Comparative study on degradation, aggregation and rheological properties of actomyosin from cold, temperate and warm water fish species

Proteolytic degradation and thermal aggregation patterns and dynamic rheological properties of actomyosin prepared from Alaska pollock (Theragra chalcogramma), Pacific whiting (Merluccius productus), bigeye snapper (Priacanthus spp.), lizardfish (Saurida spp.) and threadfin bream (Nemipterus spp.) surimi were comparatively studied. There was a significant endogenous protease activity observed in crude actomyosin samples where Pacific whiting and lizardfish exhibited the highest proteolytic activity. SDS-PAGE analysis showed that intensity of myosin heavy chain bands of Pacific whiting, bigeye snapper, lizardfish and threadfin bream decreased with extended incubation time, resulting in medium and low molecular weight proteins. For all tested fish species, a 0.5 °C min^-1 heating rate resulted in higher turbidity values followed by 1.0 °C min^-1 and then 2.0 °C min^-1. Temperature onset point for turbidity increase was significantly affected by species. Storage modulus peak temperatures, obtained from temperature sweep tests of actomyosins, were similar to thermal transition values obtained from differential scanning calorimetry, indicating that peaks obtained from the dynamic tests were related to protein denaturation temperatures. Slower heating rate shifted the thermal transition temperature to a lower value. These observations should give better understanding of the thermal sensitivity of fish species with regards to gelation properties and proteolytic degradation.