c t e r i c bananas contain 0.1 - 0.2 ppm ethylene i n t h e i r t i s s u e , and that t h i s l e v e l increases d r a m a t i c a l l y a few hours before the c l i m a c t e r i c . Endogenous ethylene w i l l induce r i p e n i n g i n the banana, but due to the d i f f e r e n c e s i n p h y s i o l o g i c a l age among f r u i t s i n a l o t , uneven r i p e n i n g i s f r e q u e n t l y encountered i n the absence of ethylene treatment. Supplementary ethylene enables a l l the f r u i t i n a l o t to a t t a i n the t h r e s h p l d l e v e l , f o r r i p e n i n g at about the same time. Ethylene production i n the banana i s temperature s e n s i t i v e (Palmer 1971), thus low temperature r i p e n i n g i s not p o s s i b l e i n the absence of a p p l i e d ethylene. In commercial p r a c t i c e ethylene i s a p p l i e d at the 8. rate of one cubic foot per 1000 cubic feet of r i p e n i n g space (United F r u i t Sales Corp. 1964). Higher concentra-t i o n s do not provide a d d i t i o n a l b e n e f i t s . The gas i s u s u a l l y a p p l i e d as soon as the green f r u i t i s stacked i n the r i p e n i n g room. Treatment may be s i n g l e or m u l t i p l e during a 24 - 36 hour pe r i o d ( H a l l 1967). Changes Associated with Ripening An extensive review of biochemical changes i n the r i p e n i n g banana was c a r r i e d out by vonLoesecke (1950). Simmonds (1966) summarized the more conspicuous biochemical features of r i p e n i n g . These are presented i n Figure 1. Recently Palmer (1971) has reviewed the compositional changes during r i p e n i n g , as w e l l as the enzymes i n v o l v e d . In t h i s s e c t i o n only those changes which are r e l e v a n t to the study w i l l be discussed. Color During r i p e n i n g the banana peel changes i n c o l o r from green to yellow. Yellowing of the peel begins at or f o l l o w s the c l i m a c t e r i c peak (Palmer 1971), while the rate of y e l l o w i n g i s dependent upon the r i p e n i n g c o n d i t i o n s . Peel c o l o r i s probably the most widely used index of the stage of r i p e n e s s . vonLoesecke (1950) summarized i n f o r m a t i o n on the pigment composition of banana p e e l . C h l o r o p h y l l , xanthophyll and carotene are the major pigments i n green banana p e e l . During r i p e n i n g c h l o r o p h y l l i s reduced from 50 - 100 ug/g f r e s h peel to near zero, carotene remains approximately constant at 1.5 - 3.5 ug/g fr e s h peel and xanthophyll also remains constant at 5 - 7 yg/g fr e s h p e e l . Looney and Patterson (1967) reported that ch1orophy11ase a c t i v i t y i n Gros Michel peel reached a maximum at the c l i m a c t e r i c peak. I t was suggested that c h l o r o p h y l l d e s t r u c t i o n was due to the' loss of s t r u c t u r a l i n t e g r i t y i n the ch 1 orop 1 as ts . The a b i l i t y of ethylene to s t i m u l a t e r i p e n i n g i n d i c a t e s that i t may have a d i r e c t e f f e c t on c h l o r o p h y l l d e s t r u c t i o n . E t h y l e n e - t r e a t e d bananas r i p e n with uniformly c o l o r e d peels (vonLoesecke 1950; United F r u i t Sales Corp. 1964). Color measurement i n bananas has received l i t t l e a t t e n t i o n . G o t t r e i c h e_tj al_. (1969) reported that e a r l y attempts to determine s t a t e of ripeness on the ba s i s of pulp c o l o r f a i l e d because of d i f f i c u l t i e s i n preparing s t a b l e standard c o l o r s . Finney e_t a_l_. (1967) used r e f l e c -tance spectrophotometry to evaluate the r e l a t i o n s h i p between peel c o l o r and firmness i n Valery bananas. They reported that loss of c h l o r o p h y l l associated with the change i n c o l o r from green to yellow was r e l a t e d to the change i n r e f l e c t a n c e at 675 nm. Texture Softening i n f r u i t s can be a t r i b u t e d to the i n t e r -conversions of seve r a l s t r u c t u r a l p o l y s a c c h a r i d e s . McCready and McComb (1954) demonstrated that p e c t i c substances play a major r o l e i n the lo s s of firmness i n f r u i t t i s s u e . h u JQ | § 2 >-. i_ (TJ I_ - I _o 1 0 o_30 Q_ | 20 10 c u l _ 30 c >. 20 0 100 (0 . C ( A W L. V D _ E 50 0 Pre-climacteric firm green Internal O? GASES Respiration (CQ 2 ) Internal C O , TRANSPIRATION Dry matter SOLIDS Starch Skin - 'ACTIVE TANNIN' Pulp Chlorophyll _ PIGMENTS Carotenes and xanthophylls Climacteric j Postclimacteric colouring anthracnose sprung eating ripe rotting 10 C c eo c •H 3 ~a rt C ca c rt </> o oo c • rt «» J3 vO (J O f-H •—I rt O 10 •H E C (D o j= e o s O -H •H CO vonLoesecke (1950) i n d i c a t e d that during r i p e n i n g , s o l u b l e p e c t i c substances i n the pulp of Gros Michel bananas increased from 0.3 to 4.0% while p r o t o p e c t i n decreased from 0.5 to 0.2% on a f r e s h weight b a s i s . The r o l e of c e l l u l c s e and h e m i c e l l u l o s e i n t e x t u r a l change i n the r i p e n i n g banana was i n v e s t i g a t e d by B a r n e l l (1943). He reported that c e l l u l o s e remained constant while hemice1lulose decreased from 8 - 10% i n the pulp of green f r u i t s to about 1 - 2% i n r i p e f r u i t s . Hemice1lulose content f l u c t u a t e d during r i p e n i n g and t h i s suggested to him that i t acted as a form of. reserve carbohydrate. I t was concluded that hemice1lulose was hydrolyzed to give substances which may serve as substrates f o r r e s p i r a t i o n . S a r k i s s i a n (1965) used a modified C h a t i l l o n F r u i t and Vegetable Tester to determine texture-firmness i n r i p e banana f r u i t t i s s u e . This device i s a pressure t e s t e r used i n t e s t i n g s o f t f r u i t s such as s t r a w b e r r i e s . Pressure was a p p l i e d at r i g h t angles to the cut surface of 2 inch unpeeled cross s e c t i o n s of f r u i t . He reported that at advanced peel c o l o r s the pulp of Valery bananas was much fi r m e r than that of Gros M i c h e l . Finney e_t a_l_. (1967) used a sonic technique to measure changes i n firmness of Valery bananas as they ripened. C y l i n d r i c a l s e c t i o n s of pulp were v i b r a t e d l o n g i -t u d i n a l l y and the resonant frequencies were used to c a l c u l a t e Young's modulus of e l a s t i c i t y which i s defined as the r a t i o of s t r e s s to s t r a i n . I t i s a measure of r e s i s t a n c e to force and t h e r e f o r e , of firmness. They found that s o f t e n i n g of the banana during r i p e n i n g was associated with a decrease i n Young's-modulus of e l a s t i c i t y from 272 X 10 dynes/cm 5 2 i n l i g h t green f r u i t to 85 X 10 dynes/cm i n the f u l l ye 11 ow stage. Carbohydrates Starch i s the predominant carbohydrate i n green bananas. During r i p e n i n g i t i s hydrolyzed to sugars. vonLoesecke (1950) reported the s t a r c h content of green banana pulp as 20 - 25% and that of r i p e f r u i t as 1 - 2%. The peel contains 3% s t a r c h which i s also hydrolyzed during r i p e n i n g . Sugars normally increase from 1 - 2% i n green f r u i t to 15 - 20% i n the pulp of r i p e f r u i t . There i s some disagreement i n the l i t e r a t u r e with regard to the form of the d i f f e r e n t sugars i n r i p e bananas. Eheart and Mason (1966) analyzed bananas bought on the wholesale market i n Washington D.C. and found that reducing sugars were present at 10.34% while sucrose content was 8.54%. United F r u i t Sales Corp. ( 1 9 6 4 ) ' l i s t s the sugar content of a f u l l y r i p e banana as f o l l o w s : sucrose 12.7%, lev u l o s e ( f r u c t o s e ) 3.7% and dextrose (glucose) 4.8%. Poland et_ a_l_. (1938) reported that during r i p e n i n g , glucose, f r u c t o s e and sucrose maintain n e a r l y constant p r o p o r t i o n s . A c i d i t y A c i d i t y of banana pulp r i s e s to a maximum at or soon a f t e r the c l i m a c t e r i c and may show a s l i g h t decrease as r i p e n i n g progresses (vonLoesecke 1950). The pH ranges from 5.0 - 5.8 f o r the pulp of green f r u i t to 4.2 - 4.8 i n p o s t - c l i m a c t e r i c f r u i t (Simmonds 1966). T i t r a b l e a c i d i t y of Gros Michel pulp changes from 2.96 i n the pre-c l i m a c t e r i c s t a t e to 4.95 f o l l o w i n g the c l i m a c t e r i c then to 3.66 m.equiv/lOOg f r e s h pulp at f u l l r i p e n e s s . Eheart and