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Textural and color responses of chicken muscle to substerilizing doses of gamma irradiation Whiting, Richard Charles, 1970

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TEXTURAL AND COLOR RESPONSES OF CHICKEN MUSCLE TO SUBSTERILIZING DOSES OF GAWMA IRRADIATION  •jy  RICHARD C H A R L E S W H I T I N G  B.S.A., U n i v e r s i t y  of Wisconsin,  1968  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE O F MASTER OF SCIENCE  i n the Department of Food Science  We accept required  THE  t h i s t h e s i s as conforming t o the standard  UNIVERSITY OF BRITISH COLUMBIA August, 1970  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 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 8, Canada  Date  August 14, 1970  ABSTRACT The P e c t o r a l i s major and P e c t o r a l i s minor  muscles  of  c h i c k e n were g i v e n s u b s t e r i l i z i n g doses of y - i r r a d i a t i o n  at  v a r y i n g times p o s t - s l a u g h t e r and the pH,  shear f o r c e ,  fragmentation, and c o l o r were e v a l u a t e d . pH measurements i n an i o d o a c e t a t e s l u r r y showed t h a t doses up to 3 0 0 , 0 0 0 rads a d m i n i s t e r e d a t § or 5 hours post-mortem nal  pH.  the  final  had no e f f e c t on e i t h e r r a t e o f pH f a l l  or f i -  I r r a d i a t i o n a t 2 , 5 t or 1 2 hours d i d not change pH taken a t 48 hours  post-mortem.  E x c i s e d P. major muscles cooked by b o i l i n g  be-  tween aluminium p l a t e s r e q u i r e d more shear f o r c e a t the p o s t e r i o r p o r t i o n than a t the a n t e r i o r .  I r r a d i a t i o n dose  l e v e l s from 3 0 , 0 0 0 t o 3 0 0 , 0 0 0 rads on P, major shear r e s i s t a n c e over u n i r r a d i a t e d muscles. (2,  increased  The  earlier  5 t and 1 2 hours p o s t - s l a u g h t e r )  the  time o f a p p l i c a t i o n  the  g r e a t e r the i n c r e a s e i n toughness when measured a t  60  hours p o s t - s l a u g h t e r .  The 3 0 0 , 0 0 0 r a d dose a t 1 2 hours,  g i v e n a f t e r attainment of maximum i n e x t e n s i b i l i t y and r e l a x a t i o n of isometric tension, s t i l l  produced a  signifi-  cant l o s s i n t e n d e r n e s s . The i r r a d i a t i o n g e n e r a l l y reduced the degree of m y o f i b r i l l a r fragmentation a f t e r a standardized blending treatment, a l t h o u g h the decrease was not always cant.  signifi-  Pasteurizing  i r r a d i a t i o n produced a pink c o l o r  i n raw muscle s t o r e d a e r o b i c a l l y f o r 55 hours t h a t i n c r e a s e d w i t h dose.  Peaks t y p i c a l of an  oxymyoglobin-like  compound emerged and the dominant wavelength toward was  l o n g e r wavelengths by 4 nm.  was  shifted  A f t e r cooking there  no v i s i b l e c o l o r d i f f e r e n c e between i r r a d i a t e d and  control  muscles. Correlations  between these parameters  on  con-  t r o l muscles i n d i c a t e d t h a t the pH d e c l i n e was p o s i t i v e l y c o r r e l a t e d to shear f o r c e , although not of h i g h v a l u e . The  fragmentation r a t i o s were not s i g n i f i c a n t l y c o r r e -  l a t e d with shear  force.  iii TABLE OF CONTENTS Page INTRODUCTION  1  LITERATURE  4  REVIEW  R i g o r M o r t i s and Aging  4  I r r a d i a t i o n o f Meat  . 15  Color  20  Shear P r e s s Determinations  24  EXPERIMENTAL METHODS  26  Sampling Method  26  Source o f Muscles  26  Irradiation  27  pH  28  Shear P r e s s Readings  28  Jl  M y o f i b r i l l a r Fragments Reflectance  "  32  S t a t i s t i c a l Analysis  32  RESULTS AND DISCUSSION  39  SUMMARY  75  LIST OF REFERENCES  77  iv LIST OP TABLES Table  '  I  Page  . E f f e c t o f E l e c t r o n I r r a d i a t i o n on Muscle Toughness  18  Experimental Procedure o f Experiment 1  34  Experimental Procedure o f Experiment 2  35  IV  Experimental Procedure o f Experiment 3  36  V  Experimental Procedure o f Experiment 4  37  II III  VI  •  E f f e c t o f S u b p a s t e u r i z i n g Doses o f Gamma I r r a d i a t i o n on pH Changes i n P. Minor. Experiment 1.  VII  P a i r e d T-Tests  40  E f f e c t o f S u b p a s t e u r i z i n g Doses o f Gamma R a d i a t i o n on Shear P r e s s Values Major.  VIII  Experiment 1  X  4l  Summary o f A n a l y s i s o f V a r i a n c e o f Shear Press Values.  IX  o f P.  Experiment 1  P a i r e d T - T e s t s o f pH V a l u e s .  42 Experiment 2  45  P a i r e d T-Test o f A n t e r i o r VS P o s t e r i o r Shear P r e s s Readings o f U n i r r a d i a t e d Muscles  46  V  Page  Table XI  Shear P r e s s Values o f Aged  Muscles  Experiment  2.  XII  F-Ratios.  Experiment  XIII  Simple C o r r e l a t i o n C o e f f i c i e n t s . periment  XIV  P a i r e d T-Test 2.  48  P a i r e d T-Test Ex-  2  52  Simple Regression E q u a t i o n s .  Experi-  ment 2 XV  51  54  Simple C o r r e l a t i o n and Regression C o e f f i c i e n t s o f Pooled A n t e r i o r and P o s t e r i o r Shear P r e s s Values and FRatios.  XVI  Experiment  56  P a i r e d T-Tests o f F i n a l pH', F - E a t i o , and Shear P r e s s .  XVII  2  Experiment  A n a l y s i s o f Shear L o c a t i o n s .  3  58  Experi-  ment 3 XVIII  60  C o r r e l a t i o n C o e f f i c i e n t s o f pH, F-Ratio, Average Shear P r e s s o f L o c a t i o n 1. periment  XIX  3  A n a l y s i s o f Shear P r e s s V a l u e s . periment  Ex-  4  6l Ex63  vi Table XX  Page A n a l y s i s o f Shear L o c a t i o n s . • E x p e r i ment 4  XXI  Summary of C o l o r A n a l y s i s . T-Tests  68 Paired  73  vii  L I S T OF FIGURES Figure 1,  Page Chemical and p h y s i c a l changes i n beef s t e r n o m a n d i b u l a r i s muscle h e l d a t  2.  c  22  R e f l e c t a n c e s p e c t r a f o r f r e s h beef samples t r e a t e d to c o n t a i n myoglobin (Mb),  predominantly 2  oxymyoglobin (MbO  Metmyoglobin (Mb ) +  3.  37°  ), o r  a t the s u r f a c e  22  L o c a t i o n of the f i v e s t r i p s f o r shear force determinations  and p o s i t i o n of  s h e a r i n g on P. major i n Experiments 3 and 4 4.  The  -  38  fragmentation  p a t t e r n of an u n i r -  r a d i a t e d muscle  50  5«  Reflectance  s p e c t r a of raw  chicken  6.  Reflectance  s p e c t r a of cooked chicken  70 71  viii ACKNOWLEDGEMENT. The  a u t h o r wishes t o 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 i n t h i s study by: Dr. J . P. Richards  for directing  this  research.  Dr. W. D. Powrie, D r . C. W. Roberts, and P r o f . E . L . Watson f o r s e r v i n g on the r e s e a r c h reviewing  this Mr.  committee and  thesis. R. Hamilton and the United P o u l t r y Co., L t d .  o f Vancouver f o r p r o v i d i n g chickens  from t h e i r  processing  plant. Appreciation  i s extended t o Atomic Energy o f  Canada, L t d . f o r f i n a n c i a l  support  of this project.  INTRODUCTION The  processing  o f foods by i o n i z i n g r a d i a t i o n  w i t h i t s unique p o t e n t i a l s and problems has been under extensive  i n v e s t i g a t i o n s i n c e the mid 1 9 5 0 s .  Desrosier  (1963) l i s t e d s i x areas f o r p o t e n t i a l a p p l i c a t i o n of i o n izing radiation: perature storage; erated  1)  s t e r i l i z a t i o n to permit ambient tem-  2) p a s t e u r i z a t i o n  storage l i f e ;  to prolong  refrig-  3) i n s e c t d i s i n f e s t a t i o n ;  k) i n -  h i b i t i o n o f p l a n t growth p r o c e s s e s ;  5) u n i t  operations,  i n c l u d i n g meat t e n d e r i z a t i o n and polymer h y d r o l y s i s ; and 6) d e s t r u c t i o n in foods.  o f s p e c i f i c human p a r a s i t e s and pathogens  Advantages o f i r r a d i a t i o n over a p p l i c a t i o n o f  heat energy i n c l u d e h i g h l y  efficient bacterial inactiv-  a t i o n and reduced t o t a l chemical changes i n i r r a d i a t e d substances (Lawrie, 1 9 6 6 ) .  Irradiation i s currently  approved i n the U n i t e d S t a t e s f o r wheat and f l o u r i n s e c t d i s i n f e s t a t i o n and p o t a t o sprout i n h i b i t i o n 1968).  (Keisner,  In Canada 1 5 , 0 0 0 rads can be used f o r p o t a t o and  onion sprout i n h i b i t i o n and 1 5 , 0 0 0 rads can be used on wheat f l o u r o r whole wheat f l o u r f o r i n s e c t d i s i n f e s t a t i o n . Approval o f i r r a d i a t i o n s t e r i l i z a t i o n o f bacon has  been withdrawn i n the United S t a t e s pending the r e -  s u l t s o f a new 2 t o 3 year t o x i c o l o g i c a l f e e d i n g the  study by  U.S. Army because o f u n r e s o l v e d q u e s t i o n s over  a t i o n - i n d u c e d t o x i c substances.  However, G o l d b l i t h  irradi(1970)  reviewed the s a f e t y a s p e c t s o f i r r a d i a t e d foods and con-  2 eluded  t h a t r i s k s to the consumer were m i n i m a l . When energy i n any  changes o c c u r .  form i s a p p l i e d to foods,  R a d i a t i o n energy i s no e x c e p t i o n .  Ef-  f e c t s of r a d i a t i o n energy on meats, i n a d d i t i o n to d e s t r u c t i o n of microorganisms, were summarized "by Urbain 1) ically  c o l o r ; raw  (1965):  meats became brownish and  anaerob-  s t o r e d cooked meats t u r n p i n k . 2)  t e x t u r e ; a s o f t e n i n g o f t i s s u e occurs,  the  degree r e l a t e d to dose. 3)  f a t s ; o x i d a t i o n and development of r a n c i d  f l a v o r occurs, depending on oxygen a v a i l a b i l i t y and 4)  odor and/or f l a v o r ; o f f odors and  including a characteristic velop. adding  dose.  flavors  " i r r a d i a t i o n o f f - o d o r " may  These changes can be reduced f r e e r a d i c a l a c c e p t o r s , and  de-  by e x c l u d i n g oxygen,  i r r a d i a t i n g a t low  tem-  peratures . Improved technology  has  b i l i t y of some i r r a d i a t e d meats.  i n c r e a s e d the Radiation  c h i c k e n has been r e p o r t e d by Heillgman be o r g a n o l e p t i c a l l y s a t i s f a c t o r y .  accepta-  sterilized  et a l . (1967)  However, t e x t u r a l  to soft-  ening and d i s c o l o r a t i o n of i r r a d i a t e d p o u l t r y have f r e q u e n t l y been observed. tative  There i s a l a c k of data on q u a n t i -  measurements o f t e x t u r a l changes i n p o u l t r y and  those r e p o r t e d p e r t a i n o n l y to s t e r i l i z i n g l e v e l s of diation.  Similarly,  irra-  i n f o r m a t i o n on the e f f e c t s of a p p l y -  ing  i r r a d i a t i o n a t v a r y i n g times p o s t - s l a u g h t e r on t e x t u r a l  changes i s s p a r s e . P i n k d i s c o l o r a t i o n s have been r e p o r t e d i n i r r a d i a t e d p o u l t r y but the time of a p p l i c a t i o n p o s t - s l a u g h t e r not c o n s i d e r e d ,  nor were the data q u a n t i t a t i v e .  T h i s study  explored  t e x t u r a l and  r e s u l t i n g from p a s t e u r i z a t i o n and of i r r a d i a t i o n administered times  was  post-slaughter.  c o l o r changes  s u b p a s t e u r l z a t i o n doses  to p o u l t r y muscles a t v a r y i n g  4 LITERATURE REVIEW R i g o r M o r t i s and Aging Great  s t r i d e s have been made i n r e c e n t y e a r s ad-  v a n c i n g our understanding chemistry o f muscle. chemistry  o f the complex o r g a n i z a t i o n and  E x c e l l e n t reviews  c o v e r i n g the b i o -  o f muscle i n c l u d e B r i s k e y e t a l .  (1967), B e n d a l l  (1969), and Huxley (1969).  (1966),  Davies  Goll"(1968).  d i s c u s s e s a s p e c t s o f the r e s o l u t i o n o f r i g o r m o r t i s . a g e n e r a l d e s c r i p t i o n compiled of  from above, v a r i o u s  After  aspects  r i g o r m o r t i s and r e s o l u t i o n o f r i g o r p e r t i n e n t t o t h i s  t h e s i s w i l l be e l a b o r a t e d on. A t s l a u g h t e r , the b l o o d c i r c u l a t i o n t o the muscle ceases and oxygen renewal i s t e r m i n a t e d .  Myoglobin-bound  oxygen i s soon d e p l e t e d f o r c i n g the t i s s u e i n t o glycolysis.  Glycogen i s converted  the pH t o f a l l .  With glycogen  anaerobic  to l a c t i c a c i d  causing  d e p l e t e d , c r e a t i n e phosphate  i s consumed i n an attempt t o m a i n t a i n ATP l e v e l s .  When a l l  sources o f renewal a r e exhausted, the ATP l e v e l w i l l decrease . ATP  r e l e a s e s energy by s p l i t t i n g  phosphate t o d r i v e the c o n t r a c t i l e p r o c e s s .  o f f the t e r m i n a l This i s t r i g -  +2 gered by a r e l e a s e o f Ca +2  from the sarcoplasmic  ATP  w i l l a c t as a  i n the absence o f Ca  p r e v e n t i n g i n t e r a c t i o n o f a c t i n and myosin.  