Abstract: A comparative analysis of the changes in indicators of myofibrillar protein oxidation and the activities of cathepsins B, H and in red shrimp during frozen storage after immersion freezing (?18 and ?30 ℃) and refrigerator freezing (?18 and ?30 ℃) was conducted. Microstructural observation of myofibrillar protein was carried out to analyze the effect of cathepsin activity on myofibrillar protein hydrolysis and its correlation with muscle tissue structure was explored. The results showed that the contents of salt-soluble protein in the immersion freezing groups at ?18 and ?30 ℃ were 92.7 and 97.8 mg/g, respectively, significantly higher than those in the refrigerator freezing groups at ?18 and ?30 ℃ (72.40 and 77.90 mg/g, respectively). The surface hydrophobicity in the immersion freezing group at ?30 ℃ was the lowest =(400.6 μg), and Ca2+-ATPase activity was higher at ?30 ℃ than at ?18 ℃ for both freezing methods. The trend of change in total sulfhydryl content was consistent with that of Ca2+-ATPase activity. At the early stage of storage (0–60 days), immersion freezing at lower temperature could better inhibit cathepsin activity and maintain myofibrillar protein structure. At the late stage of storage (60–120 days), the cathepsin inhibitory effect decreased. Based on the above results, it was clear that during a certain storage period, immersion freezing could better attenuate the oxidation of myofibrillar protein and cathepsin activity of Solenocera crassicornis than refrigerator freezing, and lower freezing temperature of antifreeze liquid resulted in higher freezing rate, weaker cathepsin activity and lower extent of myofibrillar protein oxidation, which was more conducive to the maintenance of myofibrillar protein structure.

Key words: Solenocera crassicornis; immersion freezing; endogenous enzyme; myofibrillary protein