‘—‘.‘ s‘ ’—M.~A4 4.4;4 STABILITY OF BROILER PIECES DURING FROZEN STORAGE Thesis for the Degree of M. S. MICHIGAN STATE UNIVERSITY PANTIPAR P. JANTAWAT 1976 ail-[BRARY k: EmichiganSm-t“ Univczsit‘y . 1fFCJ/I'fl2565 72M.“ ‘Er—x /3 . _ V ,W [J /C¢/C'J 0/; ABSTRACT STABILITY OF BROILER PIECES DURING FROZEN STORAGE BY Pantipar P. Jantawat Raw and precooked chicken pieces with and without antioxidant treatment (combination of butylated hydroxy anisole, propyl gallate, and citric acid in propylene glycol) were frozen by air blast or in a C02 tunnel, vacuum packaged, and stored at -18°C. Samples were evaluated for rancid off-flavor (sensory evaluation), lipid oxidation (2-thiobarbituric acid test, peroxide oxygen, and titratable acidity of extract), desiccation (moisture content), and total lipid periodically from 0 to 6 months of storage. Light meat of every treatment gave significantly lower TBA numbers than dark meat of corresponding treat- ment. Precooked meat developed significantly higher TBA numbers than those of raw meat. The antioxidant treat- ment of precooked meat showed a significant advantage for the prevention of lipid oxidation, while that of raw meat showed little difference until late in the storage Pantipar P. Jantawat period. Air blast freezing showed a significant advantage over liquid CO2 freezing under conditions used in this experiment. Panel scores of chicken pieces during storage periods showed little difference between light and dark meat, cooked and raw meat, and between control and anti- oxidant treated products. However, as storage time increased, significant differences were recorded between cooked and raw products and between antioxidant treated and control chicken pieces. No significant differences were found with respect to the two types of meat (light and dark) and freezing methods. Little peroxide oxygen was formed in raw meat, however, precooked meat exhibited a significant peroxide development during six-month storage. No significant difference was detected between light and dark meat. The antioxidant treatment resulted in a significantly lower peroxide oxygen development than found in untreated chicken. Total titratable acid of extracts from both light and dark raw meat increased substantially more than that from precooked meat at the end of 6 months of storage. Little difference was detected in the concen- tration of titratable acid from chicken meat between the two freezing methods. Pantipar P. Jantawat Cooking chicken pieces resulted in a significantly lower moisture and higher total lipid content. Treating the meat with an antioxidant solution in corn oil sig- nificantly decreased the moisture and increased the total lipid content of the precooked meat pieces. Increase in storage time also significantly decreased moisture content and thus increased total lipid content. There were no significant differences in moisture and total lipid contents of meat frozen by the two methods. Total lipid content of dark meat was significantly higher, while moisture content was lower, than for light meat. STABILITY OF BROILER PIECES DURING FROZEN STORAGE BY ‘. ,'\ \_ ,7 9 V f o “ 1 Pantipar P: Jantawat A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science and Human Nutrition 1976 TO My Parents, Col. and Mrs. P. Patanapan ii ACKNOWLEDGMENTS My very sincere appreciation and gratitude are expressed to my major professor, Dr. L. E. Dawson, Food Science and Human Nutrition Department, for his marvelous and never-ending kindness, guidance, patience, and encouragement. Special thanks are extended to the poultry group members for their help in processing of the chickens and for their regular service as panel members for the sensory evaluation test. I also would like to extend my appreciation to Drs. D. E. Ullrey and C. M. Stine for their serving as members of my committee. Finally, to my husband, Somjate, goes indescrib- able gratitude for his love, understanding, support, and sacrifices. iii TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . LITERATURE REVIEW' . . . . . . . . . Oxidative Rancidity. . . Autoxidation . . . . . Muscle Lipid Oxidation. . Composition of Meat Lipid. Muscle Lipid Prooxidants . . . Development of Oxidative Rancidity in Cooked Meat. . . . . . . . . . Rancidity in Light and Dark Poultry Meat. Frozen Storage of Poultry Meats. . . . Prefreezing Hold Time . . . . . . . Quick vs. Slow Freezing . . . . . . Use of Antioxidants. . . . . . . Application of Antioxidant to Meat and Poultry Products . . . . . . . . EXPERIMENTAL PROCEDURE. . . . . . . . Source of Chicken . . Antioxidant Solution . Cooking Process . . . Antioxidant Application Air Blast Freezing . . Liquid C02 Freezing. . Packaging and Storage . Chemical Tests . . 2-Thiobarbituric Acid (TB Peroxide Value . . Total Titratable Acids. Total Lipid . . . . Moisture Content. . . Sensory Evaluation . . ) o o o o 0 we 0 o o o o o o o o o o o a. o o o o o o o (D U) o o o o o “-0 o o o o o o 0 Cooking and Reheating . . Flavor Evaluation Method . . . . . Panelists . . . . . . . . . . Statistical Analyses . . . . . . . iv 34 34 35 35 Page RESULTS AND DISCUSSION . . . . . . . . . . 36 2—Thiobarbituric Acid (TBA) Test. . . . . . 36 Sensory Evaluations . . . . . . . . . 47 Correlation of TBA Numbers and Sensory Scores . 52 Peroxide Value . . . . . . . . . . . 58 Titratable ACids O O O O O O O O O O O 63 Moisture Content . . . . . . . . . . . 66 Total Lipid O O O O O O O O O O I O 70 SUMMARY AND CONCLUSIONS. . . . . . . . . . 75 APPENDIX C O O O O O O O O O O O O O 78 LITERATURE CITED . . . . . . . . . . . . 80 LIST OF TABLES Table Page 1. Mean TBA numbers for cooked and raw chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -18°C . . . . . . . 37 2. Mean sensory score for raw and cooked chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -l8°C . . . . . . . 48 3. Correlation coefficient between TBA numbers and sensory scores . . . . . . . . 53 4. Mean Peroxide Value (PV) for raw and cooked chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -18°C . . . 59 5. Analyses of variance of the TBA numbers, sensory scores, and PV . . . . . . . 60 6. Mean percentage total titratable acids for raw and cooked chicken pieces frozen at different rates with and without antioxi- dant treatments and stored up to 6 months at .180C 0 o o o o o o o o o o o 64 7. Moisture content (%) for raw and cooked chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -l8°C . . . 67 8. Total lipid content (%) for raw and cooked chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -18°C . . . 71 9. Analyses of variance of titratable acid, moisture content, and total lipid . . . 72 vi Table Page A-l. Fried chicken rating score sheet . . . . 78 A-2. Mean % BHA for cooked and raw chicken pieces frozen at different rates and stored up to 6 months at -18°C . . . . 79 vii LIST OF FIGURES Figure Page 1. TBA numbers of raw and precooked chicken pieces frozen by air blast following antioxidant treatment . . . . . . . . 38 2. TBA numbers of raw and precooked chicken pieces frozen by liquid C02 following antioxidant treatment . . . . . . . . 39 3. Sensory evaluation of chicken pieces, raw and precooked, frozen by air blast, follow- ing antioxidant treatment. . . . . . . 49 4. Sensory evaluation of chicken pieces, raw and precooked, frozen by liquid C02 follow— ing antioxidant treatment. . . . . . . 50 5. Comparison of TBA numbers and sensory scores for raw light and dark chicken pieces sub- jected to various treatments and stored up to 6 months . . . . . . . . . . 55 6a. Comparison of TBA numbers and sensory scores for light and dark chicken pieces subjected to various treatments and stored up to 6 months . . . . . . . . . . . . . 56 6b. Comparison of TBA numbers and sensory scores for light and dark chicken pieces subjected to various treatments and stored up to 6 months . . . . . . . . . . . . . 57 viii INTRODUCTION The marketing of poultry as frozen products has many well-recognized advantages. Preservation by freezing has permitted the leveling out of seasonal fluctuations in production. It has provided a means of minimizing marketing losses due to microbial spoilage and has per- mitted overseas shipments for international trade. In addition, consumers should benefit since proper freezing and frozen storage should enhance the assurance of whole- someness and optimum appearance, eating quality, and convenience. However, complaints of storage flavor are some- times received in connection with poultry and poultry products that have been frozen and stored. The aroma and flavor of chickens and turkeys have been reported to become noticeably "stale" or, in severe cases, "rancid" after extended frozen storage. Many studies have been conducted to evaluate the development of these off- flavors. In almost every case, the oxidation of lipids was found to have a very important role, and the lipid fractions chiefly involved are not the triglycerides, but rather proteolipids and phospholipids. The trend towards precooking of poultry products in processing plants followed by storage as frozen ready- to-eat products has been increasing. As a result, there has been an increasing interest in their storage sta- bility. Rancidity, which is already considered to be one of the most serious limitations to adequate storage life of raw meat, has been found to create a more serious problem for cut-up-precooked-frozen meat. The character- istic flavor of freshly cooked meat is rapidly lost during short holding periods, even in frozen products. Oxidation of muscle lipids has been found to contribute markedly and very rapidly to undesirable flavor changes in cooked meat. The heat treatment itself has been found to be responsible for the initiation of the muscle oxidative changes. These flavor deteriorations account for a large part of economic losses due to lower quality products. Frozen fried chickens have been marketed to a limited extent because of these off-flavor problems. Besides oxidative rancidity, evaporation of moisture from the surface of frozen meat could add to the serious deterioration of the products by contributing to a bleached unattractive appearance and could adversely affect their eating qualities. The benefits of antioxidant treatments for frozen foods have long been recognized. The best known practices in processing, packaging, freezing, and storing poultry have been recognized and adopted by the industry to provide consumers with the most desirable quality of frozen foods. This experiment was conducted to provide information on the development and control of rancidity in raw and precooked chicken pieces during frozen storage. Studies included the use of an antioxidant treatment in combination with vacuum packing in materials with low gas and vapor permeability, low storage temper- ature, and different freezing methods in order to deter- mine the most effective way to minimize chemical or physical changes in the frozen products. Specific objectives were: (1) To determine the effect of rapid freezing (C02) of chicken pieces on lipid oxidation and flavor changes during frozen storage; (2) To ascertain the effect of antioxidant on lipid oxidation and flavor changes of raw and pre- cooked chicken pieces during freezing and frozen storage; (3) To evaluate the effect of vacuum packaging raw and pre-cooked chicken pieces using a film.with low moisture and gas permeability on lipid oxi- dation and flavor changes during freezing and frozen storage; (4) To evaluate interaction effects of freezing, antioxidant treatments, and packaging treatments related to oxidation and flavor of chicken pieces. LITERATURE REVIEW Oxidative Rancidity Labuza (1971) defined the word rancidity as the development of an off-flavor which made the food unacceptable on a consumer market level. He further clarified that "flavors“ here were those which developed as a result of the reaction between oxygen and unsatur- ated fatty acids, which may or may not be part of tri- glyceride or phospholipid. Dugan (1961) classified oxidative rancidity according to the differences in initiation processes, activation energies and rates of oxidation, into three types: autoxidation, lipoxidase- catalyzed oxidation, and hematin catalyzed oxidation. Autoxidation The mechanism of lipid autoxidation has been reviewed extensively by many authors, including: Lea (1939), Dugan (1961), Schultz et a1. (1962), Swern (1961), Labuza (1971), and Sherwin (1972). The generally recognized oxidative mechanisms involve three step series of reactions: initiation, propagation, and termination. According to Dugan (1961), the initiation step involves the formation of a free radical (R°) which can be formulated as: RH + O 4#% R° + OH° 2 The development of the free radical (R°) mechanism.was described in detail by Swern (1961). The propagation step involves the combination of the first free radical formed with molecular oxygen to form peroxy radical (ROO°). A new free radical is then formed as a result of the reaction between the peroxy radical and a nonoxidized unsaturated fatty acid molecule (RH). R° + 02 4% ROO° ROO° + RH ) ROOH + R° Watts (1962) stated that the hydroperoxides (ROOH) formed in this step did not themselves contribute to the rancid odor, but they were unstable and broke down to a great variety of decomposition products, some of which contributed to rancidity. Formation of the nonfree radical products was considered to be the termination of the chain reaction. R° + R° ) RR R° + ROO° \V ROOR ROO° + ROO° ROOR + O \I 2 Muscle Lipid Oxidation Oxidation of muscle lipids has been the subject of numerous studies since 1946. Oxidation was found to contribute markedly to the undesirable flavor changes which