reticulum.  plasticizer, With the ab-  sence o f ATP, i n t e r a c t i o n occurs and the f i l a m e n t s a r e p e r -  5 manently bound and the muscle i s i n e x t e n s i b l e .  Reduction  i n the e x t e n s i b i l i t y g e n e r a l l y begins when ATP to approximately  bility.  fallen  30 percent of i t s i n i t i a l l e v e l and  mally progresses u n t i l sible.  has  the muscle i s completely  nor-  inexten-  R i g o r m o r t i s i s d e f i n e d as t h i s l o s s of e x t e n s i Depending on post-mortem temperature  f a c t o r s s h o r t e n i n g may  and  other  occur, p o s s i b l y i n response  to a  +2 r e l e a s e of Ca  by the s a r c o p l a s m i c r e t i c u l u m .  These  events are b r i e f l y summarized i n F i g u r e 1. Davies bonding  (1967) t h e o r i z e s t h a t the permanent  r e s u l t s from the a t t r a c t i v e f o r c e s of the p o s i -  t i v e l y charged ATP  b i n d i n g s i t e s of the heavy meromyosin  t o the n e g a t i v e l y charged ADP  on the a c t i n .  The post-mortem pH f a l l i m a t e l y pH 7 to pH 5«8 t o 5*9 (de Fremery and P o o l , 1958,  i n chickens from approx-  r e q u i r e s 2 to 4.5  I960;  hours  P e t e r s and Dodge,  1959;  Dodge and P e t e r s , I960; and Dodge and Stadelman, i960) . Working w i t h ox muscle, Cassens and  Newbold  (1967  a) found t h a t the r a t e of pH d e c l i n e i n c r e a s e d as o the temperature i n c r e a s e d from 5 t o 37 C, but was a l s o g r e a t e r a t 1 than a t 5°C. U l t i m a t e pH was h i g h e r a t 1 t o o * 5 C than a t h i g h e r temperatures. De Fremery and P o o l (i960) observed t h a t ATP disappeared more r a p i d l y a t 0 o than 10 C i n c h i c k e n s . They showed f u r t h e r t h a t the r e l -  6 a t i v e r a t e of onset of r i g o r m o r t i s can be measured by ATP  disappearance, glycogen decrease, or pH f a l l .  Busch  et a l . (1967) confirmed t h i s w i t h bovine muscle. al.  (1962) claimed t h a t tenderness was  closely  May  et  related  to pH, a l t h o u g h i n d i r e c t l y through the a s s o c i a t i o n of pH t o onset of r i g o r m o r t i s . Unless r e s t r a i n e d , a muscle w i l l Junction with r i g o r mortis.  s h o r t e n i n con-  Locker and Hagyard (1963)  observed i n beef t h a t a t h i g h e r temperatures  kJ°C)  (19 t o  s h o r t e n i n g c o i n c i d e d w i t h the onset of r i g o r m o r t i s , but a t low temperatures immediately  s h o r t e n i n g began r a p i d l y and  ( a l s o Busch et a l . ,  1967)*  They a l s o n o t i c e d  a dependence of the degree of s h o r t e n i n g on the " c o l d s h o r t e n i n g e f f e c t " . ening was  slow and minimal  temperatures.  usually  Between Ik  temperature,  and 19°C  short-  compared t o h i g h e r o r lower  At 0°C s h o r t e n i n g was  r a p i d and  extreme.  Cassens and Newbold (1967 *>) a t t r i b u t e d c o l d s h o r t e n i n g t o a r e l e a s e of c a l c i u m i o n s by the s a r c o t u b u l a r system i n response to low temperatures.  Smith e_t a l . (1969)  observed a s i m i l a r response i n p o u l t r y , w i t h the minimum o s h o r t e n i n g between 12 to 18 C. each temperature  was  They found s h o r t e n i n g a t  e s s e n t i a l l y completed w i t h i n 3 hours  and t h a t post-mortem pH d e c l i n e d i d not correlate with shortening.  significantly  7 L o c k e r (i960) r e p o r t e d t h a t the s t a t e of cont r a c t i o n i s a s i g n i f i c a n t f a c t o r i n tenderness of bovine meat, more tender meat being a s s o c i a t e d w i t h minimal contraction. Marsh and L e e t and at  (1966) s t u d y i n g c o l d  shortening  tenderness agreed t h a t minimal c o n t r a c t i o n occurred o 15 to 20 C.  20 percent  They found f u r t h e r t h a t s h o r t e n i n g  o f the i n i t i a l  l e n g t h d i d not e x e r t a  to  signif-  i c a n t e f f e c t on toughness, but toughness i n c r e a s e d r a p i d l y w i t h f u r t h e r s h o r t e n i n g , peaking a t 4-0 p e r c e n t .  However,  muscles shortened  length  were sheared  to 60 percent  as r e a d i l y as nonshortened muscle.  s h o r t e n i n g e f f e c t was  r e l a t e d to pH,  h i b i t i n g greater shortening. at  pH 6.5*  of t h e i r i n i t i a l  The  The  cold  h i g h e r pH muscle  ex-  maximum shear f o r c e  was  They a l s o demonstrated t h a t a muscle r e -  s t r a i n e d by attachment to the s k e l e t o n (or  mechanically  r e s t r a i n e d e x c i s e d muscle) c o u l d a l s o develop c o l d s h o r t ening induced  toughness because of l o c a l c o n t r a c t i o n and  e x t e n s i o n , p a r t i c u l a r l y i f c o o l i n g was  uneven.  c l u d e d t h a t u l t i m a t e tenderness i s e f f e c t e d by t u r e d u r i n g the f i r s t  few  hours post-mortem.  They contempera-  Davey et a l .  (1967) s u b s t a n t i a t e d these f i n d i n g s adding t h a t as ening i n c r e a s e d beyond 20 percent a p r o g r e s s i v e occurred i n the extent  z a t i o n had  ceased.  decrease  to which meat t e n d e r i z e s w i t h  sequent aging, u n t i l a t 40 percent  short-  sub-  shortening, t e n d e r i -  8 Marsh et a l . (1968) found t h i s e f f e c t to be of g r e a t importance with f r o z e n lamb. in  S i g n i f i c a n t increases  toughness were avoided i f f r e e z i n g was  delayed a t l e a s t  16 hours a f t e r s l a u g h t e r . S e v e r a l workers have c o n s i d e r e d adding t e n s i o n and s t r e t c h i n g the muscle d u r i n g r i g o r m o r t i s .  The  con-  c l u s i o n s o f H e r r i n g e t a l . (1967 b ) , Buck and B l a c k and G i l l i s  and Hendrickson  (1969) a l l p e r t a i n i n g to bovine  muscle, were t h a t w h i l e l e s s f o r c e was s t r e t c h e d muscles  i t was  (1967),  r e q u i r e d t o shear  o f more p r a c t i c a l  importance  to  prevent shortening. H e r r i n g e t a l . (1967 b) found h i g h c o e f f i c i e n t s 2 of  d e t e r m i n a t i o n (R ) between tenderness, and f i b e r diam-  e t e r and sarcomere  l e n g t h which are r e l a t e d to s h o r t e n -  ing. The  s t i f f e n i n g and toughness  m o r t i s i s not n e c e s s a r i l y permanent;  of meat i n r i g o r w i t h time muscle  r e v e r t s to a more p l i a b l e s t a t e , a process c a l l e d r e s o l u t i o n of r i g o r or a g i n g .  A muscle d u r i n g t h i s  time  l o o s e s i t s a b i l i t y to m a i n t a i n i s o m e t r i c t e n s i o n a l t h o u g h complete macroscopic 1968). at  Deatherage o  33 to 35  F  a  nd  e x t e n s i b i l i t y does not r e t u r n  (Goll,  and Harsham (19^7) s t u d i e d beef aged  found an i n c r e a s e i n tenderness over  2| weeks except f o r animals w i t h h i g h i n i t i a l  tenderness.  9 P o o l e t a l . (1959), Dodge and Stadelman and May e t a l , (1962) r e p o r t e d c h i c k e n muscle in  (1959),  increased  tenderness immediately a f t e r s l a u g h t e r and most t e n -  derlzation  took p l a c e w i t h i n 4 h o u r s .  Very l i t t l e  change  0 occurred a f t e r 12 hours o f a g i n g .  C a r l i n e t a l . (1949)  found t h a t b r o i l e r s a c h i e v e d maximum tenderness i n app r o x i m a t e l y 10 hours but added t h a t mature fowl may take up t o 48 h o u r s .  Little  change i n tenderness of b r e a s t  muscle d u r i n g the 3 r d t o 8 t h day a f t e r i n i t i a l  a g i n g was  r e p o r t e d by van den Berg et a l . (1964). Koonz e t a l . (1954), de Fremery  (I966), and de  Fremery and S t r e e t e r (1969) observed a maximum  toughness  reached between 3 and 4 hours post-mortem a t 2°C f o l lowed by a decrease t o a minimum i n 12 to 24 hours w i t h little  subsequent  change.  Goll  (1968) r e p o r t e d two  d i f f e r e n t p a t t e r n s o f shear f o r c e w i t h time i n bovine muscle depending on whether the muscle was e x c i s e d o r l e f t on the s k e l e t o n .  E x c i s e d muscle  i n c r e a s e d then de-  creased i n shear f o r c e while a t t a c h e d muscle s h a r p l y from the time o f s l a u g h t e r .  decreased  Inextensibility  changes were i d e n t i c a l i n both muscles but the e x c i s e d muscle  could shorten. £Ji  (1962) s t u d i e d the e f f e c t o f tempero a t u r e and found t h a t c a r c a s s e s aged a t 37 were tougher o than c a r c a s s e s aged a t 0 o r 19 C. Dodge and Stadelman c  10 (1959) a l s o found a g e n e r a l Increase i n tenderness a t lower temperatures i n d i c a t i n g t h a t p o u l t r y o q u a t e l y a t 0 C. £i  #  can  tenderize  ade-  (1962) found t h a t o l d e r chickens were  tougher, both i n i t i a l l y and  throughout a g i n g .  Many o t h e r f a c t o r s have been i n v e s t i g a t e d termine t h e i r e f f e c t on r e s o l u t i o n of r i g o r m o r t i s tenderness.  De  Fremery (1966) s t a t e d  treatment such as f r e e z i n g and ture,  scalding, beating,  e r a t e d ATP  and  would i n c r e a s e l y reversed  glycogen l o s s and This  by prolonged a g i n g .  that breast  increase He  was  only  stated that the  partial-  i t was  the  acceler-  toughness.  Pool (i960) had  muscles e x c i s e d  tempera-  onset of r i g o r m o r t i s  a t i o n of r i g o r m o r t i s , t h a t i n c r e a s e d Fremery and  and  c u t t i n g that a c c e l -  a c c e l e r a t i o n o f post-mortem g l y c o l y s i s , not  De  de-  prerigor  thawing, e l e v a t i n g  e x c i s i n g , and  toughness.  that any  to  shown e a r l i e r  from the c h i c k e n p r i o r to  on-  s e t o f r i g o r m o r t i s were l e s s tender than t h e i r c o n t r o l s , 12.6  and  5.8  l b shear f o r c e  respectively.  While some workers were s t u d y i n g f e c t i n g tenderness and  factors af-  a g i n g , o t h e r s were p r o b i n g  the  mechanism behind r e s o l u t i o n of r i g o r . Wierbicki (1967  et a l . (1954) and  a) have i n v e s t i g a t e d  Herring  et a l .  connective t i s s u e , p r i m a r i l y  11 collagen.  They concluded that, w h i l e c o l l a g e n content and  s o l u b i l i t y were r e l a t e d to tenderness n e i t h e r were a f f e c t e d by a g i n g p r o c e s s e s and d i d not c o n t r i b u t e t o t e n d e r i z a t i o n . B a c t e r i a l p r o t e o l y s i s had been suggested by some t o be r e s p o n s i b l e . and  Sharp (1963) working w i t h a s e p t i c meat  Davey and G i l b e r t (1966) have d i s c r e d i t e d t h i s  theory.  Bodwell and Pearson (1964) working w i t h bovine muscle and M a r t i n s and Whitaker (1968) working w i t h en muscle i n v e s t i g a t e d the theory  chick-  t h a t c a t h e p t i c enzymes  r e l e a s e d from the lysosomes a r e the agents o f a g i n g . found t h a t muscle t i s s u e had r e l a t i v e l y low of cathepsins them.  concentrations  and t h a t actomyosin was n o t a c t e d upon by  Sarcoplasmic p r o t e i n s were found t o be r e a d i l y  hydrolysed  (Bodwell and Pearson, 1964).  (1966) claimed  Davey and G i l b e r t  that d i f f e r e n c e s i n rates o f t e n d e r i z i n g  of d i f f e r e n t c a r c a s s e s  a r e not p a r a l l e l e d by s i m i l a r d i f f -  erences i n r a t e s o f p r o t e o l y s i s .  In some o f the beef a n i -  mals s t u d i e d , t e n d e r i z a t i o n was almost complete any  They  p r o t e o l y t i c changes were  before  detected.  I t has f r e q u e n t l y been observed, however, t h a t the e x t r a c t a b i l i t y o f m y o f i b r i l l a r p r o t e i n s ,  particularly  a c t i n and actomyosin, i n c r e a s e w i t h time, (Khan and van den  Berg, 1964;  1968).  Davey and G i l b e r t , 1968 ab;  and Sayre,  Davey and G i l b e r t (1968 a) found t h a t the u l t i m a t e  pH v a l u e l a r g e l y determines the r a t e o f i n c r e a s e  i n ex-  12 t r a c t a b i l i t y of m y o f i b r i l l a r proteins during aging. e r pH v a l u e s were a s s o c i a t e d w i t h h i g h e r  High-  extractability.  S e v e r a l workers have i n f e r r e d from t h i s t h a t a p r o t e o l y s i s t h a t weakens o r breaks the l i n k a g e s between the I band Z l i n e was  r e s p o n s i b l e f o r the i n c r e a s e i n  and  tenderness.  Mcintosh (1967) r e p o r t e d actomyosin e x t r a c t a b i l i t y i n c h i c k e n decreased  r a p i d l y d u r i n g the f i r s t  minimum a t 12 hours and  5 hours to a  then i n c r e a s e d to a maximum i n 4  t o 6 days. E l e c t r o n microscopic  evidence  strongly  cated t h a t the above i n f e r e n c e s were c o r r e c t .  