Activity of endogenous muscle proteases from 4 Australian underutilized fish species as affected by ionic strength, pH, and temperature.

Storage conditions may influence the hydrolytic activity of endogenous muscle enzymes postmortem, rate of autolysis of myofibrillar proteins, and biological properties of hydrolyzed end products. This study investigated the effect of ionic strength, pH, and temperature on the activity of endogenous calpain-like, cathepsins B and B+L measured in crude extract obtained from deepwater flathead, silver warehou, ribaldo, and ribbonfish muscles. Activity of calpain-like enzymes in 3 examined species was significantly higher at pH 6.5 than pH 6.0 or 5.5. Raising the reaction temperature increased (P < 0.05) calpain-like activity in ribaldo. Endogenous activity of cathepsin B in ribbonfish and silver warehou declined significantly with increasing ionic strength at pH 6.5 to 6.0. The obtained results will further expand our understanding of the impact that postmortem storage conditions have on the activity of endogenous fish proteases with respect to quality and bioactivity of fish proteins and potentially diversify utilization of underutilized fish species.