occurred in stored meat, especially in the cooked products. This kind of oxidative reaction was designated as ”tissue rancidity“ by Younathan and Watts (1959). They reported that the site of oxidation was the protein bound phospholipid fraction not readily extractable with fat solvents. These protein bound lipids, as reported by Tappel (1953), autoxidized much more readily than the free glyceride fat. Chipault and Hawkin (1971) postu- lated that autoxidation of meat lipid occurred in two stages. The protein bound lipids autoxidized first without an induction period; their initial rate of autoxidation then decreased as time increased. After a period of lower oxygen absorption, the free glyceride fats began to autoxidize in the autocatalytic manner characteristic of autoxidation in isolated glyceride fat. Composition of Meat Lipid Meat lipids are classified according to their sites of distribution and composition into two major groups. Intramuscular lipid or depot fat is stored as large deposits in the adipose tissue. This fraction is composed mainly of the triglycerides (Love, 1972). Another group which, according to Watts (1961) and Younathan and Watts (1959, 1960), played a very important role in muscle oxidative rancidity was found intracellu- larly. These muscle tissue lipids are integral parts of such cellular structures as mitochondria and microsomes. They are spacially separated from the depot fat, highly unsaturated and many of them are combined with proteins. Tissue lipids have been reported to contain a significant portion of phospholipids. Because of their high content of unsaturated fatty acids, these phospho- lipids were found to be very susceptible to oxidative attack (Watts, 1954; Younathan & Watts, 1959; Love & Pearson, 1971). El Gharbawi and Dugan (1965) claimed that unsaturated fatty acids in phospholipids were autoxidized more readily than the fatty acids in neutral lipids. Certain fats, such as those of poultry and pork, are much more easily oxidized than those from other animals such as beef and lamb. These differences are largely attributed to the fatty acid compositions. Hilditch et a1. (1934) revealed that 65% of the fatty acids present in poultry meat were unsaturated. Many investigators have studied the composition of phospholipids from poultry fats and reported that the significant fatty acids of the phospholipids are pal- mitic, stearic, oleic, linoleic, and arachidonic acids. These fatty acids comprise 75% of the total fatty acids (Peng, 1965; Katz et al., 1966). Marion et a1. (1967) postulated that concentration and kind of fatty acids in phospholipids varied among different tissues. White meat, as studied and reported by Katz et a1. (1966) and Marion and Woodroof (1966), from chicken muscle contained lowest of the total lipids, while dark meat contained as much as two times that of the light meat. Further studies revealed that white meat contained almost equal amounts of neutral and phospholipids whereas 79% of neutral lipid and 21% of phospholipids were found in dark meat. Skin fat contained 98% of neutral lipids and only 2% of phospholipids. Muscle Lipid Prooxidants Many substances have been recognized as prooxi- dants for meat lipid oxidation. Watts and Peng (1947) postulated that heme compounds were responsible for tissue oxidation. Barron and Lyman (1938) reported that p-aminophenol, the chain reaction inhibitor, could be used as a hematin catalysis inhibitor in oxidation of linseed oil. Zipser and Watts (1961) found that the degree of flavor change was dependent upon character of lipid and quantity of heme pigments in the tissue. 10 Recent work by Froning and Johnson (1973) indicated that removal of hemoglobin from.mechanically deboned meat resulted in a decrease in the TBA number of the meat. Banks (1944) and Tappel (1953) proposed that preformed linoleate peroxide was necessary for hematin catalysis. Tappel (1962) suggested that hematin cataly— sis involved in the formation of lipid-peroxide hematin compound and its subsequent decomposition into free radicals could propagate a chain reaction oxidation. Younathan and Watts (1959) suggested ferric hemochromogen as the active catalyst for meat lipid oxidation. Tar- ladgis (1961) hypothesized the mechanism of heme catalyzed lipid oxidation. He postulated that iron in methemoglobin was a paramagnetic which could induce the formation of the first free radical of the chain reaction. Nonheme iron has also been reported to play a major role in accelerating oxidation of muscle lipids (Smith & Dunkley, 1962; Liu & Watts, 1970; Love, 1972). Smith and Dunkley (1962) reported that heavy metals (Co, Cu, Fe, Mn, Ni, etc.) generally increased the rate of oxidative deterioration of food lipids. The peroxi- dation on mitochondrial and microsomal fractions was easily induced by iron (Wills, 1966). According to Uri (1961) and Heaton and Uri (1961), metals that were oxi- dized by one electron transfer were the most active. 11 Other factors affecting lipid oxidation in meat were light, temperature and salts (Dugan, 1961). The accelerating effect of salt on rancidity in meat has also been reviewed by Watts (1954). Sherwin (1968) men— tioned other factors affecting lipid oxidation. These included enzymes, moisture, heat, light, other oxidized fats, acids, and anything that might inactivate antioxi- dants. Development of Oxidative Rancidity in CookedfiMeat Hanson et a1. (1959) designated flavor change in stored frozen fried chickens in a stepwise fashion as: loss of "freshly cooked" chicken flavor; then, develop- ment of "warmed over" flavor or slight staleness; and finally, the production of an objectionable "rancid“ flavor. Watts (1954) reported that cooked meat developed rancid flavor as a result of oxidative changes in muscle lipid during subsequent storage. Tims and Watts (1958) found that TBA number of cooked meat products surpaSsed the limit of acceptability within a few hours after cooking. Off-flavor, as stated by Hanson (1954), developed more rapidly in frozen cooked meats than in uncooked frozen products. Carlin et a1. (1959) demon- strated that after 15 weeks of storage at 0°F, untreated broilers were superior to precooked broilers in all palatability factors. Rancidity development was also 12 found to be lower for fresh frozen turkey roasts than for roasts precooked before storage at 0°F (Cash & Carlin, 1968). Other research workers reported unani- mously that more lipid oxidation was involved in the development of stale reheated flavors in precooked meats (Lineweaver & Pippen, 1961; Chang et al., 1961; Cipra & Bowers, 1970; Jacobson & Koehler, 1970). Recent studies by Harris and Lindsay (1972); Sato et a1. (1973), and Yamauchi (1973) also showed similar results. Younathan and Watts (1960) hypothesized that a rapid oxidative reaction of lipids took place in cooked meat because of the intensive reaction, induced by heat. Metabolically active lipid components of lean muscle tissue oxidized very rapidly following heat denaturation of associated heme proteins and the hematin compounds were supposed to be the active catalyst in this oxi- dation. Watts (1962) further stated that heating of fresh lean animal muscle resulted in denaturation of protein and thus higher susceptibility of the lipid fraction to oxidative deterioration. According to Sato and Hegarty (1971), cooking or grinding caused disruption of muscle membranes. As a result, lipid components, being exposed to air and prooxidant compounds, could become involved more readily in oxidative rancidity. Yamauchi (1972) seemed to agree with Watts (1962). He suggested that the main reason why heat treatments 13 accelerated the development of rancidity in meat was that heat caused denaturation of proteins in the lipo- protein complex. Thus, unsaturated fatty acid fractions were released and became more susceptible to oxidation by heme pigment and other prooxidants. Rancidity in Light and Dark PouItrpreat Barron and Lyman (1938) mentioned that it was likely that heme catalyzed oxidation was more active in red muscle which contained a larger amount of myoglobin than did the white muscle. Subsequent work by Keskinel et a1. (1964) showed that the extent of lipid oxidation in raw ground dark turkey meat was greater than that which occurred in light meat. Marion and Forsythe (1964) found that red muscle from turkey stored at 40°C for 1 to 7 days gave a faster and higher final TBA than did white muscle. They then established that this difference resulted from the higher total lipid content of dark muscle. Thigh-drum portion of cooked chicken was also reported by Webb and Goodwin (1970) to develop a higher TBA number than breast meat after frozen storage. Jacobson and Koehler (1970), after studying the develOp- ment of rancidity during short time storage of light and dark cooked poultry meat, concluded that TBA numbers of the dark pigmented muscle of chicken and turkey were greater than those of the light colored muscle, both initially and after storage. 14 Frozen Storage of Poultry Meats Various kinds of deterioration have been reported to occur in meat during frozen storage. Among these, microstructural and chemical alterations are quite evi- dent (Cook & White, 1940; Love, 1966; Awad et al., 1968). Early studies on oxidation and CO2 refrigerated temper- ature by Lea (1934) indicated that poultry fat was com- paratively stable towards oxidation and that hydrolysis of the fat was negligible. Cook (1939a, 1939b) stated that physical changes, like surface desiccation, might cause deterioration of frozen poultry stored over a period of a few months. In a further study, Cook and White (1940) reported on rancidification and dehydration of poultry at 10°F under various degrees of package pro- tection, and established that rancidity of poultry fat could be restricted under storage conditions that pre- vent surface drying. They also pointed out that storage temperature and relative humidity were the most important factors determining oxidative deterioration of poultry fat. Other workers also observed the interrelationship between desiccation or "freezer burn" with oxidative rancidity and discoloration (Winkler, 1939; Ramsbottom, 1947). Steinberg et a1. (1949) ably separated the effect of desiccation from oxygen levels with and without a desiccant. Under such storage conditions, 15 they found that color was adversely affected by the desiccant, while palatability scores depended only on oxygen levels. Numerous studies on frozen meats and poultry have emphasized the importance of low storage temperatures in retarding rancidity (Cook & White, 1939, 1940; Rams- bottom, 1947; Hall et al., 1949; Klose et al., 1959). Koonz et a1. (1947) studied stability of eviscerated dressed poultry at different storage temperatures and reported that appreciable deterioration occurred after 9 months at 0°F, but only after progressively shorter periods as storage temperature was increased to 10, 20, and 28°F. Fryer and roaster chickens also showed con— siderable quality losses at 20°F in less than 3 months, while those stored at 0°F deteriorated to the same degree after 9 months storage (Wills et al., 1948). Klose et a1. (1959) recommended a storage temperature of 0°F or lower for frozen cut-up chickens. They reported that storage life of chicken pieces at 20°F ranged from less than one month to 6 months, at 10°F from 3 to 10 months, while at 0°F storage life was at least 6 months. Chang et al. (1961) studied the lipid oxidation in precooked beef preserved by refrigeration, freezing, and irradiation and concluded that oxidation was very much slower in a freezer than in a refrigerator. Jacobson and Koehler (1970) also reported small flavor losses during low tem- perature frozen storage of chicken meat. 16 Of equal importance to low storage temperature is the optimal packaging condition. In freezing preservation of fresh and cured meats, emphasis has been placed on using packages which are impermeable to oxygen and moisture. Watts (1954) stated that any type of packag- ing which reduces contact with oxygen retarded both ran- cidity and discoloration. Steinberg et a1. (1949) found that fresh meats, when packed in nitrogen, could be stored for a longer period of time, in frozen condition, than when packed without oxygen. Urbain and Ramsbottom (1948), Ramsbottom et a1. (1951), and Hiner et a1. (1951) stressed the desirability of vacuum packing for both cured and fresh frozen meat. Wills et a1. (1948) found that good packaging was significantly beneficial for products held at high storage temperatures (20°F). Hanson et a1. (1950) reported that types of packages were of greater importance than storage temperature in quality and flavor retention of frozen fried chickens. Stewart and Lowe (1948) after studying the effects of storing eviscerated frozen poultry reported that tight and moisture—vapor-proof packages were important in controlling visible dehydration for 6-9 months at 0°F. Gemmer (1972) concluded that good tight packing was of supreme importance during storage and distribution of frozen meats. This together with storage temperature were major factors in influencing the keeping quality, 17 particularly in delaying rancidity of the muscle lipid. Hanson et a1. (1959) found that frozen fried chickens packed in nitroqen were acceptable after storage periods of longer than nine months. Prefreezing Hold Time Another factor which may influence storage sta- bility of frozen meat and poultry products is prefreezing hold time. Dubois and Tressler (1943) demonstrated that holding ground pork at chilling temperature before freezing resulted in higher susceptibility of fat to oxidation during subsequent frozen storage. Stewart et a1. (1945) stated that aging before freezing had no effect on palatability scores of frozen storage meat. Wagoner et a1. (1947), on the contrary, reported that holding dressed poultry at chill room temperature for one day or longer before evisceration and freezing sig- nificantly decreased the storage stability. Pool et al. (1950) found that the holding of eviscerated turkey halves at 36°F for 30 hours prior to freezing did not result in detectable flavor differences upon subsequent storage. In contrast, Watts (1961) reported that the characteristic flavor of cooked poultry meat would be rapidly lost during a short holding period if meat were not frozen immediately after cooking. 