Mason (1966) reported the a c i d i t y of f u l l y r i p e banana pulp as 0.27% malic a c i d ['4.03 m . equiv/ 1 OOg ] . Studies by Stewart e_t_ al_. (1960) and M i l l e r and Ross (1963) i n d i c a t e that L-malic and c i t r i c acids are the predominant acids i n banana pulp at a l l stages of ripe n e s s . Moisture In s p i t e of t r a n s p i r a t i o n l o s s e s , the moisture content of banana pulp increases during r i p e n i n g . vonLoesecke (1950) gave values f o r f i v e clones ranging from 63 - 74% to 68 77%. Palmer (1971) suggested that the net increase i n pulp moisture i s the combined e f f e c t of r e s p i r a t i o n and osmosis. Sugar increases more r a p i d l y i n the pulp than i n the peel and t h i s creates an osmotic gradient causing water to move from peel to pulp. S t r a t t o n and vonLoesecke (1931) found that during r i p e n i n g the osmotic pressure of Gros Michel peel increases from 6 to 11.5 atmospheres and that of the pulp increases from 6 to 25 - 27 atmospheres. Osmotic t r a n s f e r of water r e s u l t s i n changes of pulp-to-peel r a t i o on a fr e s h weight b a s i s . Simmonds (1966) observed that the r a t i o i s about 1.2 - 1.6 i n green f r u i t and r i s e s with normal r i p e n i n g to 2.2 - 2.4 at advanced r i p e n i n g . M i c r o b i a l i n v a s i o n and dehydration give r i s e to f u r t h e r increases i n the pulp- t o - p e e l r a t i o . vonLoesecke (1950) suggested that pulp-to-peel r a t i o could be u s e f u l as an index of ripe n e s s . Anatomy and H i s t o l o g y Bananas are arranged i n nodal c l u s t e r s or "hands" which are borne on a nodal base or "cushion" attached to a s t a l k . This e n t i r e s t r u c t u r e i s roughly c y l i n d r i c a l i n shape and i s known commercially as a bunch or "stem". The f r u i t i s v e g e t a t i v e l y parthenocar.pic; i . e . i t develops a mass of e d i b l e t i s s u e without p o l l i n a t i o n . The pulp c o n s i s t s of r e l a t i v e l y u n d i f f e r e n t i a t e d t i s s u e d i v i d e d i n t o 3 segments by the c a r p e l l a r y margins. The degenerated ovules are arranged c e n t r i p e t a l l y i n each seg-ment. Wolfson (1928) has studi e d the anatomy of the f r u i t , and h i s work forms the b a s i s f o r subsequent observations by vonLoesecke (1950). The peel c o n s i s t s of an epidermal l a y e r which i s underlayed by parenchyma c e l l s i n t e r s p e r s e d with f i b r o v a s c u l a r bundles. C h l o r o p l a s t s are found i n the outer l a y e r of parenchyma known as the chlorenchyma. The epidermal c e l l s are s l i g h t l y convex on the 15 . upper surface and s l i g h t grooves appear where the edges of a d j o i n i n g c e l l s meet, g i v i n g a s t r i a t e d appearance to the peel s u r f a c e . T r a n s p i r a t i o n and gaseous exchange take place through stomata and a t h i n l a y e r of c u t i n p r o t e c t s the epidermis from d e s i c c a t i o n and other forms of i n j u r y . Parenchyma c e l l s make up the bulk of the peel t i s s u e . They are large and t h i n w a l l e d , i n c r e a s i n g i n s i z e away from the epidermis. A t h i n l a y e r of cytoplasm c o n t a i n i n g numerous p l a s t i d s , l i n e the i n s i d e of the c e l l w a l l . In the inner-most c e l l s of the peel the p l a s t i d s become centers of s t a r c h accumulation. A s a p - f i l l e d vacuole occupies the center of the c e l l . The c e l l sap i s a c l e a r f l u i d which c o n s i s t s mainly of d i s s o l v e d sugars, organic a c i d s , phenolic compounds and water. The f i b r o v a s c u l a r bundles are s c a t t e r e d throughout the parenchyma and run p a r a l l e l to the l o n g i t u d i n a l axis of the f r u i t . In a d d i t i o n to imparting strength and r i g i d i t y to the peel they serve as conveyors of water and m e t a b o l i t e s . I n d i v i d u a l f i b e r c e l l s are long, narrow and t h i c k walled. Inner bundles are l e s s f i b r o u s but more, complex. They are surrounded by a r i n g of l a t i c i f e r o u s t i s s u e i n t e r s p e r s e d with parenchyma c e l l s (Ram et_ a_l_.. 1962). The v a s c u l a r elements of the f r u i t a l l converge and anastomose i n the region of the p e d i c e l . The l a t e x system i s found i n both the peel and the pulp, and c o n s i s t s of large t h i n - w a l l e d , b a r r e l shaped c e l l s which are j o i n e d end to end i n s i n g l e l i n e s . In the peel they are g e n e r a l l y a s s o c i a t e d with v a s c u l a r bundles, although they f r e q u e n t l y occur by themselves. B a r n e l l and B a r n e l l (1945) noted that l a t e x c e l l s i n the peel are of two w e l l - d e f i n e d types. Most of the tannin i n the f r u i t i s found i n the l a t e x ( B a r n e l l and B a r n e l l 1945). The pulp-peel boundary c o n s i s t s of a few la y e r s of parenchyma c e l l s with large i n t e r c e l l u l a r -spaces. During r i p e n i n g t h i s region becomes more porous with the r e s u l t that p e e l i n g of the f r u i t i s made e a s i e r . Upon removal of the peel prominent l o n g i t u d i n a l bundles are seen adhering to the p e e l . These bundles give r i s e to the c h a r a c t e r i s t i c depressions on the surface of the pulp. Pulp c e l l s are t h i n walled and may be long or i s o d i a m e t r i c . The inner c e l l s are arranged i n rows r a d i a t i n g from the septae. These c o n s i s t l a r g e l y of paren chyma c e l l s and v a s c u l a r bundles which pass i n t o the p l a c e n t a l a x i s . The p l a c e n t a l axis c o n s i s t s c h i e f l y of spongy parenchymatous t i s s u e s . In green as w e l l as r i p e bananas there are few or no i n t e r c e l l u l a r spaces. During r i p e n i n g , c e l l s i z e remains constant whi l s t a r c h granules decrease i n s i z e and number (vonLoesecke 1950). Latex tubes are present i n the pulp of r i p e f r u i t , but they contain no l a t e x . This i s a t t r i b u t e d to tannin condensation ( B a r n e l l 1943). The r i p e n i n g behavior of the c e l l w a l l and i t s components has not been s t u d i e d . EXPERIMENTAL METHODS Sampling Procedures M a t e r i a l s Hard green Valery bananas ( C h i q u i t a brand) were purchased from a l o c a l wholesale establishment. The f r u i t s had been brought i n by truck from the docks at S e a t t l e , 3 Washington and were t r e a t e d with ethylene (approx. 1 f t 3 per 1000 f t storage space) f o r 24 hr before being used i n the experiments. Ripening A c l o s e d - c y c l e heated a i r dryer equipped with a c o o l i n g c o i l attached to a r e f r i g e r a t i o n u n i t was used as a r i p e n i n g chamber. This apparatus i s described i n d e t a i l by Bhargava (1970). F r u i t s were ripened at 16 ± 1°C and 25 ± 1°C. A r e l a t i v e humidity of 85 - 95% was maintained during r i p e n i n g , by i n j e c t i n g steam i n t o the u n i t . Temperature and r e l a t i v e humidity i n the r i p e n i n g compart-ment were recorded by a hygrometer (Hydrodynamics Inc. Model 15-4050 E) and a hygrothermograph. A 40 lb carton of f r u i t was used f o r each r i p e n i n g t r i a l . Upon r e c e i v i n g the f r u i t s the "hands" were broken up and i n d i v i d u a l f r u i t s were replaced at random i n the ca r t o n , which was then placed i n the r i p e n i n g chamber. Each temperature treatment was r e p l i c a t e d three times. Groups 1, 2 and 3 were ripened at 16 ± 1°C and groups 4, 5 and 6 at 25 ± 1°C. Experiments were terminated 18 . when the f r u i t s acquired a peel c o l o r index of 8. Sampling Eight f r u i t s were sampled every 2 - 3 days during r i p e n i n g at 16 ± 1°C, and every day during r i p e n i n g at 25 ± 1°C. Five f r u i t s were used i n d i v i d u a l l y i n the determina-t i o n of l e n g t h , p u l p - t o - p e e l r a t i o , c o l o r and force-deforma-t i o n behavior. The pulp from these f r u i t s was pooled and used to study flow behavior. The other three f r u i t s were c o l l e c t i v e l y used i n the determination of a l c o h o l i n s o l u b l e s o l i d s (AIS), sugars, moisture, pH and t i t r a b l e a c i d i t y . P h y s i c a l P r o p e r t i e s Length A v i n y l metric tape