Differential Scanning Calorimetry (DSC) has been used to study the thermal properties of fish muscle proteins and to measure the extent of their denaturation under various processing conditions. Fish myosin was susceptible to denaturation by frozen storage and dehydration. Denaturation of certain fish proteins was partially reversible. Although fish myosin was very unstable, its thermal stability was found to increase in species adapted, to higher environmental temperatures.

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The variation in myofibrillar protein thermostability was compared for various fish species, using differential scanning calorimetry. The tropical fish, catfish (Clariw gariepinus), carp (Cyprinus carpio), Nile perch (Lutes niloticus) , red snapper (Lutianus sebae) , red mullet (Parpeneus barberinus), sea bream (Gyrnnocranius 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. KeywordsCold-water fish muscle, protein stability, storage, thermal denaturation temperature, warm-water fish muscle.

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