EFFECT OF SALT CONCENTRATION AND TEMPERATURE ON HEAT-INDUCED AGGREGATION AND GELATION OF FISH MYOSIN

Thermal aggregation of myosins prepared from cod (Gadus morhua) and herring (Clupea harengus) was investigated by turbidimetric methods and by means of phase contrast microscopy. Turbidity measurements and microscopical studies showed that the extent of aggregation of cod myosin molecules increased with temperature (35-55-degrees-C) and was consistently higher than those for herring at all temperatures. Thermal aggregation of herring myosin showed little dependence on salt concentration (0.6 - 1.4 M NaCl, pH 6.5) but salt enhanced aggregation of cod myosin at heating temperatures greater-than-or-equal-to 50-degrees-C. In addition, the effects of temperature and salt on the rheological properties of heated cod and herring surimi were examined and the relevance to the myosin system was discussed. Torsion tests revealed that cod surimi gels prepared at all temperatures (35-55-degrees-C) yielded higher shear strains at failure than those for herring, and gels from either species were not affected by salt levels ranging from 0.6 to 1.4 M NaCl. The present study indicates the importance of ordered intermolecular aggregation as well as clustering of myosin aggregates for the formation of superior surimi gels. Herring myosin formed smaller aggregates and inferior surimi gels compared to those of cod.