was used to measure the distance from the trimmed stem end to the d i s t a l end of the f r u i t . This was done along both the convex and concave s i d e s . The mean of these two measurements was taken as the length of the f r u i t . P u l p-to-peel r a t i o Whole and peeled f r u i t s were weighed to obtain gross and pulp weight. Peel weight was then derived by d i f f e r e n c e and the p u l p - t o - p e e l r a t i o was c a l c u l a t e d as the quotient of pulp and peel weights. Color A banana r i p e n i n g chart with c o l o r p l a t e s was used to evaluate the c o l o r index (CI) of f r u i t s , (United F r u i t Sales Corp. 1 9 6 4 ) . The CI f o r a given day represented 19 . the mean f o r the e i g h t f r u i t s sampled. Spectrophotometric measurement of peel c o l o r was c a r r i e d out on two 35 mm d i s c s of peel removed from the f r u i t at the d i s t a l and stem ends. Each d i s c was p l a c e d i n a p l a s t i c t i s s u e c u l t u r e dish and f l a t t e n e d with a black b a c k i n g . The dish was covered and clamped to the sample h o l d e r of the r e f l e c t a n c e u n i t of a Unicam SP 800 r e c o r d i n g spectrophotometer. D i f f u s e r e f l e c t a n c e of the peel w i t h i n the v i s i b l e spectrum (450 to 800 nm) was recorded on a l o g a r i t h m i c s c a l e at a scan rate of 200 nm/min. Fresh magnesium oxide was used to c a l i b r a t e the instrument at 100% r e f l e c t a n c e . R e f l e c t a n c e values at 470, 672 and 730 nm were read from the s p e c t r a and the mean r e f l e c t a n c e obtained f o r the two s e c t i o n s c o n s t i t u t e d the r e f l e c t a n c e data f o r each f r u i t . R e f l e c t a n c e r a t i o s were then computed f o r 470 and 672, 672 and 470 as w e l l as 730 and 672 nm respec-t i v e l y . The Index of Variance R e f l e c t a n c e (IVR) proposed by Powers ejt a^. (1953) as a c r i t e r i o n f o r c o l o r measure-ment i n f r u i t s , was c a l c u l a t e d using the f o l l o w i n g formula: I V R - ! z i ° _ _ ! i Z l c n 672 R h e o l o g i c a l P r o p e r t i e s F orce-deformation b e h a v i o r A c y l i n d r i c a l specimen of t i s s u e was prepared by 20 . c u t t i n g a s e c t i o n of the peeled f r u i t 2.5 cm long, using a p a r a l l e l s t r i n g s l i c i n g device. Cross s e c t i o n a l area at each c y l i n d e r end was c a l c u l a t e d from the average diameter measured with v e r n i e r c a l i p e r s . The mean of these measure-ments was designated as the cross s e c t i o n a l area of the specimen. The s e c t i o n was subjected to p a r a l l e l p l a t e compression along the l o n g i t u d i n a l axis using an Inst r o n Model TMM u n i v e r s a l t e s t i n g machine. Loading rate was 0.5 cm/min and chart speeds of 2 and 5 cm/min were used. Force-deformation curves of the type shown i n Figure 2 were obtained f o r f i v e f r u i t s on each sampling day. From these curves values were obtained f o r maximum f o r c e , l i n e a r l i m i t , deformation at one kg of force and the energy absorbed by the sample from i n i t i a l loading to the l i n e a r l i m i t ( l i n e a r l i m i t energy). To compensate f o r d i f f e r e n c e s i n cross s e c t i o n a l area-of the c y l i n d r i c a l samples, maximum force and l i n e a r l i m i t were d i v i d e d by the cross s e c t i o n a l area and the one kg deformation was m u l t i p l i e d by that area. Flow behavior Pulp from the f r u i t s used i n ' t h e study of f o r c e -deformation c h a r a c t e r i s t i c s was s l i c e d and blended with 25% (W/W) water i n a high speed -Waring blendor f o r 8 min. P r e l i m i n a r y t r i a l s i n d i c a t e d t h i s amount of water was optimum f o r s l u r r y p r e p a r a t i o n since green pulp could be macerated to a smooth consistency while the p a r t i c u l a t e 21 . D e f o r m a t i o n , m m FIGURE 2 T y p i c a l f o r c e - d e f o r m a t i o n c u r v e f o r banana p u l p t i s s u e . MF, maximum f o r c e ; LL, l i n e a r l i m i t ; U l , d e f o r m a t i o n due t o 1 kg f o r c e . 22 . matter i n ov e r - r i p e puree did not s e t t l e out of the suspen-s i o n . A f t e r b l e n d i n g , the puree was allowed to stand at room temperature f o r 30 min. About 100 ml of puree was used f o r each determina-t i o n . A l l measurements were obtained with a Haake Rotovisko c o n c e n t r i c c y l i n d e r viscometer equipped with an MV1 s p i n d l e (gap width 0.96 mm). The sample was kept at 20°C using a Kryomat constant temperature bath connected to the water jac k e t that surrounded the sample holder. During each determination the s p i n d l e r o t a t i o n speed was v a r i e d stepwise from maximum to minimum. The viscometer t r a n s m i s s i o n was then disengaged and the shear s t r e s s r e l a x a t i o n was recorded u n t i l a constant value was a t t a i n e d . This measurement was used as a y i e l d s t r e s s f o r the sample. The sample was then t e s t e d from low to high shear rates to complete the v i s c o m e t r i c measurements. Shear rates ranged from 8.5 to 1370 sec-'''. The torque due to viscous drag i n the f l u i d at known shear rates was sensed by a Moseley Autograf s t r i p chart recorder. Flow behavior curves were constructed using shear r a t e , shear s t r e s s and y i e l d s t r e s s dat'a derived from the v i s c o m e t r i c t e s t s . Two forms of the widely used power-law flow model were f i t t e d to these data. . mt" [2] 23. and x = ray11 + T [ 3 ] y _ 2 where T = s h e a r s t r e s s (dynes cm ) - 2 Ty = y i e l d s t r e s s (dynes cm ) Y = s h e a r r a t e ( s e c *) m = a p a r a m e t e r , the c o n s i s t e n c y c o e f f i c i e n t n = a p a r a m e t e r , the f l o w - b e h a v i o r i n d e x . The f l o w p a r a m e t e r s m and _n were e v a l u a t e d w i t h a computer u s i n g the method o f l e a s t s q u a r e s and a n o n - l i n e a r c u r v e f i t t i n g t e c h n i q u e . T h i s p r o c e d u r e i n c l u d e d e v a l u a t i o n o f s t a t i s t i c a l p a r a m e t e r s t h a t would i n d i c a t e the a c c u r a c y w i t h w h i c h t h e f l o w models f i t t e d the d a t a . C h e m i c a l P r o p e r t i e s M o i s t u r e A m o d i f i e d AOAC (1965) method was use d i n wh i c h d u p l i c a t e 5 g samples were d r i e d i n a h o t a i r oven a t 100 -103°C f o r 18 h r . A f t e r c o o l i n g i n a d e s i c c a t o r f o r 30 min, the d r i e d s a m p l e s were weighed and p e r c e n t m o i s t u r e computed on a f r e s h w e i g h t b a s i s . P'H A 40% s l u r r y was made by m i x i n g an a p p r o p r i a t e amount o f p u r e e w i t h d i s t i l l e d w a t e r and t h e pH was measured w i t h an I n s t r u m e n t L a b o r a t o r y pH m e t e r . A l c o h o l I n 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 o f a l c o h o l i n s o l u b l e s o l i d s (AIS) was b a s e d on an AOAC (1965) method. D u p l i c a t e 5 g samples o f p u r e e were e x t r a c t e d i n 250 ml b o i l i n g 80% e t h y l a l c o h o l . E x t r a c t i o n was c a r r i e d o ut f o r 30 min i n a w a t e r b a t h a t 24 . about 85°C. The hot s o l u t i o n was vacuum-filtered through Whatman No.2 f i l t e r paper i n a Buchner fun n e l . The residue was washed with an equal volume of hot 80% e t h y l a l c o h o l , then dried, i n a hot a i r oven at 100 - 103°C f o r 2 hr. A f t e r c o o l i n g i n a d e s i c c a t o r f o r 15 min, the samples were weighed and AIS c a l c u l a t e d as a percentage of fr e s h weight. Dried AIS m a t e r i a l was placed i n sample b o t t l e s and stored i n a d e s i c c a t o r to be used l a t e r f o r determination of s t a r c h . Reducing sugars These were measured by the method of Ting (1956) with some m o d i f i c a t i o n s by Furuholmen e_t al_. (1964). The method i s based on the redu c t i o n of a l k a l i n e f e r r i c y a n i d e , which i s then converted to a blue-green arsenomolybdate complex. The absorbance of t h i s complex at 515 nm i s then measured with a spectrophotometer. A l l reagents used i n t h i s method were as described by Ting (1956). The f i l t r a t e obtained during AIS determination was cooled to room temperature and made up to 1000 ml with d i s t i l l e d water. At t h i s c o n c e n t r a t i o n ethanol d i d not i n t e r f e r e with the t e s t . A one ml a l i q u o t of t h i s d i l u t e e x t r a c t was t r a n s f e r r e d by p i p e t t e to a' 100 ml volumetric f l a s k and 5 ml f e r r i c y a n i d e reagent added. The f l a s k was s w i r l e d then heated i n a b o i l i n g "water bath f o r 10 min. A f t e r heating the f l a s k was q u i c k l y cooled i n a running water bath. The contents were then p a r t i a l l y n e u t r a l i z e d with 10 ml IM H„S0 and shaken u n t i l gas e v o l u t i o n ceased. 