18 Quick vs. Slow Freezing Freezing rate influences the extent of physical changes of muscle tissue. When muscle tissues are rapidly frozen, the ice crystals formed are small and located only in the muscle fibers. On the other hand, when meats are slowly frozen, ice crystals are larger in size and are usually formed outside of the muscle fibers. This type of freezing, according to some researchers, could bring about mechanical damage to the muscle fibers. Experimental studies, which agreed with the above hypothesis, were those of Koonz and Ramsbottom (1939), and Dubois et a1. (1942). They studied the effects of rapid blast freezing and conventional freezing of poultry meat, and reached the conclusion that only the extremely rapid freezing rate preserved integrity of the muscle fiber. Eklund et a1. (1957) found that turkey carcasses frozen at -29°C and -40°C in air blast were superior in appearance to those frozen at -l7.8°C. Van den Berg and Lentz (1964) also concluded that rapid freezing and thawing caused less loss in fluids and solids than slow freezing and thawing. Novak and Rao (1966) reported that liquid nitrogen spraying of poultry parts provided products of smoother texture and more normal flesh color than those of parts frozen in air blast. Crigler and Dawson (1968) studied cell disruption in chicken breast muscle at various freezing times, and 19 concluded that increased freezing time generally resulted in greater cell disruption. Berry and Cunningham (1970) determined the influence of different freezing methods on cooked chicken. They established that temperature and rate of freezing influenced quality of cooked chickens. Liquid nitrogen freezing produced a more desirable product than did blast freezing. Recent results on frozen turkey halves (Streeter & Spencer, 1973) also demonstrated the advantages of cryogenic over conventional freezing with respect to drip loss and cooking loss of poultry products. Controversies concerning the advantages of rapid freezing are evident. Stewart et a1. (1945) reported no differences in palatability scores of broilers, frozen at -67.8°C for 10 minutes and at -20.6°C for 5 hours. Marion and Stadelman (1958) presented data showing that method of freezing had no effect on percentage drip, percentage of total cooking loss, or tenderness of breast turkey muscle. Pickett et a1. (1967) found that turkeys frozen by liquid nitrogen dipping had comparable texture and color to those frozen in an air blast. very few studies have been conducted to evaluate the effect of freezing method on the development of rancid, off-flavor in animal tissue. Berry and Cunning- ham (1970) determined the TBA numbers of cooked chicken 20 frozen in a household freezer (-10°C), by blast freezing (-30°C), and liquid nitrogen freezing (-50°C). They concluded that liquid nitrogen freezing was the most advantageous, the blast freezing intermediate, and freezing in a household freezer the least desirable. Wyche et a1. (1972) indicated no advantages for quick freon freezing over the slower blast freezing with respect to oxidation. Use of Antioxidants Scotts (1965) classified antioxidants according to their mechanisms into three major groups. Free radical chain stoppers--butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), propyl gallate (PG), and tocopherol--represent this group. Free radical pro— duction preventors, including citric acid, various form of ascorbic acid, and EDTA are examples of the second group. And the third group, according to Scotts (1965), includes environmental factors, such as lowering of oxygen partial pressure in the package and holding the moisture content of dehydrated foods below critical levels. Primary antioxidants function in two different ways (Dugan, 1961). At high concentration, they will act as peroxide decomposers, while at low application level, they will react with the chain-carrying free radicals to form inert products as a terminal step in 21 the chain reaction mechanisms. For food preservative purposes, only very low concentration of antioxidants are permitted. Thus, the mechanisms of action of primary antioxidants in food are to function as free radical inhibitors only. Acidic compounds, such as citric and ascorbic acids, do not, themselves, react as primary antioxidants. Their role in delaying the onset of oxidative rancidity is to provide an enhancing effect when used in combination with phenolic antioxidants. The mechanism of action of these acidic compounds is the inactivation of the pro- oxidant metals which would otherwise accelerate oxidation. Morris et a1. (1950) stated that citric acid was more effective against iron and nickel while ascorbic acid and its derivatives were effective against copper but not iron. Application of Antioxidant to Meat and Poultry Products Watts (1961) stated that, to adequately protect meats, the antioxidant had to protect the fat when it was in contact with muscle juice. In addition, it had to be capable of being uniformly distributed in the meats. Various attempts have been made to effectively incorporate antioxidants into muscle tissues. Barnes et a1. (1943) showed that stability of rat body fat was reduced when fed a ration deficient in vitamin E 22 and other fat soluble antioxidants. Kummerow et al. (1948) reported a lowering of oxidative rancidity in turkey tissue fat when the birds were fed diets supple- mented with tocopherol concentrate. Hood et a1. (1950) fed broilers a diet containing 5% crude peanut oil, as a natural source of tocopherol. They found that the deposited fat was slightly less susceptible to oxidation than fat deposited by the control group. Mecchi et a1. (1956) successfully improved the tocopherol content, and thus stability, of chicken and turkey body fat by feeding the birds with diets containing added tocopherol. Webb et a1. (1972) investigated the effect of feeding a-tocopherol acetate, ethoxyquin and BHT on rancidity development in prefried, frozen broiler parts. As a result, they reached the conclusion that a diet contain- ing BHT did not significantly reduce rancidity develop- ment while diets containing 220 IU of vitamin E per kg. and those containing 0.04% ethoxyquin effectively held TBA numbers below those of the control group. Surface applications of antioxidants to meat pieces have been investigated by numerous researchers. Brady et a1. (1946) showed that the application of phenolic antioxidant solutions in vegetable oil resulted in a prolonged oxidative induction period in sliced bacon. Davis and Bywaters (1951) lengthened the frozen storage life of eviscerated broilers by dipping or 23 spraying them.with solutions of NDGA, ascorbic acid, and a vegetable gel in melted vegetable fat. Klose et a1. (1952) demonstrated a marked reduction in ran- cidity of skin and cut meat surface of turkey in frozen storage by applying an aqueous gelatin coating contain- ing either BHA, PG, or a combination of these two sub- stances. Chang et a1. (1961) successfully reduced oxi- dative rancidity and thus improved the odor of refrig- erated frozen beef by the application of an antioxidant combination of ascorbate and polyphosphate, either as a dip or as a cover solution. Thomson (1964) demon- strated that a phosphate mixture was effective in inhibiting oxidative deterioration during commercial production of frozen cooked chicken. Jenney and Hale (1971) added 0.5% BHT and 0.5% BHA into the batter for fried chicken. Subsequent panel evaluation of products after storage for 0-3 hours at 71°C indicated no improve- ment in the flavor. May and Farr (1972) patented an antioxidant dipping process for cooked poultry which included immediate immersion of poultry in a polyphos- phate solution during cooling to enhance the retention of moisture and to improve oxidative stability. Olson and Rust (1973) recently reported a marked reduction of rancidity in dry cured ham as a result of treating the meat with a salt mixture containing BHA, BHT, citric acid, and propylene glycol. 24 Another procedure for the application of an antioxidant to meat pieces is by invivo injection. Watts et a1. (1946) failed to improve the stability of pork fat by using toc0pherol injection. They explained that this failure was due to poor absorption of tocopherol into the pork muscle. VOth et a1. (1958) injected solutions of alpha tocopherol intravenously into chicken carcasses and found that neither the deposition of tocopherol nor the resistance of fat to oxidative ran- cidity were significantly improved. Pickett et a1. (1967), on the contrary, reported a dramatic increase in stability of male turkey carcasses upon injection of vitamin E at 15 to 16 weeks of age. Mickelberry (1970) studied the injection of solutions of BHA, BHT, PG, and mixture of these three substances at either 25 hours or 5 minutes prior to slaughter of male turkeys. None of the treatments resulted in marked increases in storage stability of the meats. Implantation has been successfully used as an antioxidant application technique by Osborn et a1. (1966). They reported a decrease in oxidative rancidity in turkey fat after the birds were implanted with estradiol-17- monopalmitate (EMP). Pickett et a1. (1967) also ably prolonged storage life of turkey carcasses by injecting 600 IU of vitamin E plus implantation of 40 mg of EMP at 15-16 weeks of age. However, subsequent results 25 (Pickett et al., 1968) revealed that implantation of turkey breeders with 200 IU of vitamin E three weeks before slaughter did not improve fat stability. The addition of an antioxidant into the cooking medium has been restricted due to the heat instability of some phenolic antioxidants such as PG and BHA. Sair and Hall (1951) found that heating of oils at cooking temperatures of 176-218°C resulted in rapid oxidation or destruction of NDGA, PG, and BHA. They suggested that the antioxidant be applied after cooking, for deep fat fried food products. Lineweaver et a1. (1952) added 0.005% of an antioxidant preparation, composed of 20% BHA, 6% PG, and 4% citric acid in 70% propylene glycol into cooking water for turkey. Subsequent storage as frozen creamed turkey showed a very good protective effect of the antioxidant over a storage period up to 12 months. Dawson et a1. (1975) reported that TBA numbers of ground turkey meat, stored at 3°C up to 10 days, were effectively controlled by the direct application of this same antioxidant preparation. EXPERIMENTAL PROCEDURE Source of Chicken Two hundred male broilers, seven weeks of age, obtained from a commercial source, were killed, scalded, defeathered, and cut into pieces identified as breasts, wings, and legs. After chilling in ice water for about 4 hours, breasts and legs were separated into two portions each; right and left for the former and thighs and drum- sticks for the latter. All pieces were then held at 4°C for further treatment. This procedure was replicated at a later date and all analyses include the two trials. Antioxidant Solution A 0.5% antioxidant solution was prepared by warming about 1800-1900 9 of corn oil on a hot plate to about 65°C with vigorous stirring. Ten 9 of Tenox II (a commercial antioxidant preparation, containing 20% butylated hydroxy anisole, 6% propyl gallate, and 4% citric acid in propylene glycol) was added slowly into the moving oil. Stirring was continued for an addi- tional 20 minutes after all the antioxidant was added. The resulting solution was cooled to room temperature and adjusted to 2000 g with corn oil. 26 27 Cooking Process One hundred pieces each of wings, breasts, thighs, and drumsticks were pressure fried in fresh corn oil, using a Mies Pressure Fryer Model C. Seven and one-half litres of corn oil were preheated in the fryer to 205°C. A11 pieces from four birds were added to the hot oil, piece by piece. After 1 to 2 minutes for prebrowning, they were cooked at 15 psi. (205°C) for 9 minutes. At the end of each cooking period, the pieces were removed and cooled on a wire rack at room temperature for 30 minutes. Antioxidant Application At the end of the 30-minute cooling period, all pieces were placed on absorbing paper towel for a few minutes to remove the excess oil. Sixteen pieces, four of each piece, were arranged in a stainless steel basket, immersed into the antioxidant solution for exactly 10 seconds, and drained for three minutes. All pieces were then transferred to a stainless steel tray and held at 4°C for 2 hours before freezing. Sixteen similar pieces were kept as nonantioxidant-treated controls and were frozen at the same time as their corresponding treated groups. The raw pieces were treated in the same manner as the precooked. They were removed from the cooler held at room temperature for 30 minutes and treated with the 28 antioxidant solution. Dipping time for the raw pieces was 30 seconds with a 3-minute draining period. Air Blast Freezing Both raw and precooked pieces were IQF frozen on stainless steel trays in one layer. Air blast freezing was accomplished at -18°C over night (about 10 hours). Liquid C02 Freezing Chicken pieces were arranged on aluminum trays, the trays were stacked in cardboard boxes and held at 4°C for 5-7 hours. They were transported to a commercial processing plant in Grand Rapids. The products were frozen by passing trays containing chicken pieces through a tunnel, on a continuous belt. Liquid CO2 was sprayed over the chicken surfaces throughout the tunnel. Freezing temperature was -34.4°C initially and —51.1°C at the end of a 6-minute freezing period. After freezing, the trays containing samples were packed along with dry ice in the boxes and transported to the Food Science laboratory. Packaging and Storage Light and dark meat pieces were packed separ- ately, 5 pieces per bag for sensory evaluation and 7 pieces per bag for chemical tests. Each lot was vacuum packed in #13 I.K.D. plastic bags. All bags of 29 one treatment, after having been sealed, were assembled in an Opaque plastic bag and stored in the freezer at -18°C. Chemical Tests One bag of light and one of dark meat from each treatment were sampled at the end of each storage inter- val. After partially thawing at room temperature for 15 minutes, skins and bones were removed. The meat was cut and ground twice in Hobart -K5 grinder, through 0.32 cm plate and mixed thoroughly. An aliquot of 45 g was selected for TBA analysis. The remaining meat was then vacuum sealed in two separate bags, one for total lipid and moisture determination, and another for analyses of peroxide and titratable acids. The ground samples, except those for TBA tests, were kept in the freezer until evaluated. 