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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., University o f W i s c o n s i n , 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Food Science We accept t h i s thesis as conforming to the required standard THE 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 Science 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 chicken were given 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 varying times post-slaughter and the pH, shear force, fragmentation, and color were evaluated. pH measurements i n an iodoacetate s l u r r y showed that doses up to 3 0 0 , 0 0 0 rads administered at § or 5 hours post-mortem had no e f f e c t on either rate of pH f a l l or f i -nal pH. I r r a d i a t i o n at 2 , 5t or 1 2 hours d i d not change the f i n a l pH taken at 48 hours post-mortem. Excised P. major muscles cooked by b o i l i n g be-tween aluminium plates required more shear force at the poster i o r portion than at 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 to 3 0 0 , 0 0 0 rads on P, major increased shear resistance over unirradiated muscles. The e a r l i e r the time of a p p l i c a t i o n ( 2 , 5t and 1 2 hours post-slaughter) the greater the increase i n toughness when measured at 6 0 hours post-slaughter. The 3 0 0 , 0 0 0 rad dose at 1 2 hours, given a f t e r attainment of maximum i n e x t e n s i b i l i t y and re-la x a t i o n of isometric tension, s t i l l produced a s i g n i f i -cant l o s s i n tenderness. The i r r a d i a t i o n generally 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, although the decrease was not always s i g n i f i -cant. Pasteurizing i r r a d i a t i o n produced a pink color i n raw muscle stored a e r o b i c a l l y f o r 55 hours that i n -creased with dose. Peaks t y p i c a l of an oxymyoglobin-like compound emerged and the dominant wavelength was s h i f t e d toward longer wavelengths by 4 nm. After cooking there was no v i s i b l e color difference 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 indicated that the pH decline was p o s i t i v e l y correlated to shear force, although not of high value. The fragmentation r a t i o s were not s i g n i f i c a n t l y corre-l a t e d with shear f o r c e . i i i TABLE OF CONTENTS Page INTRODUCTION 1 LITERATURE REVIEW 4 Rigor Mortis and Aging 4 Ir r a d i a t i o n of Meat . 15 Color 20 Shear Press Determinations 24 EXPERIMENTAL METHODS 26 Sampling Method 26 Source of Muscles 26 Ir r a d i a t i o n 27 pH 28 Shear Press Readings 28 M y o f i b r i l l a r Fragments Jl 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 i v LIST OP TABLES Table ' Page I . E f f e c t of Electron I r r a d i a t i o n on Muscle Toughness 18 II Experimental Procedure of Experiment 1 34 III • Experimental Procedure of Experiment 2 35 IV Experimental Procedure of Experiment 3 36 V Experimental Procedure of Experiment 4 37 VI E f f e c t of Subpasteurizing Doses of Gamma Ir r a d i a t i o n on pH Changes i n P. Minor. Experiment 1. Paired T-Tests 40 VII E f f e c t of Subpasteurizing Doses of Gamma Radiation on Shear Press Values of P. Major. Experiment 1 4l VIII Summary of Analysis of Variance of Shear Press Values. Experiment 1 42 IX Paired T-Tests of pH Values. Experiment 2 45 X Paired T-Test of Anterior VS Posterior Shear Press Readings of Unirradiated Mus-cles 46 V Table XI XII XIV XV XVI XVII Shear Press Values of Aged Muscles Experiment 2. Paired T-Test Paired T-Tests of F i n a l pH', F-Eatio, and Shear Press. Experiment 3 XIX Analysis of Shear Press Values. Ex-periment 4 Page 48 F-Ratios. Experiment 2. Paired T-Test 51 XIII Simple Correlation C o e f f i c i e n t s . Ex-periment 2 52 Simple Regression Equations. Experi-ment 2 54 Simple Correlation and Regression C o e f f i c i e n t s of Pooled Anterior and Posterior Shear Press Values and F-Ratios. Experiment 2 56 58 Analysis of Shear Locations. Experi-ment 3 60 XVIII Correlation C o e f f i c i e n t s of pH, F-Ratio, Average Shear Press of Location 1. Ex-periment 3 6l 63 v i Table Page XX Analysis of Shear Locations. • Experi-ment 4 68 XXI Summary of Color Analysis. Paired T-Tests 73 v i i LIST OF FIGURES Figure Page 1, Chemical and physical changes i n beef sternomandibularis muscle held at 37°c 22 2. Reflectance spectra f o r fresh beef samples treated to contain predominantly 2 myoglobin (Mb), oxymyoglobin (MbO ), or Metmyoglobin (Mb+) at the surface 22 3. Location 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 shearing on P. major in Experiments 3 and 4 - 38 4. The fragmentation pattern of an u n i r -radiated muscle 50 5« Reflectance spectra of raw chicken 70 6. Reflectance spectra of cooked chicken 71 v i i i ACKNOWLEDGEMENT. The author wishes to express his appreciation f o r assistance in t h i s study by: Dr. J . P. Richards f o r d i r e c t i n g t h i s research. Dr. W. D. Powrie, Dr. C. W. Roberts, and Prof. E. L. Watson f o r serving on the research committee and reviewing t h i s t h e s i s . Mr. R. Hamilton and the United Poultry Co., Ltd . of Vancouver f o r providing chickens from t h e i r processing plant. Appreciation i s extended to Atomic Energy of Canada, L t d . f o r f i n a n c i a l support of t h i s p r o j e c t . INTRODUCTION The processing of foods by i o n i z i n g r a d i a t i o n with i t s unique potentials and problems has been under ex-tensive i n v e s t i g a t i o n since 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 ion-i z i n g r a d i a t i o n : 1) s t e r i l i z a t i o n to permit ambient tem-perature storage; 2) pasteurization to prolong r e f r i g -erated storage l i f e ; 3) insect 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 of plant growth processes; 5) unit operations, including meat tenderization and polymer hydrolysis; and 6) destruction of s p e c i f i c human parasites and pathogens i n foods. Advantages of i r r a d i a t i o n over a p p l i c a t i o n of heat energy include highly e f f i c i e n t b a c t e r i a l i n a c t i v -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 ). Ir r a d i a t i o n i s currently approved i n the United States f o r wheat and f l o u r insect d i s i n f e s t a t i o n and potato sprout i n h i b i t i o n (Keisner, 1 9 6 8 ) . In Canada 1 5 , 0 0 0 rads can be used f o r potato 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 or whole wheat f l o u r for insect d i s i n f e s t a t i o n . Approval of i r r a d i a t i o n s t e r i l i z a t i o n of bacon has been withdrawn i n the United States pending the re-su l t s of a new 2 to 3 year t o x i c o l o g i c a l feeding study by the U.S. Army because of unresolved questions over i r r a d i -ation-induced toxic substances. However, Goldb l i t h (1970) reviewed the safety aspects of i r r a d i a t e d foods and con-2 eluded that r i s k s to the consumer were minimal. When energy i n any form i s applied to foods, changes occur. Radiation energy i s no exception. Ef-f e c t s of r a d i a t i o n energy on meats, i n addition to destruc-t i o n of microorganisms, were summarized "by Urbain (1965): 1) color; raw meats became brownish and anaerob-i c a l l y stored cooked meats turn pink. 2) texture; a softening of tissue occurs, the degree rel a t e d to dose. 3) f a t s ; oxidation and development of rancid f l a v o r occurs, depending on oxygen a v a i l a b i l i t y and dose. 4) odor and/or f l a v o r ; o f f odors and flavors including a c h a r a c t e r i s t i c " i r r a d i a t i o n off-odor" may de-velop. These changes can be reduced by excluding oxygen, adding free r a d i c a l acceptors, and i r r a d i a t i n g at low tem-peratures . Improved technology has increased the accepta-b i l i t y of some i r r a d i a t e d meats. Radiation s t e r i l i z e d chicken has been reported by Heillgman et a l . ( 1 9 6 7 ) to be organoleptically s a t i s f a c t o r y . However, textural s o f t -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 poultry have f r e -quently been observed. There i s a lack of data on quanti-t a t i v e measurements of textural changes in poultry and those reported p e r t a i n only to s t e r i l i z i n g l e v e l s of i r r a -d i a t i o n . S i m i l a r l y , information on the e f f e c t s of apply-ing i r r a d i a t i o n at varying times post-slaughter on textural changes i s sparse. Pink discolorations have been reported i n i r r a d i -ated poultry but the time of a p p l i c a t i o n post-slaughter was not considered, nor were the data quantitative. This study explored textural and color changes r e s u l t i n g from pasteurization and subpasteurlzation doses of i r r a d i a t i o n administered to poultry muscles at varying times post-slaughter. 4 LITERATURE REVIEW Rigor Mortis and Aging Great st r i d e s have been made i n recent years ad-vancing our understanding of the complex organization and chemistry of muscle. Excellent reviews covering the bio-chemistry of muscle include Briskey et a l . (1966), Davies (1967), Bendall (1969), and Huxley (1969). Goll"(1968). discusses aspects of the resolution of r i g o r mortis. A f t e r a general description compiled from above, various aspects of r i g o r mortis and resolution of r i g o r pertinent to t h i s thesis w i l l be elaborated on. At slaughter, the blood c i r c u l a t i o n to the muscle ceases and oxygen renewal i s terminated. Myoglobin-bound oxygen i s soon depleted fo r c i n g the tissue into anaerobic g l y c o l y s i s . Glycogen i s converted to l a c t i c a c i d causing the pH to f a l l . With glycogen depleted, creatine phosphate i s consumed i n an attempt to maintain ATP l e v e l s . When a l l sources of renewal are exhausted, the ATP l e v e l w i l l de-crease . ATP releases energy by s p l i t t i n g o f f the terminal phosphate to drive the c o n t r a c t i l e process. This i s t r i g -+2 gered by a release of Ca from the sarcoplasmic reticulum. +2 ATP i n the absence of Ca w i l l act as a p l a s t i c i z e r , preventing i n t e r a c t i o n of a c t i n and myosin. With the ab-sence of ATP, i n t e r a c t i o n occurs and the filaments are per-5 manently bound and the muscle i s inextensible. Reduction i n the e x t e n s i b i l i t y generally begins when ATP has f a l l e n to approximately 30 percent of i t s i n i t i a l l e v e l and nor-mally progresses u n t i l the muscle i s completely inexten-s i b l e . Rigor