25 . Four ml of arsenomolybdate reagent were added, the mixture was mixed thoroughly and made up to volume. The f l a s k was allowed to stand f o r 15 min. Absorbance of the ferrocyanide-arsenomolybdate complex was measured at 515 nm and a s l i t width of 0.016 mm with a H i t a c h i - P e r k i n Elmer spectrophotometer. A reagent blank with water was used to standardize the spectrophoto-meter and glucose and f r u c t o s e s o l u t i o n s were used to con-s t r u c t a standard curve. The reducing sugar content of each a l c o h o l i c e x t r a c t was determined i n d u p l i c a t e . T o t a l sugars A 5 0 ml sample of the d i l u t e e x t r a c t was placed i n a 200 ml beaker with 10 ml 6M HC1. The beaker was s w i r l e d and allowed to stand at room temperature f o r 18 hr. Following i n v e r s i o n the mixture was p a r t i a l l y n e u t r a l i z e d with 5 ml 10M NaOH and the pH adjusted between 5 and 7 with IM NaOH. The s o l u t i o n was then t r a n s f e r r e d to a 200 or 250 ml vol u m e t r i c f l a s k and made up to volume. One ml of t h i s s o l u t i o n was t r a n s f e r r e d to a 100 ml volumetric f l a s k and t o t a l sugars were determined using the procedure described f o r reducing sugars. Two determinations were c a r r i e d out on each i n v e r t e d sample. St arch A modified AOAC (1965) method was used to measure s t a r c h . A sample of d r i e d AIS (<\,0.5g) was added to a mixture of 200 ml water and 20 ml 6M HC1. This was then r e f l u x e d f o r 2.5 hr and a f t e r c o o l i n g at 20°C i n an i c e bath, t r e a t e d with 10 ml 10M NaOH. The pH was adjus t e d between 5 - 7 with IM NaOH and one ml of s a t u r a t e d lead a c etate s o l u t i o n was added f o r c l a r i f i c a t i o n . The mixture was then l e f t o v e r n i g h t i n a r e f r i g e r a t o r to allow s e t t l i n g of the suspended p a r t i c l e s . The supernatant was f i l t e r e d through Whatman No.2 f i l t e r paper using a l i g h t vacuum, then t r a n s f e r r e d to a 500 or 1000 ml v o l u m e t r i c f l a s k and made up to volume. A one ml a l i q u o t of t h i s s o l u t i o n was used to determine reducing sugars as o u t l i n e d b e f o r e . S t a r c h was c a l c u l a t e d i n d u p l i c a t e as 0.90 times the reducing sugar e q u i v a l e n t . T i t r a b l e a c i d i t y The AOAC (1965) method was used to determine t i t r a b l e a c i d i t y i n samples of f r o z e n puree. The puree had been s e a l e d i n p l a s t i c bags and kept f r o z e n at -37°C. Twenty g of puree was used to make a s l u r r y with 100 ml d i s t i l l e d water. The s l u r r y was t i t r a t e d with 0.10M NaOH to pH 8.1 us i n g a pH meter and magnetic s t i r r e r . T i t r a b l e a c i d i t y was determined i n d u p l i c a t e and expressed i n m.equiv/1OOg. H i s t o c h e m i c a l P r o p e r t i e s F r u i t s used i n these s t u d i e s were r i p e n e d at 15 - 17°C and 85% r e l a t i v e humidity. During r i p e n i n g a sample of f i v e f r u i t s were removed every two days f o r h i s t o c h e m i c a l and h i s t o l o g i c a l s t u d i e s . Free-hand 27 t r a n s v e r s e s e c t i o n s of f r e s h pulp t i s s u e were cut with a r a z o r blade and t e s t e d f o r s t a r c h and e s t e r i f i e d p e c t i n s . Cross s e c t i o n s of pulp 5 mm t h i c k from the middle of the f r u i t were used to study " t a n n i n " d i s t r i b u t i o n . Starch The method of Jensen (1962) was used i n t h i s d e t e r m i n a t i o n . An IKI s o l u t i o n c o n s i s t i n g of 0.3g i o d i n e and 1.5g potassium i o d i d e d i s s o l v e d i n 100 ml d i s -t i l l e d water was the reagent used. The t i s s u e s e c t i o n was p l a c e d on a g l a s s s l i d e and 3 drops of reagent added. A f t e r 2 min excess reagent was washed o f f with d i s t i l l e d water and the s e c t i o n examined under a microscope. Starch granules were s t a i n e d dark b l u e . E s t e r i f i e d p e c t i n s The hydroxy 1 a m i n e - f e r r i c c h l o r i d e r e a c t i o n (Gee et a l . 1959) was the t e s t used. Fi v e drops of an a l k a l i n e hydroxylamine reagent was p l a c e d on a s l i d e and a s e c t i o n lowered on to i t . A f t e r 5 min an equal volume of s o l u t i o n c o n s i s t i n g of one p a r t c oncentrated HC1 and 2 p a r t s 95% e t h y l a l c o h o l was added. Excess s o l u t i o n was d r a i n e d o f f and the s l i d e f l o o d e d with 10% F e C l ^ i n . 60% e t h y l a l c o h o l c o n t a i n i n g 0.1M HC1. The presence of e s t e r i f i e d p e c t i n was i n d i c a t e d by a red c o l o r when, the s e c t i o n was examined under a microscope. Tannins (polyphenols) This t e s t was adapted from the method of Jensen 28 . ( 1 9 6 2 ) . I t i s n o t s p e c i f i c f o r t a n n i n s i n c e o t h e r p o l y -p h e n o l s r e a c t w i t h t h e r e a g e n t ; h o w e v e r , i n f r u i t s s u c h as b a n a n a s where t a n n i n s c o n s t i t u t e t h e l a r g e s t g r o u p o f p o l y p h e n o l s t h i s t e s t i s u s e f u l . C r o s s s e c t i o n s o f p u l p c u t f r o m t h e m i d d l e o f t h e f r u i t were p l a c e d i n a p e t r i d i s h and c o v e r e d w i t h a 10% s o l u t i o n o f f e r r i c c h l o r i d e i n 60% e t h y l a l c o h o l c o n t a i n i n g 0.1M HC1. A f t e r 5 min t h e s e c t i o n s were t h o r o u g h l y washed w i t h d i s t i l l e d w a t e r and e x a m i n e d f o r " t a n n i n " l o c a t i o n . T h i s was i n d i c a t e d by a d a r k b l u e p r e c i p i t a t e . H i s t o l o g i c a l P r o p e r t i e s Sample p r e p a r a t i o n A 2.5 cm c r o s s s e c t i o n o f p u l p f r o m t h e m i d d l e o f t h e f r u i t was c u t i n t o 4 mm s l i c e s . C y l i n d r i c a l c o r e s o f t i s s u e 5 mm i n d i a m e t e r were t h e n c u t o u t w i t h i n t h e s e p t a e c l o s e t o t h e d e g e n e r a t e d o v u l e s . T i s s u e c o r e s were f i x e d i n N a v a s h i n ' s s o l u t i o n ( J e n s e n 1962) a t 0°C f o r 24 h r . A 15 min vacuum i n f i l t r a -t i o n was n e c e s s a r y a t t h e o u t s e t o f f i x a t i o n t o remove a i r f r o m t h e t i s s u e . N a v a s h i n ' s s o l u t i o n i s made f r o m two s o l u t i o n s m i x e d ( 1 : 1 ) b e f o r e u s e . S o l u t i o n A c o n s i s t s o f 5g c h r o m i u m t r i o x i d e , 50 ml g l a c i a l a c e t i c a c i d and 320 ml d i s t i l l e d w a t e r . S o l u t i o n B i s a" m a x t u r e o f 200 ml f o r m a l i n and 175 ml d i s t i l l e d w a t e r . A f t e r f i x a t i o n t h e t i s s u e was washed f o r 30 min i n c o l d w a t e r and t h e n d e h y d r a t e d a t 0°C u s i n g t h e s c h e d u l e o f F e d e r and O ' B r i e n ( 1 9 6 8 ) . T h e t i s s u e was i n f i l t r a t e d w i t h T i s s u e m a t p a r a f f i n ( m e l t i n g p o i n t 5 6 . 