Recovery of emulsifying and gelling protein from waste chicken exudate by using a sustainable pH-shifting treatment

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 28.3N to 40.4N) (P<0.05), but the further increase of freeze-thaw cycles would lead to decrease of cutting force. The decreases in Ca(2+)- 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.