Thermal stability of fish myofibrils: a differential scanning calorimetric study

The variation in myofibrillar protein thermostability was compared for various fish species, using differential scanning calorimetry. The tropical fish, catfish ( Clarius gariepinus ), carp ( Cyprinus carpio ), Nile perch ( Lates niloticus ), red snapper ( Lutianus sebae ), red mullet ( Parpeneus barberinus ), sea bream ( Gymnocranius rivalatus ), and cold-water reared trout ( Salmo gairdneri ) and cod ( Gadus morhua ) were analysed. Onset temperature of myofibrillar protein denaturation occurred at up to 11°C higher for tropical species (43.5°C, catfish), than cod (32.6°C) at pH 7 and low ionic strength (I). As pH (6.0-8.0) and I (0.05-1.00) were increased, thermal denaturation temperatures of myosins from tropical, but not cold-water, species decreased. Enthalpies of myofibrillar denaturation decreased for all species with increasing pH and I. Only one thermal transition was detected for myosin at pH 6 and low I, increasing to three as pH and I were increased. Changes in thermal characteristics of myosin subunits over iced and frozen storage suggest more rapid deterioration in cold-water than in tropical fish. The differences in myofibrillar stability of fish from different habitat temperatures have implications for the processing and storage of tropical fish.