indi-  Weidemann  et a l . (1967) working w i t h ox muscle s t a t e d t h a t ness on a g i n g was f i l a m e n t s and  produced by d i s r u p t i o n of the  tenderactin  by a weakening of the l i n k a g e s between the  a c t i n and myosin f i l a m e n t s i n the sarcomeres.  The  tronphotomicrographs showed breakage a t the Z l i n e s t r e t c h e d muscle as w e l l as l e s s o v e r l a p of A and  elecof I band  filaments. Davey and  Gilbert  (1967) found the most n o t a b l e  changes when a g i n g bovine muscle were the complete d i s appearance of the Z l i n e s and  the l e n g t h e n i n g  A bands a t the expense of the I bands. weakening of the Z l i n e s was l a t e d t o meat a g i n g .  of  the  They concluded t h a t  the event most c l o s e l y r e -  13 Davey and G i l b e r t (1969 b) working on beef r e p o r t e d two a g i n g e f f e c t s , 1) an i n c r e a s e d f i b e r pieces during  r e a d i n e s s of  to disintegrate into i n d i v i d u a l m y o f i b r i l s  a period of standardized  p h y s i c a l d i s r u p t i o n , and  2) a l t e r a t i o n s o f the m y o f i b r i l s themselves i n the r e g i o n s o f the Z l i n e s . Fukazawa e t a l . (19^9) s t u d y i n g  c h i c k e n found  d e g r a d a t i o n and disappearance of the Z l i n e and breakdown of the j u n c t i o n of the Z l i n e and I f i l a m e n t s . and sile  Dickson (1970) r e p o r t e d strength  Davey  the 5 t o 10 f o l d l o s s o f t e n -  on a g i n g o f bovine muscle to be due t o  weakening o f the I band-Z d i s c i n t e r f a c e but saw no s t r u c t u r a l change i n the I  filaments.  From chemical and m i c r o s c o p i c evidence, Davey and  Dickson (1970) proposed two events d u r i n g  of r i g o r .  resolution  The f i r s t was the breakdown of l a t e r a l  struc-  tures, probably sarcoplasmic reticulum  elements, which  maintained the o r d e r between f i b r i l s .  The second was a  weakening o f the m y o f i b r i l s by b r e a k i n g a t the I Z d i s c j u n c t i o n and o c c a s i o n a l l y , o f the A band.  filament-  they found, a t the edge  The l o s s o f l a t e r a l , i n t e r f i b r i l  reduced the d i s s i p a t i o n o f shear f o r c e w i t h i n allowing  l o c a l force i n t e n s i t i e s to increase  gressive  f a i l u r e a t i n d i v i d u a l Z-I j u n c t i o n s .  linkages  the muscle, with proUnaged 2  meat y i e l d e d t o s t r e t c h l o a d i n g s  o f 1 to 3 kg/cm  by  14 withdrawal  of the I f i l a m e n t s from the myosin. 2  separated a t the I-Z a r e a with o n l y 50 g/cm was  Evidence  d i s c u s s e d i n d i c a t i n g t h a t both Z d i s c and I f i l a m e n t  ( a c t i n , tropomyosin, Takahashi ing  .  Aged meat  and t r o p o n i n ) change w i t h a g i n g . e t a l , (19^7) has s t u d i e d the i n c r e a s -  weakening of m y o f i b r i l s as an i n d i c a t i o n of a g i n g .  They found t h a t a f t e r a s t a n d a r d i z e d b l e n d i n g unaged p o u l t r y meat produced  long f i b r i l s ,  treatment  and w i t h i n -  c r e a s i n g a g i n g m y o f i b r i l s tend to break i n t o s m a l l e r f r a g ments of 4 or l e s s sarcomeres.  They assumed t h a t t h i s  f r a g m e n t a t i o n p a t t e r n had a d i r e c t r e l a t i o n s h i p to the tenderness  of the meat. Sayre  (1970) s t u d i e d the v a r i o u s e f f e c t s of  f a c t o r s i n f l u e n c i n g p o u l t r y meat a g i n g on shear f o r c e , sarcomere l e n g t h , pH, of  and  fragmentation.  p r e r i g o r muscle produced  defined p a r t i c l e s .  Fragmentation  s m a l l , c o n t r a c t e d , and p o o r l y  As the muscle began to e n t e r r i g o r ,  fragments became l o n g e r , more r i g i d , and c l e a r l y d e f i n e d . With a d d i t i o n a l aging, b l e n d i n g produced p r o g r e s s i v e l y s m a l l e r fragments.  Maximum shear f o r c e was  at f u l l  Sayre found t h a t the fragmentation p a t t e r n o f et  a l . (1967) corresponded  not an  a c c u r a t e index of  rigor.  Takahashi  t o changes i n tenderness but tenderness.  was  I r r a d i a t i o n of Meat The use of i o n i z i n g r a d i a t i o n f o r p r e s e r v a t i o n of meats has been reviewed by Urbain (1965) • F l a v o r and odor changes have been s t u d i e d a t s t e r i l i z i n g doses by K i r n e t aT. (1956), C a i n e t a l . (1958) , Pearson e t a l . (1958), Coleby (1959). and Coleby et a l . (1961 a ) , and a t p a s t e u r i z i n g doses by Rhodes and 1  Shepherd (1966 and 1967) . Hanson e t a l , (1964) and Heiligman et a l . (1967) have s t u d i e d f l a v o r i n s t e r i l i z e d c h i c k e n .  The  l a t t e r a u t h o r r e p o r t e d the development o f an o r g a n o l e p t i c a l l y acceptable product.  Both used 4.5 to 4.6 Mrads to  s t e r i l i z e the c h i c k e n . Two terms d e s c r i b i n g p a s t e u r i z i n g  ( i . e . under  6 10  rads) i r r a d i a t i o n have been i n t r o d u c e d .  Radicidation  i s d e f i n e d as the r e d u c t i o n o f the number o f v i a b l e nonspore forming pathogenic b a c t e r i a , and r a d u r i z a t i o n as the  enhancement o f the keeping q u a l i t y by r e d u c i n g the  number of s p o i l a g e organisms ( G o l d b l i t h , 1970) • The e f f e c t of p a s t e u r i z i n g doses o f i r r a d i a t i o n on p o u l t r y f l a v o r has been s t u d i e d by M c G i l l e t a l . (1959) . Hannon and Shepherd (1959). Coleby e t a l . (1961 ab),  M e r c u r i e t a l . (1967), and MacLeod et a l .  among o t h e r s .  (1969)  16 S e l e c t e d works on the m i c r o b i o l o g y o f i r r a d i a t e d p o u l t r y to determine  e f f e c t i v e dosages and  e f f e c t s on p a r t i c u l a r organisms (1959),  irradiation  i n c l u d e M c G i l l et a l .  Coleby et a l . ( i 9 6 0 ab), Erdman et a l . ( 1 9 6 1 ) ,  Rhodes ( 1 9 6 5 ) , M e r c u r i e_t a l . ( 1 9 6 7 ) , (1968).  and I d z i a k and  Although r e s u l t s v a r i e d , t h e r e was  Incze  g e n e r a l agree-  ment t h a t a 3 0 0 , 0 0 0 rad dose extending storage l i f e ap- • p r o x i m a t e l y 3 times would be o r g a n o l e p t i c a l l y a c c e p t a b l e . A s o f t e n i n g of t e x t u r e i n s t e r i l i z e d r e d meats has been r e p o r t e d by many workers.  Pearson et  a l . (1958)  observed a t e x t u r e l o s s i n precooked meat t h a t became more n o t i c e a b l e a t h i g h storage temperatures. al.  (1961  Coleby e t  a) r e p o r t e d p a n e l i s t s commented on a s o f t e n i n g  of raw beef and pork t e x t u r e immediately a f t e r i r r a d i a t i o n o which worsened w i t h s t o r a g e a t 25 and 37 and which was o c  g r e a t l y minimized a t - 2 0 C s t o r a g e .  B a i l e y and Rhodes  ( 1 9 6 4 ) r e p o r t e d i r r a d i a t i o n a f t e r p a r t i a l cooking reduced the t e n d e r i z a t i o n , a l t h o u g h t e n d e r l z a t i o n was a b l e immediately a f t e r i r r a d i a t i o n .  still  notice-  Pearson e t a l . ( i 9 6 0  found that raw beef g i v e n 5 Mrads d i s p l a y e d poor t e x t u r e a f t e r 32 days.  Heat i n a c t i v a t e d  (74 C) beef delayed de-  velopment of t e x t u r e l o s s but d i d not prevent i t . Cain et a r , ( 1 9 5 8 ) u s i n g f r e s h and precooked beef and pork o given 1.9  and 2 . 8  Mrads and aged a t 72 F f o r 250 days  found t h a t f r e s h meat had e x t e n s i v e d e g r a d a t i v e changes  b)  w h i l e precooked samples had l i t t l e (1956)  irradiated cold  change.  K i r n et a l .  (1°C) and f r o z e n (-29°C) meats  and p a n e l i s t s e v a l u a t e d the t e x t u r e o f b o t h raw and zen  fro-  samples to g e n e r a l l y be v e r y good. Rhodes and Shepherd o  (1966) experimented w i t h  beef and lamb a t 0 C under a n a e r o b i c storage and conc l u d e d t h a t the l a r g e s t dose that would not cause organol e p t i c changes d e t e c t a b l e by a t r a i n e d t a s t e panel was 0.4  Mrads, a p a s t e u r i z i n g dose.  was  extended from 4 to 20 weeks w i t h 0.44  and Shepherd in  The s h e l f l i f e  o f bacon  Mrads by Rhodes  (1967) w i t h a s l i g h t i r r a d i a t i o n odor only  the raw p r o d u c t . L i c c i a r d e l l o et a l .  (1959)t Pearson e t a l .  (I960 b ) , Stadelman and Wise (1961), and B a i l e y and Rhodes (1964) r e p o r t e d reduced o r no s o f t e n i n g from meat t h a t r e c e i v e d a heat treatment t o i n a c t i v a t e enzymes. o Lower temperature s t o r a g e (approaching 0 C or lower) seems t o reduce t e x t u r a l d i s i n t e g r a t i o n as w e l l (Coleby et  al.,  1961 a) . De Fremery and P o o l (i960) e x c i s e d the P.  major muscles immediately a f t e r s l a u g h t e r , s e a l e d them in 0.5  p l a s t i c bags and i r r a d i a t e d one w i t h 2 Mrep a t e i t h e r o r 25.O hours a f t e r s l a u g h t e r .  The o t h e r muscle of  each p a i r was used as a c o n t r o l and both were s t o r e d a t  2 C. Muscles i r r a d i a t e d p r e r i g o r were s i g n i f i c a n t l y l e s s tender than u n i r r a d i a t e d  controls  TABLE EFFECT OF ELECTRON Aging time Pre-irr Total  (Table I ) .  I  IRRADIATION  Mean shear value Cont Irr  ON MUSCLE TOUGHNESS P  Mean p a i r difference  b  hr  hr  lb  lb  lb  0.5  2.8  32.0  17.0  +15.0  *o.oo5  0.5  27.1  30.1  11.5  +18.6  *0.001  25.0  28.0  13.6  + 4.4  >0.2  9.2  Each v a l u e r e p r e s e n t s the mean d i f f e r e n c e o f the s i x muscle p a i r s , the value f o r the c o n t r o l b e i n g subt r a c t e d from t h a t f o r the i r r a d i a t e d . P r o b a b i l i t y t h a t the mean p a i r d i f f e r e n c e sampling e r r o r .  i s due t o  I t can be seen t h a t toughening was r a p i d ( 1 s t group), d i d not r e s o l v e  (2nd  group), and was not s i g -  nificant  i f i r r a d i a t i o n was a p p l i e d p o s t - r i g o r  group).  L i c c i a r d e l l o e t a l . (1959) u s i n g  3 Mrep on  aged and blanched c h i c k e n s found a s o f t e n i n g  of texture  over 2 months o f ambient o r h i g h e r temperature Stadelman and Wise (1961)  studied  (3rd  storage.  e f f e c t s of 0 , 1,  3,  and  5 Mrad on aged and  12.7,  and  10.0  respectively.  frozen poultry obtaining  by  Meat g i v e n v a r i o u s  texture  irradiation.  4.3,  pounds of shear f o r c e per gram of meat cooking treatments  f o r e i r r a d i a t i o n responded s i m i l a r l y . t h a t the  7.7,  be-  They concluded  of adequately aged meat was  unaffected  Hanson e_t a l . (1963) gave doses of  4.5  t o 4.6  Mrads to aged p o u l t r y h e l d a t 4°C f o r 2 days to o 2 weeks, then h e l d a t 22 o r 38 C f o r a g i v e n time and r e f r o z e n a t -23°C u n t i l t e s t e d . o held a t -23  C throughout.  The  C o n t r o l muscles were raw  muscles were not  f e r e n t from c o n t r o l s b e f o r e storage, mushy, d i s i n t e g r a t e d t e x t u r e  developed.  heat i n a c t i v a t i o n o f enzymes was texture by  changes s t i l l  the t a s t e p a n e l as  but by  occurred,  3 months a  Preirradiation  then t r i e d but  variously  dif-  serious  characterized  s t r i n g y , mushy, d i s i n t e g r a t e d ,  tough, and d r y . Changes were more severe f o r a l l t e s t s o o a t 38 C storage than a t 22 C. P a s t e u r i z i n g doses on p o u l t r y have a l s o been s t u d i e d f o r extending r e f r i g e r a t e d storage l i f e .  McGill  e t a l . (1959) aged b i r d s on s l u s h i c e f o r 24 hours, i r r a d i a t e d a t 0.0, 0.1, and 0.5 Mrep and s t o r e d a t 0, o 40, and 50 P. The meat was cooked f o r o r g a n o l e p t i c evaluation t h a t had  a l o n g w i t h an u n i r r a d i a t e d r e f e r e n c e . o  been s t o r e d a t -40  F.  A f t e r two  p a n e l i s t s could not d i f f e r e n t i a t e the  days  34,  sample storage,  i r r a d i a t e d and  un-  20 i r r a d i a t e d samples from any  treatment combination.  Fur-  t h e r t e s t s a f t e r ? days of storage showed t h a t i r r a d i a t e d and  c o n t r o l meat had  changed e q u a l l y ,  MacLeod et a l .  (1969) compared aged precooked c h i c k e n i r r a d i a t e d w i t h 0.46  and  O.69  Mrads t h a t had  been s t o r e d up  to 3 weeks  o a t 1.1  or 6.7  p a n e l was  C with unirradiated  able  An  expert  to d i f f e r e n t i a t e samples on the b a s i s  odor, t a s t e , c o l o r , and t i t a t i v e information changes*.  