Physicochemical change and protein oxidation in porcine longissimus dorsi as influenced by different freeze–thaw cycles

Effects of different freeze–thaw cycles (0, 1, 3 and 5) on physicochemical change and protein oxidation in porcine longissimus dorsi were investigated. When the number of freeze–thaw cycles increased, the thawing losses, cooking loss and b*-value increased (P < 0.05), a*-value decreased (P < 0.05). The cutting forces of pork increased after one cycle of freeze–thaw (from 28.3 N to 40.4 N) (P < 0.05), but the further increase of freeze–thaw cycles would lead to decrease of cutting force. The decreases in Ca2+- and K+-ATPase activity and sulfhydryl group (P < 0.05) content with concomitant increases in carbonyl content and thiobarbituric acid-reactive substances (TBARS) value (P < 0.05) showed that multiple freeze–thaw could cause the porcine protein and fat oxidation, especially for the pork subjected to five freeze–thaw cycles. Gel electrophoresis patterns of porcine muscle showed that multiple freeze–thaw cycles could cause cross-linking of protein in myofibril. Overall, the freeze–thaw process has a detrimental effect on the quality of pork.