5 ° C ) i n a v a c u u m o v e n a t 6 2 ° C . T h e same m a t e r i a l was u s e d f o r e m b e d d i n g t h e t i s s u e . T h e m o l t e n p - a r a f f i n was p o u r e d i n t o p a p e r m o l d s a n d t i s s u e c o r e s w e r e p r o p e r l y o r i e n t e d u s i n g h o t n e e d l e s . T h e m o l d s w e r e t h e n l o w e r e d i n t o a w a t e r b a t h c o n t a i n i n g c r u s h e d i c e . When t h e s u r f a c e a h d s o l i d i f i e d t h e m o l d was s u b m e r g e d a n d a l l o w e d t o h a r d e n c o m p l e t e l y . A f t e r t h e b l o c k h a d c o m p l e t e l y c o o l e d , i t was r e m o v e d f r o m t h e w a t e r , w r a p p e d i n a l u m i n u m f o i l a n d s t o r e d i n a r e f r i g e r a t o r . S e c t i o n i n g a n d s t a i n i n g P i e c e s o f p a r a f f i n c o n t a i n i n g t i s s u e w e r e a t t a c h e d t o w o o d e n b l o c k s u s i n g a h o t s p a t u l a . E x c e s s p a r a f f i n was r e m o v e d f r o m a r o u n d t h e t i s s u e a n d t h e w o o d e n b l o c k s w e r e p l a c e d i n t h e j a w s o f a S p e n c e r r o t a r y m i c r o t o m e w h i c h was u s e d t o o b t a i n r i b b o n s 10 - 12 u t h i c k . T h e u p p e r s u r f a c e o f a p r e c l e a n e d s l i d e was c o a t e d w i t h a t h i n l a y e r o f H a u p t ' s a d h e s i v e ( J e n s e n 1 9 6 2 ) . A f e w d r o p s o f 4% f o r m a l i n w e r e a d d e d a n d s e g m e n t s o f t h e r i b b o n s w e r e f l o a t e d o n t h e s l i d e w h i c h was t h e n p l a c e d on a h o t p l a t e a t 35°C t o a l l o w t h e s e c t i o n s t o e x p a n d . E x c e s s f o r m a l i r i was d r a i n e d a n d t h e s l i d e was l e f t t o d r y o v e r n i g h t o n t h e h o t p l a t e . T i s s u e m a t was r e m o v e d f r o m t h e s l i d e s b y s o a k i n g i n x y l e n e . A f t e r p a r t i a l h y d r a t i o n i n a n e t h y l a l c o h o l s e r i e s ( 1 0 0 , 9 5 , ' 70 a n d 5 0 % ) , t h e s l i d e s w e r e s t a i n e d w i t h s a f r a n i n - t o l u i d i n e b l u e . The s t a i n i n g schedule was adapted from the s a f r a n i n - f a s t green method o u t l i n e d by Jensen (1962). S t a i n e d s l i d e s were passed through an a l c o h o l s e r i e s (70, 95 and 100%) and f i n a l l y through 3 changes of xylene. They were then d r i e d f o r 24 hours before mounting i n Permount with 22 x 60 mm c o v e r s l i p s ( N o . l ) . A f u r t h e r d r y i n g p e r i o d of 24 hr was necessary before examination. A Wild M20 l i g h t microscope f i t t e d with a 35 mm Asahi Pentax camera was used to observe and photograph the s e c t i o n s at m a g n i f i c a t i o n s of 100 and 400 diameters. RESULTS AND DISCUSSION Changes During Ripening P h y s i c a l p r o p e r t i e s F r u i t s i z e : A l l v a r i a b l e s examined were c l o s e l y r e l a t e d to each other (Table 1). G e n e r a l l y there was not much d i f f e r e n c e among groups although f r u i t s i n groups 1 and were longer and h e a v i e r than the others (Table 2). . Length and gross weight showed the most v a r i a t i o n i n a l l e x p e r i -mental groups. V a r i a t i o n i n s i z e was not c o n s i d e r e d e x c e s s i v e because the f r u i t s were d e r i v e d from d i f f e r e n t "hands" and bunches and were s u b j e c t to seasonal and g e o g r a p h i c a l e f f e c t s . TABLE 1. SIMPLE CORRELATIONS AMONG SIZE CHARACTERISTICS OF BANANAS (pooled data, n = 195) Length Gross wt. Pulp wt. Gross wt. 0.847 Pulp wt. 0.805 0.962 Cross s e c t i o n area 0.489 0.762 0.831 P u l p - t o - p e e l r a t i o : A l l groups of f r u i t showed a steady i n c r e a s e i n p u l p - t o - p e e l r a t i o ( F igure 3). R a t i o s ranged from 1.35 i n green f r u i t s to 2.14 i n o v e r - r i p e f r u i t s The r e s u l t s of t h i s study are i n agreement with the o b s e r v a t i o n s of vonLoesecke (1950) and Simmonds (1966) . TABLE 2. MEANS, STANDARD DEVIATIONS AND t - T E S T RESULTS FOR SIZE CHARACTERISTICS OF BANANAS. Group L e n g t h (cm) G r o s s wt. (g) P u l p wt. (g) A r e a ( c m 2 ) 1 2 3 . 2 2 a b l 181.0 a b 114 . 73 a 6 . 97 a 1. 64 17.63 14.41 0.48 2 21.76 c d 172 . 84 c 111 . 05 a 7 . 18 a 1.91 25 . 36 16.67 0 . 64 3 21 . 26 C 171.89 a C 110.87 a 7 . 24 a 1.75 31 .07 31.07 0 .80 4 22 . 0 3 c e 1 7 3 . 7 2 a c d 111 . 67 a 7 . 06 a 2 . 33 42.57 31 . 2 1.11 5 23.90 a 191 .46 b d 119 . 93 a 7. 04 a 2. 00 35.13 24 . 89 0 .99 6 2 2 . 6 6 b d e 178.29 b c 109.58 a 6 . 90 a 2.46 33.02 22.18 0 . 70 1 Means i n a c o l u m n s h a r i n g t h e same l e t t e r do n o t d i f f e r a t P = 0.05. 33. FIGURE 3. Changes i n p u l p - t o -d u r i n g r i p e n i n g . p e e l r a t i o o f bananas C o l o r : The change i n c o l o r index during r i p e n i n g i s shown i n F i g u r e 4. In most groups a change i n c o l o r was observed a f t e r one day of r i p e n i n g . Rate of change was somewhat-variable although that of groups 4, 5 and 6 tended t o b e l e s s s o . T y p i c a l r e f l e c t a n c e curves of banana peel during r i p e n i n g are shown i n F i g u r e s 5 and 6. There was an o v e r a l l i n c r e a s e i n r e f l e c t a n c e during r i p e n i n g with the g r e a t e s t changes o c c u r r i n g at 672 nm. R e f l e c t a n c e changes at t h a t wavelength were a s s o c i a t e d with the r e d u c t i o n i n c h l o r o p h y l l content of the p e e l . Finney et al_. (1967) found that c h l o r o p h y l l i n banana peel was a s s o c i a t e d with a change i n r e f l e c t a n c e at 675 nm while Powers ejt a l . (1953) r e p o r t e d that r e f l e c t a n c e at 678 nm was r e l a t e d to changes i n s u r f a c e c o n c e n t r a t i o n of c h l o r o p h y l l i n lemons. Index of Variance R e f l e c t a n c e (IVR) decreased during r i p e n i n g , but r i p e f r u i t s i n groups 4, 5 and 6 tended to have h i g h e r values than groups 1, 2 and 3. R h e o l o g i c a l p r o p e r t i e s Force-deformation b e h a v i o r : Green f r u i t with a c o l o r index of 2 were hard and b r i t t l e with c y l i n d r i c a l s e c t i o n s able to withstand up to 65 kg of f o r c e . A f t e r one or two days the r i p e n i n g of a l l groups showed a marked i n c r e a s e i n s o f t e n i n g . T h i s was r e f l e c t e d by sudden changes i n maximum f o r c e , l i n e a r l i m i t and l i n e a r l i m i t energy. 35 . I I ] I I , I I L 0 2 4 6 8 10 12 14 Time, days FIGURE 4. Changes i n r i p e n i n g . c o l o r i n d e x o f bananas d u r i n g 450 500 550 600 650 700 75 0 W a v e I„-e n g t h , n m FIGURE 5. R e f l e c t a n c e c u r v e s f o r the p e e l o f bananas r i p e n e d at 16 ± 1°C. Numbers on t h e c u r v e s i n d i c a t e p e e l c o l o r i n d e x . FIGURE 6. R e f l e c t a n c e c u r v e s f o r the p e e l o f bananas r i p e n e d a t 25 ± 1°C. Numbers on t h e c u r v e s i n d i c a t e p e e l c o l o r i n d e x . Changes i n l i n e a r l i m i t during r i p e n i n g are i l l u s t r a t e d i n Figure 7. When the f r u i t s from a l l groups a t t a i n e d f u l l ripeness ( f u l l y e l l o w ) , l i n e a r l i m i t remained r e l a t i v e l y constant and showed less v a r i a t i o n among groups. Deformation increased s t e a d i l y during e a r l y r i p e n i n g . In groups 1, 2 and 3 the r i p e f r u i t s were not as r e a d i l y deformed as i n the other groups. Linear l i m i t energy decreased with r i p e n i n g i n a l l groups with the rate of change being greatest i n groups 4, 5 and 6. There was much v a r i a t i o n i n green f r u i t and, to a l e s s e r extent, i n r i p e f r u i t . Flow behavior: Data from a l l groups f i t t e d the two power-law flow models w e l l . The mean c o e f f i c i e n t of determination f o r the power-law with y i e l d s t r e s s (Equation [3]) was 0.97 and that f o r power-law (Equation [2]) was 0.96. Thus both models a c c u r a t e l y describe the flow behavior of banana puree, however the power-law with y i e l d s t r e s s was s e l e c t e d f o r d i s c u s s i o n i n t h i s p r e s e n t a t i o n . During r i p e n i n g the f r u i t puree decreased i n consistency. The power-law consistency c o e f f i c i e n t (m) decreased and flow behavior index (n_) inc r e a s e d , i . e . the puree approached Newtonian flow. The rate of change i n m was greatest i n groups 4, 5 and- 6 (Figure. 