Postmortem changes in actomyosin dissociation, myofibril fragmentation and endogenous enzyme activities of grass carp (Ctenopharyngodon idellus) muscle

•Strong actomyosin dissociation was observed in the storage of grass carp.•Myofibril fragmentation index was increased during postmortem aging.•Cathepsin B, D, H activities were highly correlated with MFI and texture.

The changes of actomyosin, proteolytic activities and myofibril fragmentation during the postmortem aging of grass carp were studied. The study revealed dramatically increased actomyosin dissociation within 6 h of storage postmortem in grass carp, and it was associated with the drop of pH from 6.9 to 6.7, while liberated actin remained almost unchanged after 6 h postmortem. The myofibril fragmentation also increased significantly with the storage time in 6 h, and a highly positive correlation (P < 0.01) existed between MFI and cathepsin B, D, H activities. The study indicated both actomyosin dissociation and cathepsin B, D, H played a role in postmortem tenderization and textural changes in grass carp.