mortis i s defined as t h i s l o s s of extensi-b i l i t y . Depending on post-mortem temperature and other factors shortening may occur, possibly i n response to a +2 release of Ca by the sarcoplasmic reticulum. These events are b r i e f l y summarized i n Figure 1. Davies (1967) theorizes that the permanent bonding r e s u l t s from the a t t r a c t i v e forces of the p o s i -t i v e l y charged ATP binding s i t e s of the heavy meromyosin to the negatively charged ADP on the a c t i n . The post-mortem pH f a l l i n chickens from approx-imately pH 7 to pH 5«8 to 5*9 requires 2 to 4.5 hours (de Fremery and Pool, 1958, I960; Peters and Dodge, 1959; Dodge and Peters, I960; and Dodge and Stadelman, i960) . Working with ox muscle, Cassens and Newbold (1967 a) found that the rate of pH decline increased as o the temperature increased from 5 to 37 C, but was also greater at 1 than at 5°C. Ultimate pH was higher at 1 to o * 5 C than at higher temperatures. De Fremery and Pool (i960) observed that ATP disappeared more rapidl y at 0 o than 10 C i n chickens. They showed further that the r e l -6 a t i v e rate of onset of r i g o r mortis can be measured by ATP disappearance, glycogen decrease, or pH f a l l . Busch et a l . (1967) confirmed t h i s with bovine muscle. May et a l . (1962) claimed that tenderness was c l o s e l y related to pH, although i n d i r e c t l y through the association of pH to onset of r i g o r mortis. Unless restrained, a muscle w i l l shorten i n con-Junction with r i g o r mortis. Locker and Hagyard (1963) observed i n beef that at higher temperatures (19 to kJ°C) shortening coincided with the onset of r i g o r mortis, but at low temperatures shortening began rapidly and usually immediately (also Busch et a l . , 1967)* They also noticed a dependence of the degree of shortening on temperature, the "cold shortening e f f e c t " . Between Ik and 19°C short-ening was slow and minimal compared to higher or lower temperatures. At 0°C shortening was rapid and extreme. Cassens and Newbold (1967 *>) a t t r i b u t e d cold shortening to a release of calcium ions by the sarcotubular system i n response to low temperatures. Smith e_t a l . (1969) observed a s i m i l a r response in poultry, with the minimum o shortening between 12 to 18 C. They found shortening at each temperature was e s s e n t i a l l y completed within 3 hours and that post-mortem pH decline did not s i g n i f i c a n t l y correlate with shortening. 7 Locker (i960) reported that the state of con-t r a c t i o n i s a s i g n i f i c a n t factor in tenderness of bovine meat, more tender meat being associated with minimal con-t r a c t i o n . Marsh and Leet (1966) studying cold shortening and tenderness agreed that minimal contraction occurred o at 15 to 20 C. They found further that shortening to 20 percent of the i n i t i a l length did not exert a s i g n i f -icant e f f e c t on toughness, but toughness increased r a p i d l y with further shortening, peaking at 4-0 percent. However, muscles shortened to 60 percent of t h e i r i n i t i a l length were sheared as r e a d i l y as nonshortened muscle. The cold shortening e f f e c t was r e l a t e d to pH, higher pH muscle ex-h i b i t i n g greater shortening. The maximum shear force was at pH 6.5* They also demonstrated that a muscle re-strained by attachment to the skeleton (or mechanically restrained excised muscle) could also develop cold short-ening induced toughness because of l o c a l contraction and extension, p a r t i c u l a r l y i f cooling was uneven. They con-cluded that ultimate tenderness i s effected by tempera-ture during the f i r s t few hours post-mortem. Davey et a l . (1967) substantiated these findings adding that as short-ening increased beyond 20 percent a progressive decrease occurred i n the extent to which meat tenderizes with sub-sequent aging, u n t i l at 40 percent shortening, tenderi-zation had ceased. 8 Marsh et a l . (1968) found t h i s e f f e c t to be of great importance with frozen lamb. S i g n i f i c a n t increases i n toughness were avoided i f freezing was delayed at l e a s t 16 hours a f t e r slaughter. Several workers have considered adding tension and stretching the muscle during r i g o r mortis. The con-clusions of Herring et a l . (1967 b), Buck and Black (1967), and G i l l i s and Hendrickson (1969) a l l pertaining to bovine muscle, were that while l e s s force was required to shear stretched muscles i t was of more p r a c t i c a l importance to prevent shortening. Herring et a l . (1967 b) found high c o e f f i c i e n t s 2 of determination (R ) between tenderness, and f i b e r diam-eter and sarcomere length which are related to shorten-ing . The s t i f f e n i n g and toughness of meat i n r i g o r mortis i s not necessarily permanent; with time muscle reverts to a more p l i a b l e state, a process c a l l e d reso-l u t i o n of r i g o r or aging. A muscle during t h i s time looses i t s a b i l i t y to maintain isometric tension although complete macroscopic e x t e n s i b i l i t y does not return ( G o l l , 1968). Deatherage and Harsham (19^7) studied beef aged o at 33 to 35 F and found an increase in tenderness over 2| weeks except f o r animals with high i n i t i a l tenderness. 9 Pool et a l . (1959), Dodge and Stadelman (1959), and May et a l , (1962) reported chicken muscle increased i n tenderness immediately a f t e r slaughter and most ten-der l z a t i o n took place within 4 hours. Very l i t t l e change 0 occurred a f t e r 12 hours of aging. C a r l i n et a l . (1949) found that b r o i l e r s achieved maximum tenderness i n ap-proximately 10 hours but added that mature fowl may take up to 48 hours. L i t t l e change i n tenderness of breast muscle during the 3rd to 8th day a f t e r i n i t i a l aging was reported by van den Berg et a l . (1964). Koonz et a l . (1954), de Fremery (I966), and de Fremery and Streeter (1969) observed a maximum toughness reached between 3 and 4 hours post-mortem at 2°C f o l -lowed by a decrease to a minimum i n 12 to 24 hours with l i t t l e subsequent change. Goll (1968) reported two d i f f e r e n t patterns of shear force with time i n bovine muscle depending on whether the muscle was excised or l e f t on the skeleton. Excised muscle increased then de-creased i n shear force while attached muscle decreased sharply from the time of slaughter. I n e x t e n s i b i l i t y changes were i d e n t i c a l i n both muscles but the excised muscle could shorten. £Ji (1962) studied the ef f e c t of temper-o ature and found that carcasses aged at 37 c were tougher o than carcasses aged at 0 or 19 C. Dodge and Stadelman 10 (1959) also found a general Increase i n tenderness at lower temperatures i n d i c a t i n g that poultry can tenderize ade-o quately at 0 C. £ i # (1962) found that older chickens were tougher, both i n i t i a l l y and throughout aging. Many other factors have been investigated to de-termine t h e i r e f f e c t on resolution of r i g o r mortis and tenderness. De Fremery (1966) stated that any prerigor treatment such as freezing and thawing, elevating tempera-ture, scalding, beating, excising, and cutting that a c c e l -erated ATP and glycogen l o s s and onset of r i g o r mortis would increase toughness. This increase was only p a r t i a l -l y reversed by prolonged aging. He stated that i t was the acceleration of post-mortem g l y c o l y s i s , not the acceler-ation of r i g o r mortis, that increased toughness. De Fremery and Pool (i960) had shown e a r l i e r that breast muscles excised from the chicken p r i o r to on-set of r i g o r mortis were l e s s tender than t h e i r controls, 12.6 and 5.8 l b shear force r e s p e c t i v e l y . While some workers were studying factors a f -f e c t i n g tenderness and aging, others were probing the mechanism behind resolution of r i g o r . Wierbicki et a l . (1954) and Herring et a l . (1967 a) have investigated connective tissue, primarily 11 collagen. They concluded that, while collagen content and s o l u b i l i t y were related to tenderness neither were affected by aging processes and did not contribute to tenderization. B a c t e r i a l proteolysis had been suggested by some to be responsible. Sharp (1963) working with aseptic meat and Davey and G i l b e r t (1966) have discredited t h i s theory. Bodwell and Pearson (1964) working with bovine muscle and Martins and Whitaker (1968) working with chick-en muscle investigated the theory that catheptic enzymes released from the lysosomes are the agents of aging. They found that muscle tissue had r e l a t i v e l y low concentrations of cathepsins and that actomyosin was not acted upon by them. Sarcoplasmic proteins were found to be r e a d i l y hydrolysed (Bodwell and Pearson, 1964). Davey and G i l b e r t (1966) claimed that differences i n rates of tenderizing of d i f f e r e n t carcasses are 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 rates of p r o t e o l y s i s . In some of the beef a n i -mals studied, tenderization was almost complete before any p r o t e o l y t i c changes were detected. I t has frequently been observed, however, that the e x 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, p a r t i c u l a r l y a c t i n and actomyosin, increase with time, (Khan and van den Berg, 1964; Davey and G i l b e r t , 1968 ab; and Sayre, 1968). Davey and G i l b e r t (1968 a) found that the ultimate pH value l a r g e l y determines the rate of increase 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. High-er pH values were associated with higher e x t r a c t a b i l i t y . Several workers have inferred from th i s that a proteolysis that weakens or breaks the linkages between the I band and Z l i n e was responsible f o r the increase i n tenderness. Mcintosh (1967) reported actomyosin e x t r a c t a b i l i t y i n chicken decreased r a p i d l y during the f i r s t 5 hours to a minimum at 12 hours and then increased to a maximum i n 4 to 6 days. Electron microscopic evidence strongly i n d i -cated that the above inferences were correct. Weidemann et a l . (1967) working with ox muscle stated that tender-ness on aging was produced by disruption of the a c t i n filaments and by a weakening of the linkages between the a c t i n and myosin filaments i n the sarcomeres. The elec-tronphotomicrographs showed breakage at the Z l i n e of stretched muscle as well as l e s s overlap of A and I band filaments. Davey and G i l b e r t (1967) found the most notable changes when aging bovine muscle were the complete d i s -appearance of the Z l i n e s and the lengthening of the A bands at the expense of the I bands. They concluded that weakening of the Z l i n e s was the event most cl o s e l y re-l a t e d to meat aging. 