8), while values f o r n_ tended to be l a r g e r i n the same groups. The parameter m c o r r e l a t e d w e l l (Table 3) with force deformation v a r i a b l e s as w e l l as with s t a r c h and sugar Time, days FIGURE 7. Changes i n l i n e a r during r i p e n i n g . l i m i t of banana pulp t i s s u e 400 39 2 4 6 8 10 12 14 Time , days FIGURE 8. Changes i n c o n s i s t e n c y c o e f f i c i e n t of banana puree during r i p e n i n g . content. Y i e l d s t r e s s values decreased during r i p e n i n g from 2 2 270 - 350 dynes/cm i n green f r u i t s to 10 - 25 dynes/cm i n ove r - r i p e f r u i t s . Decrease i n y i e l d s t r e s s followed a pa t t e r n s i m i l a r to that of the parameter m. Chemical p r o p e r t i e s Moisture: Moisture content increased from 71.3 to 76.0% i n groups, 1, 2 and 3 and from 72.6 to 78.7% i n groups 4, 5 and 6 (Figure 9). Increases were w i t h i n the range of tabul a t e d values (vonLoesecke 1950) and were steady throughout r i p e n i n g i n a l l groups. A c i d i t y : Peak a c i d i t y occurred i n f u l l y r i p e f r u i t s although l e v e l s were v a r i a b l e among groups. pH decreased from 5.0 - 5.4 i n green f r u i t s to 4.2 - 4.8 i n f u l l y r i p e f r u i t s , then increased with advanced r i p e n i n g . T i t r a b l e a c i d i t y increased with i n i t i a l r i p e n i n g but decreased with continued r i p e n i n g . Values ranged from 3.3 - 5.0 m.equiv/lOOg i n green f r u i t s to 4.85 - 6.0 m.equiv/lOOg i n f u l l y r i p e f r u i t s and 4.0 - 5.5 m.equiv/lOOg i n o v e r - r i p e ( h e a v i l y spotted) f r u i t s . This suggests that acids are used as r e s p i r a t o r y s u b s t r a t e s . Maximum t i t r a b l e a c i d i t y d i d riot g e n e r a l l y c o i n c i d e with minimum pH. This i s probably due to d i f f e r e n c e s i n b u f f e r i n g c a p a c i t y of the org a n i c " a c i d s present at d i f f e r e n t stages of ri p e n e s s . A l c o h o l i n s o l u b l e s o l i d s : There was a steady decrease i n AIS during r i p e n i n g . Green f r u i t s contained 41 . FIGURE 9. Changes i n m o i s t u r e c o n t e n t o f b a n a n a p u l p d u r i n g r i p e n i n g . 20 - 25% while i n o v e r - r i p e f r u i t s the l e v e l was g e n e r a l l y less than 5%. The rate of decrease was f a s t e r and more uniform i n groups 4, 5 and 6 (Figure 10). In a d d i t i o n these groups tended to have less AIS than the others. Changes i n AIS during r i p e n i n g represents tr a n s -formation of s t a r c h and s t r u c t u r a l m a t e r i a l s such as c e l l u l o s e , h e m i c e l l u l o s e and p e c t i c substances and are c l o s e l y r e l a t e d to r h e o l o g i c a l p r o p e r t i e s . Sugars: T o t a l sugar increased during r i p e n i n g i n a l l groups (Figure 11). Groups 4, 5 and 6 appeared to have s l i g h t l y large amounts of sugar i n o v e r - r i p e f r u i t s . With advanced r i p e n i n g , the sugar content appeared to reach a p l a t e a u . Reducing sugars increased s t e a d i l y during r i p e n i n g (Figure 12). The rate of increase as w e l l as the f i n a l amount i n o v e r - r i p e f r u i t was greatest i n groups 4, 5 and 6. Reducing sugars did not decrease i n o v e r - r i p e f r u i t s , i n d i c a t i n g that non-reducing sugars are probably u t i l i z e d i n r e s p i r a t i o n before reducing sugars. In t h i s study non-reducing sugars c o n s t i t u t e a l a r g e r percentage of t o t a l sugar. This i s i n agreement with compositional data given by United F r u i t Sales Corp. (1964). In general reducing sugars accounted f o r about 25% of t o t a l sugar content up to f u l l r i p e n e s s . Starch : Changes i n s t a r c h were g e n e r a l l y p a r a l l e l to those of AIS (Figures 10 and 13). Starch content v a r i e d 43 . FIGURE 10. Changes i n AIS content of banana pulp during r i p e n i n g . 44 . FIGURE 11. Changes i n t o t a l sugar pulp during r i p e n i n g . content of banana i 0 2 4 6 8 10 12 14 T i m e , days FIGURE 1 2 . Changes i n reducing sugar content of banana pulp during r i p e n i n g . 46 . from 17 - 22% i n green f r u i t s to l e s s than 2% i n r i p e f r u i t s . Histochemical p r o p e r t i e s Figure 14 shows that tannins are a s s o c i a t e d p r i m a r i l y with the c a r p e l l a r y margins. A l o n g i t u d i n a l sec-t i o n through one of the margins reveals that l a t e x c e l l s are present i n large numbers. B a r n e l l and B a r n e l l (1945) also found that banana f r u i t tannins occur mainly i n l a t e x c e l l s . During r i p e n i n g there was a d e c l i n e i n the l e v e l of tannins (polyphenols) i n the pulp (Figure 14). G o l d s t e i n and Swain (1963) have sta t e d that loss of astringency i n r i p e bananas r e s u l t s from a decrease i n " a c t i v e " tannins due to poly-m e r i z a t i o n . Starch disappearance began i n the p l a c e n t a l region at c o l o r index 3 and progressed towards the p e e l . At c o l o r index 7, s t a r c h was confined l a r g e l y to the c e l l s at the periphery of the pulp with some starch-laden c e l l s s c a t t e r e d at random throughout the pulp t i s s u e s . Starch granules i n the c e n t r a l part of part of r i p e f r u i t s appeared to decrease i n s i z e , however the p e r s i s t e n c e of s t a r c h at the periphery made i t d i f f i c u l t to observe whether a s i m i l a i * trend occurred. Pulp t i s s u e from green f r u i t ( c o l o r index 2) d i d not give a p o s i t i v e r e a c t i o n with hydroxy 1 amine reagent. At the onset of y e l l o w i n g ( c o l o r index 3) an intense red c o l o r , i n d i c a t i v e of e s t e r i f i e d p e c t i n s , was obtained with the 48. • FIGURE 14. Sections of banana pulp t i s s u e showing tannin d i s t r i b u t i o n . A = c o l o r index 2; B = c o l o r index 4; C = c o l o r index 6.5. reagent. The f i r s t appearance of e s t e r i f i e d p e c t i n s c o i n -c i d e d with the decrease i n s t a r c h at the p l a c e n t a l r e g i o n . As r i p e n i n g progressed the red c o l o r decreased i n i n t e n s i t y and at c o l o r index 7 e s t e r i f i e d p e c t i n s were present only i n v a s c u l a r t i s s u e . Changes i n p e c t i c c o n s t i t u e n t s are c o n s i d e r e d a major f a c t o r i n the t e x t u r a l q u a l i t i e s of f r u i t s (McCready and McComb 1954; P i l n i k and Voragen 1970). These changes are c h a r a c t e r i z e d by an i n c r e a s e i n the p r o p o r t i o n of s o l u b l e to i n s o l u b l e f r a c t i o n s r e s u l t i n g from depolymeriza-t i o n and d e - e s t e r i f i c a t i o n ( P i l n i k and Voragen 1970). Thus s o f t e n i n g i s a s s o c i a t e d with a decrease i n e s t e r i f i e d p e c t i n s . In t h i s study e s t e r i f i e d p e c t i n s were present i n l a r g e r amounts at c o l o r index 3 than i n hard green bananas. S i m i l a r o b s e r v a t i o n s i n peaches were r e p o r t e d by Reeve (1959). It i s apparent that the r a t i o of s o l u b l e to i n s o l u b l e p e c t i c substances does not e x p l a i n adequately the r o l e of these substances i n banana f r u i t t e x t u r e . H i s t o l o g i c a l p r o p e r t i e s T h i s study r e v e a l e d that d u r i n g r i p e n i n g the c e l l w a l l i n pulp t i s s u e l o s e s i t s r i g i d i t y . , F i g u r e 15A shows that the c e l l w a l l i n pulp t i s s u e at c o l o r index 2 i s r i g i d and w e l l d e f i n e d , but as r i p e n i n g p r o g r e s s e s the c e l l w a l l s o f t e n s such that c e l l s l o se t h e i r c h a r a c t e r i s t i c shapes. At c o l o r index 6.5 to 7.0 there was an apparent t h i c k e n i n g of the c e l l w a l l (Figure 15C). In c o n t r a s t to FIGURE 15. Photomicrographs of banana pulp t i s s u e during r i p e n i n g at 16 ± 1°C (X 320) . A = c o l o r index 2; B = c o l o r index 4; C = c o l o r index 7. 51 . loss of r i g i d i t y , c e l l w a l l t h i c k e n i n g d i d not occur gradu-a l l y . This phenomenon has not been p r e v i o u s l y reported i n banana t i s s u e , but has been observed i n peaches at e a r l y stages of ripeness by Reeve (1959). C e l l w a l l h y d r a t i o n can r e s u l t i n thickening,but h y d r a t i o n i n banana pulp i s associated with the c l i m a c t e r i c (Bauer and Workman 1964). I t i s p o s s i b l e that w a l l t h i c k e n i n g may have been induced by sample p r e p a r a t i o n , but i f t h i s i s so, there occurs at advanced r i p e n i n g a sudden s t r u c t u r a l m o d i f i c a t i o n which predisposes the c e l l w a l l to such t h i c k e n i n g . At advanced r i p e n i n g pulp t i s s u e d i s i n t e g r a t e s during handling and s e c t i o n s from such t i s s u e .