Abstract: The pH, water loss rate, cook loss, shear force, color parameters, thiobarbituric acid reactive substances (TBARS), carnonyl content and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) pattern of carp back muscles were measured after different freeze-thaw cycles (0, 1, 3 and 5) with the aim of determining the effect of number of freeze-thaw cycles on the physicochemical characteristics of carp muscle. Results indicated that pH value showed a trend to first increase and then decrease as the number of freeze-thaw cycle increased. Water loss rate and cooking loss exhibited an upward trend and were increased by 8.77% and 20.28%, respectively, after the fifth freeze-thaw cycle (P＜0.05). Shearing force was decreased by 56.3% after one freeze-thaw cycle (P＜0.05), followed by a slow decline. Five freeze-thaw cycles could significantly increase TBARS, carnonyl content, L*value and b*value, and decrease a* values (P＜0.05). All myofibrillar protein bands in the SDS-PAGE pattern got lighter in color and even disappeared with increasing number of freeze-thaw cycles, indicating protein degradation and denaturation. Good correlations were found between lipid oxidation and either protein oxidation or color change. In summary, repeated freeze-thaw could cause protein denaturation and has a detrimental effect on the quality of carp muscle.

Key words: carp, freeze-thaw cycle, quality, denaturation