13 Davey and G i l b e r t (1969 b) working on beef r e -ported two aging e f f e c t s , 1) an increased readiness of f i b e r pieces to disintegrate into i n d i v i d u a l myofibrils during a period of standardized physical disruption, and 2) a l t e r a t i o n s of the myofibrils themselves i n the regions of the Z l i n e s . Fukazawa et a l . (19^9) studying chicken found degradation and disappearance of the Z l i n e and break-down of the junction of the Z l i n e and I filaments. Davey and Dickson (1970) reported the 5 to 10 f o l d l o s s of ten-s i l e strength on aging of bovine muscle to be due to weakening of the I band-Z disc interface but saw no struc-t u r a l change i n the I filaments. From chemical and microscopic evidence, Davey and Dickson (1970) proposed two events during resolution of r i g o r . 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 order between f i b r i l s . The second was a weakening of the my o f i b r i l s by breaking at the I filament-Z disc junction and occasionally, they found, at the edge of the A band. The l o s s of l a t e r a l , i n t e r f i b r i l linkages reduced the d i s s i p a t i o n of shear force within the muscle, allowing l o c a l force i n t e n s i t i e s to increase with pro-gressive f a i l u r e at i n d i v i d u a l Z-I junctions. Unaged 2 meat yielded to stretch loadings of 1 to 3 kg/cm by 14 withdrawal of the I filaments from the myosin. Aged meat 2 separated at the I-Z area with only 50 g/cm . Evidence was discussed i n d i c a t i n g that both Z disc and I filament (actin, tropomyosin, and troponin) change with aging. Takahashi et a l , (19^7) has studied the increas-ing weakening of myof i b r i l s as an i n d i c a t i o n of aging. They found that a f t e r a standardized blending treatment unaged poultry meat produced long f i b r i l s , and with i n -creasing aging myofibrils tend to break into smaller f r a g -ments of 4 or l e s s sarcomeres. They assumed that t h i s fragmentation pattern 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) studied the various e f f e c t s of factors influencing poultry meat aging on shear force, sarcomere length, pH, and fragmentation. Fragmentation of prerigor muscle produced small, contracted, and poorly defined p a r t i c l e s . As the muscle began to enter r i g o r , fragments became longer, more r i g i d , and c l e a r l y defined. With addi t i o n a l aging, blending produced progressively smaller fragments. Maximum shear force was at f u l l r i g o r . Sayre found that the fragmentation pattern of Takahashi et a l . (1967) corresponded to changes i n tenderness but was not an accurate index of tenderness. 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 preservation of meats has been reviewed by Urbain (1965) • Flavor and odor changes have been studied at s t e r i l i z i n g doses by Kirn et aT. (1956), Cain et a l . (1958) , Pearson et a l . (1958), Coleby (1959). and Coleby et a l 1 . (1961 a), and at pasteurizing doses by Rhodes and Shepherd (1966 and 1967) . Hanson et a l , (1964) and Heiligman et a l . (1967) have studied f l a v o r i n s t e r i l i z e d chicken. The l a t t e r author reported the development of an organolepti-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 chicken. Two terms describing pasteurizing ( i . e . under 6 10 rads) i r r a d i a t i o n have been introduced. Radicidation i s defined as the reduction of the number of viable non-spore forming pathogenic bacteria, and radurization as the enhancement of the keeping q u a l i t y by reducing the number of spoilage organisms (Goldblith, 1970) • The e f f e c t of pasteurizing doses of i r r a d i a t i o n on poultry f l a v o r has been studied by McGill et a l . (1959) . Hannon and Shepherd (1959). Coleby et a l . (1961 ab), Mercuri et a l . (1967), and MacLeod et a l . (1969) among others. 16 Selected works on the microbiology of i r r a d i a t e d poultry to determine e f f e c t i v e dosages and i r r a d i a t i o n e f f e c t s on p a r t i c u l a r organisms include McGill et a l . ( 1 9 5 9 ) , Coleby et a l . ( i 9 6 0 ab), Erdman et a l . ( 1 9 6 1 ) , Rhodes ( 1 9 6 5 ), Mercuri e_t a l . ( 1 9 6 7 ) , and Idziak and Incze ( 1 9 6 8 ) . Although r e s u l t s varied, there was general agree-ment that a 3 0 0 , 0 0 0 rad dose extending storage l i f e ap- • proximately 3 times would be organoleptically acceptable. A softening of texture i n s t e r i l i z e d red meats has been reported by many workers. Pearson et a l . (1958) observed a texture l o s s i n precooked meat that became more noticeable at high storage temperatures. Coleby et a l . (1961 a) reported panelists commented on a softening of raw beef and pork texture immediately a f t e r i r r a d i a t i o n o which worsened with storage at 25 and 37 c and which was o greatly minimized at - 2 0 C storage. Bailey and Rhodes (1964) reported 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 tenderization, although tenderlzation was s t i l l n otice-able immediately a f t e r i r r a d i a t i o n . Pearson et a l . ( i 9 6 0 b) found that raw beef given 5 Mrads displayed poor texture a f t e r 32 days. Heat inactivated (74 C) beef delayed de-velopment of texture l o s s but did not prevent i t . Cain et a r , (1958) using fresh and precooked beef and pork o given 1 . 9 and 2 . 8 Mrads and aged at 72 F f o r 250 days found that f r e s h meat had extensive degradative changes while precooked samples had l i t t l e change. Kirn et a l . ( 1 9 5 6 ) i r r a d i a t e d cold (1°C) and frozen (-29°C) meats and panelists evaluated the texture of both raw and f r o -zen samples to generally be very good. Rhodes and Shepherd (1966) experimented with o beef and lamb at 0 C under anaerobic storage and con-cluded that the l a r g e s t dose that would not cause organo-l e p t i c changes detectable by a trained taste panel was 0.4 Mrads, a pasteurizing dose. The shelf l i f e of bacon was extended from 4 to 20 weeks with 0.44 Mrads by Rhodes and Shepherd (1967) with a s l i g h t i r r a d i a t i o n odor only in the raw product. L i c c i a r d e l l o et a l . (1959) t Pearson et a l . (I960 b), Stadelman and Wise (1961), and Bailey and Rho-des (1964) reported reduced or no softening from meat that received a heat treatment to inactivate enzymes. o Lower temperature storage (approaching 0 C or lower) seems to reduce textural d i s i n t e g r a t i o n as well (Coleby et a l . , 1961 a) . De Fremery and Pool (i960) excised the P. major muscles immediately a f t e r slaughter, sealed them in p l a s t i c bags and i r r a d i a t e d one with 2 Mrep at either 0 . 5 or 25.O hours a f t e r slaughter. The other muscle of each p a i r was used as a control and both were stored at 2 C. Muscles i r r a d i a t e d prerigor were s i g n i f i c a n t l y l e s s tender than unirradiated controls (Table I ) . TABLE I EFFECT OF ELECTRON IRRADIATION ON MUSCLE TOUGHNESS Aging time Mean shear value Mean p a i r P b P r e - i r r Total I r r Cont difference hr hr l b l b l b 0.5 2.8 32.0 17.0 +15.0 *o . o o 5 0.5 27.1 30.1 11 .5 +18.6 *0.001 25.0 28.0 13.6 9.2 + 4.4 >0.2 Each value represents the mean difference of the six muscle p a i r s , the value f o r the control being sub-tracted from that 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 that the mean p a i r difference i s due to sampling e r r o r . I t can be seen that toughening was rapid (1st group), did not resolve (2nd group), and was not s i g -n i f i c a n t i f i r r a d i a t i o n was applied post-rigor ( 3 r d group). L i c c i a r d e l l o et a l . (1959) using 3 Mrep on aged and blanched chickens found a softening of texture over 2 months of ambient or higher temperature storage. Stadelman and Wise (1961) studied e f f e c t s of 0 , 1, 3 , and 5 Mrad on aged and frozen poultry obtaining 7.7, 4.3, 12.7, and 10.0 pounds of shear force per gram of meat res p e c t i v e l y . Meat given various cooking treatments be-fore i r r a d i a t i o n responded s i m i l a r l y . They concluded that the texture of adequately aged meat was unaffected by i r r a d i a t i o n . Hanson e_t a l . (1963) gave doses of 4.5 to 4.6 Mrads to aged poultry held at 4°C f o r 2 days to o 2 weeks, then held at 22 or 38 C f o r a given time and refrozen at -23°C u n t i l tested. Control muscles were o held at -23 C throughout. The raw muscles were not d i f -ferent from controls before storage, but by 3 months a mushy, disintegrated texture developed. P r e i r r a d i a t i o n heat i n a c t i v a t i o n of enzymes was then t r i e d but serious texture changes s t i l l occurred, variously characterized by the taste panel as stringy, mushy, disintegrated, tough, and dry. Changes were more severe f o r a l l tests o o at 38 C storage than at 22 C. Pasteurizing doses on poultry have also been studied f o r extending r e f r i g e r a t e d storage l i f e . McGill et a l . (1959) aged birds on slush ice f o r 24 hours, i r -radiated at 0.0, 0.1, and 0.5 Mrep and stored at 0, 34, o 40, and 50 P. The meat was cooked f o r organoleptic evaluation along with an unirradiated reference sample . o that had been stored at -40 F. A f t e r two days storage, 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 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-ther tests a f t e r ? days of storage showed that i r r a d i a t e d and control meat had changed equally, MacLeod et a l . (1969) compared aged precooked chicken i r r a d i a t e d with 0.46 and O.69 Mrads that had been stored up to 3 weeks o at 1.1 or 6.7 C with unirradiated controls. An expert panel was able to d i f f e r e n t i a t e samples on the basis of odor, taste, color, and texture. No description or quan-t i t a t i v e information was presented f o r the textural changes*. MacLeod et a l . (1969) l i s t s greater p r e c i s i o n i n organoleptic tests as a possible reason f o r the d i s -crepancy with McGill et a l . (1959). Coleby et a l . (1961 b) reported i r r a d i a t i o n at 5 Mrads increased the pH of pork about 0.1 pH units and of beef 0.15 to 0.20 pH u n i t s . Lower temperatures during i r r a d i a t i o n reduced the pH increase. Color The color of fresh meats i s a function of the hematin compounds, p a r t i c u l a r l y myoglobin. Fox (1966) described the chemistry of myoglobin i n fresh meats as a dynamic cycle where i n the presence of oxygen the three pigment forms (myoglobin, oxymyoglobin, and metmyoglobin) were continually being interconverted. Snyder (1965) published the reflectance spectra of the three pigments, Figure 2. Kirn et a l . (1956) and Coleby et a l . (1961 a) while studying other i r r a d i a t i o n e f f e c t s observed that color changed towards pinks 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 with the formation of metmyoglobin either 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 radiated i n i n e r t atmospheres, a bright red coloration i s commonly observed." With p r i o r research i n d i c a t i n g that the red pigment pro-duced by anaerobic i r r a d i a t i o n was oxymyoglobin, Tappel .