controls.  was  texture.  No d e s c r i p t i o n o r quan-  presented f o r the  textural  MacLeod et a l . (1969) l i s t s g r e a t e r  in organoleptic  of  precision  t e s t s as a p o s s i b l e reason f o r the d i s -  crepancy w i t h M c G i l l et a l . (1959). Coleby et a l . (1961 5 Mrads i n c r e a s e d of beef 0.15  the pH  to 0.20  b) r e p o r t e d  i r r a d i a t i o n at  of pork about 0.1  pH u n i t s .  i r r a d i a t i o n reduced the pH  pH u n i t s  Lower temperatures  and during  increase.  Color The  c o l o r of f r e s h meats i s a f u n c t i o n of  hematin compounds, p a r t i c u l a r l y myoglobin. described  the  Fox  the  (1966)  chemistry o f myoglobin i n f r e s h meats as  a dynamic c y c l e where i n the presence o f oxygen the pigment forms (myoglobin, oxymyoglobin, and were c o n t i n u a l l y b e i n g i n t e r c o n v e r t e d .  three  metmyoglobin)  Snyder (1965)  p u b l i s h e d the r e f l e c t a n c e s p e c t r a of the three pigments, Figure  2. K i r n et a l .  (1956) and Coleby e t a l .  (1961 a)  w h i l e s t u d y i n g o t h e r i r r a d i a t i o n e f f e c t s observed t h a t c o l o r changed towards p i n k s and  browns.  Tappel (1956) summarized  the changes:  "meat i r r a d i a t e d i n excess oxygen undergoes brown d i s c o l o r a t i o n w i t h the f o r m a t i o n o f metmyoglobin e i t h e r immediately a f t e r i r r a d i a t i o n or upon subsequent storage ...... When meat i s r a d i a t e d i n i n e r t atmospheres, a b r i g h t r e d c o l o r a t i o n i s commonly observed." With p r i o r r e s e a r c h i n d i c a t i n g t h a t the r e d pigment p r o duced by a n a e r o b i c i r r a d i a t i o n was oxymyoglobin, Tappel .(1956) proposed a r e g e n e r a t i o n o f oxymyoglobin by f r e e r a d i c a l r e a c t i o n s w i t h metmyoglobin.  Tappel  (1957)  examined the r e d pigments produced by c o n v e r s i o n o f n o r mal brown o r gray pigments by i r r a d i a t i o n o f precooked meats.  He c h a r a c t e r i z e d the r e a c t i o n as a c o n v e r s i o n o f  the normal brown denatured g l o b i n hemichrome o f cooked meats t o a r e d denatured g l o b i n hemochrome.  Tappel  (1958) s t a t e d t h a t the brownish pigment of a e r o b i c a l l y i r r a d i a t e d f r e s h meats was  metmyoglobin.  Brown and Akoyunoglou (1964) d i s a g r e e d suggest i n g t h a t oxymyoglobins were converted t o substances simi l a r t o but not i d e n t i c a l t o oxymyoglobins.  22  pM 12  <  - O  o "s in ui _J o £  ACID-LABILE  7.0  20  40  6.5  ui  Q.  (fl a.  - 60  o X  ui z  ui J  < m ui a. o  o  3h  40  L  6.0 - 80  5.5  £ o <7> z  100 HOURS  F i g u r e 1.  Chemical and p h y s i c a l changes i n beef s t e r n o m a n d i b u l a r i s muscle h e l d a t 37° C. (Newbold, 1966)  r-i  a O W  4) O c cd  u o  to  3 co  o c a -p o  a>  rH  «  Figure 2 .  450  S00 550 600 WAVELENGTH m/i  650  700  R e f l e c t a n c e s p e c t r a f o r f r e s h beef samples t r e a t e d t o c o n t a i n predominantly myoglobin (Mb), oxymyoglobin (MbO ), o r Metmyoglobin (Mb ) a t the s u r f a c e . (Snyder, 1965) +  Working with, i r r a d i a t i o n s t e r i l i z e d  chicken,  Hanson et a l . (1963) found an o b j e c t i o n a b l e r e d c o l o r veloped a f t e r a n a e r o b i c , h i g h temperature o  de-  storage u n l e s s  a p r e i r r a d i a t i o n heat treatment  ( t o 80 C) was  given.  Samples s t o r e d i n a i r developed  l e s s red c o l o r .  M c G i l l e t a l . (1959) found a panel was  unable  t o d i s t i n g u i s h p a s t e u r i z e d b i r d s (1 and 5 X 10^ rep) t h a t were aged p r i o r to i r r a d i a t i o n and o  s t o r e d a t 4 tempera-  t u r e s from 0 to 50 F i n p o l y e t h y l e n e bags from c o n t r o l s on the b a s i s of c o l o r . Coleby e t a l . (i960 ab) gave doses up t o Mrads t o aged and polyethylene-bagged o temperatures  0.8  chickens s t o r e d a t  from 0 to 10 C and r e p o r t e d a p i n k c o l o r i n  the i r r a d i a t e d c a r c a s s e s . by the panel and was  The  change was  judged  slight  a t t r i b u t e d to d e s t r u c t i o n of c a r o -  t e n o i d s and i n c r e a s e d t r a n s p a r e n c y . Coleby et a l . (i960 ab) and Hanson et a l . (I963) commented on the c o l o r of raw  c h i c k e n but made  no mention of the c o l o r of o t h e r b i r d s t h a t were cooked. M c G i l l et a l . (1959) r e p o r t e d no c o l o r d i f f e r e n c e w i t h p o u l t r y cooked a f t e r i r r a d i a t i o n . al.  However, MacLeod et  (1969) r e p o r t e d t h a t a t r a i n e d p a n e l c o u l d i d e n t i f y  a f t e r cooking the meat i r r a d i a t e d a t 0.46  and 0.69  Mrads.  24 Shear P r e s s  Determinations  S z c z e s n i a k and Torgeson  (1965) reviewed the  v a r i o u s methods of. measuring meat t e n d e r n e s s . mer  The K r a -  Shear P r e s s has been shown t o g i v e h i g h c o r r e l a t i o n s  w i t h t a s t e panel e v a l u a t i o n s o f tenderness al.,  1957;  1965;  Dodge and Stadelman, I960;  and Sharrah e t a l . ,  (Shannan e t  Pangborn e t a l . ,  19^5).  Dodge and Stadelman (i960) r e p o r t e d t h a t shear p r e s s d e t e r m i n a t i o n s o f cooked p o u l t r y meat c o r r e l a t e d b e t t e r w i t h the t a s t e panel e v a l u a t i o n s o f tenderness than d i d raw meat. temperature for  May e t a l . (1962) used an i n t e r n a l  o  o f 88 C as an index o f s u f f i c i e n t  p o u l t r y and Welbourn e t a l , (1968) used 83  cooking  o  Many workers c a r e f u l l y s i z e d meat samples f o r the standard shear c e l l Shrimpton and M i l l e r , non  (Dodge and Stadelman, 1959;  I 9 6 0 ;  and May e t a l . ,  1962); Shan-  e t al;. (1957) d i d not s t a n d a r d i z e the dimensions o f  the sample.  The above workers r e p o r t e d shear p r e s s  v a l u e s as maximum pounds o f f o r c e p e r gram o f sample. P o o l e t a l . (1959) and Buck e t a l . (1970) c u t s t r i p s p a r a l l e l t o t h e f i b e r d i r e c t i o n and sheared w i t h the s i n g l e bladed c e l l .  Shear v a l u e s were recorded as  maximum pounds o f f o r c e p e r shear.  Shrimpton and M i l l e r p r e s s i o n c e l l of t h e i r own der the f o r c e - t i m e curve  (i960) with a shear com-  d e s i g n found t h a t the a r e a  un-  (a measure o f work) c o r r e l a t e d  more s t r o n g l y w i t h a panel e v a l u a t i o n of tenderness the maximum h e i g h t of the curve  (force).  than  .  Cover et a l . (1962) r e p o r t e d t h a t shear readings v a r y depending on the r e l a t i o n of f i b e r d i r e c t i o n shear p l a n e .  Toughness a c r o s s the f i b e r was  f i b e r c o n s t i t u e n t s and  due  to the to i n t r a -  collagenous f i b e r s w h i l e toughness  p a r a l l e l t o the f i b e r s was  only from c o l l a g e n o u s  fibers.  De Fremery (1966) r e p o r t e d t h a t muscle p a i r s from the same b i r d respond undergone i d e n t i c a l May  remarkedly  treatments.  alike  T h i s was  i f they have  confirmed  e t a l . (1962) and u t i l i z e d by Buck and B l a c k  and Smith e t a l . ( I 9 6 9 ) .  by  (196?)  26 EXPERIMENTAL METHODS SamplIng Method The  t r e a t e d muscle on one side vs the c o n t r o l  muscle on the other estimating  s i d e o f the same b i r d was used f o r  a l l treatment e f f e c t s because muscle param-  e t e r s e x h i b i t wide v a r i a t i o n among b i r d s as w e l l as i n response t o treatments (de Fremery, I 9 6 6 ) .  In a d d i t i o n  to comparison t e s t i n g , the c o n t r o l muscles were a n a l y s e d separately  to provide  information  on s e l e c t e d parameters  pf u n i r r a d i a t e d muscles. The  b r e a s t muscles, P e c t o r a l i s major and Pecto-  r a l i s minor, were used f o r a l l t e s t s . Assignment o f b i r d s and muscles t o treatments, and  t o i r r a d i a t e d and c o n t r o l groups was random.  Source o f Muscles The  chickens f o r Experiment 1 were a c t i v e l y -  l a y i n g S i n g l e Comb White Leghorn (S. C. W. L.) fowl 2 years o l d obtained  from the U n i v e r s i t y o f B r i t i s h  Columbia P o u l t r y Farm. followed  over  Slaughter  by e x s a n g u i n a t i o n was  immediately by e x c i s i o n o f the b r e a s t muscles  without s c a l d i n g o r p i c k i n g . were p l a c e d  The u n r e s t r a i n e d  on i c e i n p l a s t i c bags.  muscles  27  The b i r d s f o r Experiment 2 were S. C. W. L . fowl and f o r Experiments 3 and 4 commercial f r y e r s obt a i n e d d i r e c t l y o f f the l i n e from a l o c a l p o u l t r y p r o cessor.  S l a u g h t e r w i t h an e l e c t r i c k n i f e was o o  followed  by a ? 0 second s c a l d a t 1 5 0 P ( 6 5 C ) , machine p i c k i n g , and e v i s c e r a t i o n on the l i n e .  Carcasses were  immediate-  l y placed  i n crushed i c e f o r t r a n s p o r t a t i o n t o the l a b o o r a t o r y where they were s t o r e d a t 0 C u n t i l r e q u i r e d . A f t e r e x c i s i o n from the c a r c a s s , , o  all  experiments were aged a t O i l C i n sealed  to p r e v e n t d e s i c c a t i o n .  Once e x c i s e d ,  muscles f o r p l a s t i c bags  muscles were not  restrained. Irradiation The muscles were I r r a d i a t e d i n a Gammacell 2 2 0 (Atomic Energy o f Canada L t d . ) .  D u r i n g the time o f ex-  p e r i m e n t a t i o n the c o b a l t 6 0 source decayed from to 1 5 . 7 0 0 daily. rads.  rads p e r minute.  17,600  The dose time was c a l c u l a t e d  A t t e n u a t o r s were used f o r doses o f 1 0 0 0 and 5 0 0 0 If irradiation  time was c a l c u l a t e d t o exceed  1 0 minutes, samples were packed i n i c e . The time of i r r a d i a t i o n was 2 0 to 2 5 minutes post-mortem i n Experiment 1 ;  5 hours i n Experiment 2 ;  and 2 , 5 t and 1 2 hours i n Experiments 3 and 4 .  28  pH pH d e t e r m i n a t i o n s were obtained on an expanded s c a l e Corning model 10 pH meter.  Initially,  in  Experi-  ment 1 a p a i r of probe e l e c t r o d e s were i n s e r t e d i n t o the P. minor muscle ( P e t e r s and Dodge, 1959)• instability  Because of  i n the readings the method u s i n g i o d o a c e t i c  a c i d d e s c r i b e d by Marsh (1952) and Cassens and Newbold (I967 b) was  subsequently adopted.  F i v e grams of  P.  minor were blended a t high speed w i t h 50 ml of 0.005 M o sodium i o d o a c e t a t e a t 0 C f o r 1 minute. was  warmed to room temperature,  A f t e r the  slurry  the standard g l a s s e l e c -  t r o d e s were i n s e r t e d and measurements taken a f t e r a l l o w i n g 3 minutes f o r pH  stabilization.  pH d e t e r m i n a t i o n s i n Experiments w i t h i o d o a c e t a t e as above except a Corning combination  e l e c t r o d e was  In Experiment  2 and  3 were  semi-micro  used.  1, pH was  recorded a t 30 minute  i n t e r v a l s w i t h the probe e l e c t r o d e s and a t §, 1, 2,  and  4 hours post-mortem w i t h the s l u r r y .  2,  In Experiment  measurements were taken a t 5§, 10, and 24 hours p o s t mortem.  F i n a l pH was  recorded i n Experiment  3 t 48 a  hours.  Shear P r e s s Readings Shear p r e s s r e a d i n g s were o b t a i n e d on an Kramer Shear P r e s s model T-2100 (Food Technology  Allo-  Corp.)  29 with recorder (Varian)•  The m u l t i p l e bladed model CS-1  Standard Shear Compression C e l l and the s i n g l e bladed model CA-1 C e l l were used. to  A l l samples were cooked p r i o r  shearing. In  Experiment 1 ,  samples o f P. major t o be  sheared were t i g h t l y wrapped u n r e s t r a i n e d i n one l a y e r o o of for  aluminium f o i l and cooked i n an oven a t 325 F (163 C) 20 minutes.  P r i o r t e s t i n g showed t h a t t h i s was  s u f f i c i e n t time f o r the i n t e r i o r o f the samples t o reach o o 85 C. The unopened f o i l was immediately p l a c e d i n a 0 C r e f r i g e r a t o r f o r c o o l i n g and s t o r a g e . P r i o r t o s h e a r i n g , sample p a i r s were warmed t o room temperature and c u t t o uniform l e n g t h and the tough e p i m y s i a l l a y e r removed. or  thickness.  There was no s i z i n g o f width  The cooked samples were weighed and sheared  w i t h the m u l t i b l a d e d Kramer shear c e l l a t a crosshead speed o f 22 cm/min.  The shear f o r c e v a l u e s were r e p o r t e d  as maximum pounds o f f o r c e p e r gram o f sample.  