^show c e l l u l a r debris w i t h i n the c e l l s and m u l t i p l e f r a c t u r e s i n the c e l l w a l l (Figure 15C) . E f f e c t of Ripening Temperature Examination of changes during r i p e n i n g showed that rates of change i n groups r e c e i v i n g s i m i l a r temperature treatments tended to be s i m i l a r , however the groups were not n e c e s s a r i l y at the same stage of ripeness when the e x p e r i -ments began. Since peel c o l o r i s the most widely used index of r i p e n e s s , changes i n p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s were studi e d as a f u n c t i o n of c o l o r index. This method would enable comparison of these p r o p e r t i e s at s i m i l a r stages of ripeness based on peel c o l o r . The e f f e c t of r i p e n i n g temperature on p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s was studied by comparing changes i n the pooled data of low and high temperature groups as a f u n c t i o n of c o l o r index. P h y s i c a l p r o p e r t i e s • During low temperature (16 ± 1°C) r i p e n i n g pulp-to-peel r a t i o increased l i n e a r l y . High temperature (25 ± 1°C) r e s u l t e d i n s l i g h t l y lower values which did not increase s t e a d i l y throughout r i p e n i n g (Figure 16). The rate of c o l o r change i n high temperature groups was roughly twice that i n low temperature groups. Change i n c o l o r index per day was 0.76, 1.18 and 0.89 f o r low temperature groups and 1.81-., 1.44 and 2.00 f o r high temperature groups. P e r s i s t e n c e of a c h l o r o p h y l l peak i n ri p e f r u i t s (Figure 6) was associated with the lack of development of f u l l yellow i n high temperature-ripened f r u i t s and r e s u l t e d i n higher IVR values. It i s p o s s i b l e that c h l o r o p h y l l r e t e n t i o n may be an i n i t i a l s i g n of " b o i l i n g " - - a commercial c o n d i t i o n which i s experienced during r i p e n i n g above 30°C (Wilkinson 1970). Intense s p o t t i n g and considerable r o t t i n g of the peel at advanced r i p e n i n g i n high temperature groups was probably due to fungal growth ( H a l l 1967). Rheological p r o p e r t i e s F r u i t s ripened at low temperature were much fi r m e r than those ripened at high temperature. Linear l i m i t of r i p e f r u i t t i s s u e i n both temperature groups were not appreciably d i f f e r e n t , however deformation due to 1 kg 1 2 3 4 5. 6 7 8 C o l o r i n d e x F I G U R E 1 6 . E f f e c t o f r i p e n i n g t e m p e r a t u r e o n p u l p - t o -p e e l r a t i o o f b a n a n a s . V e r t i c a l b a r s r e p r e s e n t ± o n e s t a n d a r d d e v i a t i o n . 54 . force showed very d i f f e r e n t patterns i n the two treatments (Figure 17). This v a r i a b l e remained more or less constant i n r i p e f r u i t s (beyond c o l o r index 4) at low temperature but increased l i n e a r l y with high temperature r i p e n i n g . The e f f e c t s of r i p e n i n g temperature on flow behavior was r e f l e c t e d i n a l l power-law parameters. Consistency c o e f f i c i e n t and y i e l d s t r e s s were g e n e r a l l y lower while flow behavior index was higher i n high temperature groups. Chemical p r o p e r t i e s High temperature r e s u l t e d i n increased moisture content i n pulp t i s s u e . This was i n contrast to lower pulp-to-peel - r a t i o s (Figure 16). Apparently weight increases due to moisture are n u l l i f i e d by increased s t r u c t u r a l breakdown and h y d r o l y s i s . A c i d i t y was not a f f e c t e d by temperature treatment. There was considerable overlapping of pH and t i t r a b l e a c i d i t y i n both treatments. Al c o h o l i n s o l u b l e s o l i d s (AIS) and s t a r c h were a f f e c t e d i n a s i m i l a r p a t t e r n by temperature. High tempera-ture r e s u l t e d i n lower l e v e l s of both v a r i a b l e s throughout r i p e n i n g ; while the AIS content of o v e r - r i p e f r u i t s remained constant i n low temperature groups, i t continued to d e c l i n e i n high temperature groups. Starch content of o v e r - r i p e f r u i t s i n both treatments decreased s l i g h t l y on continued ri p e n i n g . 55 . 1-2 1 2 3 4 5 6 7 8 C o l o r i n d e x FIGURE 17. E f f e c t of r i p e n i n g temperature on deformation of banana pulp t i s s u e ujider 1 kg f o r c e . V e r t i c a l bars r e p r e s e n t ± one standard d e v i a t i o n . 56 . Tot a l sugar content of banana pulp was increased by high temperature, although there was more v a r i a t i o n i n high temperature groups (Figure 18). The 16°C treatment was c h a r a c t e r i z e d by a more or less constant l e v e l of reducing sugars i n r i p e f r u i t s , while the 25°C temperature r e s u l t e d i n a l i n e a r increase i n these sugars throughout r i p e n i n g . This accounted f o r the o v e r a l l increase i n sugar content of high temperature groups. In t h i s study the r i p e n i n g treatment was ap p l i e d during the e n t i r e experimental p e r i o d . Under commercial c o n d i t i o n s the f r u i t i s considered r i p e at c o l o r index 4, thus the e f f e c t of r i p e n i n g temperature should be considered up to that stage of ripe n e s s . Subsequent changes are g e n e r a l l y r e f e r r e d to as storage changes and are t r e a t e d s e p a r a t e l y . Furthermore, since the study was l i m i t e d to two temperature treatments, i t i s not p o s s i b l e to discuss f u l l y the e f f e c t s of temperature on r i p e n i n g behavior. The r e s u l t s support the observations of Sanchez Nieva ejt aj_. (1969) and Dalai ejt aj_. (1969) that bananas ripened at high temperature are more s u s c e p t i b l e to mechanical i n j u r y . Reduction of s h e l f l i f e by high temperature (United F r u i t Sales Corp. 1964) i s also i l l u s t r a t e d by the rates of r i p e n i n g i n high temperature groups. The lack of complete y e l l o w i n g i n high temperature-ripened f r u i t i s probably the i n i t i a l symptom of a p h y s i o l o g i c a l d i s o r d e r . Haard and 57 . 25 1 2 3 4 5 6 7 8 C o l o r i n d e x FIGURE 18. E f f e c t o f r i p e n i n g t emperature on t o t a l sugar c o n t e n t of banana p u l p t i s s u e . V e r t i c a l b ars r e p r e s e n t ± one s t a n d a r d d e v i a t i o n . H u l t i n (1969) reported that a s i m i l a r e f f e c t on y e l l o w i n g was brought about by low r e l a t i v e humidity. R e l a t i o n s h i p s Among P r o p e r t i e s I t has been demonstrated elsewhere i n t h i s study that r i p e n i n g i s accompanied by se v e r a l changes and that r i p e n i n g temperatures exert a considerable e f f e c t on the p r o p e r t i e s of bananas. The r e l a t i o n s h i p s among represen-t a t i v e parameters of p h y s i c a l , r h e o l o g i c a l and chemical p r o p e r t i e s were studi e d by pool i n g data from the three groups i n each temperature treatment and c a l c u l a t i n g simple c o r r e l a t i o n s . This would i n d i c a t e whether r e l a t i o n s h i p s between d i f f e r e n t v a r i a b l e s are the same at both r i p e n i n g temperatures. In a d d i t i o n , i t would be p o s s i b l e to assess the value of peel c o l o r as an index of ripeness under d i f f e r e n t r i p e n i n g c o n d i t i o n s . Simple c o r r e l a t i o n s among s e l e c t e d v a r i a b l e s during r i p e n i n g at 16 ± 1°C and 25 ± 1°C are shown i n Tables 3 and 4 r e s p e c t i v e l y . In genera l , the c o r r e l a t i o n s were h i g h l y s i g n i f i c a n t (P < 0.01) during both treatments. When data from both treatments were pooled (Table 5) c o r r e l a t i o n c o e f f i c i e n t s were g e n e r a l l y intermediate between those obtained f r o the separate treatments. However, c o r r e l a t i o n s between pulp-to-peel r a t i o and other v a r i a b l e s decreased when the data were pooled. There i s l i t t l e i n d i c a t i o n that r i p e n i n g temperature exerts a major i n f l u e n c e on the TABLE 3. SIMPLE CORRELATIONS AMONG SELECTED PHYSICAL, RHEOLOGICAL AND CHEMICAL PROPERTIES OF BANANAS RIPENED AT 16 ± 1°C. (n = 110). Color Pulp/ Linear Maxi- Defor- T o t a l Reduc-index peel IVR l i m i t mum mation m* sugar ing AIS Starch force sugar Pulp/peel 0.810 IVR -0.754 -0.672 Linear l i m i t -0.452 -0.311 0.606 Maximum force -0.474 -0.332 0.628 0.996 Deformation 0.645 0.532 -0.716 -0.645 -0.654 'f> m* -0.670 -0.540 0.704 0.709 0.715 -0.531 Tota l sugar 0.881 0.746 -0.904 -0,587 -0.607 0.781 -0.702 Reducing sugar 0.94*7 0.814 -0.814 -0.516 -0.535 0.729 -0.696 0.959 AIS -0.903 -0.751 0.896 0.597 0.617 -0.781 0.670 -0.994 -0.999 Starch -0.896 -0.744 0.904 0.632 0.632 -0.778 0.719 -0.993 -0.943 0.999 Moisture 0.952 0.791 -0.798 -0.533 -0.552 0.734 -0.634 0.921 0.966 -0.949 -0.940 Power-law consistency c o e f f i c i e n t TABLE 4. SIMPLE CORRELATIONS AMONG SELECTED PHYSICAL, RHEOLOGICAL AND CHEMICAL PROPERTIES OF BANANAS RIPENED AT 25 + 1°C. (n = 8 5 ) . Color Pulp/ index peel IVR Linear Maxi- Defor-l i m i t mum mation force Total Reduc-m* sugar ing sugar AIS Starch Pulp/peel IVR Linear l i m i t Maxi mum force De format ion m* Tota l sugar Reducing sugar AIS Starch Mois ture 0.661 •0.734 -0.629 •0.427 -0.483 0.645 •0.432 0. 