Effect of shio-koji on proteolysis of bovine protein and beef tenderization

In this study, we investigated the effects of shio-koji treatment on beef tenderization and proteolysis under varying conditions of temperature, pH, and NaCl concentration. Bovine protein hydrolysis was maximized at 40–50 oC and pH 5.0 with shio-koji treatment. The addition of 3 % (w/v) or more NaCl slightly reduced the degree of hydrolysis. SDS-PAGE analysis and phase-contrast microscopy revealed that bovine myofibrils were partially hydrolyzed. Although bovine myofibrils were hydrolyzed at 4 °C, the degree of degradation was limited. Immersion in shio-koji solution tenderized beef and reduced its breaking stress. On the other hand, beef samples subjected to treatment with heat-inactivated shio-koji also exhibited a marginal decrease in breaking stress compared to the untreated control group. These results suggest that, in addition to proteases, shio-koji contains non-enzymatic meat tenderizing factors, such as acids and salts, which may contribute to optimal beef tenderization.