(1956) proposed a regeneration of oxymyoglobin by free r a d i c a l reactions with metmyoglobin. Tappel (1957) examined the red pigments produced by conversion of nor-mal brown or gray pigments by i r r a d i a t i o n of precooked meats. He characterized the reaction as a conversion of the normal brown denatured globin hemichrome of cooked meats to a red denatured globin hemochrome. Tappel (1958) stated that 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 fresh meats was metmyoglobin. Brown and Akoyunoglou (1964) disagreed suggest ing that oxymyoglobins were converted to substances simi l a r to but not i d e n t i c a l to oxymyoglobins. 2 2 < o " s in ui _J o £ 12 ui Q. (fl o X a. ui ui z J 3 h < ui a. o m o 4 pM 7.0 6.5 6.0 0 L 5.5 - O ACID-LABILE HOURS 20 40 - 60 £ - 80 o <7> z 100 Figure 1. Chemical and physical changes i n beef sterno-mandibularis muscle held at 37° C. (Newbold, 1966) r-i a O W 4) O c cd u o to 3 co o c a - p o a> r H « 450 S00 550 600 WAVELENGTH m/i 650 700 Figure 2 . Reflectance spectra f o r fresh beef samples treated to contain predominantly myoglobin (Mb), oxymyoglobin (MbO ), or Metmyoglobin (Mb+) at the surface. (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 objectionable red color de-veloped a f t e r anaerobic, high temperature storage unless o a p r e i r r a d i a t i o n heat treatment (to 80 C) was given. Samples stored i n a i r developed l e s s red c o l o r . McGill et a l . (1959) found a panel was unable to d i s t i n g u i s h pasteurized birds (1 and 5 X 10^ rep) that were aged p r i o r to i r r a d i a t i o n and stored at 4 tempera-o tures from 0 to 50 F i n polyethylene bags from controls on the basis of c o l o r . Coleby et a l . (i960 ab) gave doses up to 0.8 Mrads to aged and polyethylene-bagged chickens stored at o temperatures from 0 to 10 C and reported a pink color i n the i r r a d i a t e d carcasses. The change was judged s l i g h t by the panel and was a t t r i b u t e d to destruction of caro-tenoids and increased transparency. Coleby et a l . (i960 ab) and Hanson et a l . (I963) commented on the color of raw chicken but made no mention of the color of other birds that were cooked. McGill et a l . (1959) reported no color difference with poultry cooked a f t e r i r r a d i a t i o n . However, MacLeod et a l . (1969) reported that a trained panel could 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 at 0.46 and 0.69 Mrads. 24 Shear Press Determinations Szczesniak and Torgeson (1965) reviewed the various methods of. measuring meat tenderness. The Kra-mer Shear Press has been shown to give high correlations with taste panel evaluations of tenderness (Shannan et a l . , 1957; Dodge and Stadelman, I960; Pangborn et a l . , 1965; and Sharrah et a l . , 19^5). Dodge and Stadelman (i960) reported that shear press determinations of cooked poultry meat correlated better with the taste panel evaluations of tenderness than did raw meat. May et a l . (1962) used an in t e r n a l o temperature of 88 C as an index of s u f f i c i e n t cooking o f o r poultry and Welbourn et a l , (1968) used 83 Many workers c a r e f u l l y sized meat samples for the standard shear c e l l (Dodge and Stadelman, 1959; Shrimpton and M i l l e r , I 9 6 0 ; and May et a l . , 1962); Shan-non et al;. (1957) did not standardize the dimensions of the sample. The above workers reported shear press values as maximum pounds of force per gram of sample. Pool et a l . (1959) and Buck et a l . (1970) cut s t r i p s p a r a l l e l to the f i b e r d i r e c t i o n and sheared with the single bladed c e l l . Shear values were recorded as maximum pounds of force per shear. Shrimpton and M i l l e r (i960) with a shear com-pression c e l l of t h e i r own design found that the area un-der the force-time curve (a measure of work) correlated more strongly with a panel evaluation of tenderness than the maximum height of the curve ( f o r c e ) . . Cover et a l . (1962) reported that shear readings vary 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 to the shear plane. Toughness across the f i b e r was due to i n t r a -f i b e r constituents and collagenous f i b e r s while toughness p a r a l l e l to the f i b e r s was only from collagenous f i b e r s . De Fremery (1966) reported that muscle pairs from the same b i r d respond remarkedly a l i k e i f they have undergone i d e n t i c a l treatments. This was confirmed by May et a l . (1962) and u t i l i z e d by Buck and Black (196?) and Smith et a l . (I969). 26 EXPERIMENTAL METHODS SamplIng Method The treated muscle on one side vs the control muscle on the other side of the same b i r d was used for estimating a l l treatment e f f e c t s because muscle param-eters exhibit wide v a r i a t i o n among birds as well as in response to treatments (de Fremery, I 9 6 6 ). In addition to comparison tes t i n g , the control muscles were analysed separately to provide information on selected parameters pf unirradiated muscles. The breast muscles, Pectoral 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 of birds and muscles to treatments, and to i r r a d i a t e d and control groups was random. Source of Muscles The chickens f o r Experiment 1 were a c t i v e l y -l a y i n g Single Comb White Leghorn (S. C. W. L.) fowl over 2 years old obtained from the University of B r i t i s h Columbia Poultry Farm. Slaughter by exsanguination was followed immediately by excision of the breast muscles without scalding or pic k i n g . The unrestrained muscles were placed on ice i n plastic bags. 2 7 The birds for Experiment 2 were S. C. W. L. fowl and for Experiments 3 and 4 commercial fry e r s ob-tained d i r e c t l y o f f the l i n e from a l o c a l poultry pro-cessor. Slaughter with an e l e c t r i c knife was followed o o by a ? 0 second scald at 1 5 0 P ( 6 5 C), machine picking, and evisceration on the l i n e . Carcasses were immediate-l y placed i n crushed ice f o r transportation to the labo-o ratory where they were stored at 0 C u n t i l required. A f t e r excision from the carcass, muscles for , o a l l experiments were aged at Oi l C i n sealed p l a s t i c bags to prevent desiccation. Once excised, muscles were not rest r a i n e d . I r r a d i a t i o n The muscles were Irradiated i n a Gammacell 2 2 0 (Atomic Energy of Canada L t d . ) . During the time of ex-perimentation the cobalt 6 0 source decayed from 1 7 , 6 0 0 to 1 5 . 7 0 0 rads per minute. The dose time was calculated d a i l y . Attenuators were used f o r doses of 1 0 0 0 and 5 0 0 0 rads. I f i r r a d i a t i o n time was calculated to 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 determinations were obtained on an expanded scale Corning model 10 pH meter. I n i t i a l l y , i n Experi-ment 1 a p a i r of probe electrodes were inserted into the P. minor muscle (Peters and Dodge, 1959)• Because of i n s t a b i l i t y i n the readings the method using iodoacetic a c i d described by Marsh (1952) and Cassens and Newbold (I967 b) was subsequently adopted. Five grams of P. minor were blended at high speed with 50 ml of 0.005 M o sodium iodoacetate at 0 C f o r 1 minute. After the s l u r r y was warmed to room temperature, the standard glass elec-trodes were inserted and measurements taken a f t e r allow-ing 3 minutes f o r pH s t a b i l i z a t i o n . pH determinations i n Experiments 2 and 3 were with iodoacetate as above except a Corning semi-micro combination electrode was used. In Experiment 1, pH was recorded at 30 minute i n t e r v a l s with the probe electrodes and at §, 1, 2, and 4 hours post-mortem with the s l u r r y . In Experiment 2, measurements were taken at 5§, 10, and 24 hours post-mortem. F i n a l pH was recorded i n Experiment 3 a t 48 hours. Shear Press Readings Shear press readings were obtained on an A l l o -Kramer Shear Press model T-2100 (Food Technology Corp.) 29 with recorder (Varian)• The multiple bladed model CS-1 Standard Shear Compression C e l l and the single bladed model CA-1 C e l l were used. A l l samples were cooked p r i o r to shearing. In Experiment 1 , samples of P. major to be sheared were t i g h t l y wrapped unrestrained in one layer o o of aluminium f o i l and cooked i n an oven at 325 F (163 C) for 20 minutes. P r i o r t e s t i n g showed that 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 of the samples to reach o o 85 C. The unopened f o i l was immediately placed i n a 0 C r e f r i g e r a t o r f o r cooling and storage. P r i o r to shearing, sample pairs were warmed to room temperature and cut to uniform length and the tough epimysial layer removed. There was no s i z i n g of width or thickness. The cooked samples were weighed and sheared with the multibladed Kramer shear c e l l at a crosshead speed of 22 cm/min. The shear force values were reported as maximum pounds of force per gram of sample. The sam-ples, approximately 4x3x1 cm, were aligned so the plane of shear cut perpendicularly across the f i b e r d i r e c t i o n . Because of the contraction on cooking and ex-tremely variable thicknesses encountered i n Experiment 1 , the muscles i n Experiments 2 , 3» and 4 were cooked between r e s t r a i n i n g plates s i m i l a r to those developed by Pool et a l . (1959) and de Fremery and Pool ( i 9 6 0 ) . The entire P. major was placed between two aluminium plates spaced i inch apart and cooked i n b o i l i n g water f o r 30 minutes. T r i a l s with a thermocouple inserted i n the center of the o muscle showed that a temperature of 99 C was reached within 5 minutes. After cooking immediate immersion in cold tap water cooled the muscle to ambient temperature. In Experiment 2, two samples were cut, one from each of the an t e r i o r and posterior portions of the P. ma j or i n a manner designed to obtain a maximum s i z e . Sam-ples were weighed, sheared perpendicularly across the f i b e r d i r e c t i o n with the multiple blade c e l l , and tender-ness reported as pounds of force per gram of meat. In Experiments 3 and 4, f i v e s t r i p s each 1.5 cm wide were cut from the muscle and a t o t a l of 9 shear values were obtained, according to the pattern i n Figure 3, at a rate of 9 cm/min with the single shear blade. Results were recorded as pounds of force. The post-mortem age of the muscle at shearing was recorded as the time from slaughter to the i n i t i a t i o n of cooking. In Experiment 1, the anter i o r portion was cooked at 2 hours and the posterior portion at 4 hours post-mortem. In Experiment 2, the entire muscle was boiled at 36 hours and i n Experiments 3 and k at 60 hours post-mortem. 