الفهرس 
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Abstract
When salt-water fish muscle is frozen and stored, alterations occur to the extent that excessive exudation (drip) accompanies thawing, the cooked fish becomes tough, the flesh may possess a yellowish hue and off-flavors are sometimes evident. So far, freezing damage to the muscle of fresh-water fish has not been studied in depth. Moreover, the deterioration of bovine muscle in frozen storage is commonly considered insignificant, yet no detailed information is available to substantiate this idea. Thus, this study was initiated to accumulate chemical and physical data on the deterioration of frozen, stored muscles from fresh-water whitefish and beef, and to compare these results with those obtained in similar studies on salt-water fish muscle.
In this study, storage temperatures of -10°C for whitefish muscle and -4°C for bovine muscle were selected so that dramatic alterations would occur within short periods of frozen storage. The durations of frozen storage for whitefish and bovine muscles were 18 and 8 weeks, respectively.
The results indicate that progressive insolubilization of myofibrillar proteins took place during frozen storage in both whitefish and bovine skeletal muscle. The solubility of sarcoplasmic protein in frozen bovine muscle gradually decreased over an 8-week storage period; yet with frozen whitefish muscle, the extractability of sarcoplasmic protein did not change significantly over a 16-week storage period.
A loss of water-holding capacity of whitefish and bovifle muscles during frozen storage was evident from the marked increase in the amount of thaw drip obtained by centrifugation. Perhaps myofibrillar protein aggregation, leading to protein insolubilization, may account for the decrease in water-binding capacity. Protein aggregation may be associated with the loss of cooked muscle tenderness since a straight line relationship existed between “actomyosin’ solubility and the tenderness score of cooked whitefish muscle previously stored for 3 to 16 weeks at -10°C. With the aid of polyacrylamide gel electrophoresis, the loss of specific proteins in the actomyosin fraction was demonstrated when bovine muscle was stored in the frozen state.
The concentration of free fatty acids (EFA) increased from about 5% to 21% of the total lipid in whitefish muscle during 16 weeks of frozen storage and from about 2 to 9% of the total
lipid in bovine muscle when stored for 8 weeks. The loss of phospholipids in frozen whitefish and bovine muscles during storage is indicative of enzymic hydrolysis by in situ phospholipases which presumably caused the release of fatty acids. The interaction of FFA with myofibrillar proteins may be responsible, in part at least, for protein insolubilization. Lipid autoxidation, evaluated by TEA numbers and peroxide values, occurred in whitefish and bovine muscles during frozen storage. The interaction of oxidized lipids with muscle proteins probably were not important in the insolubilization of proteins in frozen muscle.
Salt -soluble whitefish 11actomyos in” and bovine actomyo -
sin were isolated from unfrozen and frozen muscles. Soluble 1tactomyosin’t from frozen, unstored whitefish muscle consisted
of about 7% total lipid, including 19% phospholipid and almost 10% FFA. The total lipid content of soluble actomyosin from unfrozen bovine muscle was about 4%,, including approximately 29% phospholipid and 2% FFA. As storage time of frozen muscle increased, the total lipid and FFA contents of soluble whitefish ‘1actomyos intt and bovine actomyosin increased markedly.