Extraction and Enzymatic Characteristics of Serine Protease from Grass Carp(Ctenopharyngodon idellus)Musle and the Effect of Soybean Trypsin Inhibitor on Its Activity
[Objective]To investigate the extraction method and enzymatic properties of crude enzyme of myofibrill-bound serine protease(MBSP)from grass carp(Ctenopharyngodon idellus),as well as the effect of soybean trypsin inhibitor on the quality of grass carp surimi gel,and to provide a theoretical basis for improving the quality of traditional grass carp surimi products in China.[Method]The crude enzyme solution of MBSP was extracted from the dorsal muscle of grass carp,and the optimal rinsing times(1-5 times),heating temperature(35,or 40,45,50,55℃)and pH vaule(pH 4.0,or pH 5.5)during the extraction process were determined by using the enzyme activity of the extract as an indicator.We also extracted the crude MBSP solution under the optimal extraction conditions,set up gradient experiments to explore the enzymatic properties of the crude MBSP,such as optimal temperature,pH,stability,etc.Finally,we investigated the effect of soybean trypsin inhibitor(STI)on the MBSP enzyme activity and its modulation on the properties of grass carp surimi gelatinization.[Result and Conclusion]The crude MBSP solution obtained after three times of rinsing,from heat treatment at 45℃and acid elution at pH 4.0 had the highest enzyme activity(P<0.05).Its optimum pH was around 9.0(P<0.05),and the optimum temperature is 45℃(P<0.05),it has good temperature stability(P<0.05).Besides,its activity could be inhibited to a certain degree by Na+and activated by K+and Ca2+(P<0.05).STI could significantly improve the texture of grass carp surimi,and it has a reversible competitive inhibition on crude MBSP,with a semi-inhibitory concentration of 10.85 μg/mL,and an inhibitory constant of Ki=0.24 μmol/L.
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