Characteristics of the Salt-Soluble Fraction of Hake (Merluccius merluccius) Fillets Stored at −20 and −30 °C

Natural actomyosin (NAM) extracted in 0.6 M NaCl from hake fillets stored at -20 and -30 degrees C for up to 49 weeks was studied. The extracted protein decreased as storage progressed and became poorer in myosin while the proportion of actin remained constant. Two major peaks composed of myosin plus actin and actin plus tropomyosin plus troponins were obtained by size exclusion chromatography. SDS-PAGE analysis of the protein retained in the precolumn filter showed that there was protein aggregated by covalent bonding. Surface hydrophobicity increased while Ca(2+)-ATPase activity, apparent viscosity, and SH groups decreased as storage progressed. The loss of Ca(2+)-ATPase activity was due mainly to denaturation of the extracted myosin, whereas the minimum viscosity values occurred earlier and were not directly due to the lower proportion of myosin in the extracts. Thus, the extracted NAM exhibited changes during frozen storage. The temperature-dependent difference was mainly quantitative due to a smaller amount of protein extracted at -20 degrees C.