31 M y o f i b r i l l a r Fragments Fragmentation of myofib r i l s described by Taka-hashi et a l . (1967) and Sayre (1970) was used as a second indicator of the physical state of the muscle. One gram of raw muscle from the extreme posterior portion of P. major was blended at medium speed (8,300 rpm) fo r 1 minute i n an Osterizer blender containing 100 ml of o 0 C, 0.08 M KC1 (Smith et a l . , 1969). A drop of the sus-pension was placed on a s l i d e with cover s l i p and observed under a Wild phase contrast microscope. F i n a l magnification of photomicrographs taken with an Asahi Pentax camera was 625X. F i b r i l fragments were counted and the F-ratio, the number of my o f i b r i l fragments of 4 or le s s sarcomeres to the t o t a l number of f i b r i l fragments, was calcu l a t e d . An average t o t a l of 164 f i b r i l s taken from 4 photomicro-graphs of each muscle made an experimental unit i n Experi-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 unit i n Experiment 3» In Experiment 2, f i b e r samples were blended f o r s l i d e preparations at 6, 12, and 29 hours post-mortem and in Experiment 3 they were blended at 50 hours. 32 Reflectance Reflectance color measurements of raw and cooked P. minor muscles i n Experiment 4 were obtained on a Unicam SP. 800B recording spectrophotometer with the reflectance c e l l . Magnesium oxide was used as the reference standard. Readings were obtained from a freshly-cut l o n g i t u d i n a l surface of raw muscle. For cooked muscle the surface adja-cent to the r e s t r a i n i n g plate during cooking .was measured. Samples were covered with 1 layer of V i t a f i l m and the v i s -i b l e l i g h t range scanned (400 to 680 nm). The data were compared on the basis of absorp-t i o n peaks, tr i s t i m u l u s values (x, y, z) computed from the spectra, and dominant wavelengths (Judd and Wyszecki, 1963). S t a t i s t i c a l Analysis An IBM/360 computer and the UBC Computing Center l i b r a r y 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 . Regres-sion and corr e l a t i o n s , analysis of variance, t - t e s t s of paired observations, and t r i s t i m u l u s values were computed. Duncan's New Multiple-range Test (p= 0.01) was performed on treatment means according to the method outlined by Steel and T o r r i e (i960). A concise outline of each of the four experi-ments summarizing each step and i t s time i s presented i n Tables II through V re s p e c t i v e l y . 34 TABLE I I EXPERIMENTAL PROCEDURE OF. EXPERIMENT 1 Time Post-mortem Operation (min)  0 to 5 K i l l chicken by cutting c a r o t i d artery and jugular vein with out-side cut. 5 to 15 Excise muscles, place i n p l a s t i c bags on i c e . 20 to 25 Irradiate one muscle of each p a i r . 30 to 35 1st pH reading on P. minor. every 30 min pH readings with probe electrodes for r e p l i c a t e s 1 & 2. 30, 60, 120, 240 pH readings with lodoacetate slurr y f o r r e p l i c a t e s 3, 4 & 5. 120 Cook anter i o r portion of P. major for subsequent shear press. 240 Cook poster i o r portion of P. major f o r subsequent shear press. ° 4 treatments (1000; 5000; 30,000; 70,000 Rads) 5 r e p l i c a t e s TABLE III EXPERIMENTAL PROCEDURE OF EXPERIMENT 2 35 Time Post-mortem Operation (hr)  0 Slaughtering time - obtain 6 ev i s -cerated and iced b i r d s . k to 5 Excise muscles. 5 to 5* Irradiate muscles. 5i to 5 3 A pH slurr y from P. minor. 6 to 61 F i b r i l s blended from P. major. 10 to 10| pH slurr y from P. minor. 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 Press. 3 treatments (5000; 100,000; 200,000 Rads) 6 r e p l i c a t i o n s TABLE IV EXPERIMENTAL PROCEDURE OF EXPERIMENT 3 Time Post-mortem Operation (hr) _ 0 Slaughtering time - obtain 12 evis -cerated and iced b i r d s . 1 to 2 Excise muscles. 2 to 2| Irradiate muscles of 4 b i r d s . 5 to 51 Irradiate muscles of 4 b i r d s . 12 to 12| Irradiate muscles of 4 b i r d s . to 48 pH slurry made from P. minor. 49l to 5 0 § F i b r i l s blended f o r F-ratios, P. major. 58 to 63 Cook P. major for shear press. 6 treatments (100,000 and 300,000 rads at 2, 5 i and 12 hours) 6 r e p l i c a t e s 37 TABLE V EXPERIMENTAL PROCEDURE OF EXPERIMENT 4 Time Post-mortem Operation (hr)  0 Slaughtering time - obtain 12 evi s -cerated and iced b i r d s . 1 to 2 Excise muscles. 2 to 2| Irradiate muscles of 4 b i r d s . 5 to 51 Irradiate muscles of 4 b i r d s . 12 to 12| Irradiate muscles of 4 b i r d s . 54 to 58 Spectra of raw muscles read; b o i l i n g muscles for subsequent cooked muscle color measurement. P. minor 58 to 63 Cook P. major for shear press. 6 treatments (100,000 and 300,000 rads at 2, 5, and 12 hours) 4 r e p l i c a t e s A n t e r i o r W i n g Dorsa l V e n t r a I P o s t e r i o r Figure 3* Location of the f i v e s t r i p s for shear force determinations and p o s i t i o n of shearing (dotted l i n e ) on P. major in Experiments 3 and 4. 39 RESULTS AND DISCUSSION Experiment 1 was designed to determine whether subpasteurization doses of i r r a d i a t i o n administered pre-r i g o r a f f e c t s the onset of r i g o r mortis (measured by pH decline) or tenderness (measured by shear press). The l i t e r a t u r e was searched unsuccessfully f o r reports of low dose i r r a d i a t i o n on the texture of 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 inherent toughness. Both breast muscle pa i r s were ex-o cised immediately a f t e r slaughter and aged i n ice at 0 C, a temperature commonly used i n ice slush cooling. This procedure although conductive to cold shortening, e l i m i -nated possible d i f f e r e n t i a l toughening due to scalding and p i c k i n g . pH was followed for 4 hours through most of i t s d e c l i n e . One shear press reading at 2 hours was made during development of i n e x t e n s i b i l i t y , and the other at 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 of the paired t-tests of pH readings are given i n Table VI. The average pH of the control mus-cles f e l l from 6.46 to 6.01 as expected (Dodge and Peters, i960)• No s i g n i f i c a n t e f f e c t of i r r a d i a t i o n at any dose on the pH f o r any time period was found. Shear press analysis (Table VII and VIII) showed that 1000 and 5000 rads produced no change i n the shear A C -T A B L E V I E F F E C T O F S U B P A S T E U R I Z I N G D O S E S O F G A M M A I R R A D I A T I O N O N P H C H A N G E S I N P . M I N O R , E X P E R I M E N T 1. P A I R E D T - T E S T S Time Post-mortem (hr)  Dose 0,5 I r r Cont I r r Cont I r r Cont I r r Cont 1000 rads Ave pH 6.39 6.39 6.29 6.25 6.08 6.11 6.04 6.04 a d 0.00 -0.04 0.03 0.00 b c a l c t 0.00 -1.170 1.245 0.098 5000 rads Ave pH 6.48 6.4? 6.35 6.34 6.12 6.13 5.97 5.98 d -0.01 -0.01 0.01 0.01 b c a l c t -0.277 -0.355 1.087 0.295 30,000 rads Ave pH 6.45 6.42 6.32 6.35 6.13 6.11 5.96 5.99 d -0.03 0.03 -0.02 0.03 lb c a l c t -0.462 0.630 -0.128 2.262 70,000 rads Ave pH 6.52 6.55 6.31 6.38 6.17 6.20 5.99 6.04 d 0.03 0.07 0.03 0.05 b c a l c t O.676 1.642 0.278 1.433 Ave C o n t r o l s 6.456 6.331 6.137 6.013 a _ d = mean d i f f e r e n c e o f ( C o n t r o l - I r r a d i a t e d ) b c a l c u l a t e d t, t a b u l a r t = 2.776 (p = 0.05)(4df) 41 TABLE VII EFFECT OF SUBPASTEURIZING DOSES OF GAMMA RADIATION ON SHEAR PRESS VALUES3, OF P. MAJOR. EXPERIMENT 1 Dose (rads) -• . Aging Time 1000 5000 30.000 70.000  I r r Cont I r r Cont I r r Cont I r r Cont 2 h r b 8.25 7.60 6.16 6.90 8.38 7.58 7.62 5.86 Sample 25.9^ 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 35.^ 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 h r c 9.71 8.10 7.52 7.87 9.01 8.31 9.73 8.53 Sample 34.68 43.24 7.54 8.97 .8.86 8.32 10.05 7.19 5^.30 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 force / g sample b 2 hr sample from ante r i o r portion of P. major  0 4 hr sample from posterior portion of 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 1,6 degrees of freedom * p _? 0.05 p -? 