The sam-  p l e s , a p p r o x i m a t e l y 4x3x1 cm, were a l i g n e d so the plane of  shear cut p e r p e n d i c u l a r l y a c r o s s the f i b e r  direction.  Because o f the c o n t r a c t i o n on cooking and extremely v a r i a b l e t h i c k n e s s e s encountered i n Experiment the  muscles i n Experiments 2 ,  1,  3» and 4 were cooked between  r e s t r a i n i n g p l a t e s s i m i l a r t o those developed by P o o l e t al.  (1959) and de Fremery and P o o l ( i 9 6 0 ) .  The e n t i r e  P. major was p l a c e d between two aluminium p l a t e s spaced i  i n c h a p a r t and cooked i n b o i l i n g water f o r 30 minutes.  T r i a l s w i t h a thermocouple i n s e r t e d i n the c e n t e r of the o muscle showed t h a t a temperature o f 99 C was reached w i t h i n 5 minutes.  A f t e r cooking immediate  c o l d tap water c o o l e d the muscle t o ambient  immersion i n temperature.  In Experiment 2, two samples were c u t , one from each o f the a n t e r i o r and p o s t e r i o r p o r t i o n s o f the P. ma j or i n a manner designed t o o b t a i n a maximum s i z e . p l e s were weighed,  Sam-  sheared p e r p e n d i c u l a r l y a c r o s s the  f i b e r d i r e c t i o n w i t h the m u l t i p l e blade c e l l , and tenderness r e p o r t e d a s pounds o f f o r c e p e r gram o f meat. In Experiments 3 and 4, f i v e s t r i p s each 1.5 cm wide were c u t from the muscle and a t o t a l o f 9 shear v a l u e s were o b t a i n e d , a c c o r d i n g t o the p a t t e r n i n F i g u r e 3, a t a r a t e o f 9 cm/min w i t h the s i n g l e shear b l a d e . R e s u l t s were recorded a s pounds o f f o r c e . The post-mortem  age o f the muscle a t s h e a r i n g  was r e c o r d e d a s the time from s l a u g h t e r t o the i n i t i a t i o n of c o o k i n g .  I n Experiment 1, the a n t e r i o r p o r t i o n was  cooked a t 2 hours and the p o s t e r i o r p o r t i o n a t 4 hours post-mortem.  In Experiment 2, the e n t i r e muscle was b o i l e d  a t 36 hours and i n Experiments 3 and k a t 60 hours p o s t mortem.  31 Myofibrillar  Fragments  Fragmentation o f m y o f i b r i l s d e s c r i b e d by Takahashi et a l .  (1967) and Sayre (1970) was used as a second  i n d i c a t o r o f the p h y s i c a l s t a t e o f the muscle. One gram o f raw muscle from the extreme  posterior  p o r t i o n o f P. major was blended a t medium speed (8,300 rpm) for o  1 minute i n an O s t e r i z e r b l e n d e r c o n t a i n i n g 100 ml o f  0 C, 0.08 M KC1 (Smith e t a l . ,  1969).  A drop o f the sus-  p e n s i o n was p l a c e d on a s l i d e w i t h cover s l i p and observed under a Wild phase c o n t r a s t microscope. of  Final magnification  photomicrographs taken w i t h an A s a h i Pentax camera was  625X. Fibril the to  fragments were counted and the F - r a t i o ,  number o f m y o f i b r i l fragments o f 4 o r l e s s the t o t a l number o f f i b r i l  sarcomeres  fragments, was c a l c u l a t e d .  An average t o t a l o f 164 f i b r i l s  taken from 4 photomicro-  graphs o f each muscle made an experimental u n i t i n E x p e r i ment 2, and an average t o t a l of 1?8 f i b r i l s  from 6 photo-  micrographs made an experimental u n i t i n Experiment 3» In  Experiment 2, f i b e r samples were blended f o r  s l i d e p r e p a r a t i o n s a t 6, 12, and 29 hours post-mortem and i n Experiment 3 they were blended a t 50 h o u r s .  32 Reflectance R e f l e c t a n c e c o l o r measurements o f raw  and  cooked  P. minor muscles i n Experiment 4 were obtained on a Unicam SP. 800B r e c o r d i n g spectrophotometer with the r e f l e c t a n c e cell.  Magnesium oxide was  used as the r e f e r e n c e  standard.  Readings were o b t a i n e d from a f r e s h l y - c u t l o n g i t u d i n a l s u r f a c e o f raw muscle.  For cooked muscle the s u r f a c e a d j a -  cent to the r e s t r a i n i n g p l a t e d u r i n g cooking .was Samples were covered  measured.  with 1 l a y e r of V i t a f i l m and  i b l e l i g h t range scanned (400  to 680  vis-  nm).  The d a t a were compared on the b a s i s of t i o n peaks, t r i s t i m u l u s v a l u e s  the  absorp-  (x, y, z) computed from  the s p e c t r a , and dominant wavelengths (Judd and  Wyszecki,  1963).  Statistical  Analysis  An IBM/360 computer and library s i o n and  the UBC  Computing  f i l e s were used f o r s t a t i s t i c a l a n a l y s i s .  Center Regres-  c o r r e l a t i o n s , a n a l y s i s of v a r i a n c e , t - t e s t s of  p a i r e d o b s e r v a t i o n s , and  t r i s t i m u l u s v a l u e s were computed.  Duncan's New  M u l t i p l e - r a n g e T e s t (p= 0.01)  was  performed  on treatment  means a c c o r d i n g t o the method o u t l i n e d by  S t e e l and T o r r i e ( i 9 6 0 ) . A c o n c i s e o u t l i n e of each o f the f o u r e x p e r i ments summarizing each step and  i t s time i s p r e s e n t e d  in  T a b l e s I I through V  respectively.  34 TABLE  II  EXPERIMENTAL PROCEDURE OF. EXPERIMENT 1 Time Post-mortem (min) 0 to  5  5 to 15  Operation K i l l c h i c k e n by c u t t i n g c a r o t i d a r t e r y and j u g u l a r v e i n w i t h outside c u t . E x c i s e muscles, bags on i c e .  place i n p l a s t i c  20 to 25  I r r a d i a t e one muscle of each p a i r .  30 to 35  1 s t pH r e a d i n g on P. minor.  every 30  30, 120,  min  60, 240  pH r e a d i n g s with probe e l e c t r o d e s for replicates 1 & 2. pH r e a d i n g s w i t h l o d o a c e t a t e s l u r r y for replicates 3, 4 & 5.  120  Cook a n t e r i o r p o r t i o n of P. major f o r subsequent shear p r e s s .  240  Cook p o s t e r i o r p o r t i o n o f P. major f o r subsequent shear p r e s s . °  4  treatments  5 replicates  (1000; 5000; 30,000; 70,000 Rads)  35 TABLE  III  EXPERIMENTAL PROCEDURE OF EXPERIMENT 2 Time Post-mortem (hr)  S l a u g h t e r i n g time - o b t a i n 6 e v i s c e r a t e d and i c e d b i r d s .  0 k  Operation  to  5 to  5i to 6 to  5  E x c i s e muscles.  5*  Irradiate  5  3A  61  muscles.  pH s l u r r y from P. minor. F i b r i l s blended from P. major.  10 to 1 0 |  pH s l u r r y from P.  12 to 12|  F i b r i l s blended from P. major.  2k to 2kh  pH s l u r r y from P. minor.  29 to 29!  F i b r i l s blended from P. major.  3k to 35!  Cook P. major f o r Shear  3 treatments 6 replications  minor.  Press.  (5000; 100,000; 200,000 Rads)  TABLE  IV  EXPERIMENTAL PROCEDURE OF EXPERIMENT 3 Time Post-mortem (hr)  0  Operation _ S l a u g h t e r i n g time - o b t a i n 12 e v i s c e r a t e d and i c e d b i r d s .  1  to  2  E x c i s e muscles.  2  to  2|  I r r a d i a t e muscles o f 4 b i r d s .  5  to  51  I r r a d i a t e muscles o f 4 b i r d s .  to 1 2 |  I r r a d i a t e muscles o f 4 b i r d s .  t o 48  pH s l u r r y made from P. minor.  12  49l t o 58  5 0 §  to 63 6 treatments 6 replicates  F i b r i l s blended f o r F - r a t i o s , P. major. Cook P. major f o r shear p r e s s . (100,000 and 300,000 rads a t 2, 5 i and 12 hours)  37 TABLE  V  EXPERIMENTAL PROCEDURE OF EXPERIMENT 4 Time Post-mortem (hr) 0  Operation S l a u g h t e r i n g time - o b t a i n 12 c e r a t e d and i c e d b i r d s .  evis-  1 to  2  E x c i s e muscles.  2 to  2|  I r r a d i a t e muscles o f 4 b i r d s .  5 to  51  I r r a d i a t e muscles o f 4 b i r d s .  12 to 1 2 |  I r r a d i a t e muscles of 4 b i r d s .  54 to 58  S p e c t r a o f raw muscles read; b o i l i n g muscles f o r subsequent cooked muscle c o l o r measurement. P. minor  58 to 63  Cook P. major f o r shear p r e s s .  6 treatments 4 replicates  (100,000 and 300,000 rads a t 2, 5, and 12 hours)  Anterior  Wing  Dorsal  VentraI  Posterior  F i g u r e 3*  L o c a t i o n o f the f i v e s t r i p s f o r shear f o r c e d e t e r m i n a t i o n s and p o s i t i o n of s h e a r i n g (dotted l i n e ) on P. major i n Experiments 3 and 4.  39 RESULTS AND DISCUSSION Experiment 1 was designed t o determine  whether  s u b p a s t e u r i z a t i o n doses o f i r r a d i a t i o n a d m i n i s t e r e d p r e r i g o r a f f e c t s the onset o f r i g o r m o r t i s (measured by pH d e c l i n e ) o r tenderness (measured by shear p r e s s ) . The l i t e r a t u r e was searched u n s u c c e s s f u l l y f o r r e p o r t s o f low dose i r r a d i a t i o n on the t e x t u r e o f meat. Fowl were choosen f o r t h e i r a v a i l a b i l i t y and i n h e r e n t toughness.  Both b r e a s t muscle p a i r s were exo  c i s e d immediately a f t e r s l a u g h t e r and aged i n i c e a t 0 C, a temperature commonly used i n i c e s l u s h c o o l i n g . procedure a l t h o u g h conductive t o c o l d s h o r t e n i n g , nated p o s s i b l e and p i c k i n g . of  This elimi-  d i f f e r e n t i a l toughening due t o s c a l d i n g pH was f o l l o w e d f o r 4 hours through most  i t s decline.  One shear p r e s s r e a d i n g a t 2 hours was  made d u r i n g development  o f i n e x t e n s i b i l i t y , and the  o t h e r a t 4 hours a f t e r f u l l development  of r i g o r mortis.  The r e s u l t s o f the p a i r e d t - t e s t s o f pH r e a d i n g s are  g i v e n i n Table V I . The average pH o f the c o n t r o l mus-  cles f e l l i960)•  from 6.46 t o 6.01 as expected (Dodge and P e t e r s ,  No s i g n i f i c a n t e f f e c t o f i r r a d i a t i o n a t any dose  on the pH f o r any time p e r i o d was found. Shear p r e s s a n a l y s i s  (Table V I I and V I I I ) showed  t h a t 1000 and 5000 rads produced no change i n t h e shear  ACT A B L E E F F E C T P H  O F S U B P A S T E U R I Z I N G  CHANGES  I N P .  M I N O R ,  V I  DOSES  O F GAMMA  E X P E R I M E N T  1.  Time P o s t - m o r t e m ( h r ) 0,5 Irr Cont I r r Cont  Dose 1000  I R R A D I A T I O N P A I R E D  O N  T - T E S T S  I r r Cont  I r r Cont  rads  Ave a  pH  d  b  calc  t  6.39  6.39  6.29  6.25  6.08  6.11  6.04  6.04  0.00  -0.04  0.03  0.00  0.00  -1.170  1.245  0.098  5000 r a d s Ave  pH  d  6.48  6.4?  6.35  6.34  6.12  6.13  5.97  5.98  -0.01  -0.01  0.01  0.01  -0.277  -0.355  1.087  0.295  6.45 6.42 -0.03  6.32 6.35 0.03  b calc  t  30,000 r a d s Ave  pH  d  6.13 6.11 -0.02  5.96 5.99 0.03  lb calc t  -0.462  0.630  -0.128  2.262  70,000 r a d s Ave  pH  d  6.52 6.55 0.03  6.31 6.38 0.07  6.17 6.20 0.03  5.99 6.04 0.05  b calc t Ave  Controls  O.676  1.642  6.456  a _ d = mean d i f f e r e n c e  of  6.331  (Control  0.278 6.137  - Irradiated)  b calculated  t , t a b u l a r t = 2.776  (p = 0.05)(4df)  1.433 6.013  41  TABLE V I I EFFECT OF SUBPASTEURIZING DOSES OF GAMMA RADIATION ON SHEAR PRESS VALUES OF P. MAJOR. EXPERIMENT 1 3,  Aging Time 2 hr Sample b  Dose (rads) -• 1000 5000 30.000 Irr Cont I r r Cont I r r Cont 8.25 25.9^  . 70.000 I r r Cont  7.60  6.16  6.90  8.38  7.58  7.62  5.86  26.56  5.28  7.74  6.45  6.02  6.08  6.28  34.65 ^2.59 33.50 25.97 27.94 3^.66 3 5 . ^ 27.08 40.53 33.86 32.81 24.57 30.73 31.80 36.86 27.11 36.55 35.80 37.60 34.24 25.53 25.00 35.80 29.92 4 hr Sample c  9.71  8.10  7.52  7.87  34.68 43.24  7.54  8.97 .8.86  5^.30  9.01  8.31  9.73  8.53  8.32 10.05  7.19  55.85 46.30 49.72 47.79 39.22 59.27 36.51  54.04 59.14 48.96 51.^9 54.22 38.58 54.29 44.49 46.06 42.33 51.21 5 0 . l l 46.45 39.67 44.94 40.69 a  l b f o r c e / g sample  b 2 h r sample from a n t e r i o r p o r t i o n o f P. major 0  4 h r sample from p o s t e r i o r p o r t i o n o f P. major  42 TABLE  VIII  SUMMARY OF ANALYSIS OP VARIANCE OF SHEAR PRESS VALUES. EXPERIMENT 1 Dose  (rads)  Time Sheared (hr)  a P  1000  2  0.00  1000  4  0.05  5000  2  2.21  5000  4  1.83  30,000  2  0.33  30,000  4  17.72  70,000  2  50.99  70,000  4  7.23  «•«•  a  calculated F  * p _? 0.05 p -? 0.01  1,6 degrees o f freedom  #  43 p r e s s r e a d i n g s of the i r r a d i a t e d muscle a t e i t h e r time.  The  samples g i v e n 30,000 rads a t 4 hours post-mortem  and 70,000 rads a t e i t h e r 2 o r 4 hours had (p_f  0.05)  4 hour of  sampling  significantly  h i g h e r shear f o r c e s than t h e i r c o n t r o l s .  The  shear p r e s s v a l u e s taken from the p o s t e r i o r p o r t i o n  P. major were g r e a t e r than the 2 hour v a l u e s taken from  the a n t e r i o r . The l a c k of s i g n i f i c a n c e between c o n t r o l and i r r a d i a t e d samples i n pH i n s p i t e of the observed d i f f e r e n c e s may  tenderness  be due t o the small number of r e p l i c a t e s  and a l a r g e sample v a r i a t i o n . l y .0.1 pH u n i t s was  A d i f f e r e n c e of  needed to be d e c l a r e d s i g n i f i c a n t .  