2—Thiobarbituric Acid (TBA) Test Four 10 9 portions of the ground meat were homo- genized with 50 m1 of distilled water, at medium speed for 2 min., in Virtis homogenizer. The resulting mixture was then quantitatively transferred, with the aid of 47.5 ml distilled water, into 500 m1 distilling flask. Two and one-half ml of 4 N HCl was added to lower the pH to about 1.5. A few glass beads were added and the mixture sprayed with Dow Corning antifoam. After 30 thorough mixing, the flask was connected to the dis- tilling apparatus. The distilling unit was composed of a 30.5 cm long distilling column connected to the condensor with a bending shoulder, and a 50 ml graduated cylinder served as a receiver. Distillation was done at a rate in which 50 ml of the distillate was collected within 10-15 min., subsequent to boiling. Two aliquot portions of the distillate were pipetted and transferred to the reacting tubes. Accurately, 5 m1 of 0.02M Thiobarbituric acid in 95% redistilled glacial acetic acid were added and the tube then capped. After thoroughly mixing and heating in a boiling water bath for 35 min., they were cooled in cold water for 10 min. The absorbance was determined at 532 nm against a reagent blank in which 5 m1 of dis- tilled water was used in place of the distillate. The TBA number was calculated by multiplying the mean absorbance by 7.8, distillation constant, (Tar- 1adgis et al., 1960) and reported as mg TBA reactive substance per 1000 g of meat. Peroxide Value Modification of the method of Wheeler (1932) was used for peroxide determination. Fifty g of ground raw sample was added to 50 g of anhydrous sodium sulfate and 100 m1 of redistilled chloroform. The mixture was homogenized at medium speed 31 in a Virtis homogenizer for 30 seconds and filtered through sintered glass. The residue was blended with an additional 50 ml of chloroform and filtered. The chloroform extract was evaporated at 25°C in a rotary vacuum evaporator to about 90 ml, transferred to a 100 m1 volumetric flask and diluted to volume with redistilled chloroform. Extracted fat was determined by evaporating 5 m1 of the chloroform solution in a forced air oven at 95-100°C to constant weight (about 5-6 hrs.). An aliquot of 25 ml was pipetted and transferred to 200 ml glass-stoppered Erlenmayer flask. Glacial acetic acid (37.5 ml) and 5 drops of freshly prepared saturated potassium iodide were added and the flask was flushed quickly with nitrogen. After this mixture stood in the dark for 15 minutes, 50 ml water were added and the solution was immediately titrated with 0.001-0.002 N sodium thiosulfate. The peroxide value was calculated as milliequivalents per 1000 g fat after subtracting the blank value. ml of thiosulfate X normality X 1000 Perox1de Value = weight of extracted’fat Total Titratable Acids A 25 m1 aliquot of the chloroform extract was accurately transferred to a 200 ml Erlenmayer flask. Fifty ml of alcohol:benzene (1:1) was added. The 32 mixture was titrated with 0.02-0.1 N NaOH to a phenolph- thalein end point (Dyer & Morton, 1956). Percentage of titratable acids was calculated as linoleic acid. m1 NaOH X normality X 0.280 X 100 % ACld = weight of’extracted fat Total Lipid Total lipid was determined by a modification of the method of Folch et a1. (1957). Fifty g of raw sample were homogenized in a Virtis homogenizer at high speed for 2 minutes with 50 m1 chloroform, 100 ml methanol, and 2 m1 of dis- tilled water. Another 50 ml each of chloroform and distilled water were added respectively, with 30-second homogenization following each addition. The resulting mixture was then transferred to a centrifuge bottle and centrifuged at 2000 rpm for 10 minutes. After centrifugation, the supernatant liquid was transferred to a 500 ml separatory funnel. The residual meat was blended with another 50 m1 of chloroform and the resulting mixture filtered through Whatman filter paper #1 into the funnel. The homogeniz- ing bottle was rinsed with two additional 10 m1 portions of chloroform and the washing was combined with the filtrate in separating funnels. The chloroform layer was then separated into a 300 m1 round bottom flask and evaporated in a rotary 33 vacuum evaporator to the final volume of about 90 ml. The residual chloroform extract was then quantitatively transferred to 100 ml volumetric flask and diluted to volume with anhydrous chloroform. I Five m1 aliquots were pipetted into a previously dried and weighed beaker. The solution was dried in a conventional hot air oven at 95-100°C to constant weight. Percent total lipid was calculated as grams of extracted fat from 100 9 meat. For precooked meat, the sample used was 25 g with 25 ml chloroform and 5 ml distilled water. Further treatments were performed in a manner similar to those for raw meat except that all reagents used were reduced to half volume. Moisture Content Each ground sample was thawed in the bag at room temperature for 2 hours. The drip and meat were then mixed thoroughly in the bag with spatula. Three to five 9 of meat were accurately weighed into a weighed aluminum dish that had been previously dried at 105°C for 2 hours and cooled in a desiccator. The sample was dried in a forced air oven at 105°C overnight. After cooling for 30 minutes in the desiccator, the dried sample was weighed. Percent moisture content was calculated as g of weight lost after drying for each one hundred g of meat. 34 Sensory Evaluation Cooking and Reheating Raw samples were thawed in bags at room temper- ature for 3 hours. Dark and light meat of the same treatment were then fried together in fresh corn oil by using Mies Pressure Fryer at 205°C (15 psi) for 9 minutes. Precooked samples were thawed in bags at room temperature for 3 hours. The chicken pieces were then reheated at 205°C in a preheated convection oven for 15 minutes with aluminum foil cover for the first ten minutes and without cover for another five minutes. Reference samples consisted of fresh whole fryers which were obtained from a commercial source on the testing date. The birds were cut into pieces and fried in the same manner as raw samples. Flavor Evaluation Method A rank order test was used for sensory evaluation in this experiment. The descriptive types of fresh vs. off-flavors were recorded on the scoring sheet. Repre- sentative numerical numbers varied from 9 to 1, with 9 representing absolutely fresh flavor, l for absolutely rancid, and 5 for neutrality (see Appendix A91). All samples were randomized when served. Each panelist was provided with 4 different treated samples and one reference sample per serving. 35 Panelists Panelists were randomly selected from staff and graduate students, Food Science and Human Nutrition department. Each tasting session included 20 panel members. Two sessions were performed at the end of each storage period, with an interval of 2 weeks between them. Statistical Analyses Statistical analyses were performed by using a Michigan State University computer program identified as Michigan State University Agricultural Experimental Station STAT Program AOV and run on a Control Data Cor- poration (CDC) 6500 computer. Correlation coefficients between TBA numbers and sensory scores were calculated by using a Wang 600 computer. RESULTS AND DISCUSSION Light and dark meat pieces from chicken fryers were processed (including cooking samples for each treat- ment), treated, packaged, and held frozen for periods up to 6 months. At each test period, samples were thawed at room temperature for 15 minutes to 3 hours and prepared for chemical and sensory evaluations. Each of these was designed to ascertain changes in lipid oxidation or the development of rancid or off-flavors. 2-Thiobarbituric Acid (TBA) Test The mean TBA numbers are reported in Table 1 and statistical analyses data are reported in Table 5. TBA numbers for chicken frozen in air at -18°C are graphi- cally shown in Figure 1, while those rapidly frozen in a C02 tunnel are shown in Figure 2. Light muscles (breast-wing combinations) developed lower TBA numbers than dark pigmented muscle (thigh-drum combinations) of corresponding treatment. This means that in all cases lipid oxidation was found to be greater in the dark than in the light muscles. For the raw group, the differences although small were observable, whereas 36 TABLE l.--Mean TBA numbers1 for cooked and raw chicken 37 pieces frozen at different rates with and without anti- oxidant treatments and stored up to 6 months at -18°C. Sample Treatments Storage Time (month) 0 2 4 6 Air blast freezing TBA numbers Light meat, raw control 0.22 0.21 0.24 0.50 antioxidant 0.14 0.14 0.12 0.19 Light meat, cooked control 0.68 0.92 1.23 2.08 antioxidant 0.61 0.44 0.44 0.60 Dark meat, raw control 0.25 0.50 0.46 0.72 antioxidant 0.14 0.20 0.16 0.21 Dark meat, cooked control 1.00 1.29 1.91 3.79 antioxidant 0.81 0.70 0.64 0.74 Liquid C02 freezing Light meat, raw control 0.22 0.30 0.24 0.59 antioxidant 0.15 0.15 0.13 0.19 Light meat, cooked control 0.78 1.11 1.40 2.53 antioxidant 0.60 0.67 0.63 0.79 Dark meat, raw control 0.31 0.48 0.50 0.72 antioxidant 0.14 0.20 0.15 0.20 Dark meat, cooked control 1.10 1.48 2.52 4.68 antioxidant 0.85 1.00 1.06 1.24 1 Mean of 2 replicates with 8 determinations, expressed as mg TBA reactive substance per 1000 9 meat. 38 4.00- PRECOOKED/ II 2.00- . ‘I‘ \ o‘ ‘0 \’b I“ as (53 ‘é§> .0 0° 00° E . :3 ‘ LOO g . T 2 d k I- 11“ *T-‘—;-.U;‘:‘r "0 ~ ‘ ~0— 59-9!- — -o-- “’ "' f O l L J Storage Time (month) Fig. 1. TBA numbers of raw and precooked chicken pieces frozen by air blast following antioxi- dant treatment. 39 4.50- / H MD. * k \ ’8‘) Q8? ZJDCT- a} \f '5 k0 L. (p? é§ Q) 0 .0 (J g . K ”‘ c: 0 Tenox 2' 9.0L ’ <1 I00 ,4———"' m '1’. T“ ‘0 F- ” ‘____0_.L910X_g"ol‘l-—a o l 1 j 0.80 RAW / 0.40 / F-===t222::3:=="‘° 0O 2 4 6 Storage Time (month) Fig. 2. TBA numbers of raw and precooked chicken pieces frozen by liquid C02 following antioxi- dant treatment. 40 for the precooked group, these differences became much more pronounced. The TBA numbers of dark meat control were initially higher and increased rapidly to a signifi- cantly higher extent than those of the light meat. The precooked antioxidant treated group also showed a similar trend, except that the differences were not as significant as those for the control group. Zipser and Watts (1961) and Webb and Goodwin (1970) reported similar results. One explanation for this phe- nomenon is that the rate of development of lipid oxi- dation is dependent on the heme pigments in the tissue. Dark meat contains more hematin pigments than light meat, thus, develOps a faster and higher tissue lipid oxidation than light meat. Another factor which contributes to this difference is that lipid content in dark meat is higher than that found in the light meat. As a result, there are more chances for dark meat than for light meat to be oxidized. A marked difference in TBA number between raw and precooked chicken meat is evident both initially and after subsequent storage (Figs. 1 and 2). For every treatment, the TBA number of raw sample was lower than that of the precooked meat. TBA numbers were signifi- cantly higher in precooked meat after 6-month storage, while those for the raw showed only slight changes over 41 the same storage period. These differences were much less pronounced for antioxidant-treated meat, but still evident. These results are in accord with Watts (1962), whose explanation was that the myoglobin pigments in raw meat, when subjected to heat in the presence of oxygen, could become denatured and changed to hematin compound. The ferric heme pigments formed then acted as active catalysts which could initiate the oxidation of lipids after normal cooking and during subsequent storage. This hypothesis was confirmed by Watts (1961) who reported that shrimp and crab, which do not contain hemoglobin or myoglobin, did not show any change in TBA number upon cooking, nor did cured meat in which the pigments were changed to nitric oxide hemochromogen. The ferric heme pigment was reported to be in a paramagnetic state with a strong magnetic field around