The role of endogenous proteases in degrading grass carp (Ctenopharyngodon idella) myofibrillar structural proteins during ice storage

Fish texture is important for consumers and degradation of myofibrillar structural proteins could cause softening. However, the role of endogenous proteases in degrading was not clear. In this study, protease inhibitors (Ac-DEVD-CHO, E -64 and EDTA-2Na) were used to distinguish the role of endogenous caspase-3, cathepsin B and L, and calpain. Results showed that caspase-3 and calpain had relatively high activity at initial ice-storage and decreased quickly afterwards, while cathepsins increased firstly and then fluctuated. Titin, nebulin and troponin-T were partially degraded by caspase-3 firstly. However subsequently, only titin and troponin-T were affected by cathepsins and calpain. Desmin showed a different degradation pattern. It was influenced by calpain significantly but not by caspase-3. Less than 2.5% of desmin remained after storage. Myofibril fragmentation index and shear force indicated that caspase-3-induced degradation occurred at initial ice-storage, while cathepsins had the greatest importance in texture softening during the whole storage.