Although not s i g n i f i c a n t  ( p > 0 . 0 5 ) , the average pH of sam-  p l e s which r e c e i v e d 70,000 rads was than the c o n t r o l  approximate-  consistently  lower  samples.  The 4 hour muscle would be expected t o be due t o the development of f u l l r i g o r , but was  tougher  interpretation  complicated by l a t e r f i n d i n g s t h a t the p o s t e r i o r sec-  t i o n was  i n h e r e n t l y tougher.  The  significant  which occurred i n the 2 hour-70,000 r a d muscles very l i t t l e tered.  toughening shows t h a t  time i s r e q u i r e d f o r the e f f e c t t o be  regis-  Coleby et a l . (1961 a) and B a i l e y and Rhodes (1964)  found an immediate t e n d e r i z a t i o n from s t e r i l i z i n g t i o n on aged meat t e x t u r e i n s t e a d of the immediate ening observed  here.  irradiatough-  44 The  shear p r e s s v a l u e s were a n a l y s e d with a  randomized complete b l o c k d e s i g n r a t h e r than the p a i r e d t - t e s t because a marked i n c r e a s e i n shear f o r c e occurred between the 2nd ment was  and  3rd  r e p l i c a t i o n s when  the e x p e r i -  suspended f o r 2 weeks w i t h d i f f i c u l t i e s i n ob-  t a i n i n g r e l i a b l e pH r e a d i n g s . toughening  i s unknown.  The  The  cause of t h i s  apparent  severe c o n t r a c t i o n of the  un-  r e s t r a i n e d muscle d u r i n g cooking, a l s o observed by Busch et a l . ( 1 9 6 7 ) , and  the d i f f i c u l t y o f removing the tough  e p i m y s i a l l a y e r made t h i s method of shear p r e s s measurements u n s a t i s f a c t o r y . (1969  Furthermore,  Davey and  Gilbert  a) have shown t h a t shear f o r c e i s not l i n e a r l y r e -  l a t e d t o sample c r o s s - s e c t i o n a l a r e a . Because Experiment  1  showed few e f f e c t s  i r r a d i a t i o n except near p a s t e u r i z a t i o n doses,  from  irradia-  t i o n l e v e l s of 1 0 0 , 0 0 0 and 2 0 0 , 0 0 0 rads were i n t r o d u c e d i n Experiment  2.  The  i r r a d i a t i o n was  5 hours p o s t - s l a u g h t e r a f t e r f u l l  administered at  r i g o r had been obtained  but b e f o r e much d e c l i n e i n i s o m e t r i c t e n s i o n would have o c c u r r e d . pH was  checked  f o r i r r a d i a t i o n produced  and a m y o f i b r i l fragmentation 1967)  was  changes  study (Takahashi e t a l . ,  added t o the shear p r e s s as a second  t e s t of  myofibrillar strength. Of the 18 p a i r e d comparison t e s t s of pH and pH changes (Table I X ) , o n l y o n e ' t e s t was  values  significant.  TABLE  45  IX  J  PAIRED T-TESTS OF PH VALUES. Mean Irr 5000 rads 5.82 5.65 5.66  51 t o 10 h r  0.1? -0.01 0.16  100,000 rads  51 h r  10 h r 24 h r  5.82 5.72 5.89  51 t o 10 h r 10 t o 24 h r 51 t o 24 h r  0.12 -0.18 -0.06  200,000 rads  b T Prob ..  5.85 5.64 5.68  -0.738 0.504 -1.387  0.498 0.638 0.223  0.20 -0.03 0.17  -0.664 2.011 -0.371  0 .540 0.099 0.721  5.81 5.69 5.79  0.481 0.848 1.605  0.652 0.439 0.168  0.12" -0.10 0.02  -0.118 -1.239 -1.004  0.876 0.270 0.363  5.88 5.68 5.76  -4.658 0.721 -0.295  0.006 0.507 0.769  0.20 -0.08 0.12  -2.298 1.282 -2.270  O.O69 0.256 0.071  ApH  PH  ApH  pH  51 h r 10 h r 24 h r  5.7B 5.71 5.75  5 l t o 10 h r 10 t o 24 h r 5 i t o 24 h r  0.06 -0.04 0.02  ApH  mean o f 6 v a l u e s 5 degrees o f freedom p -? 0 .01  T Value  pH  5i hr 10 h r 24 h r  10 t o 24 h r 5| t o 24 h r  a Values Cont  EXPERIMENT 2  46 I t was p r o b a b l y not meaningful because one i n d i v i d u a l sam p i e p a i r produced most of the d i f f e r e n c e . The a n t e r i o r and p o s t e r i o r p o r t i o n s were intended as r e p l i c a t i o n s t o i n c r e a s e the  statistical tests.  the power o f  The p o s t e r i o r sample, however,  was c o n s i s t e n t l y tougher d e s p i t e ble  o f P. major  i d e n t i c a l treatment, Ta-  X.  . TABLE  X  PAIRED T-TEST OF ANTERIOR VS POSTERIOR SHEAR PRESS READINGS OF UNIRRADIATED MUSCLES Muscle  Portion  Ave.  Shear  Anterior  18.24  Posterior  23.58  l b f o r c e p e r gram  a  T  b T Prob. •  -5.96  0.00002  sample  1? degrees of freedom  T h i s d i f f e r e n c e may be an a r t i f a c t o f the cooki n g method.  The 4 i n c h gap between the aluminium  compresses and s t r e t c h e s  plates  the t h i c k e r a n t e r i o r p o r t i o n o f  the muscle-while e x e r t i n g l e s s p r e s s u r e , o r w i t h  small  4? samples,  even a l l o w i n g  portion.  some c o n t r a c t i o n  Secondly, v i s u a l  examination o f the muscle  showed t h e p o s t e r i o r was more a  thick  epimysial  appeared effect  However,  1966).  Thirdly, appeared  the p o s t e r i o r  (George  of the f i b e r s  o t h e r may  •  Lastly,  i n less  lysed  the actomyosin  tions  5000  be more  t o each  (Cover e t a l . ,  concentrated or  o f P.  major.  comparison  r a d s h a d no s i g n i f i c a n t  although the  on  filaments or sarcoplasmic  t h e two p a s t e u r i z i n g d o s e s  o f P> m a j o r ,  b l e XI) .  parallel  thus c o n f i r m i n g the r e s u l t s  the p o s t e r i o r  tend-  a n t e r i o r a n d p o s t e r i o r p o r t i o n s were  application of  However,  The  than  the attachment  shear value  separately with the p a i r e d  tenderness,  portion  shearing perpendicularly  i n the p o s t e r i o r p o r t i o n  The  1966)•  toward  than remain  r e t i c u l u m a n d sarcolemma may stronger  i n the a n t e r i o r  and Berger,  a c r o s s t h e f i b e r and a l o w e r  (Clayson  uniform i n o r i e n t a t i o n  t o converge  have r e s u l t e d  cooking  t h u s m i n i m i z i n g any  on t e n d e r n e s s ,  fibers  less  t h e humerous bone r a t h e r  1962)  the severe  t o b r e a k down t h e c o l l a g e n  o f the muscle  ency  completely covered with  o f the e p i m y s i a l l a y e r  et a l . ,  in  layer.  of the p o s t e r i o r  test.  The  effect  on  from Experiment  toughened  200,000  ana-  both  por-  rad treatment to  s e c t i o n was n o t s i g n i f i c a n t  (p= 0.22)  (Ta-  1.  TABLE  XI  SHEAR PRESS VALUES OF AGED MUSCLES. EXPERIMENT 2 . PAIRED T-TEST  Dose (rads)  5000  100,000  200,000  Location  Shear P r e s s Mean Values Cont Irr  T Value  Anterior  18.62  19.50  -0.690  0.525  Posterior  23.13  22.84  0.138  0.864  Anterior  20.16  14.91  2.863  0.035*  Posterior  28.36  21.91  2.712  0.042*  Anterior  25.07  20.30  2.576  0.049*  Posterior  28.00  25.99  1.400  0.220  l b f o r c e / g sample mean o f 6 v a l u e s 5 degrees o f freedom  p ^ 0.05  ... T P r o b  b  49 The average  F - r a t i o s o f the c o n t r o l muscles  were found t o d i s p l a y a p a t t e r n s i m i l a r t o t h a t r e p o r t e d by Takahashi  et a l . (I967).  F - r a t i o s a t 6, 1 2 , and 29  hours p o s t - s l a u g h t e r were 0.468, 0 . 5 3 5 . and 0.655 r e spectively.  F i g u r e 4 i l l u s t r a t e s the fragmentation  changes w i t h time.  Paired  t - t e s t s o f the response to  i r r a d i a t i o n a r e i n Table X I I . The F - r a t i o s o f the samples i r r a d i a t e d w i t h  100,000 o r 200,000 rads were c o n s i s t e n t l y lower than the corresponding c o n t r o l s .  A lower r a t i o from l e s s  f r a g m e n t a t i o n would be expected  fibril  o f tougher meat.  Only  the 29 hour samples were s i g n i f i c a n t , probably i n d i c a t i n g i n s u f f i c i e n t sampling o r perhaps a time dependence.  The  s i g n i f i c a n t 12 hour-5000 r a d treatment w i t h the i r r a d i a t e d sample having a h i g h e r r a t i o i s an i s o l a t e d case and i n the absence o f any s u p p o r t i n g evidence from  other  t e s t s , i t may have been a chance o c c u r r e n c e . The  c o n t r o l muscles were a n a l y s e d t o determine  the r e l a t i o n s h i p s among pH, r a t e o f pH f a l l , change i n F - r a t i o , and a n t e r i o r shear f o r c e . r e l a t i o n m a t r i x i s presented i n Table The (p* 0.05)  initial  F-ratio, The c o r -  XIII.  ( 5 | h r ) pH was s i g n i f i c a n t l y  r e l a t e d t o a l l F - r a t i o s , a n t e r i o r shear  v a l u e s , and i n i t i a l  ( 5 | t o 12 hr) and t o t a l  force  ( 5 | t o 24 hr)  5 0  : '•-y?f:-,'j*.-S v t  Mi*.''.'.  Figure 4 .  6 hours p o s t s l a u g h t e r , Fr a t l o = 0.346  12 hours posts l a u g h t e r , Fratio = 0 . 4  4  5  29 hours posts l a u g h t e r , Fratio = 0 . 6  8  0  The Fragmentation P a t t e r n of an Uni r r a d i a t e d Muscle  TABLE F-RATIOS.  XII  EXPERIMENT 2.  PAIRED T-TEST  F-• r a t l o Irr Cont  T Value  T Prob  .470 .607 .718 .137 .112 .248  .480 .563 .674 .083 .111 .194  -0.267 2.819 1.370 1.964 0.005 1.274  0.787 0.037* 0.228 0.105 0.944 0.258  .448 .481 .546 .034 .065 .099  .480 .531 .667 .051 .136 .186  -0.689 -1.126 . -4.205 -0.231 -1.148 -1.840  0.526 0.312 0.009** 0.809 0.303 0.123  .443 .513 .625 .070 .112 .182  -0.996 -1.373 -2.628 -0.174 -2.123 -1.230  0.367 0.227 0.046* 0.844 0.086 0.273  a  b  5000 rads 6 12 29 6 - 12 12 - 29 6 - 29  hr hr hr hr hr hr  100,000 rads 6 12 29 6 - 12 12 - 29 6-29  hr hr hr hr hr hr  200,000 rads 6 12 29 6 - 12 12 - 29 6 - 29  hr hr hr hr hr hr  •  .404 .467 .534 .063 .066 .130  mean o f 6 v a l u e s b  * **  p 0.05 p -= 0.01  '  52 TABLE  XIII  SIMPLE CORRELATION COEFFICIENTS EXPERIMENT 2 Shear  51 h r  pH pH pH  .555 -.425 -.010  10 h r 24  1 ApH 2  hr  .646  A P H  -.370 .606 -.372  ApH T o t F 6 hr F 12 h r F 29 h r  A F  A F  -.420  -.293 -.022 .349 .329  1  AF 2 AF T o t  Tot  .521 -.479 -.020 .655 -.411  .576 -.872 -.661 -.406 .450  A F  2  .419 -.576 .230 .643 -.644  .307  -.486  -.819  -.181  -.450  -.168  .215 -.729 .798  pH 10  pH 2 4  ApH 1  r(.o5)(i7) = .456  f(.oi)(i7) = .575 5 | h r - pH 10 h r - pH  5ir h r  1 .114 .108  -.277 .013 .258  .299  -.428  .176 -.250  .595  .120 .416  APH 1 = pH ApH 2 = pH APH T o t = pH  A F  - pH  10 h r 24 24  A F 1 = F 12 h r - F 6 h r AF 2 = F 29 h r - F 1 2 h r A F T o t = F 29 h r - F 6 h r  hr hr  -.770 -.481  .812  -.393  ApH 2  F 29  F 12  -.518 .444 - .430 -.632  -.601 .671 -.415  .645 -.288 .801  .712  -.120 .726  - .184 -.258  .817  ApH T o t  -.828  -.836 -.387 .814  ApH APH pH PH PH  F 6  -.619 .552 -.217 -.767 .615 -.531  2 1  24  hr  10 h r 5* h r  pH f a l l . high.  Except f o r pH changes, the r v a l u e s were not  The  correlated  final  (24 hr) pH was  o n l y w i t h the second pH change.  r e l a t i o n w i t h shear was  (p4 0 . 0 5 )  significantly  very low.  Its cor-  The v a r i o u s pH  changes were s i g n i f i c a n t l y c o r r e l a t e d  with each o t h e r  and  F-ratio.  i n some cases w i t h changes i n the  A s i m i l a r p a t t e r n occurred w i t h the The  6 hour F - r a t i o was  correlated  w i t h the  F-ratios.  F-ratios  a t o t h e r times and w i t h changes i n F - r a t i o s and but not w i t h shear f o r c e . was  v e r y s i m i l a r t o the 1 2  The  shear p r e s s v a l u e s were s i g n i f i c a n t l y r e l a t e d o n l y w i t h i n i t i a l pH, tal  pH  (29  final F-ratio  hour F - r a t i o .  The  anterior  (p^ 0 . 0 5 )  i n i t i a l pH f a l l ,  corand t o -  c o n t a i n s simple l i n e a r r e g r e s s i o n  equations f o r shear f o r c e a g a i n s t a l l o t h e r i l l u s t r a t i n g the low c o r r e l a t i o n s .  variables To  whether the poor f i t between f i n a l F - r a t i o and f o r c e was was  hr)  fall. Table XIV  further  pH,  due  plotted.  to a c u r v i l i n e a r r e l a t i o n s h i p , The low c o r r e l a t i o n proved  test shear  the data  t o be from a  s c a t t e r i n g o f p o i n t s and not from the e x i s t e n c e o f any recognizable  relationship.  Anterior  shear was  t i o n s because the p o s s i b l e portion  chosen f o r these  s h o r t e n i n g of the  d u r i n g cooking would not be  uniform.  correlaposterior  TABLE  54  XIV  SIMPLE REGRESSION EQUATIONS EXPERIMENT 2 Dependent Variable  Independent Variable  5 hr  R  Constant  Slope  -88.99  18.34  - 0.308  -15.96  0.181  2  Shear  pH  Shear  pH 10 h r  Shear  pH 24 h r  21.58  -0.58  0.000  Shear  _pH 1  15.66  14.82  0.417  Shear  APH 2  17.41  -12.24  0.137  Shear  APH Tot  15.94  21.66  0.368  Shear  F  5§ h r  25.39  -15.28  0.139  Shear  F  12 h r  28.29  -18.77  0.176  Shear  F  29 h r  32.93  -22.42  0.086  Shear  AF 1  18.35  -1.52  0.001  Shear  AF 2  15.63  21.86  0.122  Shear  A F Tot  14.37  20.63  0.108  Symbols same as Table X I I I  108.7  .  I f the assumption that  of Takahashi  et a l . (196?)  