0.01 43 press readings of the i r r a d i a t e d muscle at either sampling time. The samples given 30,000 rads at 4 hours post-mortem and 70,000 rads at either 2 or 4 hours had s i g n i f i c a n t l y (p_f 0.05) higher shear forces than t h e i r c o n t r o l s . The 4 hour shear press values taken from the poste r i o r portion of P. major were greater than the 2 hour values taken from the a n t e r i o r . The lack of significance between control and i r -radiated samples i n pH i n spite of the observed tenderness differences may be due to the small number of r e p l i c a t e s and a large sample v a r i a t i o n . A difference of approximate-l y .0.1 pH units was needed to be declared 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>0.05), the average pH of sam-ples which received 70,000 rads was consistently lower than the control samples. The 4 hour muscle would be expected to be tougher due to the development of f u l l r i g o r , but int e r p r e t a t i o n was complicated by l a t e r findings that the posterior sec-t i o n was inherently tougher. The s i g n i f i c a n t toughening which occurred i n the 2 hour-70,000 rad muscles shows that very l i t t l e time i s required f o r the e f f e c t to be r e g i s -tered. Coleby et a l . (1961 a) and Bailey and Rhodes (1964) found an immediate tenderization from s t e r i l i z i n g i r r a d i a -t i o n on aged meat texture instead of the immediate tough-ening observed here. 44 The shear press values were analysed with a randomized complete block design rather than the paired t - t e s t because a marked increase i n shear force occurred between the 2nd and 3 r d r e p l i c a t i o n s when the experi-ment was suspended f o r 2 weeks with 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 readings. The cause of t h i s apparent toughening i s unknown. The severe contraction of the un-restrained muscle during cooking, also observed by Busch et a l . ( 1 9 6 7 ) , and the d i f f i c u l t y of removing the tough epimysial layer made t h i s method of shear press measure-ments unsatisfactory. Furthermore, Davey and G i l b e r t (1969 a) have shown that shear force i s not l i n e a r l y re-l a t e d to sample cross-sectional area. Because Experiment 1 showed few e f f e c t s from i r r a d i a t i o n except near pasteurization doses, i r r a d i a -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 introduced i n Experiment 2 . The i r r a d i a t i o n was administered at 5 hours post-slaughter a f t e r f u l l r i g o r had been obtained but before much decline i n isometric tension would have occurred. pH was checked f o r i r r a d i a t i o n produced changes and a m y o f i b r i l fragmentation study (Takahashi et a l . , 1967) was added to the shear press as a second t e s t of m y o f i b r i l l a r strength. Of the 18 paired comparison tests of pH values and pH changes (Table IX), only one'test was s i g n i f i c a n t . 45 TABLE IX J PAIRED T-TESTS OF PH VALUES. EXPERIMENT 2 a b Mean Values T Value T Prob .. I r r Cont 5000 rads 5i hr pH 0.498 5.82 5.85 -0.738 10 hr 5.65 5.64 0.504 0.638 24 hr 5.66 5.68 -1.387 0.223 51 to 10 hr ApH -0.664 0.1? 0.20 0 .540 10 to 24 hr -0.01 -0.03 2.011 0.099 5| to 24 hr 0.16 0.17 -0.371 0.721 100,000 rads 51 hr PH 5.82 5.81 0.481 0.652 10 hr 5.72 5.69 0.848 0.439 24 hr 5.89 5.79 1.605 0.168 ApH 51 to 10 hr 0.12 0.12" -0.118 0.876 10 to 24 hr -0.18 -0.10 -1.239 0.270 51 to 24 hr -0.06 0.02 -1.004 0.363 200,000 rads 5.7B pH 51 hr 5.88 -4.658 0.006 10 hr 5.71 5.68 0.721 0.507 24 hr 5.75 5.76 -0.295 0.769 0.06 ApH 5l to 10 hr 0.20 -2.298 O.O69 10 to 24 hr -0.04 -0.08 1.282 0.256 5i to 24 hr 0.02 0.12 -2.270 0.071 mean of 6 values 5 degrees of freedom p -? 0 .01 46 I t was probably not meaningful because one i n d i v i d u a l sam pie p a i r produced most of the di f f e r e n c e . The a n t e r i o r and posterior portions of P. major were intended as r e p l i c a t i o n s to increase the power of the s t a t i s t i c a l t e s t s . The posterior sample, however, was consistently tougher despite i d e n t i c a l treatment, Ta-ble X. . TABLE X PAIRED T-TEST OF ANTERIOR VS POSTERIOR SHEAR PRESS READINGS OF UNIRRADIATED MUSCLES Muscle Portion Ave. Shear a T b T Prob. Anterior 18.24 • -5.96 0.00002 Posterior 23.58 l b force per gram sample 1? degrees of freedom This difference may be an a r t i f a c t of the cook-ing method. The 4 inch gap between the aluminium plates compresses and stretches the thicker a n t e r i o r portion of the muscle-while exerting l e s s pressure, or with small 4? samples, even a l l o w i n g some c o n t r a c t i o n of the p o s t e r i o r p o r t i o n . Secondly, v i s u a l examination of the muscle showed the p o s t e r i o r was more completely covered w i t h a t h i c k e p i m y s i a l l a y e r . However, the severe cooking appeared to break down the c o l l a g e n thus m i n i m i z i n g any e f f e c t o f the e p i m y s i a l l a y e r on tenderness, (Clayson e t a l . , 1966). T h i r d l y , f i b e r s i n the a n t e r i o r p o r t i o n of the muscle appeared l e s s uniform i n o r i e n t a t i o n than i n the p o s t e r i o r (George and Berger, 1966)• The tend-ency of the f i b e r s t o converge toward the attachment on the humerous bone r a t h e r than remain p a r a l l e l t o each o t h e r may have r e s u l t e d i n l e s s s h e a r i n g 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 and a lower shear value (Cover et a l . , 1962) • L a s t l y , the actomyosin f i l a m e n t s or s a r c o p l a s m i c r e t i c u l u m and sarcolemma may be more con c e n t r a t e d or s t r o n g e r i n the p o s t e r i o r p o r t i o n of P. major. 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 ana-l y s e d s e p a r a t e l y w i t h the p a i r e d comparison t e s t . The a p p l i c a t i o n o f 5000 rads had no s i g n i f i c a n t e f f e c t on tenderness, thus c o n f i r m i n g the r e s u l t s from Experiment 1 . However, the two p a s t e u r i z i n g doses toughened both por-t i o n s of P> major, a l t h o u g h the 200,000 rad treatment to the p o s t e r i o r s e c t i o n was not s i g n i f i c a n t (p= 0.22) (Ta-b l e XI) . TABLE XI SHEAR PRESS VALUES OF AGED MUSCLES. EXPERIMENT 2 . PAIRED T-TEST Dose Location Shear Mean Press Values T Value ... T Prob b (rads) I r r Cont 5000 Anterior 18.62 19.50 -0 .690 0.525 P o s t e r i o r 23.13 22.84 0.138 0.864 100,000 Anterior 20.16 14.91 2.863 0.035* Posterior 28.36 21.91 2.712 0.042* 200,000 Anterior 25.07 20.30 2.576 0.049* Posterior 28.00 25.99 1.400 0.220 l b force / g sample mean of 6 values 5 degrees of freedom p ^ 0.05 49 The average F-ratios of the control muscles were found to display a pattern s i m i l a r to that reported by Takahashi et a l . ( I967) . F-ratios at 6, 12, and 29 hours post-slaughter were 0.468, 0.535. and 0.655 re-spectively. Figure 4 i l l u s t r a t e s the fragmentation changes with time. Paired t - t e s t s of the response to i r r a d i a t i o n are i n Table XII. The F-ratios of the samples i r r a d i a t e d with 100,000 or 200,000 rads were consistently lower than the corresponding cont r o l s . A lower r a t i o from l e s s f i b r i l fragmentation would be expected of 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 or perhaps a time dependence. The s i g n i f i c a n t 12 hour -5000 rad treatment with the i r r a d i -ated sample having a higher r a t i o i s an i s o l a t e d case and i n the absence of any supporting evidence from other tes t s , i t may have been a chance occurrence. The control muscles were analysed to determine the relationships among pH, rate of pH f a l l , F - r a t i o , change i n F-ratio, and anter i o r shear f o r c e . The cor-r e l a t i o n matrix i s presented i n Table XIII. The i n i t i a l ( 5 | hr) pH was s i g n i f i c a n t l y (p* 0.05) related to a l l F-ratios, anterior shear force values, and i n i t i a l ( 5 | to 12 hr) and t o t a l ( 5 | to 24 hr) : '•-y?f:-,'j*.-S 5 0 6 hours post-t v slaughter, F-r a t l o = 0.346 Mi*.''.'. 12 hours post-slaughter, F-r a t i o = 0 . 4 4 5 29 hours post-slaughter, F-r a t i o = 0 . 6 8 0 Figure 4 . The Fragmentation Pattern of an Un-i r r a d i a t e d Muscle TABLE XII F-RATIOS. EXPERIMENT 2. PAIRED T-TEST F-I r r • r a t l o a Cont T Value T Prob b 5000 rads 6 hr .470 .480 -0 .267 0.787 12 hr .607 .563 2.819 0.037* 29 hr .718 .674 1.370 0.228 6 - 12 hr .137 .083 1.964 0.105 12 - 29 hr .112 .111 0.005 0.944 6 - 29 hr .248 .194 1.274 0.258 100,000 rads 6 hr .448 .480 -0.689 0.526 12 hr .481 .531 -1 .126 0.312 29 hr .546 .667 . -4 .205 0.009** 6 - 12 hr .034 .051 -0 .231 0.809 12 - 29 hr .065 .136 -1.148 0.303 6 - 2 9 hr .099 .186 -1.840 0.123 200,000 rads • 6 hr .404 .443 -0 .996 0.367 12 hr .467 .513 -1 .373 0.227 29 hr .534 .625 -2 .628 0.046* 6 - 12 hr .063 .070 -0 .174 0.844 12 - 29 hr .066 .112 -2 .123 ' 0.086 6 - 29 hr .130 .182 -1 .230 0.273 mean of 6 values b * p 0.05 ** p -= 0.01 52 TABLE XIII SIMPLE CORRELATION COEFFICIENTS EXPERIMENT 2 Shear A F Tot A F 2 A F 1 F 29 F 12 F 6 pH 51 hr .555 .521 .419 .114 - . 5 1 8 - . 6 0 1 - . 6 1 9 pH 10 hr - . 4 2 5 - . 4 7 9 - . 5 7 6 .108 .444 .671 .552 pH 24 hr - . 0 1 0 - . 0 2 0 .230 - . 2 7 7 - .430 - . 4 1 5 - . 2 1 7 A P H 1 .646 .655 .643 .013 - . 6 3 2 -.828 - . 7 6 7 ApH 2 - . 3 7 0 -.411 -.644 .258 .645 - . 8 3 6 .615 ApH Tot .606 .576 .307 .299 -.288 - . 3 8 7 - . 5 3 1 F 6 hr - . 3 7 2 - . 8 7 2 -.486 -.428 .801 .814 F 12 hr -.420 - . 6 6 1 - . 8 1 9 .176 .712 F 29 hr - . 2 9 3 - . 4 0 6 -.181 - . 2 5 0 A F 1 - . 0 2 2 .450 - . 4 5 0 AF 2 .349 .595 AF Tot .329 - . 1 2 0 ApH 2 - . 7 7 0 .726 APH 1 .215 - . 4 8 1 - .184 pH 24 hr .120 - . 7 2 9 .812 -.258 PH 10 hr -.168 .416 .798 - . 3 9 3 .817 PH 5* hr pH 10 pH 24 ApH 1 ApH 2 ApH Tot r(.o5)(i7) = .456 f(.oi ) ( i 7 ) = .575 APH 1 = pH 5| hr - pH 10 hr ApH 2 = pH 10 hr - pH 24 hr APH Tot = pH 5ir hr - pH 24 hr A F 1 = F 12 hr -AF 2 = F 29 hr -AF Tot = F 29 hr -F 6 hr F 12 hr F 6 hr pH f a l l . Except f o r pH changes, the r values were not high. The f i n a l (24 hr) pH was s i g n i f i c a n t l y (p4 0 . 0 5 ) correlated only with the second pH change. Its cor-r e l a t i o n with shear was very low. The various pH changes were s i g n i f i c a n t l y correlated with each other and i n some cases with changes i n the F - r a t i o . A s i m i l a r pattern occurred with the F - r a t i o s . The 6 hour F - r a t i o was correlated with the F-ratios at other times and with changes i n F-ratios and pH, but not with shear force. The f i n a l F - r a t i o ( 2 9 hr) was very s i m i l a r to the 1 2 hour F - r a t i o . The a n t e r i o r shear press values were s i g n i f i c a n t l y (p^ 0 . 