Changes in Physicochemical and Protein Structural Properties of Common Carp (Cyprinus carpio) Muscle Subjected to Different Freeze-Thaw Cycles

The present study investigated physicochemical and protein structural changes in common carp muscle subjected to different freeze-thaw (FT) cycles. With increasing number of FT cycles, the thawing losses, cooking loss, L*- and b*-value increased, and shear forces and a*-value decreased (p < 0.05). The study showed that multiple FT processes were detrimental to color and water-holding capacity of carp muscle. The increases in thiobarbituric acid reactive substances and carbonyl content with concomitant decrease in sulfhydryl group content (p < 0.05) showed that multiple FT caused carp lipid and protein oxidation, especially for the carp muscle subjected to five freeze-thaw cycles. Myofibrillar protein isolated from FT muscle showed an increased hydrophobicity, reduced ATPase activity, and enhanced susceptibility to thermal aggregation (p < 0.05). These protein structural changes resulted in major losses in muscle quality. Overall, the disrupted protein structure, together with the denaturation of myofibrillar protein induced by FT, was most likely associated with lowered muscle quality.