726 0 .934 •0.816 •0.826 0. 805 •0.520 0. 690 -0.885 -0.702 0. 630 -0.583 0. 703 0.982 -0.464 -0. 4 7/7 0.413 0.427 -0.680 0.761 0.538 .0.814 -0.549 -0.510 0.492 -0.760 0. 674 •0.599 •0 .599 0.477 0.818 0 . 867 0. 849 0.694 •0.521 0.583 0.533 0.503 •0.507 0.551 0.503 0.473 0.725 -0.905 0.838 •0.609 0.802 -0.933 -0.927 •0.604 0.811 -0.919 -0.925 0.981 0.716 -0.795 0.683 0.884 -0.828 -0.829 Power-law consistency c o e f f i c i e n t . o TABLE 5. SIMPLE CORRELATIONS AMONG SELECTED PHYSICAL, RHEOLOGICAL AND CHEMICAL PROPERTIES OF RIPENING BANANAS. (Pooled data, n = 195). Color Pulp/ Linear Maxi- Defor-index peel IVR l i m i t mum mation f o rce Total Reduc-m* sugar ing sugar AIS Starch Pulp/peel IVR Linear l i m i t Maxi mum force Deformation m* Tota l sugar Reducing sugar AIS S tarch Moi s ture 0.718 -0.613 -0.613 -0.380 -0.212 0.556 -0.402 -0.230 0.579 0.996 0.598 0.356 -0.583 -0.505 -0.640 -0.420 0.677 0.710 •0.566?, 0.719 -0.566 0.820 0.570 -0.866 -0.544 -0.566 0.681 -0.709 0.909 0.625 -0.785 -0.457 -0.481 0.853 -0.597 0.877 0.555 0.578 •0.853 -0.594 0.878 0.564 0.587 0.873 0.561 -0.749 -0.474 -0.496 0 . 757 0.711 •0 . 706 •0.702 0.713 0 . 727 0.740 -0.648 0.905 •0.936 -0.936 •0.933 -0.933 0.850 0.939 0 .994 0.911 -0.906 Power-law consistency c o e f f i c i e n t 62 r e l a t i o n s h i p between s e l e c t e d v a r i a b l e s , although c o r r e l a t i o n c o e f f i c i e n t s tended to be higher at the lower temperature (Table 3). V a r i a t i o n s i n c o l o r . i n d e x account f o r 63.7 and 82.6% of the v a r i a t i o n i n moisture and reducing sugar r e s p e c t i v e l y , when a l l the data were pooled. At both r i p e n -ing temperatures, Index of Variance Reflectance (IVR) was c l o s e l y r e l a t e d to c o l o r index with c o r r e l a t i o n c o e f f i c i e n t s of -0.754 and -0.734 f o r low and high temperature respec-t i v e l y . This v a r i a b l e , on the average, surpassed c o l o r index i n c o r r e l a t i o n s with r h e o l o g i c a l p r o p e r t i e s . C o r r e l a t i o n s among r h e o l o g i c a l and chemical p r o p e r t i e s were on the average higher during r i p e n i n g at low temperature. An exception to t h i s trend was found i n the r e l a t i o n s h i p between reducing sugars and consistency c o e f f i c i e n t where the c o r r e l a t i o n c o e f f i c i e n t s were -0.905 and -0.696 during high and low temperatures r e s p e c t i v e l y . Some r h e o l o g i c a l p r o p e r t i e s , such as deformation and c o n s i s -tency c o e f f i c i e n t s , were c l o s e l y r e l a t e d to chemical p r o p e r t i e s . C o r r e l a t i o n s among chemical c o n s t i t u e n t s were very high during both treatments. Moisture c o r r e l a t e d w e l l with a l l v a r i a b l e s except p u l p - t o - p e e l r a t i o during r i p e n i n g at high temperature. This i s probably due to the high degree of v a r i a b i l i t y i n pulp-to-peel r a t i o during t h i s 63. t r e atment. In s p i t e of i t s r e l a t i v e l y low c o r r e l a t i o n with r h e o l o g i c a l p r o p e r t i e s , c o l o r index was the best o v e r a l l index o f . f r u i t q u a l i t y . Yet the demonstrated e f f e c t of r i p e n i n g temperature on t o t a l sugar, moisture and deforma-t i o n i n d i c a t e s that i t should be given c a r e f u l c o n s i d e r a t i o n i f e x t e r n a l appearance i s used to estimate i n t e r n a l q u a l i t y of bananas. P u l p - t o - p e e l r a t i o may be a good index of maturity i n green f r u i t s (Simmonds 1966) but does not appear to be a good index of stage of r i p e n e s s . It i s i n f l u e n c e d to a large extent by f r u i t s i z e and r i p e n i n g temperature. Among the r h e o l o g i c a l parameters, deformation and c o n s i s t e n c y c o e f f i c i e n t had the best c o r r e l a t i o n with chemical p r o p e r t i e s but t h e i r u s e f u l n e s s as i n d i c e s of r i p e n e s s are l i m i t e d by the time and equipment needed f o r d e t e r m i n a t i o n . CONCLUSIONS The r i p e n i n g rate of bananas at 25 ± 1°C was roughly twice that at 16 ± 1°C. High temperature-ripened f r u i t s were c h a r a c t e r i z e d by c h l o r o p h y l l r e t e n t i o n which prevented the development of f u l l yellow c o l o r . Pulp-to-peel r a t i o increased during r i p e n i n g i n both treatments but was somewhat lower i n f r u i t s ripened at the higher temperature. Deformation due to 1 kg force increased l i n e a r l y during r i p e n i n g at high temperature, while i t remained f a i r l y s t a b l e beyond c o l o r index 6 during r i p e n i n g at low temperature. Maximum force and l i n e a r l i m i t as w e l l as consistency c o e f f i c i e n t were g e n e r a l l y lower during r i p e n i n g at high temperature. T o t a l sugar and moisture content of pulp t i s s u e were higher i n f r u i t s ripened at high temperature. Reducing sugars increased l i n e a r l y throughout r i p e n i n g at high temperature while at low temperature they remained e s s e n t i a l l y constant beyond c o l o r index 6. Starch and AIS l e v e l s were somewhat higher i n low temperature-ripened f r u i t s . This i n d i c a t e s that s t a r c h h y d r o l y s i s was enhanced by high temperature treatment. Ripening was c h a r a c t e r i z e d by a gradual loss of r i g i d i t y as w e l l as an apparent t h i c k e n i n g of the c e l l w a l l 65 . i n the pulp of o v e r - r i p e f r u i t s . Tannins decreased but did not completely disappear during r i p e n i n g . E s t e r i f i e d p e c t i n s were present i n the l a r g e s t amount at c o l o r index 3 and decreased during r i p e n i n g . Starch granule disappearance began i n the c e n t r a l region of the pulp t i s s u e and progressed towards the peel as r i p e n i n g continued. Peel c o l o r was evaluated by c o l o r index and IVR was the best index of stage of ripeness i n f r u i t s ripened at both low and high temperature. However, i n view of the e f f e c t s of r i p e n i n g temperature on some chemical and r h e o l o g i c a l p r o p e r t i e s , the r e l a t i o n s between these p r o p e r t i e s and c o l o r index would be i n f l u e n c e d by r i p e n i n g temperature. This suggested that r i p e n i n g temperature may a f f e c t e a ting q u a l i t y of the r i p e f r u i t , as w e l l as the accuracy of peel c o l o r as an index of ripeness. C o r r e l a t i o n s among r h e o l o g i c a l and chemical p r o p e r t i e s were h i g h l y s i g n i f i c a n t although c o r r e l a t i o n s among the chemical v a r i a b l e s were higher than those among the r h e o l o g i c a l v a r i a b l e s . V a r i a t i o n s i n t i s s u e strength (maximum force) could be explained l a r g e l y by v a r i a t i o n s i n st a r c h and AIS while v a r i a t i o n s i n s o f t e n i n g (deformation) could be accounted f o r mainly by v a r i a t i o n s i n t o t a l and reducing sugars. In ge n e r a l , r i p e n i n g temperatures did not appear to i n f l u e n c e g r e a t l y the c o r r e l a t i o n c o e f f i c i e n t s among the d i f f e r e n t p r o p e r t i e s examined. 66. LITERATURE CITED Art h u r , H.B., Houck, J.P. and Beckford, G.L. 1968. T r o p i c a l Agribusiness S t r u c t u r e s and Adjustments - Bananas. 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