0 5 ) cor-related only with i n i t i a l pH, i n i t i a l pH f a l l , and to-t a l pH f a l l . Table XIV contains simple l i n e a r regression equations f o r shear force against a l l other variables further 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 . To test whether the poor f i t between f i n a l F - r a t i o and shear force was due 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 data was p l o t t e d . The low c o r r e l a t i o n proved to be from a scattering of points and not from the existence of any recognizable r e l a t i o n s h i p . Anterior shear was chosen f o r these c o r r e l a -tions because the possible shortening of the posterior portion during cooking would not be uniform. TABLE XIV 54 SIMPLE REGRESSION EQUATIONS EXPERIMENT 2 Dependent Variable Independent Variable Constant Slope R 2 . Shear pH 5 hr -88.99 18.34 - 0.308 Shear pH 10 hr 108.7 -15.96 0.181 Shear pH 24 hr 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§ hr 25.39 -15.28 0.139 Shear F 12 hr 28.29 -18.77 0.176 Shear F 29 hr 32.93 -22.42 0.086 Shear A F 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 XIII I f the assumption of Takahashi et a l . (196?) that the su s c e p t a b i l i t y of muscle to fragmentation 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 . Therefore, i r r a d i a t e d and control mus-cles were pooled, increasing the sample size and theo-r e t i c a l l y the range, and correlations and regressions of f i n a l F - r a t i o , and anterior and posterior shear force were calculated, Table XV. There were s i g n i f i c a n t correlations between posterior shear force and both the anterior shear force and the F - r a t i o . However, the predictive value of the f i n a l F - r a t i o f o r poste r i o r shear was low. The several researchers who have demonstrated that i r r a d i a t i o n produced a softer texture invariably i r r a d i a t e d the meat a f t e r isometric tension had sub-sided. The only work examining e f f e c t s of pre-rigor i r r a d i a t i o n was conducted by de Fremery and Pool (i960) and showed that s t e r i l i z i n g doses of i r r a d i a t i o n i n -creased toughness. Therefore, Experiment 3 was designed to examine the e f f e c t of time of a p p l i c a t i o n of pasteur-i z i n g doses of i r r a d i a t i o n on ultimate pH, F - r a t i o , and tenderness. Pasteurization doses of 100,000 and 300,000 rads were administered at 2, 5 i and 12 hours post-mortem. Table I I I (p. 35) summarizes the procedure. TABLE XV 56 SIMPLE CORRELATION AND REGRESSION COEFFICIENTS OF POOLED ANTERIOR AND POSTERIOR SHEAR PRESS VALUES AND F-RATIOS. EXPERIMENT 2 F - r a t i o Shear Press Anterior Posterior Posterior Shear -0.452 0.798 1.000 Anterior Shear -0.272 1.000 F - r a t i o 1.000 r ( . 0 5)(35) H.Ol)(35) = .325 = .418 Dependent Variable Independent Variable Constant Slope R 2 Anterior Shear Post e r i o r Shear 2.37 0.69 0.637 Anterior Shear F- r a t i o 30.58 -17.24 0.0?4 Posterior Shear F- r a t i o 45.88 -33.07 0.204 To examine the changes i n shear strength with l o c a t i o n , 5 s t r i p s of tissue were cut from each muscle and a t o t a l of 9 shear readings were obtained according to the pattern shown i n Figure 3» This procedure mini-mized v a r i a t i o n from nonparallel f i b e r s and allowed comparisons between d i f f e r e n t areas of the muscle. The r e s u l t s of the paired comparison tests, Table XVI, indicated that none of the treatments pro-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 r e s u l t was consistent with the findings of e a r l i e r experiments The F-ratios of samples treated pre-rigor (2 hours) at either dose showed that 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 unirradiated. The 12 hour-300,000 rad treatment also decreased the F- r a t i o s i g n i f i c a n t l y (p_r 0.01) Two other samples (100,000 rad -12 hours and 300,000 rad - 5 hours) approached significance at the 5% l e v e l . 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 controls i n d i c a t i n g that l a r g e r samples or 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 difference f o r each treatment. Average shear values were higher f o r a l l i r -radiated 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 SHEAR PRESS. EXPERIMENT 3 Test Dose Time Means8- T Value b T Prob (rad) (hr) I r r Cont Shear 100,000 2 14.75 10.56 2.174 0.080 Press 5 13.74 11.08 3.144 0.026* 12 11.68 10.02 1.665 0.155 300,000 2 13.78 11.04 2.165 0.081 5 13.47 10.15 2.634 0.046* 12 12.84 10.98 1.746 0.139 pH 100,000 2 5.72 5.70 1.328 0.241 5 5.72 5.74 -0 .775 0.478 12 5.73 5.76 -0 .920 0.403 300,000 2 5.6o 5.62 -0 .713 0.512 5 5.70 5.71 -0 .567 0.598 12 5.65 5.62 0.813 0.457 F 100,000 2 .622 .747 -4 .220 0.009** 5 .670 .754 -1 .813 0.128 12 .708 .760 -2 .289 0.069 300,000 2 .610 .757 -4 .766 0.006** 5 .596 .716 -2 .353 0.064 12 .662 .784 -5 .206 0.004** mean of 6 values b * p -? 0.05 ** p 0.01 59 An analysis of variance and Duncan's New Multi-ple-range Test were conducted on the data from d i f f e r e n t locations of the 36 control muscles, Table XVII. The major conclusion was that samples from the 3 posterior locations were l e s s tender than the others. The v a r i a t i o n i n the orientation of f i b e r s to the shearing crosshead had been eliminated i n t h i s experiment. Thus the greater toughness of the posterior portion could have been caused by shortening during cooking, differences i n connective tissue, or v a r i a t i o n i n the strength of the my o f i b r i l i t s e l f . This f i n d i n g explains the difference observed between an t e r i o r and posterior portions i n Experiment 2 and at l e a s t some of the increase between the 2 hour an t e r i o r shear and the 4 hour posterior shear of Experi-ment 1 . Correlations among f i n a l pH, f i n a l F - r a t i o , average shear value and shear value at l o c a t i o n I (near the sample taken f o r the F-ratio) were calculated f o r control muscle data and i r r a d i a t e d muscle data singly and i n combination, Table XVIII. For the control and i r r a d i a t e d muscle data separately, the average shear value and shear value at lo c a t i o n I were s i g n i f i c a n t l y (p* 0.01) correlated. Correlation of average shear value with the f i n a l F-r a t i o or the f i n a l pH was very low.' The combined data TABLE XVII ANALYSIS OP SHEAR LOCATIONS. EXPERIMENT 3 60 A n a l y s i s of V a r i a n c e Source df SS MS F L o c a t i o n 8 3163-5 395.43 21.40** Sample E r r o r 3_5 5820.2 18 .48 T o t a l 323 8983.7 Duncan's m u l t i p l e range t e s t 99$ l e v e l L o c a t i o n s : a C B A D E F I G H 6.68 8.01 8.18 8.64 9.24 10.10 14.49 1 4 . 8 3 1 5 . 1 8 t—: • • ••" I • 1 I • 1 Averages: n = 36 ** p ^ 0.01 a L o c a t i o n s A through I are i l l u s t r a t e d i n F i g u r e 3 . TABLE XVIII 61 CORRELATION COEFFICIENTS OF PH, F-RATIO, AVERAGE SHEAR PRESS, AND SHEAR PRESS OF LOCATION I. EXPERIMENT 3 a • Control Muscles F Location I Ave. Shear PH pH 0*094 Ave. Shear 0.030 Loc. I -0.072 F 1.000 -0.013 0.660 1.000 -0.145 1.000 1.000 Irradiated Muscles a F Location I Ave. Shear PH pH 0.190 Ave. Shear -0.319 Loc. I -0.113 F 1.000 0.140 0.674 1.000 -0.068 1.000 1.000 Pooled Irradiated and Control Muscles*3 F Location I Ave• Shear PH pH 0.133 Ave. Shear -0.359 Loc. I -0.263 F 1.000 0.054 0.706 1.000 -0.101 1.000 1.000 a 35 degrees of freedom r(.05) = .325 r ( . o i ) = .418 b 71 degrees of freedom r(.05) = .232 r(.01) = .302 62 showed a highly 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 value and l o c a t i o n I shear value (p_? 0 . 0 1 ) . In addition, the F-rat i o had a low but s i g n i f i c a n t c o r r e l a -t i o n with average shear (p_r 0.01) and a s i g n i f i c a n t cor-r e l a t i o n with 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 correlated to any of the other v a r i -ables.. Average shear values were plotted against the F-ratios 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 evident. Experiment 4 was designed to increase the num-ber of shear press comparisons from 6 (Experiment 3) to 10 i n each treatment. In addition, i t had been observed that raw i r r a d i a t e d muscles consistently appeared pinker than the unirradiated, while a f t e r cooking there was no v i s i b l e d i f f e r e n c e . Visual observations were made and spectral curves obtained on the 4 r e p l i c a t i o n s of each treatment to provide more precise information on t h i s phenomenon. Shear press data from Experiments 3 and 4 com-bined are presented i n Table XIX. With the exception of 100,000 rads at 12 hours a l l treatments produced a s i g -n i f i c a n t (p^ 0.05) toughening e f f e c t when judged against controls at 60 hours post-mortem. Regardless of dose, the increase i n toughness decreased as time of i r r a d i a -t i o n increased from 2 to 12 hours post-mortem. 63 TABLE XIX ANALYSIS OP SHEAR PRESS VALUES EXPERIMENT, 4 Dose Time Mean Shear a d = -J ~ Tough-T Value T b Prob (rad) (hr) I r r Cont ening 100,000 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 0.204 300,000 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* l b force mean of 10 samples b * p < 0.05 ** p _ 0.01 64 The biochemical events associated with r i g o r mortis and changing i n e x t e n s i b i l i t y i n poultry muscle should have been completed p r i o r to the 12 hour a p p l i -cation of i r r a d i a t i o n , De Fremery and Pool (i960) demonstrated a s i g n i f i c a n t toughening p e r s i s t i n g to 27 hours when muscles were i r r a d i a t e d with 2 Mrads at 0.5 hours post-slaughter, but the re s u l t s based on 6 muscle pairs were nonsignificant (despite a 48 per-cent increase in toughness) when i r r a d i a t e d at 25 hours. They concluded that i r r a d i a t i o n increased toughness by accelerating the onset of r i g o r mortis. The s i g n i f i c a n t toughening observed i n t h i s work when muscles were i r -radiated at 12 hours post-slaughter suggests that the textural changes observed were not related d i r e c t l y to onset of r i g o r mortis. In a l l these experiments i r r a d i a t i o n consist-ently produced tougher meat, even a f t e r aging, and p a r t i c u l a r l y when administered before r i g o r . Conditions were s i m i l a r to de Fremery and Pool (i960) who demon-strated p a r a l l e l r e s u l t s using s t e r i l i z i n g dosages. The workers who found meat softened by s t e r i l i z i n g t r e a t -ments of i r r a d i a t i o n apparently aged the meat, and then i r r a d i a t e d and stored the meat at warm temperatures. An explanation 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 require more knowledge of the normal mecha-65 nism of resolution of r i g o r . The dependence of the i n -crease in toughening on the time of ap p l i c a t i o n of i r -r a d i a t i o n suggests the involvement of a c t i n and myosin. Because the pH decline appeared to be unaffected by the i r r a d i a t i o n an acceleration of the normal r i g o r mortis reactions may not have been involved. One possible mechanism would be an increase i n the number of cross-bridges between a c t i n and myosin. However, t h i s does not explain the irradiation-induced resistance to myo-f i b r i l l a r fragmentation that depends more on the Z l i n e and I band junction than actomyosin bonding. Fukazawa et a l . (1969) presented evidence that the sarcoplasmic