itself. This excited state of Fe+++ could initiate the first free radical of the autoxidation chain reaction when it comes close to a system that has very labile hydrogen atoms like in the CH2 group between two double bond of polyunsaturated fatty acids (Tarladgis, 1961). Another reason for this result is that, in raw meat, lipid is bound to protein and exists in the form of a lipoprotein complex. High temperatures, as during cooking, could result in the breakdown of this complex. As a result, the lipid 42 fraction could be released and become more susceptible to oxidation attack. Refined corn oil was used as the carrier for the antioxidant in this experiment. Corn oil was used because it is an organoleptically accepted solvent, thus, won't create any off odors and flavors in the treated products. Another reason is that it is an accepted medium for precooked chicken pieces. From Figures 1 and 2 it is apparent that the antioxidant treatment had a marked observable effect on oxidative changes in both raw and precooked meat. During early storage periods, the TBA numbers of the antioxidant-treated and nontreated control were only slightly different, for raw-light meat from both freezing methods. As storage time increased to 6 months, this difference became more noticeable. Even more pronounced was the lower TBA numbers observed for stored dark-raw meat. The benefit of the antioxidant treatment was significant in stored precooked meat. As can be seen from Figures 1 and 2, the TBA numbers of both light and dark meats with antioxidant treatments were held constant when meat was frozen in air, and increased only slightly in meat which was frozen in liquid C02 throughout the storage period. However, TBA numbers for the nontreated control samples increased constantly during early storage periods and then very rapidly between 4 and 6 months. Statistical analyses 43 of individual group data also show significant numerical differences (Table 5). When considering the mean TBA numbers for raw meat, it is obvious that, even for the control group, the changes in TBA numbers are quite small (from about 0.2-0.3 mg malonaldehyde/lOOO 9 meat). Thus when compared with the results from the treated group, it is difficult to predict or conclude that these dif— ferences originated from the influence of the antioxidant treatment. Different values may occur as a result of oxidation, developed during subsequent thawing and handling of the meat rather than due to storage effect. Thus, at this low level of oxidation, the antioxidant does not clearly affect the development of compounds associated with rancidity. Increasing the storage time or changing the storage conditions will be the key to overcome this problem. As can be seen, the small development of oxidative compounds here is the result of very careful meat processing, the use of vacuum packaging with materials that are impermeable to moisture and gases, and a low storage temperature (-18°C). When optimum processing and packaging are not feasible, the benefit of antioxidant treatments might be more readily observed. However, in precooked meat, the effects of an antioxidant treatment are very obvious. With liquid CO 2 freezing, the TBA numbers for the stored sample increased 44 from about 0.6-0.9 to 0.8-1.3 whereas those for the untreated meat showed values as high as 2.5-4.7 mg malonaldehyde/lOOO 9 meat over the same storage period. When meat was frozen in air, TBA numbers actually declined in the antioxidant-treated group during 2-4 months of storage, then increased to about the initial value. This deviation might result from the variation in lipids from different birds, either in quantity or in composition or both. These unexplained reductions might have occurred in treated meat, or may have been due to sampling errors or involved in the complexities of the TBA test itself. On the other hand, different results were obtained from meat subjected to different freezing methods, and although the general level of fat deterioration was greater for the meat frozen in liquid C02, the relative beneficial effects of the antioxidant dip for meat prior to freezing by both methods are considered to be in good agreement. Thus, it is quite clear that, even when meat was packed, the oxygen was excluded; but when the bag was Opened and the meat contacted 02 followed by the thawing procedure, oxidative deterioration could rapidly occur. When samples are treated with an antioxidant before frozen storage, the treatment can affect oxidation, not 45 only during storage, but also during subsequent thawing, handling, and even testing. The TBA numbers obtained from all treated samples indicate that there were minimal, if any advantages, for quick cryogenic freezing over the slower air freezing method with respect to lipid oxidation. Instead, the meat frozen in air developed lower TBA numbers than did that frozen in liquid C02. These differences are obvious in precooked meat, especially the control group. The TBA numbers for products frozen by the air method are in the range of 0.7-1.0 to 2.0-3.8 while those frozen in liquid CO2 are as high as 0.8-1.1 to 2.5-4.7 mg MA/1000 9 meat. Differences in values for the antioxidant-treated meat are smaller than for controls but still show the same trend. The cryogenic frozen meat was expected to be superior in quality to the slower frozen meat with respect to lipid oxidation, since oxidation might also develop during the freezing Operation. However, under the conditions in this experiment, there was a dif- ference of 6-8 hours in the prefreezing holding period between the two freezing methods. The chicken pieces prepared for air blast freezing were held for 2 hours at 4°C before they were transferred into the freezer, while those for liquid CO2 freezing were held approxi- mately 5-7 hours at 4°C including an additional 3 hours 46 at higher than 4°C before they were frozen. This time elapsed did not significantly affect the TBA number of raw meat but it did affect the precooked meat. The oxidation of lipids in cooked meat had already been initiated by the cooking process itself. Thus, the refrigerated holding temperature with surface of the meat exposed to the air combined with the catalytic effect of metmyoglobin induced by the heat of cooking, could result in a rapid development of initiation and chain propagation step of lipid oxidation. Other factors which may or may not have contributed to these results is the procedure for liquid CO2 freezing employed in this experiment. Chicken pieces were frozen in 6 minutes at -34.4°C (initially) to -51°C (out of the tunnel). At this time-temperature combination, only the outer layer of the chicken pieces were completely frozen. Complete temperature equalization throughout the pieces might consequently have occurred after they were packed with dry ice and when they were transferred back to the laboratory freezer. When thoroughly chilled meat is frozen, the rate of freezing probably will not affect the quality of the product. Lipid oxidation may sig- nificantly occur during the freezing step only when meat is warmed up before freezing. In summary, cooking resulted in highly signifi- cant increases in TBA numbers over raw meat. Storage 47 resulted in highly significant increases in TBA numbers. Antioxidant treatments resulted in highly significant lowering of TBA numbers and freezing methods had little influence on such values. Sensory Evaluations Dark and light chicken pieces were evaluated by a panel of 40 persons using a score card designed to record flavor reactions. A sample score card is shown in the Appendix (Table A-l). The mean flavor scores for all chicken samples evaluated over a 6-month period are reported in Table 2 and statistical analyses of data in Table 5. Figures 3 and 4 show graphic presentation of the mean flavor scores for samples frozen in air and in liquid CO2 respectively. It is apparent that flavor scores were influenced most by two factors namely storage time and antioxidant treatment, both showing highly significant mean value differences. Precooked pieces also had highly signifi- cant lower flavor scores than those frozen and stored as raw products. Dark meat samples were initially rated higher than light meat in most instances. As storage time increased, the scores for dark precooked meat decreased and became significantly lower especially in case of the control meat. The flavor scores between light and dark raw meats varied irregularly throughout the storage 48 TABLE 2.--Mean sensory score1 for raw and cooked chicken pieces frozen at different rates with and without anti- oxidant treatments and stored up to 6 months at -18°C. Storage Time (month) Sample Treatments 0 2 4 6 Air blast freezing Flavor Score Light meat, raw control 6.7 5.8 5.8 5.7 antioxidant 6.5 6.6 6.2 6.5 Light meat, cooked control 6.6 6.4 5.3 5.0 antioxidant 7.1 6.9 6.7 6.3 Dark meat, raw control 7.4 6.6 5.6 6.3 antioxidant 7.4 6.7 6.3 6.9 Dark meat, cooked control 7.4 6.1 5.2 4.6 antioxidant 7.0 6.8 6.6 6.3 Liquid C02 freezing Light meat, raw control 6.6 6.3 6.0 6.2 antioxidant 6.9 7.0 6.9 6.3 Light meat, cooked control 6.2 5.9 5.1 4.7 antioxidant 6.6 6.4 6.3 6.4 Dark meat, raw control 7.0 6.2 6.4 5.8 antioxidant 6.6 6.9 6.6 6.5 Dark meat, cooked control 6.8 6.4 5.4 4.9 antioxidant 7.0 6.2 6.3 6.0 1 Rating score ranges from 9 to 1: 9 = absolutely fresh; 1 = absolutely rancid; and 5 = neutral. Sensory Score 49 PREQQOKEQ Tenox 2- light ~:‘::3: 2 :\-- - _ \” *2 s Tenox 2- dark Te Control-light 1 , r . . o 2 4 :3 raw and oxidant Storage Time (month) Fig. 3. Sensory evaluation of chicken pieces, precooked, frozen by air blast, following anti- treatment. 50 - light Control - / light Sensory Score 4) ' L n 1 o 2 4 6 Storage Time (month) Fig. 4. Sensory evaluation of chicken pieces, raw and precooked, frozen by liquid C02 following anti- oxidant treatment. 51 period. Statistical analyses revealed that no signifi- cant differences were found between the flavor scores of dark and light meat. However, what is evident here is that the panel members seem to prefer dark meat to light meat. Thus during early storage periods, when off— flavor could not be detected, dark meat was rated higher. As storage time increased, flavor scores of the dark precooked meat declined rapidly due to the loss of freshly cooked flavor followed by the development of stale or warmed over flavor, even if none of the rancid off-flavor could be detected. During early storage periods, the differences in palatability scores between raw and precooked stored meat were not obvious. With longer storage, the scores for precooked meat decreased markedly while those for raw meat fluctuated irregularly. The flavor of cooked stored meat changed rapidly and was easily detected by the panelists. Various terms such as "warmed over," "stale," or "rancid" were used to describe the character- istic of these changes. In general, differences in odor and flavor between raw and the precooked meat were first detected by the panel members after about 4 months of storage, and this difference became more apparent after 6 months of storage. Most panel members easily detected the beneficial effects of the antioxidant treatment in precooked meat 52 late in the storage period. This was expected. In most cases the flavor scores of precooked chicken which received the antioxidant treatment were higher than those for the nontreated controls. These differences are significant at the 1% level. The mean panel scores for raw meat did not show any clear—cut differences between these two treatments. No significant differences were found in panel scores of meat samples between the two freezing methods, both initially and after subsequent storage. As stated in the previous discussion, storage time has an obvious effect on the development of Off-flavors. When signifi— cant differences in flavor scores were found, the panelists were able to detect those differences only after products had been stored for at least 4 months and in many cases only after 6-month storage. Correlation of TBA Numbers and Sensory Scores Sensory evaluations, although not providing accurate quantitative measurements of oxidative ran- cidity, are still widely accepted due to their sensi- tivity and reliability. In order to determine if a relationship existed between the subjective and Objective results of this experiment, the mean sensory scores were correlated with the mean TBA numbers. The results are shown in Table 3. 53 TABLE 3.--Corre1ation coefficient between TBA numbers and sensory scores. Correlation Sample Treatments Coefficients Air blast freezing Light meat, raw control -0.44 antioxidant 0.54 Light meat, cooked control —0.89 antioxidant -0.10 Dark meat, raw control -0.54 antioxidant -0.28 Dark meat, cooked control -0.85 antioxidant 0.40 Liquid C02 freezing Light meat, raw control -0.24 antioxidant -0.9l Light meat, cooked control —0.91 antioxidant -0.32 Dark meat, raw control -0.95 antioxidant 0.35 Dark meat, cooked control -0.93 antioxidant -0.89 54 Correlation coefficients for raw meat varied irregularly between treatments (Table 3, Figure 5). The TBA numbers were found to be at variance with the sensory scores in some cases. Positive correlations were obtained for light-raw meat-antioxidant treated, and dark-anti- oxidant treated meat. Lower correlation coefficients were found for the light meat-control group, dark meat- control group, and dark meat-antioxidant treated group. The only two groups of raw meats that showed a good cor- relation between TBA number and sensory scores were: light-antioxidant treated-CO2 frozen and dark-control-CO2 frozen. However, in the precooked meat, good correlations were found between many treatments (Figures 6a and 6b). Here, the correlation coefficients are significantly high {-0.91 to -0.93) in case of light-control-liquid CO2 freezing and dark-control-liquid CO2 freezing. Good correlations were found in light-control-air freezing (—0.89), dark-control-air freezing {-0.85), and dark-treated-liquid CO2 freezing (-0.89). Few groups of antioxidant treated, precooked meat showed a poor relationship between these Objective values and sensory scores. Low correlations were, in general, found between those groups of chickens which developed small changes in TBA numbers during storage. With these low levels of oxidative off flavors, it is obvious that the panel TBA number 0.30 RAW - DARK- LIQUID Tenox 2 55 co, 5.0 -7.0 5.0 6.0 7.0 5.0 6.0 7.0 8.0 0-70 ‘ RAW- DARK- LIQUID co2 Control TBA 0.50- Sensory 0.3 ' .4 0.20)- RAw-LIGHT-AIR BLAST > c Tenox 2 TBA .l - O. . L 0,50L RAW- LIGHT-AIR BLAST Control Sensory 0.4’0b d TBA 0.30 . 