The effect of soybean trypsin inhibitor on the degradation of myofibrillar proteins by an endogenous serine proteinase of crucian carp

The effect of soybean trypsin inhibitor (STI) on the degradation of crucian carp myofibrillar proteins caused by an endogenous myofibril-bound serine proteinase (MBSP) was studied. Soybean trypsin inhibitor was purified to high homogeneity and mixed with myofibrils and its inhibitory effect on myofibrillar protein degradation was investigated. In the absence of STI, proteolysis of myofibrillar proteins including myosin heavy chain, α-actinin, actin and tropomyosin could be identified after incubation at 55 °C for 5–20 min depending on the kind of the protein. In contrast, in the presence of STI, with final concentration of 0.75 μg/ml, proteolysis of these proteins was greatly suppressed even after incubation for 1 h, suggesting STI is an effective inhibitor in preventing myofibrillar protein degradation caused by a serine proteinase that is quite possibly MBSP. Though STI has disadvantages for food digestion, as a native food grade inhibitor, it is safe as a food additive, especially at low concentration. Because in surimi production, the decrease of elasticity is always accompanied with the degradation of myofibrillar proteins, thus, the present result suggested the possibility that STI could be applicable in surimi production in order to enhance the elasticity that is the quality of the final products.