proteins, 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 cycle, may play a role i n the fragmentation of the m y o f i b r i l s . I f these proteins are responsible f o r the Z l i n e and Z-I junction breakdown, r a d i a t i o n may i n t e r f e r e with t h e i r normal a c t i v i t y . The softening observed by many workers would have been from increased p r o t e o l y t i c a c t i v i t y at e l e -vated storage temperatures accelerating the breakdown of the sarcoplasmic reticulum and weakening the Z l i n e -I band junction. Drake et a l . (1957) and Schweigert (1959) have shown that s t e r i l i z i n g doses of i r r a d i a t i o n are not s u f f i c i e n t to cause a cessation of enzymatic a c t i v i t y . This p r o t e o l y t i c a c t i v i t y may override the 66 i r r a d i a t i o n produced toughening. The consistent f a i l u r e to detect any s i g n i f -icant pH change from i r r a d i a t i o n i n spite of the con-s i s t e n t toughening does not support the concept of toughness being increased by an increase i n rate of onset of r i g o r mortis as implied by de Fremery and Pool ( i960). However, i n t h e i r work on i r r a d i a t i o n the on-set rate of r i g o r mortis was judged by t a c t i l e observa-t i o n with no supporting chemical determinations. Sub-sequently, Busch et a l . (1967) and Smith et a l . (1969) were unable to f i n d high correlations between shear resistance and e i t h e r pH decline or 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 f r a g -mentation but the r e s u l t s were not s i g n i f i c a n t . A l a r g e r sampling of f i b r i l s may have provided s i g n i f i c a n t d i f f e r e n c e s . Sayre (1970) has shown that the F - r a t i o responded to changes i n tenderness within a muscle but was not a good predictor of tenderness, and these re-s u l t s support his conclusion. He adds that while me-chanical breaking of the myof i b r i l s i s l i k e l y a mani-f e s t a t i o n of the s t r u c t u r a l weakening taking place during tenderization, either l o c a l i z e d areas of weakening or widely 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-scopic increase i n tenderness not detectable by micro-scopic methods. One factor that may account f o r some of these Inconclusive correlations i s shortening. Except f o r Ex-periment 2 when excision was at 5 hours, a l l muscles were excised pre-rigor~and kept unrestrained. Marsh and Leet (1966) showed that shortening was related to tenderness and to pH and temperature. The pH of the mus cle when i t was cooled had an important e f f e c t on short-ening. More precise temperature control between the slaughter house and laboratory or mechanical r e s t r a i n t of the muscles a f t e r excision might have produced higher correlations between some of the v a r i a b l e s . The pooled data (Experiments 3 and 4) con-firmed the existence of higher shear values i n the 3 p o s t e r i o r l o cations of the muscle as shown in Experi-ment 3 , Table XX. Visual observations of 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 permitted the author to i d e n t i f y the i r r a d i a t e d muscle i n 21 of 24 p a i r s . The 300,000 rad dose general-l y produced more noticeable coloration than 100,000 rads the three p a i r s where the i r r a d i a t e d samples could not be distinguished had a l l been given 100,000 rads. None of the cooked muscle pa i r s could be d i f f e r e n t i a t e d by v i s u a l inspection. TABLE XX ANALYSIS OF SHEAR LOCATIONS. EXPERIMENT 4 68 Analysis of Variance Source df SS ' MS Location 8 495^ 619.28 32*83** Sampling Error 531 10017 18.86 Total 539 14971 Duncan's multiple range test 99# l e v e l a Locations: C B A D E F I G H 6.81 7.^6 8.13 8.81 9.13 10.44 14.19 14.41 15.02 1 : 1 v 1 1 1 Averages: n = 60 ** p 4 0.01 a Locations A through I are i l l u s t r a t e d i n Figure 3 . 69 The polyethylene 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 provide an aerobic environment, but were intended to control moisture loss. only. Both are considered to be aerobic (oxygen permeable) fi l m s , but the exact oxygen tension was not determined. These observations agree with Coleby et a l . (i960 a) and MacLeod et aT. (1969) that raw meat would pro-duce a red color under aerobic storage, although not to the i n t e n s i t y of anaerobically stored meats. Coleby et a l . (i960 a) reported that the pinkish color appeared at 0.125 Mrads and increased with dose. A consumer panel, hoxfever, r a r e l y commented on the color, i n d i c a t i n g the change was not objectionable. The spectral curves of raw and cooked, and i r -radiated and unirradiated meats were obtained. The 4 curves from a sample i r r a d i a t e d 2 hours post-mortem with 300,000 rads are given on Figures 5 and 6 . The unirradiated raw -chicken had minimum re-flectance at klk and 5^8 nm and maximum reflectance at 504 and 630 nm, suggesting that myoglobin predominated. The appearance of a shoulder or occasionally a low peak at 571 nm and a low shoulder between 530 and 5^0 nm were t y p i c a l responses to i r r a d i a t i o n . They were consistent-l y present i n muscles given 300,000 rads, but were s l i g h t Figure 5. Reflectance Spectra of raw chicken (P. minor) Figure 6. Reflectance Spectra of cooked chicken (P. minor) 72 or non-existent at 100,000 rads. The shoulders at 530 to 5 -^0 and 571 nm were probably due to the oxymyoglobin-l i k e compound discussed by Tappel (1956) and Brown and Akoyunoglow (1964)-. The x, y, and z chromaticity coordinates and luminance (Y) were computed and the dominant wavelength and purity of the raw meat were obtained from a chart (Hardy, 1936) • Average values and the conclusions of the paired t - t e s t are given i n Table XXI. The control 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 r e s p e c t i v e l y . The luminance or brightness of the color was not s i g n i f i c a n t l y affected by the treatments. Luminance readings e s p e c i a l l y were affected by a surface shape fact o r due to d i f f i c u l t i e s i n obtaining a f l a t surface from the p l i a b l e muscle. A s h i f t i n the i r r a d i a t e d mus-cles to a higher x and lower y occurred, while only 1 difference was s i g n i f i c a n t among the 100,000 rad muscles, 5 of the 6 were s i g n i f i c a n t at 300,000 rads. This i s further r e f e l c t e d i n the s i g n i f i c a n t increase i n the dominant wavelength to a more reddish color at a l l 300,000 rad treatments. Similar trends appeared at 100,000 rads but the changes were smaller and with the small number of TABLE XXI 73 SUMMARY OF COLOR ANALYSIS PAIRED T-TESTS Treatment x y z Y Domn. Purity ; ; ; Way.  100,000 rads 2 hr I r r Cont T Prob .368 .364 ns .348 .354 ns .284 .281 ns 21.82 23.56 ns 586 582 ns 23.8 25.0 ns 5 hr I r r Cont T Prob a .366 .366 ns .352 .354 .019 -.282 .280 ns 22.95 23.50 ns 584 583 ns 24.5 25.2 ns 12 hr I r r Cont T Prob a .371 .368 ns .352 .353 ns .277 .279 ns 20 .82 23.58 hs 585 584 ns 25.8 25.2 ns 300,000 rads I r r 2 hr Cont T Prob .380 .365 .014 .346 .352 .041 .274 .284 ns 20.22 21.14 hs 589 584 .018 26.8 23.8 ns 5 hr I r r Cont T Prob .375 .368 ns .352 .359 .012 .273 .273 ns 22.82 23.29 ns 586 582 .019 27.0 26.8 ns 12 hr I r r Cont a T Prob .378 .369 .036 .349 .354 .035 .273 .278 ns.' 19.57 20.72 ns 588 584 .045 27.0 25.5 ns 3 degrees of freedom 74 samples none of the differences 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 did not a f f e c t the change of the dominant wavelength. Spectral curves of the white, cooked meat showed only remnants of the peaks at 4 l 6 , 548, and 571 nm c h a r a c t e r i s t i c of raw meat. The i r r a d i a t e d and control muscles showed i d e n t i c a l curves except f o r reflectance i n t e n s i t y which was probably due to the surface of the sample rather than any color d i f f e r e n c e . There was no color difference v i s u a l l y detectable. The reflectance peaks of the cooked control mus-cle were s i m i l a r to those reported by Tappel (1957), with low peaks at 412 and 535 nm. He found i r r a d i a t i o n of cooked meats produced two new peaks at 540 and 566 nm with a l o s s of one peak at 545 nm. These r e s u l t s indicate cooking a f t e r i r r a d i a t i o n did not produce any d i f f e r e n t peaks than did cooking unirradiated meat. The oxymyo-gl o b i n - l i k e form present i n the i r r a d i a t e d raw meat pro-ducing the pink color was apparently destroyed by cooking. Whether the meat would produce the pink denatured globin hemochrome (Tappel, 1957) upon r e i r r a d i a t i o n was not de-termined. 75 SUMMARY Tenderness and color changes of chicken breast muscles (Pectoralis major and P e c t o r a l i s minor) i n re-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 studied by measuring shear resistance, pH, m y o f i b r i l l a r fragmenta-t i o n and spectrophotometry. 1. I r r a d i a t i o n doses from 30,000 to 300,000 rads increased the shear resistance of subsequently cooked muscles. This increase i n toughness was not re-solved by aging f o r 60 hours. The e a r l i e r the a p p l i c a -t i o n of i r r a d i a t i o n , the greater the toughening. I r -rad 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 obtained s t i l l decreased tenderness. 2. The rate of pH f a l l and f i n a l pH i n P. minor were not affected by the i r r a d i a t i o n treatments. 3. Shear force i n unirradiated muscles was not correlated with pH f a l l or f i n a l pH. 4. The fragmentation of myofi b r i l s decreased with i r r a d i a t i o n within a chicken, r e f l e c t i n g induced toughening. However, neither the rate of change nor the absolute amount of m y o f i b r i l l a r fragmentation was capa-ble of accurately pr e d i c t i n g shear force. 5. Pasteurizing i r r a d i a t i o n produced a pink color i n a e r o b i c a l l y stored muscle, p a r t i c u l a r l y 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. The dominant wave-lengths were sh i f t e d from 5 8 4 to 5 8 8 nm with 3 0 0 , 0 0 0 rads and from 5 8 3 to 5 8 5 nm with 1 0 0 , 0 0 0 rads. There was no color difference between i r r a d i a t e d or control muscles a f t e r cooking. 6. The posterior portion of P» major was tougher than the a n t e r i o r p o r t i o n . 77 LIST OF REFERENCES Bailey, A.J., and D. N. Rhodes. 1964. 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