0.20 L O 2 4 6 Storage Time (month) Fig. 5. Comparison of TBA numbers and sensory scores for raw light and dark chicken pieces subjected to various treatments and stored up to 6 months. Sensory Score 56 4.00 - 4.0 PRECOOKED- LlGHT- LIQ. (:02 FREEZING 3.00 . 993.1191 5.0 Sensory 2.00 TBA number 4.00 3.00 2.00 TBA number o 2 4 68'0 Storage Time (month) Fig. 6a. Comparison of TBA numbers and sensory scores for light and dark chicken pieces subjected to various treatments and stored up to 6 months. Sensory Score Sensory Score 57 0.80 - 4.0 PRECOOKED- LIGHT- I.I0. (:02 FREEZING h Tenox 2 8 0 0.70 " d 5.0 o .n o E U) 3 0 so . e o >~ c ’ Sensory ' 3 4 4* A m m 5 .— 0.50 " q 7'0 m 0.40 L ‘ 8.0 0.90 - 1 4.0 PRECOOKED- DARK- AIR BLAST FREEZING < Tenox 2 a, ‘- 0.8O —_ 5 o o 13 C) E (D :3 c 0.70 g <[ I» m 5 I- O.60 (O 0.50- I ‘ 8.0 0 2 4 6 Storage Time (month) Fig. 6b. Comparison of TBA numbers and sensory scores for light and dark chicken pieces subjected to various treatments and stored up to 6 months. 58 members, with little experience in determining off-odor and flavor, would undoubtedly have difficulty in identify- ing such small differences. Only when the off-flavor development was very pronounced, such as in the precooked control group, would TBA numbers and panel scores give highest confidence level for predicting actual rancidity development. Samples of precooked control chicken pieces (develOped a detectable flavor change and received con- sistent comments of staleness after 4 to 6 months storage. Comments on rancid off-flavors were also recorded for products during this period but only ran- domly. On the average, the sensory scores for this group of chicken pieces were within the range of 4-5 which indicates only slightly stale or warmed-over flavor. So, here, when TBA numbers reached as high as 4.5-4.6, such as in the dark control-precoOked meat, the panel members appeared inconsistent in reporting the rancid off-flavor development. Thus, under the testing methods used, the TBA number of about 4.0 mg MA/1000 9 meat are correlated with the sensory score of 4-5 which repre- sented the warmed-over flavor development. Peroxide Value The mean Peroxide value (PV) and appropriate analyses of variance of the data are shown in Tables 4 and 5 respectively. TABLE 4.--Mean Peroxide Value 59 1 (PV) for raw and cooked chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -18°C. Sample Treatments Storage Time (month) 0 2 4 6 Air blast freezing E! Light meat, raw control 0.47 0.36 1.55 3.01 antioxidant 1.01 0.79 1.55 1.65 Light meat, cooked control 1.10 8.13 14.24 21.55 antioxidant 0.64 1.60 4.15 3.41 Dark meat, raw control 1.45 0.75 1.65 2.81 antioxidant 0.96 1.00 2.05 2.41 Dark meat, cooked control 1.01 9.10 15.26 26.50 antioxidant 1.46 1.78 4.70 8.05 Liquid C02 freezing Light meat, raw control 0.46 1.06 2.25 1.96 antioxidant 0.55 0.66 1.05 1.55 Light meat, cooked control 1.00 8.13 17.16 26.91 antioxidant 0.91 2.58 4.58 12.03 Dark meat, raw control 0.57 0.88 0.67 2.46 antioxidant 1.00 1.61 0.65 2.67 Dark meat, cooked control 1.33 9.45 18.41 24.81 antioxidant 0.89 1.62 6.71 14.45 1Expressed as meq/lOOOg extracted fat. 60 TABLE 5.--Ana1yses of variance of the TBA numbers, sensory scores, and PV. Mean Squares Source of Variation TBA Sensory d'f' Number Score PV Cooking 1 15.2a 1.60a 805a Meat 1 1.85a 0.30 3.16 Antioxidant 1 6.57a 6.32a 274a Freezing 1 0.37b 0.09 12.2a Storage 3 1.68a 2.90a 213a Cooking meat 1 0.92a 0.06 1.85 Cooking antioxidant 1 2.58a 0.81a 249a Cooking freezing l 0.29b 0.37 23.5a Cooking storage 3 0.89a 0.37a 152a Meat antioxidant l 0.56a 0.10 1.10 Meat freezing l 0.03 0.05 0.87 Meat storage 3 0.16b 0.13 0.08 Antioxidant freezing l 0.02 0.003 0.01 Antioxidant storage 3 1.28a 0.86a 43.2a Freezing storage 3 0.04 0.14 5.64a Cooking meat antioxidant l 0.20 0.00 0.48 Cooking meat freezing l 0.04 0.45b 0.00 Cooking meat storage . 3 0.14b 0.02 0.69 Cooking antioxidant freezing 1 0.01 0.01 0.31 Cooking antioxidant storage 3 0.74a 0.32b 32.4a Cooking freezing storage 3 0.04 0.13 9.69a Meat antioxidant freezing l 0.00 0.02 0.00 Meat antioxidant storage 3 0.14b 0.82 1.42 Meat freezing storage 3 0.01 0.04 0.31 Antioxidant freezing storage 3 0.01 0.02 1.30 aSignificant at 99% level. bSignificant at 95% level. 61 The results obtained showed that little peroxide oxygen was formed in raw meat during the six-months storage period (1-3 meq/kg extracted fat) while those for precooked meat exhibited a significantly increased value (1-27 meq/kg extracted fat). These results are in agreement with those for TBA numbers. Between light and dark meat from both raw and precooked chickens, the peroxide values obtained were not as clear-cut. The statistical analyses of data did not show significant differences while those results for TBA numbers did indicate significant differences in this respect. In contrast with the TBA numbers, the differences in values between the two freezing methods is noticeable. What is evident here is that liquid CO2 freezing showed an advantage over the air freezing in some treatments, such as for control-raw-light and control—precooked-dark meat; but these advantages are not apparent in other treatments. Development of peroxides was reduced by the anti- oxidant treatment in all groups of chickens especially in the precooked group. These results agreed with the TBA numbers found. The general trend of increasing peroxide development with increasing storage times also agrees, in general, with the TBA numbers in the precooked meat. The increase of PV for raw meat as function of storage time, although somewhat irregular, indicates that the peroxide oxygen does increase. 62 A generally recognized limitation in using peroxide values as an objective method is due to the fact that it measures an intermediate reaction. Such values will relate to oxidative rancidity only as long as its develOping rate is higher than that of the decom- position to other rancid products. Besides, peroxides are transitory in nature, since they will break down easily in some stress conditions such as high cooking temperatures or in abrupt environmental temperature changes. The significance of PV in this experiment for precooked meats is somewhat doubtful for two reasons. First, during the cooking process, peroxide oxygen might be developed. At the same time, preformed peroxides could decompose. As a result, the peroxide obtained subsequent to cooking will be lower than the actual value found. In addition, the TBA numbers of products stored 4-6 months increased so rapidly that they may have already passed the induction period for the typical pattern of lipid oxidation into the rapid oxidation phase. Since Malonaldehyde, which is found to be the major TBA reactive substance, is the decomposition pro- duct of the preformed peroxides, it is very reasonable to postulate that as malonaldehyde increases the rate of peroxide decomposition should exceed their formation. Thus, during storage for 4-6 months, it might be possible for the peroxide oxygen to increase to maximum level and 63 then decrease with the increase in development of secondary oxidation products such as malonaldehyde. These possible chemical reactions will not exist in the raw chickens since there is a minimal accumulation of preformed peroxide oxygen and malonaldehyde. Titratable Acids Percentage of total titratable acids found in all meat samples are reported in Table 6. The analyses of variance of the data are reported in Table 9. Sherwin (1968) stated that hydrolytic rancidity occurs as a result of a splitting of the glyceride molecule at the ester linkage with the formation of fatty acids which contribute objectionable odor, flavor, and other characteristics. Olley and Lovern (1960) reported that hydrolysis of phosPholipids occurred during frozen storage of cod muscle with formation of free fatty acids. Results of this research agreed with those of Awad et a1. (1968) who also indicated a con- siderable decrease in phospholipid content with an increase in free fatty acid in bovine muscle, as storage time progressed. The results shown in Tables 6 and 9 indicate that titratable acid content of raw meat was higher than those for precooked meats. The titratable acid expressed as percentage of linoleic acid in the extracted fat gradually increased up to about 5-9% for raw meat and to 2-3% for precooked meat. Since TABLE 6.--Mean percentage total titratable acids1 64 for raw and cooked chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -18°C. Sample Treatments Storage Time (month) 0 2 4 6 Air blast freezing % Acid Light meat, raw control 1.78 4.68 7.91 9.36 antioxidant 1.54 3.18 5.58 5.62 Light meat, cooked control 0.95 1.85 2.90 3.06 antioxidant 0.75 1.38 1.99 3.06 Dark meat, raw control 1.60 2.84 3.97 5.22 antioxidant 1.56 0.98 4.14 4.76 Dark meat, cooked control 0.89 1.56 2.79 2.72 antioxidant 0.89 1.74 2.04 2.66 Liquid C02 freezing Light meat, raw control 1.81 3.99 6.47 8.17 antioxidant 1.69 3.66 5.68 6.61 Light meat, cooked control 0.88 1.65 2.54 3.57 antioxidant 0.84 1.44 2.02 2.42 Dark meat, raw control 1.54 2.87 4.43 5.54 antioxidant 1.46 3.02 4.73 4.83 Dark meat, cooked control 0.79 1.10 2.47 2.43 antioxidant 0.78 1.56 2.21 3.04 1 extracted fat basis. Calculated as percentage Linoleic acid on 65 this is an enzymatic reaction, enzymic activity in muscle tissue could become inactivated during the cooking process. As a result, hydrolysis of phospho- lipids during subsequent storage in the precooked meat was lower than that in the raw meat. The titratable acid content of light meat was obviously higher than that for dark meat. White meat from chicken contains less total lipid than dark meat. However, it contains almost equal amounts of phospholipids and neutral lipids. Dark meat contains about 79-80% neutral lipid and 20-21% phospholipid. Since hydrolysis of phospholipids is responsible for the formation of titratable acids, the considerably higher values in the light meat were expected. The antioxidant treatments were also found to have a significant affect on the development of acids. These effects are obvious in raw meat. These results are difficult to explain since the formation of acids during frozen storage originates from enzymatic hydrolysis rather than from autoxidation of the muscle lipid. How- ever, Sherwin (1968) explained that the method used for fatty acid determination here would show no distinction between the ”free fatty acids” formed through hydrolysis and those acids from such other sources as oxidation or acid-type metal chelators. Thus, it might be possible that not only the acids from hydrolysis but also those 66 from oxidation products contribute to the value of the total titratable acids. This would explain why the anti- oxidant treatment resulted in the lowering of acid for- mation. Significant differences in the development of acids were not found between the two freezing methods. This appears reasonable since the freezing methods used do not cause any loss in crude fat content of the meat pieces. As expected, the titratable acid content of chicken lipids increased as storage time increased. These results are significant in both control and anti- oxidant-treated raw meat groups. Cooked meats also showed an increase in acid but to a lesser degree than raw meat, over the same storage period. Moisture Content The moisture content of poultry meat is important from standpoints of meat acceptability and yield of saleable product. Moisture along with fat contributes to mouthful, tenderness, and juiciness of consumer products. Moisture levels were determined to correlate the effect of freezing method, packaging material, storage condition, and cooking on physical appearance and flavor deterioration of meat samples. Actual moisture levels of raw and cooked products, as percentage of total weights, are reported in Table 7. 67 TABLE 7.