EFFECTS OF ENDOGENOUS CATHEPSINS B AND L ON DEGRADATION OF SILVER CARP (HYPOPHTHALMICHTHYS MOLITRIX) MYOFIBRILLAR PROTEINS

Abstract

ABSTRACT The activities of cathepsins B and L in minced silver carp meat were 4.89 and 3.81 units/g, respectively. About 11.30% activity for cathepsin B and 25.61% activity for cathepsin L were left after washing with distilled water, suggesting a short wash removed a large portion of both cathepsins B and L, but the activities of cathepsins still remained to some extent, and the remaining activity of cathepsin L was higher than that of cathepsin B. Higher cathepsin residual activity was correlated with the autolytic rate of myosin heavy chain (MHC) during the autolysis of myofibrillar proteins at 50C. The sodium dodecyl sulfate‐polyacrylamide gel electrophoresis analysis indicated that both of the purified cathepsins B and L could result in significant degradation of MHC at 50 and 35C, which was close to the temperature of gel softening and setting, respectively, but cathepsin L seemed to be a key proteinase for hydrolyzing the myofibrillar protein. PRACTICAL APPLICATIONThere is a possibility of consuming silver carp surimi in the future because the catches are large. Silver carp is very suitable for surimi because of its attractive white color and taste. Consumption in China and India as fresh fish is large. However, silver carp surimi exhibited considerable gel softening (modori) in the course of heating, resulting in a decrease in textural quality, eventually having a negative effect on acceptance and price of the surimi products. For this purpose, this paper investigates the effects of cathepsins B and L on modori, and compares the roles of pure cathepsins in degradation of myosin at similar conditions as for processing of silver carp surimi products.