the s u s c e p t a b i l i t y of muscle to f r a g m e n t a t i o n  has  a d i r e c t r e l a t i o n s h i p with the tenderness of meat i s correct,  the tougher i r r a d i a t e d muscles should have  lower F - r a t i o s .  T h e r e f o r e , i r r a d i a t e d and c o n t r o l mus-  c l e s were pooled, i n c r e a s i n g retically  the sample s i z e and  theo-  the range, and c o r r e l a t i o n s and r e g r e s s i o n s  of f i n a l F - r a t i o , and a n t e r i o r and p o s t e r i o r f o r c e were c a l c u l a t e d ,  Table  shear  XV.  There were s i g n i f i c a n t c o r r e l a t i o n s between posterior  shear f o r c e and both the a n t e r i o r shear  and the F - r a t i o .  However, the p r e d i c t i v e v a l u e of the  f i n a l F-ratio for posterior The that  several  irradiation  shear was  low.  r e s e a r c h e r s who  have  produced  demonstrated  a softer texture invariably  i r r a d i a t e d the meat a f t e r i s o m e t r i c sided.  force  The o n l y work examining  t e n s i o n had  e f f e c t s of  sub-  pre-rigor  (i960)  i r r a d i a t i o n was  conducted by de Fremery and P o o l  and  s t e r i l i z i n g doses o f i r r a d i a t i o n i n -  showed t h a t  creased toughness.  T h e r e f o r e , Experiment  3 was  designed  t o examine the e f f e c t of time of a p p l i c a t i o n o f p a s t e u r i z i n g doses of i r r a d i a t i o n on u l t i m a t e pH, tenderness.  Pasteurization  rads were a d m i n i s t e r e d a t 2, Table I I I ( p . 35)  F-ratio,  doses of 100,000 and 5i  and  300,000  and 12 hours post-mortem.  summarizes the p r o c e d u r e .  TABLE  56  XV  SIMPLE CORRELATION AND REGRESSION COEFFICIENTS OF POOLED ANTERIOR AND POSTERIOR SHEAR PRESS VALUES AND F-RATIOS. EXPERIMENT 2 F-ratio  Shear Anterior  P o s t e r i o r Shear  -0.452  0.798  A n t e r i o r Shear  -0.272  1.000  Press Posterior  1.000  1.000  F-ratio  r  ( . 0 5 ) ( 3 5 ) = .325  H.Ol)(35) = .418  Dependent Variable  Independent Variable  Anterior Shear  Posterior Shear  Anterior Shear  F-ratio  Posterior Shear  F-ratio  Constant  Slope  R  2.37  0.69  0.637  30.58  -17.24  0.0?4  45.88  -33.07  0.204  2  To examine the changes i n shear s t r e n g t h with l o c a t i o n , 5 s t r i p s of t i s s u e were cut from each muscle and a t o t a l of 9 shear r e a d i n g s were o b t a i n e d a c c o r d i n g to the p a t t e r n shown i n F i g u r e 3»  T h i s procedure m i n i -  mized v a r i a t i o n from n o n p a r a l l e l f i b e r s and a l l o w e d comparisons between d i f f e r e n t areas o f the muscle. The r e s u l t s o f the p a i r e d comparison  tests,  T a b l e XVI, i n d i c a t e d t h a t none of the treatments p r o duced a s i g n i f i c a n t e f f e c t on f i n a l pH.  This  result  was c o n s i s t e n t w i t h the f i n d i n g s o f e a r l i e r experiments The F - r a t i o s o f samples t r e a t e d p r e - r i g o r (2 hours) a t e i t h e r dose showed t h a t i r r a d i a t e d muscle f i b e r s d i d not fragment as r e a d i l y as u n i r r a d i a t e d .  The 12 hour-  300,000 r a d treatment a l s o decreased the F - r a t i o s i g n i f icantly  (p_r 0.01)  Two o t h e r samples  (100,000 r a d - 1 2  hours and 300,000 r a d - 5 hours) approached a t the 5% l e v e l .  significance  Averages of a l l i r r a d i a t e d treatment  combinations were lower than t h e i r c o n t r o l s  indicating  t h a t l a r g e r samples o r more r e p l i c a t e s might show a s i g n i f i c a n t d i f f e r e n c e f o r each treatment. Average  shear v a l u e s were h i g h e r f o r a l l i r -  r a d i a t e d treatments, however only the two 5 hour t r e a t ments were s i g n i f i c a n t  (p_? 0 . 0 5 ) .  58 TABLE  XVI  PAIRED T-TESTS OF FINAL PH, F-RATIO, AND EXPERIMENT 3 Test Shear Press  Time (hr)  Irr  100,000  2 5 12 2 5 12  14.75 13.74 11.68 13.78 13.47 12.84  10.56 11.08 10.02 11.04 10.15 10.98  2.174 3.144 1.665 2.165 2.634 1.746  2 5 12 2 5 12  5.72 5.72 5.73 5.6o 5.70 5.65  5.70 5.74 5.76 5.62 5.71 5.62  1.328 -0.775 -0.920 -0.713 -0.567 0.813  0.241 0.478 0.403 0.512 0.598 0.457  -4.220 -1.813 -2.289 -4.766 -2.353 -5.206  0.009** 0.128 0.069 0.006** 0.064 0.004**  100,000 300,000 100,000  F  300,000  2 5 12 2 5 12  mean o f 6 v a l u e s b  * **  b T Prob  Dose (rad)  300,000  pH  SHEAR PRESS.  p -? 0.05 p 0.01  Means  .622 .670 .708 .610  .596  .662  8-  Cont  .747 .754 .760 .757 .716 .784  T Value  0.080 0.026* 0.155 0.081 0.046* 0.139  59 An a n a l y s i s o f v a r i a n c e and Duncan's New ple-range T e s t were conducted  on the data from  l o c a t i o n s o f the 36 c o n t r o l muscles,  Multi-  different  Table XVII.  The  major c o n c l u s i o n was t h a t samples from the 3 p o s t e r i o r l o c a t i o n s were l e s s tender than the o t h e r s .  The v a r i a t i o n  i n the o r i e n t a t i o n o f f i b e r s t o the s h e a r i n g crosshead had been e l i m i n a t e d i n t h i s experiment.  Thus the g r e a t e r  toughness o f the p o s t e r i o r p o r t i o n c o u l d have been  caused  by s h o r t e n i n g d u r i n g cooking, d i f f e r e n c e s i n c o n n e c t i v e t i s s u e , o r v a r i a t i o n i n the s t r e n g t h o f the m y o f i b r i l itself.  T h i s f i n d i n g e x p l a i n s the d i f f e r e n c e  observed  between a n t e r i o r and p o s t e r i o r p o r t i o n s i n Experiment and a t l e a s t some o f the i n c r e a s e between  2  the 2 hour  a n t e r i o r shear and the 4 hour p o s t e r i o r shear o f E x p e r i ment 1 . C o r r e l a t i o n s among f i n a l pH, f i n a l average  F-ratio,  shear v a l u e and shear value a t l o c a t i o n I (near  the sample taken f o r the F - r a t i o ) were c a l c u l a t e d f o r c o n t r o l muscle d a t a and i r r a d i a t e d muscle data and  i n combination,  Table  singly  XVIII.  F o r the c o n t r o l and i r r a d i a t e d muscle data s e p a r a t e l y , the average  shear value and shear v a l u e a t  l o c a t i o n I were s i g n i f i c a n t l y C o r r e l a t i o n o f average  ( p * 0.01)  correlated.  shear value w i t h the f i n a l F-  r a t i o o r the f i n a l pH was very low.'  The combined data  TABLE  60  XVII  ANALYSIS OP SHEAR LOCATIONS.  EXPERIMENT 3  Analysis of Variance Source  df  SS  MS  8  3163-5  395.43  Error  3_5  5820.2  18.48  Total  323  8983.7  Location  F  21.40**  Sample  Duncan's m u l t i p l e  range  Locations: C  6.68  B  8.01  A  E  8.64  t—:  F  9.24  • I  level  a  D  8.18  99$  test  •  •  I  G  H  10.10 14.49 1 4 . 8 3 1 5 . 1 8 ••" 1  I  •  Averages:  n = 36 **  p ^ 0.01  a Locations A through  I are illustrated  i n Figure  3.  1  TABLE  61  XVIII  CORRELATION COEFFICIENTS OF PH, F-RATIO, AVERAGE SHEAR PRESS, AND SHEAR PRESS OF LOCATION I . EXPERIMENT 3 a C o n t r o l Muscles  • F  pH  Location I  0*094  PH 1.000  a  F  Location I  35  degrees o f freedom  71  degrees o f freedom  PH 1.000  3  Location I 0.054 0.706 1.000  pH 0.133 Ave. Shear -0.359 Loc. I -0.263 F 1.000 a  -0.068 1.000  0.674 1.000  Pooled I r r a d i a t e d and C o n t r o l Muscles* F  Ave. Shear  0.140  pH 0.190 Ave. Shear -0.319 Loc. I -0.113 F 1.000  b  -0.145 1.000  -0.013 0.660 1.000  Ave. Shear 0.030 Loc. I -0.072 F 1.000 Irradiated Muscles  Ave. Shear  Ave• Shear -0.101 1.000  PH 1.000  r  (.05) = .325  r  ( . o i ) = .418  r  ( . 0 5 ) = .232  r  ( . 0 1 ) = .302  62 showed a h i g h l y s i g n i f i c a n t c o r r e l a t i o n between average shear v a l u e and l o c a t i o n I shear v a l u e (p_? 0 . 0 1 ) . a d d i t i o n , the F - r a t i o had a low but s i g n i f i c a n t t i o n w i t h average  shear (p_r 0.01)  In  correla-  and a s i g n i f i c a n t c o r -  r e l a t i o n w i t h l o c a t i o n I shear (p-? 0.05) •  F i n a l pH was  not s i g n i f i c a n t l y c o r r e l a t e d t o any o f the o t h e r v a r i a b l e s . . Average shear v a l u e s were p l o t t e d a g a i n s t the F - r a t i o s but no c u r v i l i n e a r r e l a t i o n s h i p was e v i d e n t . Experiment  4 was designed t o i n c r e a s e the num-  ber o f shear p r e s s comparisons 10 i n each treatment.  from 6 (Experiment  In a d d i t i o n ,  t h a t raw i r r a d i a t e d muscles  3) to  i t had been observed  c o n s i s t e n t l y appeared p i n k e r  than the u n i r r a d i a t e d , w h i l e a f t e r cooking t h e r e was no visible difference.  V i s u a l o b s e r v a t i o n s were made and  s p e c t r a l curves o b t a i n e d on the 4 r e p l i c a t i o n s o f each treatment t o p r o v i d e more p r e c i s e i n f o r m a t i o n on t h i s phenomenon. Shear p r e s s data from Experiments b i n e d a r e p r e s e n t e d i n Table XIX.  3 and 4 com-  With the e x c e p t i o n o f  100,000 rads a t 12 hours a l l treatments produced a s i g nificant  ( p ^ 0.05)  toughening e f f e c t when judged a g a i n s t  c o n t r o l s a t 60 hours post-mortem. the i n c r e a s e i n toughness  Regardless o f dose,  decreased as time o f i r r a d i a -  t i o n i n c r e a s e d from 2 to 12 hours post-mortem.  63 TABLE  XIX  ANALYSIS OP SHEAR PRESS VALUES EXPERIMENT, 4  = -J ~  Dose (rad)  Time (hr)  100,000  Mean S h e a r Irr Cont a  d  T T Tough- Value Prob ening  b  2  14.21  10.75  3.46  32.2  2.691  0.024*  5  12.72  10.05  2.67  26.6  3.457  0.007**  12  11.64  10.34  1.30  12.6  1.363  0.204  2  14.70  11.06  3.64  32.9  3.979  0.003**  5  12.45  9.74  2.71  27.8  2.702  0.024*  12  13.66  11.35  2.31  20.4  2.590  0.028*  300,000  l b force mean o f 10 samples b  * **  p < 0.05 p _ 0.01  64 The  b i o c h e m i c a l events a s s o c i a t e d with  m o r t i s and changing  inextensibility  rigor  i n p o u l t r y muscle  should have been completed p r i o r t o the 12 hour a p p l i c a t i o n of i r r a d i a t i o n ,  De Fremery and Pool  demonstrated a s i g n i f i c a n t  toughening  27 hours when muscles were i r r a d i a t e d  p e r s i s t i n g to w i t h 2 Mrads a t  0 . 5 hours p o s t - s l a u g h t e r , but the r e s u l t s 6 muscle p a i r s  (i960)  based on  were n o n s i g n i f i c a n t ( d e s p i t e a 48 pera t 25 hours.  cent i n c r e a s e i n toughness) when i r r a d i a t e d They concluded  that i r r a d i a t i o n  i n c r e a s e d toughness by  a c c e l e r a t i n g the onset o f r i g o r m o r t i s . toughening  observed  The  i n t h i s work when muscles were i r -  r a d i a t e d a t 12 hours p o s t - s l a u g h t e r suggests textural  significant  changes observed  were not r e l a t e d  t h a t the  d i r e c t l y to  onset o f r i g o r m o r t i s . In a l l these experiments i r r a d i a t i o n ently  consist-  produced tougher meat, even a f t e r aging, and  p a r t i c u l a r l y when a d m i n i s t e r e d b e f o r e r i g o r . were s i m i l a r strated  t o de Fremery and Pool  parallel results  Conditions  (i960) who demon-  u s i n g s t e r i l i z i n g dosages.  workers who found meat softened by s t e r i l i z i n g  The  treat-  ments o f i r r a d i a t i o n a p p a r e n t l y aged the meat, and then irradiated  and s t o r e d the meat a t warm  temperatures.  An e x p l a n a t i o n f o r the i r r a d i a t i o n e f f e c t s  ob-  served w i l l r e q u i r e more knowledge o f the normal mecha-  65 nism o f r e s o l u t i o n o f r i g o r .  The dependence o f the i n -  crease i n toughening on the time o f a p p l i c a t i o n o f i r r a d i a t i o n suggests the involvement o f a c t i n and myosin. Because the pH d e c l i n e appeared t o be u n a f f e c t e d  by the  i r r a d i a t i o n an a c c e l e r a t i o n o f the normal r i g o r m o r t i s r e a c t i o n s may n o t have been i n v o l v e d . mechanism would be an i n c r e a s e bridges not  One p o s s i b l e  i n the number o f c r o s s -  between a c t i n and myosin.  However, t h i s does  e x p l a i n the i r r a d i a t i o n - i n d u c e d r e s i s t a n c e  to myo-  f i b r i l l a r fragmentation t h a t depends more on the Z l i n e and  I band j u n c t i o n than actomyosin bonding. Fukazawa e t a l . (1969) p r e s e n t e d evidence  t h a t the s a r c o p l a s m i c p r o t e i n s , p a r t i c i p a t i n g i n the g l y c o l y t i c c y c l e , may p l a y a r o l e i n the fragmentation of the m y o f i b r i l s .  I f these p r o t e i n s a r e r e s p o n s i b l e  f o r the Z l i n e and Z-I j u n c t i o n breakdown, r a d i a t i o n may i n t e r f e r e w i t h t h e i r normal a c t i v i t y . The  s o f t e n i n g observed by many workers would  have been from i n c r e a s e d  proteolytic activity at ele-  vated storage temperatures a c c e l e r a t i n g the breakdown o f the s a r c o p l a s m i c r e t i c u l u m  I band j u n c t i o n .  