--MOisture content (%) for raw and cooked chicken pieces frozen at different rates with and without anti- oxidant treatments and stored up to 6 months at -18°C. Sample Treatments Storage Time (month) 0 2 4 6 Air blast freezing» % Moisture Light meat, raw control 75.85 75.70 75.59 75.08 antioxidant 75.14 75.04 74.86 74.20 Light meat, cooked control 57.02 57.00 56.67 56.65 antioxidant 54.03 53.84 52.55 53.48 Dark meat, raw control 75.70 75.65 75.39 75.54 antioxidant 75.09 74.64 74.40 75.01 Dark meat, cooked control 56.98 56.40 55.17 54.93 antioxidant 53.90 53.00 53.71 52.98 Liquid C02 freezing Light meat, raw control 76.25 75.01 75.84 76.71 antioxidant 75.65 75.54 74.84 74.88 Light meat, cooked control 57.40 56.99 56.77 56.58 antioxidant 54.10 53.65 52.44 52.73 Dark meat, raw control 75.15 75.03 74.95 76.09 antioxidant 75.31 74.87 74.77 74.96 Dark meat, cooked control 56.21 55.95 55.30 55.51 antioxidant 53.40 53.70 53.59 52.76 68 All raw meat sample contained approximately 75% moisture and cooked meat, 55%. This loss during cooking represents moisture evaporation at the high cooking temperature. No apparent differences are seen due to meat type, freezing rates, or storage time, with antioxidant-treated products showing lower moisture contents than controls presumably due to corn oil absorbed during antioxidant treatment. Table 9 reports analyses of variance for moisture content data. Highly significant lower moisture contents were found due to cooking vs raw, antioxidant treatment, storage, and with cooking-antioxidant interaction. All of these differences were expected. Moisture is lost during cooking and during treatments involved soaking chicken pieces in corn Oil solution containing the anti- oxidant. Thus, the increased Oil absorption resulted in appropriate lower percentage of water content and total product weight. Light and dark meat of both raw and precooked chickens showed small differences in moisture content. Light meat with a lower lipid content had a higher moisture content after freezing. This difference became more evident in precooked meat. However, these values were significantly different at low level. No significant difference was found between freezing methods, although losses during liquid CO 2 freezing were less than those during air freezing. 69 During air freezing, the uncovered surfaces of the chicken pieces were exposed to the moving air for 9-10 hours. Thus, moisture losses by this freezing method were expected to be higher than those by liquid CO2 freezing, in which the freezing time was only 6 minutes without high circulation in the freezing chamber. Significant differences in moisture content were found between samples treated with antioxidant and the controls. Corn oil was used as the antioxidant carrier. After immersion of chicken pieces in the antioxidant solution, precooked meat absorbed a considerable quantity of Oil, as shown in Table 9. As the total lipid content of the meat increased, moisture content thus, decreased. This is more evident in the precooked meat since it absorbed a higher quantity of antioxidant solution than did the raw meat samples. Chicken pieces stored for 6 months had less moisture than before storage. These losses indicated that some desiccation occurred during storage. When considering the type of packaging material used, the lower moisture levels were not expected. I.K.D. plastic is recognized as a satisfactory moisture and gas impermeable material, and samples stored in such packages were not expected to develop evidence of dehydration during prolonged storage. However, a 70 decrease in moisture content of the meat did occur, but no freezer burn was observed even after 6-month storage. Total Lipid Mean lipid concentrations of all meat samples expressed as grams of fat extracted per 100 g of meat on a wet basis are reported in Table 8 and their analyses of variance in Table 9. Total lipid composition of all meat samples was inversely related to moisture content. Raw meats, with higher moisture contents were significantly lower in lipid content than precooked meats. This was true for both light and dark meat of every treatment. Lipid con- tent of the thigh-drum combination was considerably higher than that of the breast-wing combination. The lipid value for dark raw muscle was about two times that of the light muscle. When meat was cooked, this magnitude became smaller. As shown in Table 8, the mean total lipid values of precooked dark meat were only about 50% higher than those for precooked light meat. During cook- ing, light meat, with more muscle surface exposed to the cooking medium, lost more moisture and absorbed a higher quantity of oil. The antioxidant-treated chicken pieces had a significantly greater increase in total lipid extracted by chloroform-methanol mixture. This result was expected in the precooked but not the raw meat caused by the use TABLE 8.--Tota1 lipid content (%) for raw and cooked 71 chicken pieces frozen at different rates with and without antioxidant treatments and stored up to 6 months at -18°C. Sample Treatments Storage Time (month) 0 2 4 6 Air blast freezing % Total Lipid Light meat, raw control 1.35 1.22 1.28 1.21 antioxidant 1.53 1.61 1.62 1.69 Light meat, cooked control 6.62 6.76 6.82 6.80 antioxidant 8.32 8.03 8.82 8.88 Dark meat, raw control 2.54 2.60 2.72 2.64 antioxidant 2.89 2.70 2.70 3.08 Dark meat, cooked control 9.86 9.52 10.72 10.05 antioxidant 12.01 11.99 13.02 12.61 Liquid C02 freezing Light meat, raw control 1.36 1.41 1.40 1.26 antioxidant 1.50 1.48 1.70 1.65 Light meat, cooked control 6.80 6.91 7.05 7.05 antioxidant 8.55 8.48 8.68 8.67 Dark meat, raw control 2.65 2.69 2.90 2.45 antioxidant 2.87 2.99 2.95 3.20 Dark meat, cooked control 9.53 9.00 10.15 9.45 antioxidant 12.00 12.53 12.83 12.20 TABLE 9.--Analyses of variance of titratable acid, moisture content, and total lipid. Source of Variation Mean Squares d f Titratable Total Moisture ' ' Acid Lipid Content Cooking 1 83.4a 850a 6675a Meat 1 8.283 90.9a 0.30b Antioxidant 1 3.673 24.4a 55.4a Freezing 1 0.01 0.00 0.74 Storage 3 34.4a 0.77a 1.85a Cooking meat 1 7.17a 16.3a 0.97b Cooking antioxidant 1 0.76b 15.3a 22.6a Cooking freezing 1 0.00 0.03 0.30b Cooking storage 3 5.91a 0.27b 0.45 Meat antioxidant 1 3.33a 0.98a 1.85b Meat freezing 1 0.05 0.13 0.00 Meat storage 3 1.07a 0.11 0.01 Antioxidant freezing 1 0.72b 0.11 0.04 Antioxidant storage 3 0.68b 0.02 0.14 Freezing storage 3 0.05 0.10 0.10 Cooking meat antioxidant l 0.48 1.22a 1.16b Cooking meat freezing 1 0.27 0.32 0.03 Cooking meat storage 3 1.02a 0.10 0.13 Cooking antioxidant ' freezing l 0.14 0.10 0.03 Cooking antioxidant storage 3 0.32 0.00 0.05 Cooking freezing storage 3 0.02 0.05 0.07 Meat antioxidant freezing 1 0.28 0.19 0.08 Meat antioxidant storage 3 0.40 0.05 0.61b Meat freezing storage 3 0.13 0.04 0.15 Antioxidant freezing storage 3 0.07 0.07 0.21 aSignificant at 99% level. b Significant at 95% level. 73 of corn oil as antioxidant carrier. Thus when fat was extracted and calculated per unit weight of the meat, it included not only that from chicken lipid and Oil absorbed during cooking, but also that oil absorbed during the antioxidant treatment. On the other hand, raw meat with a high water content absorbs less oil carrying the antioxidant. Thus, total lipid of the antioxidant-treated raw meat was only slightly higher than that of the untreated control. No significant differences in lipid content were detected between products frozen by the two methods. These results were expected, since liquid CO2 does not act as a fat solvent and the chicken pieces were not dipped in the freezing medium. Thus, no losses of fat from the tissue occurred during the cryogenic freezing process. Some moisture loss from the meat surface occurred during the air freezing process but this loss was not significant, since air velocity in the freezer is low. The low losses of moisture, in turn, resulted in a slight percentage increase in lipid content of the meat. Total lipid content changed very little during storage, due mostly to loss of product moisture during storage. This change is difficult to explain since packaging material was considered to be moisture-vapor impermeable. However, the variability found in actual 74 lipid content among chicken pieces and treatments probably indicates that there were some variations in lipid content among the individual chicken pieces. SUMMARY AND CONCLUSIONS The development of Off-flavors and muscle lipid oxidation of raw and precooked chicken pieces following different antioxidant and freezing treatments was evalu- ated for light and dark meat. Sensory evaluations were conducted to determine the off-flavor developments. The oxidation of muscle lipid which occurred during storage was followed by the 2-thiobarbituric acid (TBA), peroxide value (PV), and total titratable acid tests. Moisture and total lipid contents were also determined in order to correlate the effect of freezing methods, packaging, storage, and cooking on physical appearance and flavor deterioration of the meat samples. From the analyses of data, the following conclusions have been reached: 1. Raw meat showed significantly lower TBA numbers PV, total lipid content, and higher sensory scores than did cooked meats. Moisture content and titratable acid, in contrast, were signifi- cantly higher in raw meat. 2. Dark meat developed higher TBA number, PV, and total lipid content than light meat of 75 76 corresponding treatment during frozen storage and precooked chicken had significantly higher values than raw products. The moisture dif- ferences were not as clear-cut between light and dark meat. No significant differences were found in sensory scores between light and dark meats. i The results indicated that antioxidant dipping offered considerable promise for increasing the frozen storage life of precooked meat. Combi- nation of butylated hydroxy anisole (BHA), propyl gallate (PG), and citric acid in corn oil carrier significantly reduced lipid deterioration as indicated by significantly lowering of TBA numbers, PV, and acid contents and better sensory scores. This advantage also showed up in raw meat but only at the end of 6-month storage. The inci- dental effect of antioxidant treatment was that the total lipid contents of the treated samples were higher while the moisture contents were lower. There was no advantage of quick cryogenic over the slower blast freezing, concerning the develOpment of oxidative rancidity, under the conditions employed in this experiment. No l¥lllll111iiliil 77 significant differences were found with respect to moisture and total lipid content of samples frozen by the two methods. Increase in storage time resulted in significantly increased TBA numbers, PV, and acid content. Significantly lower sensory scores were also found in some products such as the precooked non- antioxidant-treated chicken pieces. Moisture and total lipid values and effects of storage on stability of chicken meat indicated that they are interrelated. However, the moisture in itself was found to have little effect on flavor deterioration or muscle lipid oxidation. Good correlation between sensory scores and TBA numbers existed in the nonantioxidant-treated precooked meat. The average sensory scores of 4-5, which indicated slightly stale or warmed over flavor, were correlated with the TBA number of about 4.0 mg TBA reactive substance per 1000 g of meat. APPENDIX APPENDIX TABLE A-l. Fried chicken rating score sheet Judge's Name Date Please evaluate each fried chicken sample according to the qualities listed below, use appropriate scale, and use code R sample as fresh reference. and juiciness in evaluating flavor. Disregard texture Evaluation Sample Code Extremely fresh flavor Very fresh flavor Moderately fresh flavor Slightly fresh flavor Flat (neutral) Warmed over flavor (slightly stale) Stale Rancid Very rancid Comment: 78 I’l'l TABLE A-Z. 79 frozen at different rates and stored up to Mean % BHAa for cooked and raw chicken pieces 6 months at -180Co Storage Time (month) Sample Treatments ob 3C 6° Air blast freezing Light meat, raw 0.011 0.021 0.016 cooked 0.020 0.022 0.013 Dark meat, raw 0.012 0.017 0.009 cooked 0.018 0.017 0.008 Liquid C02 freezing Light meat, raw 0.009 0.019 0.010 cooked 0.020 0.022 0.012 Dark meat, raw 0.008 0.020 0.008 cooked 0.021 0.017 0.008 aPercentage calculated on fat basis. bCalculated from the difference between total lipid contents before and after antioxidant treatments. CDetermined by method of Anglin et a1. (1956). LITERATURE CITED LITERATURE CITED Anglin, C., J. H. Mahon and R. A. Chapman. 1956. Deter- mination of antioxidants in edible fat. J. Agr. and Food Chem. 4(12):1018. Awad, A., W. D. Powrie and O. Fennema. 1968. Chemical deterioration of frozen bovine muscle at -4°C. J. Food Sci. 33:227. Banks, A. 1944. A method for studying the effect of anti- oxidants on the oxidation of aqueous suspensions of unsaturated fatty acids. J. Soc. Chem. Ind. 63:8. Barnes, R. H., W. O. Lundberg, H. T. Hanson and G. O. Burr. 1943. The effect of certain dietary ingredients on the keeping quality of body fat. J. Biol. Chem. 149:313. Barron, E. S. G. and C. M. Lyman. 1938. Studies on bio- logical oxidations X. The oxidation of unsaturated fatty acids with blood hematins and hemochromogens as catalysts. J. Biol. Chem. 123:229. Berry, J. G. and F. E. Cunningham. 1970. Factors affect- ing the flavor of frozen fried chicken. Poultry Sci. 49:1236. Brady, D. E., F. H. Smith and L. N. Tucker. 1946. Con- trol of rancidity in soybean fed pork. J. Animal Sci. 5:358. Carlin, A. F., R. M. V. Pangborn, O. J. Cotterill and P. G. Homeyer. 1959. Effect of pretreatments and types of packaging material on quality of frozen fried chicken. Food Technol. 13:557. Cash, D. B. and A. F. Carlin. 1968. Quality of frozen boneless turkey roasts precooked to different internal temperatures. Food Technol. 22:1477. 80 81 Chang, P. Y., M. T. Younathan and B. M. Watts. 1961. Lipid oxidation in precooked beef preserved by refrigeration, freezing, and irradiation. Food Technol. 15:168. Chipault, J. R. and J. M. Hawkin. 1971. Lipid autoxi- dation in freeze-dried meat. J. Agr. Food Chem. 19(3):495. Cipra, J. S. and J. A. Bowers. 1970. Precooked turkey flavor and certain chemical changes caused by refrigeration and reheating. Food Technol. 24:921. Cook, W. H. 1939a. Surface drying of frozen poultry during storage. Food Res. 4:407. Cook, W. H. 1939b. Frozen storage of poultry II. Bloom. Food Res. 4:419. Cook, W. H. and W. H. White. 