Aggregation of minced hake during frozen storage

Aggregation in minced bake muscle (Merluccius merluccius) during storage at -20 degrees C was studied in conditions where there is progressive deterio ration of functionality and texture as measured by apparent viscosity and s hear resistance. Natural actomyosin was extracted with 0.6 M NaCl over a pe riod of 49 weeks. Insoluble residue was extracted successively with 2% sodi um dodecyl sulphate (SDS) and 2% SDS plus 5% beta-mercaptoethanol (ME) solu tions. SDS-polyacrylamide gel electrophoresis was performed on the extracte d fractions. The results showed a 75% decrease in 0.6 M NaCl extractability by the end of the storage period. Initially the remaining precipitate was all extracted in 2% SDS and although the amount extracted in this solution increased as storage time progressed, its proportion decreased, accounting for as little as 40-50% of the protein aggregate by the end of storage. The proteins most involved in formation of the aggregate not extracted in 0.6 M NaCl were myosin and actin. Neither of these proteins was fully recovered in the fractions extracted with 0.6 M NaCl, 2% SDS, or 2% SDS plus 5% ME, and therefore it was inferred that they were forming part of the aggregates , bound by covalent bonds.