and weakening the Z l i n e -  Drake e t a l . (1957) and Schweigert  (1959) have shown t h a t s t e r i l i z i n g doses o f i r r a d i a t i o n are not s u f f i c i e n t t o cause a c e s s a t i o n o f enzymatic activity.  T h i s p r o t e o l y t i c a c t i v i t y may o v e r r i d e the  66 i r r a d i a t i o n produced  toughening.  The c o n s i s t e n t f a i l u r e to d e t e c t any  signif-  i c a n t pH change from i r r a d i a t i o n i n s p i t e o f the cons i s t e n t toughening does not support the concept of toughness b e i n g i n c r e a s e d by an i n c r e a s e i n r a t e o f onset o f r i g o r m o r t i s as i m p l i e d by de Fremery (i960). set  and P o o l  However, i n t h e i r work on i r r a d i a t i o n the on-  r a t e of r i g o r m o r t i s was  judged by t a c t i l e observa-  t i o n w i t h no s u p p o r t i n g chemical d e t e r m i n a t i o n s .  Sub-  sequently, Busch e t a l . (1967) and Smith et a l . (1969) were unable t o f i n d h i g h c o r r e l a t i o n s between shear r e s i s t a n c e and e i t h e r pH d e c l i n e o r ATP  breakdown.  I r r a d i a t i o n caused the f i b e r s to r e s i s t mentation but the r e s u l t s were not s i g n i f i c a n t . l a r g e r sampling o f f i b r i l s may differences.  Sayre  fragA  have p r o v i d e d s i g n i f i c a n t  (1970) has shown that the F - r a t i o  responded t o changes i n tenderness w i t h i n a muscle  but  was not a good p r e d i c t o r of tenderness, and these r e s u l t s support h i s c o n c l u s i o n .  He adds t h a t w h i l e  me-  c h a n i c a l b r e a k i n g o f the m y o f i b r i l s i s l i k e l y a manif e s t a t i o n o f the s t r u c t u r a l weakening t a k i n g p l a c e d u r i n g t e n d e r i z a t i o n , e i t h e r l o c a l i z e d a r e a s o f weakening or w i d e l y d i s t r i b u t e d breaks i n f i b r i l s may  cause a macro-  s c o p i c i n c r e a s e i n tenderness not d e t e c t a b l e by m i c r o s c o p i c methods.  One  f a c t o r t h a t may  account f o r some of  Inconclusive c o r r e l a t i o n s i s shortening. periment 2 when e x c i s i o n was  Except f o r Ex-  a t 5 hours, a l l muscles  were e x c i s e d p r e - r i g o r ~ a n d kept u n r e s t r a i n e d . and L e e t  Marsh  (1966) showed t h a t s h o r t e n i n g was r e l a t e d to  tenderness and  to pH and  c l e when i t was ening.  these  temperature.  cooled had an important  The  pH of the  e f f e c t on  mus  short-  More p r e c i s e temperature c o n t r o l between the  s l a u g h t e r house and l a b o r a t o r y o r mechanical  restraint  o f the muscles a f t e r e x c i s i o n might have produced  higher  c o r r e l a t i o n s between some o f the v a r i a b l e s . The  pooled  data  (Experiments 3 and 4)  f i r m e d the e x i s t e n c e of h i g h e r shear v a l u e s  con-  i n the 3  p o s t e r i o r l o c a t i o n s of the muscle as shown i n E x p e r i ment 3,  Table  XX.  V i s u a l observations  o f the aged raw meat con-  s i s t e n t l y showed a pink t i n t i n i r r a d i a t e d  samples  which p e r m i t t e d  irradiated  the a u t h o r to i d e n t i f y the  muscle i n 21 of 24 p a i r s .  The  300,000 rad dose g e n e r a l -  l y produced more n o t i c e a b l e c o l o r a t i o n than 100,000  rads  the three p a i r s where the i r r a d i a t e d samples c o u l d  not  be d i s t i n g u i s h e d had a l l been g i v e n 100,000  None  rads.  o f the cooked muscle p a i r s c o u l d be d i f f e r e n t i a t e d visual inspection.  by  TABLE  68  XX  ANALYSIS OF SHEAR LOCATIONS.  EXPERIMENT 4  A n a l y s i s o f Variance Source  df  SS  Location  8  Sampling Error  531  10017  Total  539  14971  6.81 1  B  7.^6  A  D  8.13  8.81  619.28  level  F  I  9.13 10.44  14.19  G  H  14.41 15.02  v  1 1  32*83**  18.86  99#  E  :  MS  495^  Duncan's m u l t i p l e range t e s t a Locations: C  '  1  1  Averages:  n = 60 **  p 4 0.01  a Locations  A through I a r e i l l u s t r a t e d  i n Figure  3.  69 The  p o l y e t h y l e n e bags and v i t a f l l m wrap were not  o r i g i n a l l y intended to p r o v i d e an a e r o b i c environment, but were intended to c o n t r o l moisture  loss. only.  Both are  c o n s i d e r e d to be a e r o b i c (oxygen permeable) f i l m s , but exact oxygen t e n s i o n was  not  the  determined.  These o b s e r v a t i o n s agree w i t h Coleby  et a l .  (i960 a) and MacLeod e t aT. (1969) t h a t raw meat would p r o duce a r e d c o l o r under a e r o b i c storage, although not to the i n t e n s i t y of a n a e r o b i c a l l y s t o r e d meats.  Coleby  et a l .  (i960 a) r e p o r t e d t h a t the p i n k i s h c o l o r appeared a t Mrads and  i n c r e a s e d w i t h dose.  A consumer p a n e l ,  0.125  hoxfever,  r a r e l y commented on the c o l o r , i n d i c a t i n g the change  was  not o b j e c t i o n a b l e . The  s p e c t r a l curves of raw  and  cooked, and i r -  r a d i a t e d and u n i r r a d i a t e d meats were o b t a i n e d .  The  4  curves from a sample i r r a d i a t e d 2 hours post-mortem w i t h  300,000 rads are g i v e n on F i g u r e s 5 and  6.  The u n i r r a d i a t e d raw -chicken had minimum r e f l e c t a n c e a t klk 504 and  630  nm,  and  5^8  nm and maximum r e f l e c t a n c e a t  s u g g e s t i n g t h a t myoglobin predominated.  The appearance of a shoulder o r o c c a s i o n a l l y a low peak a t 571 nm and a low t y p i c a l responses  shoulder between 530  to i r r a d i a t i o n .  and 5^0  nm were  They were c o n s i s t e n t -  l y p r e s e n t i n muscles g i v e n 300,000 rads, but were s l i g h t  F i g u r e 5.  Reflectance  Spectra of raw  chicken  (P. minor)  F i g u r e 6.  Reflectance  S p e c t r a o f cooked c h i c k e n  (P. minor)  72 or n o n - e x i s t e n t a t 100,000 r a d s .  The shoulders a t 530  t o 5^-0 and 571 nm were probably due t o the oxymyoglobinl i k e compound d i s c u s s e d by Tappel  (1956) and Brown and  Akoyunoglow (1964)-. The x, y, and z c h r o m a t i c i t y c o o r d i n a t e s and luminance (Y) were computed and the dominant wavelength and p u r i t y of the raw meat were obtained from a c h a r t (Hardy, 1936) •  Average values and the c o n c l u s i o n s o f  the p a i r e d t - t e s t a r e g i v e n i n Table XXI.  The c o n t r o l  muscle means f o r x, y, z, Y, dominant wavelength, and  p u r i t y were O.367, 0.354, O.279, 22.42, 583, and 24.6 respectively. The luminance o r b r i g h t n e s s of the c o l o r was not s i g n i f i c a n t l y a f f e c t e d by the treatments.  Luminance  r e a d i n g s e s p e c i a l l y were a f f e c t e d by a s u r f a c e shape f a c t o r due to d i f f i c u l t i e s i n o b t a i n i n g a f l a t from the p l i a b l e muscle.  surface  A s h i f t i n the i r r a d i a t e d mus-  c l e s t o a h i g h e r x and lower y occurred, w h i l e o n l y 1 d i f f e r e n c e was s i g n i f i c a n t among the 100,000 r a d muscles,  5 o f the 6 were s i g n i f i c a n t a t 300,000 r a d s .  This i s  f u r t h e r r e f e l c t e d i n the s i g n i f i c a n t i n c r e a s e i n the dominant wavelength t o a more r e d d i s h c o l o r a t a l l 300,000 r a d treatments.  S i m i l a r trends appeared a t 100,000  rads  but the changes were s m a l l e r and with the small number of  TABLE  73  XXI  SUMMARY OF COLOR ANALYSIS PAIRED T-TESTS Treatment  x ;  100,000 rads  2 hr  5 hr  12 h r 300,000 rads  z  Y  .348 .354  .284 .281  ns  ns  21.82 23.56  .354  .352  -.282 .280  .352 .353  ;  23.8 25.0  ns  ns  22.95 23.50  584 583  24.5 25.2  .277 .279  20 .82 23.58  585  25.8 25.2  ns  ns  hs  .380  .346  .274  .365 .014  .352  .041  .284 ns  20.22 21.14  589 584 .018  26.8 23.8  .375  .352  .012  22.82 23.29  586  ns  .273 .273  27.0 26.8  ns  ns  .019  ns  .378  .349 .354  .273  19.57 20.72  588  27.0 25.5  .368 .364  Irr Cont T Prob  .366 .366  Irr Cont T Prob Irr Cont T Prob  5 hr  Irr Cont T Prob Irr Cont T Prob  a  ns  a  ns  .371  .368 a  Domn. P u r i t y Way.  586 582  Irr Cont T Prob  2 hr  12 h r  y  ;  ns  .368  .369 .036  3 degrees o f freedom  .019  .359  .035  ns  .278 ns.'  ns  ns  hs  ns  ns  584 ns  582  584  .045  ns  ns  ns  ns  74 samples none of the d i f f e r e n c e s were s i g n i f i c a n t .  At  300,000'rads, the time of i r r a d i a t i o n d i d not a f f e c t the change of the dominant wavelength. S p e c t r a l curves of the white,  cooked meat  showed o n l y remnants of the peaks a t 4 l 6 , c h a r a c t e r i s t i c of raw  meat.  The  548,  571  and  i r r a d i a t e d and  nm  control  muscles showed i d e n t i c a l curves except f o r r e f l e c t a n c e i n t e n s i t y which was  probably due  sample r a t h e r than any  to the s u r f a c e of the  color difference.  There was  no  color difference visually detectable. The  r e f l e c t a n c e peaks o f the cooked c o n t r o l mus-  c l e were s i m i l a r to those r e p o r t e d by Tappel low peaks a t 412  and 535 nm.  cooked meats produced  two new  He found  i r r a d i a t i o n of  peaks a t 540  w i t h a l o s s of one peak a t 545 nm.  (1957), with  and  566  These r e s u l t s  cooking a f t e r i r r a d i a t i o n d i d not produce any peaks than d i d cooking u n i r r a d i a t e d meat.  The  nm indicate  different oxymyo-  g l o b i n - l i k e form p r e s e n t i n the i r r a d i a t e d raw meat p r o d u c i n g the p i n k c o l o r was  a p p a r e n t l y d e s t r o y e d by  cooking.  Whether the meat would produce the p i n k denatured g l o b i n hemochrome (Tappel, 1957) termined.  upon r e i r r a d i a t i o n was  not  de-  75 SUMMARY Tenderness  and c o l o r changes o f c h i c k e n b r e a s t  muscles ( P e c t o r a l i s major and P e c t o r a l i s minor) i n r e sponse to s u b s t e r i l i z i n g i r r a d i a t i o n was s t u d i e d by measuring  shear r e s i s t a n c e , pH, m y o f i b r i l l a r  t i o n and  spectrophotometry. 1.  I r r a d i a t i o n doses  fragmenta-  from 30,000 t o 300,000  r a d s i n c r e a s e d the shear r e s i s t a n c e o f subsequently cooked muscles.  T h i s i n c r e a s e i n toughness  s o l v e d by a g i n g f o r 60 hours. t i o n of i r r a d i a t i o n ,  was n o t r e -  The e a r l i e r the a p p l i c a -  the g r e a t e r the toughening.  Ir-  r a d i a t i o n a f t e r maximum i n e x t e n s i b i l i t y was o b t a i n e d s t i l l decreased 2.  tenderness.  The r a t e o f pH f a l l and f i n a l pH i n P.  minor were not a f f e c t e d by the i r r a d i a t i o n 3.  Shear f o r c e i n u n i r r a d i a t e d muscles was  n o t c o r r e l a t e d w i t h pH f a l l 4.  treatments.  or f i n a l  pH.  The f r a g m e n t a t i o n o f m y o f i b r i l s  with i r r a d i a t i o n w i t h i n a chicken, r e f l e c t i n g toughening.  decreased induced  However, n e i t h e r the r a t e o f change n o r the  a b s o l u t e amount o f m y o f i b r i l l a r fragmentation was ble  capa-  o f a c c u r a t e l y p r e d i c t i n g shear f o r c e . 5.  P a s t e u r i z i n g i r r a d i a t i o n produced  c o l o r i n a e r o b i c a l l y s t o r e d muscle, p a r t i c u l a r l y  a pink i n mus-  c l e s i r r a d i a t e d with 3 0 0 , 0 0 0 rads. l e n g t h s were s h i f t e d from 5 8 4 rads and from 5 8 3 was  The dominant wave-  to 5 8 8 nm w i t h  300,000  to 5 8 5 nm with 1 0 0 , 0 0 0 r a d s .  There  no c o l o r d i f f e r e n c e between i r r a d i a t e d or c o n t r o l  muscles a f t e r c o o k i n g . 6.  The p o s t e r i o r p o r t i o n o f P» major  tougher than the a n t e r i o r  portion.  was  77 LIST OF REFERENCES B a i l e y , A.J., and D. N. Rhodes. 1964. Treatment of meats w i t h i o n i s i n g r a d i a t i o n s . X I . Changes i n the t e x t u r e of meat. J . S c i . Food A g r i c . 15:  504-508.  B e n d a l l , J . R. 1969. Muscles, molecules and movement. Heinemann E d u c a t i o n a l Books, L t d . London. 219p. Bodwell, 0 . E. and A. M. Pearson. 1964. The a c t i v i t y of p a r t i a l l y p u r i f i e d bovine c a t h e p t i c enzymes on v a r i o u s n a t u r a l and s y n t h e t i c s u b s t r a t e s . J . Food  Sci.  29:  602-607.  B r i s k e y , E . J . , R. G. Cassens and J . C. Trautman. 1966. The p h y s i o l o g y and b i o c h e m i s t r y of muscle as a f o o d . Univ. of Wisconsin P r e s s . 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