Species dependence of fish myosin stability to heat and frozen storage

The thermal stabilities of the proteins of a range of fish muscles of different habitat temperatures were determined by differential scanning calorimetry before and after frozen storage at 20°C.
In whole muscle a clear relationship was seen between habitat temperature and the thermal denaturation of myosin, which persisted when isolated myosins were analysed under conditions close to physiological pH and ionic strength. the ionic environment of the myosin molecules in the whole tissue will, however, not be exactly the same as in the myosin solution.
No significant correlations were seen between habitat temperature, ultimate pH and other analytical parameters.
After frozen storage, the myosin transitions in red snapper, a warm water species, was markedly changed in whole muscle but not in isolated myosin, suggesting the post mortem development of an interaction with other muscle proteins. In contrast, in cod, a cold water species, changes in myosin transitions were very similar, both in whole muscle and isolated myosin.
The implications of species differences in the 'melting' of myosin domains and changes in textural quality during frozen storage are discussed briefly.