Effect of Freeze-thaw Cycles on Proteins and Muscle Quality of Dosidicus gigas

Effects of different freeze-thaw cycles on proteins and muscle quality of Dosidicus gigas were studied to provide a theoretical basis for the preservation of aquatic products. Protein carbonyl content, total sulfhydryl content, surface hydrophobicity, sodium dodecyl sulphate polyacrylamide gel electrophoresis(SDS-PAGE) pattern, turbidity, emulsifying activity index(EAI) and emulsifying stability index(ESI) of the treated samples were measured after 0, 1, 3,5 and 7 freeze-thaw cycles. And the thawing loss, cooking loss, color, tenderness, texture and thiobarbituric acid reactive substances(TBARS) of squid muscle were analyzed combined with organoleptic evaluation. With increasing the number of freeze-thaw cycles, protein carbonyl content and surface hydrophobicity increased but total sulfhydryl content of myofibrillar proteins exhibited the opposite trend. Aggregation of proteins was found during the process and EAI and ESI dropped markedly. Moreover, TBARS, thawing loss, cooking loss and b* significantly increased(p<0.05), while L*, a*, whiteness, tenderness, springiness and hardness decreased. Results from organoleptic evaluation were in consistence with the instrumental ones. In summary, repeated freeze-thaw cycles promotes oxidation of protein and lipid and has a detrimental effect on the qualities of squid muscle.