Abstract: In order to investigate the quality changes of Crassostrea gigas during cold storage at 0 and 4 ℃, the changes in the visual appearance of different tissues (adductor muscle, mantle, gills and visceral mass) during cold storage were observed. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to analyze the changes of total proteins in oyster tissues. The degradation of myosin heavy chain (MHC), actin, paramyosin (PM) and tropomyosin (TM) in adductor muscle was identified by Western blotting. The activity of endogenous serine protease and cathepsin B was measured using fluorescent spectrum. The quality change of adductor muscle during cold storage was evaluated in terms of its pH, K value and texture properties. The results showed that during cold storage, the texture of adductor muscle changed from tight to soft. Western blotting showed that MHC in adductor muscle began to degrade on days 3 and 1 for 0 and 4 ℃, respectively, indicating that low temperature is beneficial to reduce the rate of protein hydrolysis. However, PM, TM and actin did not change obviously. The activity of serine protease and cathepsin B in adductor muscle first rose and then decreased during cold storage. After cold storage for 11 days, the pH decreased from an initial value of 6.79 to 6.52 and 5.84 for 0 and 4 ℃, respectively. The K value exceeded the second degree of freshness range (40%) on days 9 and 5 for 0 and 4 ℃, respectively. The hardness and chewiness of adductor muscle peaked on day 1 and then decreased gradually, and elasticity decreased with storage time. The degradation of MHC in adductor muscle was most remarkable and closely related to the deterioration of oyster quality during cold storage. This study can provide a theoretical reference for oyster cold storage and preservation.

Key words: Crassostrea gigas; protein degradation; cold storage; texture; enzyme activity