Milk-coagulating enzymes of tuna fish waste as a rennet substitute.

Extraction and activation of the tuna zymogen is influenced by temperature, pH, salt concentration and freshness of the stomach tissue. The presence of 25% NaCl in the extraction process markedly enhanced the yield of tuna gastric enzyme. The milk-coagulating time for both tuna protease and rennet, at an incubation temperature of 32 degrees C, was dependent, at similar level, on the pH (5.5-6.4) of the milk as a substrate. Tuna protease was less sensitive to losses of activity than rennet at pH values above 6.4. Both enzymes became unstable beyond pH 7.0 and completely lost their activities at pH 8.0. The purpose of this study was to determine the best conditions for recovery of the fish enzyme and to compare its behavior to that of rennet.