Relation between Protein Extractability and Free Fatty Acid Production in Cod Muscle Aged in Ice

Protein extractability decreased as free fatty acid (FFA) was produced in cod muscle aged in ice. The decrease was small compared with that occurring in frozen-stored muscle of similar FFA content. Prolonged extraction in neutral salt solution in the presence and absence of bovine serum albumin (BSA) showed that loss in protein extractability in muscle aged in ice was reversible through dissociation of inextractable material and that the presence of BSA, a FFA acceptor, favored greater dissociation. Ultracentrifugal patterns of protein extracted from ageing muscle showed increasing polydispersity. Phase contrast microscopy showed that the inextractable material contained muscle fragments consisting of bundles of myofibrils, some of full fiber width. These results indicate that in ageing muscle, interaction of contractile protein with FFA results in the formation of a cross-linking network within the muscle fiber causing resistance to fragmentation and to protein extractability, and that the observed smaller loss during ageing in ice is in part due to dissociation occurring during extraction. They suggest that in muscle aged in the frozen state, the reaction between contractile protein and FFA increases and the complexes formed are stabilized.