Contribution of myofibril filament disassembly to textural deterioration of ice-stored grass carp fillet: Significance of endogenous proteolytic activity, loss of heat shock protein and dephosphorylation of myosin light chain

To investigate the underlying mechanism of softening of ice-stored grass carp fillet, changes in assembly structure of myofibrillar proteins and potential candidates for regulating this change including myosin regulatory chain phosphorylation, heat shock proteins (Hsp27, Hsp90, alpha B-crystallin and UNC45) and endogenous protease activity were studied. Comparison of SDS-PAGE pattern of myofibrillar proteins treated with EDC crosslinking showed that thin filament experienced rapid disassembly within initial 8 h, followed by depolymerization of thick filament consisting of myosin, which further exacerbated the myofibril disorganization of fillets. Pearson coefficient analysis showed that UNC45, Hsp90, Hsp27 and alpha B-crystallin concentration and cathepsin B, D, L activities were significantly correlated with dissociated MHC and actin. Therefore, the significant correlation between shear force and dissociated MHC and actin clearly demonstrated that post mortem disassembly of myofibril filaments, which was regulated by endogenous proteolytic activity and loss of Hsp, contributed to the softening of ice-stored grass carp fillets.