The diffusion of sodium chloride and acetic acid into herring muscle and their subsequent effects on the myotibrillar proteins were studied at different temperatures and fish:cure ratios. Acid was found to penetrate tissue more quickly than salt. The acid and salt cause an initial "hardening" of the tissue, the extent of which is proportional to the concentration of each, but it is considered that the resultant fall in pH activates muscle cathepsins. SDS PAGE indicated that proteolysis of the myosin heavy chains was concomitant with subsequent tissue softening. Electron microscopy detected little disintegration of myofilaments, but extensive break-up of Z-lines.

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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A highly active protease exists in squid muscle. After comminution the muscle can autolyze to such a degree that its rheological properties show extensive change, SDS gel electrophoresis showed that this change is concomitant with progressive myosin degradation but Differential Scanning Calorimetry of autolyzed cornminutes showed no change in the characteristic thermal transitions relative to a control sample. Similarly sensory assessment of a cooked autolyzed comminute did not reflect the extent of change exhibited in the raw state. This preliminary evidence suggests that proteolysis of a raw muscle comminute need not affect its sensory properties.

No abstract