1939. Frozen storage of poultry III. Peroxide oxygen and free fatty acid. Food Res. 4:433. Cook, W. H. and W. H. White. 1940. Frozen storage of poultry IV. Further observations on surface drying and peroxide oxygen formation. Can. J. Res. 18(D)363. Crigler, J. C. and L. E. Dawson. 1968. 'Cell disruption in broiler breast muscle related to freezing time. J. Food Sci. 33:248. Davis, L. L. and J. H. Bywaters. 1951. Preliminary report on prolonging storage life of frozen broilers. Unpublished data from the Virginia Agricultural Experimental Station. Dawson, L. E., K. E. Stevenson and E. Gertonson. 1975. Flavor, bacterial and TBA changes in ground turkey patties treated with antioxidants. Poultry Sci. 54:1134. Dubois, C. W., D. K. Tressler and F. Fenton. 1942. The effect of the rate of freezing and temperature of storage on quality of frozen poultry. Refrig. Eng. 44:93. Dubois, C. W. and D. K. Tressler. 1943. Seasonings, their effects on maintenance of quality in storage frozen ground pork and beef. Proc. Inst. Food Technol. 3:202. 82 Dugan, L. R., Jr. 1961. Development and inhibition of oxidative rancidity in food. Food Technol. 15:10. Dyer, W. J. and M. L. Morton. 1956. Storage Of frozen Plaice fillets. J. Fish. Res. Bd. Canada. l3(1):129-134. Eklund, M. W., W. E. Matson and J. V. Spencer. 1957. Freezing characteristics of eviscerated poultry using liquid immersion and air blast systems. Poultry Sci. 36:1115. El—Gharbawi, M. I. and L. R. Dugan, Jr. 1965. Stability of nitrogeneous compounds and lipids during storage of freeze-dried raw beef. J. Food Sci. 30:817. Folch, J., M. Lees and G. H. S. Stanley. 1957. A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226:497. Froning, G. W. and F. Johnson. 1973. Improving the quality of mechanically deboned fowl meat by centrifugation. J. Food Sci. 38:279. Gemmer, H. 1972. Characteristic of frozen poultry. Archiv. ffir Lebensmittelhygiene. 23(7):156. Hall, J., B. Lowe, J. Kalen, B. D. Westerman, D. L. Mackintosh and G. E. Vail. 1949. Keep the temperature low when storing pork. Refrig. Eng. 57:247. Hanson, H. L., M. Winegarden, M. B. Horton and H. Line- weaver. 1950. Preparation and storage of frozen cooked poultry and vegetables. Food Technol. 4:430. Hanson, H. L. 1954. Processing pre-cooked frozen poultry products. Proc. Inst. Am. Poultry Ind., Fact Finding Conference. Hanson, H. L., L. R. Fletcher, H. Lineweaver. 1959. Time-temperature tolerance of frozen foods XVII. Frozen fried chicken. Food Technol. 13:221. Harris, N. D. and R. C. Lindsay. 1972. Flavor changes in reheated chicken. J. Food Sci. 37:19. 83 Heaton, F. W. and N. Uri. 1961. The aerobic oxidation of unsaturated fatty acids and their esters: Cobalt Stearate-catalyzed oxidation of linoleic acid. J. Lipid Res. 2(2):152. Hilditch, T. P., E. C. Jones and A. J. Rhead. 1934. The body fat of the hen. Biochem. J. 28:786. Hiner, R. L., A. M. Gaddis and O. G. Hankins. 1951. Effect of methods of protection on palatability of freezer stored meat. Food Technol. 5:223. Hood, M. P., R. S. Wheeler and J. B. McGlamery. 1950. Oxidative change in estrogen stimulated fat and influence of natural tocopherols on stability of fat in normal chickens. Poultry Sci. 29:824. Jacobson, M. and H. H. Koehler. 1970. Development of rancidity during short time storage of cooked poultry meat. J. Agr. Food Chem. 18:1069. Janney, C. and K. K. Hale, Jr. 1971. Effect of anti- oxidants on off-flavor development of fried chicken held in a warming cabinet. Poultry Sci. 50:1588. Katz, M. A., L. R. Dugan, Jr. and L. E. Dawson. 1966. Fatty acids in neutral lipids and phospholipids from chicken tissue. J. Food Sci. 31:717. Keskinel, A., J. C. Ayres and H. E. Snyder. 1964. Determination of oxidative changes in raw meats by the 2-thiobarbituric acid method. Food Technol. 18:223. Klose, A. A., E. P. Mecchi and H. L. Hanson. 1952. Use of antioxidants in the frozen storage of turkeys. Food Technol. 6:308. Klose, A. A., M. F. Pool, A. A. Campbell and H. L. Hanson. 1959. Time-temperature tolerance of frozen food XIX. Ready-to-cook cut-up chicken. Food Technol. 13:477. Koonz, C. H. and J. M. Ramsbottom. 1939. A method for studying the histological structure of frozen products I. Poultry. Food Res. 4:117. Koonz, C. H., R. D. Trelease and H. E. Robinson. 1947. Low storage temperatures keep dressed poultry good longer. U. S. Egg and Poultry Mag. 53(2):12. 84 Kummerow, F. A., G. E. Vail, R. M. Conrad and T. B. Avery. 1948. Fat rancidity in eviscerated poultry. Poultry Sci. 27:635. Labuza, T. P. 1971. Kinetics of lipid oxidation in foods. Crit. Rev. in Food Technol. 2:355. Lea, C. H. 1934. Cold storage of poultry II. Chemistry changes in the fat of gas stored chickens. J. Soc. Chem. Ind. 53:347T. Lea, C. H. 1939. Rancidity in edible fat. Chemical Publishing Co., New York. Lineweaver, H., J. D. Anderson and H. L. Hanson. 1952. Effect of antioxidants on rancidity development in frozen creamed turkey. Food Technol. 6:1. Lineweaver, H. and E. L. Pippen. 1961. Chicken flavor. Proceedings Flavor Chemistry Symposium, Campbell Soup Co., Camden, New Jersey, p. 21. Liu, H. P. and B. M. Watts. 1970. Catalysts of lipid per- oxidation in meats III. Catalysts of oxidative rancidity in meats. J. Food Sci. 35:596. Love, R. M. 1966. The freezing of animal tissue. Cryobiology, H. T. Meryman, Ed., Academic Press, New York, p. 317. Love, J. D. and A. M. Pearson. 1971. Lipid oxidation in meat and meat products. J. Am. Oil Chemists' Soc. 48:547. Love, J. D. 1972. A comparison of myoglobin and non- heme iron as prooxidants in cooked meats and dispersion of phospholipid. Ph.D. Thesis, Michigan State University, East Lansing, Michigan. Marion, J. E. and J. G. Woodroof. 1966. Composition and stability of broiler carcasses as affected by dietary protein and fat. Poultry Sci. 45:241. Marion, J. E., T. S. Boggess, Jr. and J. G. Woodroof. 1967. Effects of dietary fat and protein on lipid composition and oxidation in chicken muscle. J. Food Sci. 32:426. 85 Marion, W. W. and W. J. Stadelman. 1958. Effect of various freezing methods on quality of poultry meat. Food Technol. 12:367. Marion, W. W. and R. H. Forsythe. 1964. Autoxidation of turkey lipids. J. Food Sci. 29:530. May, K. N. and A. J. Farr. 1972. Poultry preservation. U.S. Patent 3689 283. Mecchi, E. P., M. F. Pool, G. A. Behman, H. Hamachi and A. A. Klose. 1956. The role of tocoPherol content in the comparative stability of chicken and turkey fat. Poultry Sci. 35:1238. Mickelberry, W. C. 1970. Effect of in vivo injection of antioxidants on turkey fat stability. Poultry Sci. 49:355. Morris, S. G., J. S. Myer, M. L. Kip and R. W. Riemen- schneider. 1950. Metal deactivation in lard. J. Am. Oil Chemists' Soc. 27:105. Novak, A. and R. Rao. 1966. Efficient freezing with liquid nitrogen. Food Eng. 38:53. Olley, J. and J. A. Lovern. 1960. Phospholipid hydrolysis in cod flesh stored at various temperatures. J. Sci. Food Agr. 11:664. Olson, D. G. and R. E. Rust. 1973. Oxidative rancidity in dry-cured hams. Effect of low pro-oxidant and antioxidant salt formulations. J. of Food Sci. 38:251. Osborn, W. E., T. E. Hartung and R. E. Moreng. 1966. Lipid characteristics of turkeys, influenced by sex and age. Poultry Sci. 45:1113. Peng, C. Y. 1965. Some studies on the composition and structure of phospholipids in chicken muscle. Ph.D. Thesis, Michigan State University, East Lansing, Michigan. Pickett, L. D., B. F. Miller and R. E. Moreng. 1967. The effect of estradiol-l7-monopalmitate and vitamin E on carcass quality of young tom turkeys. Poultry Sci. 46:1306. II'IIII 86 Pickett, L. D., B. F. Miller and R. E. Moreng. 1968. Carcass quality of turkeys as affected by estradiol-l7-mon0palmitate and vitamin E. Poultry Sci. 47:1493. Pool, M. F., H. L. Hanson and A. A. Klose. 1950. Effect of prefreezing, hold time and antioxidant Spray on storage stability of frozen eviscerated turkeys. Poultry Sci. 29:347. Ramsbottom, J. M. 1947. Freezer storage effect on fresh meat quality. Refrig. Eng. 53:19. Ramsbottom, J. M., P. A. Goeser and H. W. Schultz. 1951. How light discolors meat: What to do about it. Food Inds. 23:120. Sair, L. and L. A. Hall. 1951. The use of antioxidants in deep fat frying. Food Technol. 5:69. Sato, K. and G. R. Hegarty. 1971. Warmed-over flavor in cooked meats. J. Food Sci. 36:1098. Sato, K., G. R. Hegarty and H. K. Herring. 1973. The inhibition of warmed-over flavor in cooked meats. J. of Food Sci. 38(3):398. Schultz, H. W., E. A. Day and R. O. Sinnhuber. 1962. I'Symposium on Foods: Lipid and Their Oxidation," Avi Publishing Co., Westport, Connecticut. Scotts, G. 1965. Atmospheric oxidation and antioxidants Elsevier Publishing Co., New York. Sherwin, E. R. 1968. Methods for stability and anti- oxidant measurements. J. of Am. Oil Chemists' Soc. 45(11):632A. Sherwin, E. R. 1972. Antioxidants for food fats and oil. J. Am. Oil Chemists' Soc. 49:468. Smith, G. J. and W. L. Dunkley. 1962. Initiation of lipid peroxidation by a reduced metal. Arch. Biochem. Biophys. 98:46. Steinberg, M. P., J. D. Winter and A. Hustrulid. 1949. Palatability of beef stored at 0°F as affected by moisture loss and oxygen availability. Food Technol. 3:367. 87 Stewart, G. F., H. L. Hanson, B. Lowe and J. J. Austin. 1945. Effects of aging, freezing rate and storage period on palatability of broilers. Food Res. 10:16. Stewart, G. F. and B. Lowe. 1948. Producing and main- taining quality in frozen eviscerated poultry. Frozen food Ind. 4(5):8. Streeter, E. M. and J. V. Spencer. 1973. Cryogenic and conventional freezing of chicken. Poultry Sci. 52(1):317. Swern, D. 1961. Primary products of olefinic autoxi- dations. In "Autoxidation and Antioxidants," Vol. I, W. O. Lundberg, Ed., Interscience, New York, p. l. Tappel, A. L. 1953. The mechanism of the oxidation of unsaturated fatty acid catalyzed by hematin compounds. Arch. Biochem. Biophys. 44:378. Tappel, A. L. 1962. Hematin compounds and lipoxidase as biocatalysts. In "Lipids and Their Oxi- dations," Avi Publishing Co., Westport, Connecti- cut, p. 122. Tarladgis, B. G., B. M. Watts, M. T. Younathan and L. R. Dugan, Jr. 1960. A distillation method for the quantitative determination of malonaldehyde in rancid foods. J. Am. Oil Chemists' Soc. 37:44. Tarladgis, B. G. 1961. Hypothesis for the mechanism of the heme catalyzed lipid oxidation in animal tissue. J. Am. Oil Chemists' Soc. 38:479. Tim, M. J. and B. M. Watts. 1958. The protection of cooked meat with phosphates. Food Technol. 12:240. Thomson, J. E. 1964. Effect of polyphosphates on oxi- dative deterioration of commercially cooked fryer chickens. Food Technol. 18:1805. Urbain, W. M. and J. M. Ramsbottom. 1948. Controlling quality changes in cured meats by packaging. Food Res. 13:432. Uri, N. 1961. Physico. chemical aspects of autoxidation. In "Autoxidation and Antioxidants," Vol. I, W. O. Lundberg, Ed., Interscience, New York, p. 55. 88 Van den Berg, L. and C. P. Lentz. 1964. Effect of cooling, freezing and thawing on chicken quality. Can. Food Ind. 35:44. Voth, O. L., R. C. Miller and W. R. Lewis. 1958. Effect of intravenous tocopherol injection on tissue content and carcass fat stability in chickens. Poultry Sci. 37:301. Wagoner, C. E., G. E. Vail and R. M. Conrad. 1947. The influence of preliminary holding conditions on deterioration of frozen poultry. Poultry Sci. 26:170. Watts, B. M., T. J. Cunha and R. Major. 1946. Effect of feeding and injecting hogs with tocopherols on the susceptibility of pork fat to rancidity. Oil and Soap. 23:254. Watts, B. M. and D. Peng. 1947. Rancidity development in raw vs precooked frozen pork sausage. J. Home Ec. 39:88. Watts, B. M. 1954. Oxidative rancidity and discolor- ation in meat. In "Advances in Food Research," Vol. 5. Academic Press Inc., New York, p. 1. Watts, B. M. 1961. The role of lipid oxidation in lean tissues in flavor deterioration of meat and fish. In "Proceedings Flavor Chemistry Symposium," Campbell Soup Co., Camden, New Jersey, p. 83. Watts, B. M. 1962. Meat products. In "Symposium on Food: Lipids and Their Oxidation," H. W. Schultz, E. A. Day and R. O. Sinnhuber, Ed., Avi Publishing Co., Westport, Connecticut, p. 202. Webb, J. E. and T. L. Goodwin. 1970. Precooked chicken: Effect of cooking methods and batter formula on yield and of storage conditions on 2-thiobarbit- uric acid value. Brit. Poultry Sci. 11:171. Webb, J. E., C. C. Brunson and J. D. Yates. 1972. Effect of feeding antioxidants on rancidity development in precooked, frozen broiler parts. Poultry Sci. 51:1601. Wheeler, D. H. 1932. Peroxide formation as a measure of autoxidative deterioration. Oil and Soap. 9:89. 89 Wills, E. D. 1966. Mechanism of lipid peroxide formation in animal tissues. Biochem. J. 99:667. Wills, R., B. Lowe, H. Slosberg and G. F. Stewart. 1948. Frozen storage of poultry. Refrig. Eng. 56:49. Winkler, C. A. 1939. Color of meat II. Effect of desiccation on the color of cured pork. Can. J. Res. 17D:29. Wyche, R. C., B. E. Love and T. L. Goodwin. 1972. Effect of skin removal, storage time and freezing methods on tenderness and rancidity of broiler. Poultry Sci. 51:655. Yamauchi, K. 1972. 2-thiobarbituric acid reactive sub- stances in distillate obtained from cooked rancid meat. Bulletin of the faculty of Agriculture Miyazaki University. l9(1):137. Yamauchi, K. 1973. Effect of heat-treatment on the amount of free lipid released from isolated mitochondrial fraction of skeletal muscle tissue. Japanese J. of Zootech. Sci. 44(4):201. Younathan, M. T. and B. M. Watts. 1959. Relationship of meat pigments to lipid oxidation. Food Res. 24:728. Younathan, M. T. and B. M. Watts. 1960. Autoxidation of tissue lipids in cooked pork. Food Res. 25:538. Zipser, M. W. and B. M. Watts. 1961. Oxidative ran- cidity in cooked mullet. Food Technol. 15:318. uuLumm 0 '1'; mm .5 l 5 I l I, i 'I l I III '9 5