Characterization of brine proteases as agents of hydrolysis during the ripening of fermented sardine with rice-bran

Abstract

The present study aims to clarify the role of brine proteases (BP) as agents of hydrolysis during the ripening of fermented sardine Etrumeus micropus with rice-bran (FSR). FSR is produced by the addition of the brine. The BP activity was highest, and visceral protease (VP) was higher than that of muscle protease (MP). Optimum temperature of BP was at 55°C. BP was very stable for heat denaturation at 45-55°C and effected by high concentrations of NaCl. A maximum activity of BP was at pH 8. The BP was strongly inhibited by serine protease inhibitors such as soybean trypin inhibitor (STI) and diisopropyl fluorophosphate (DFP). Trypsin-like, chymotrypsin-like, and aminopeptidase-like activity was detected in BP. These proteases were stable in the presence of 12% NaCl. In conclusion, BP as the agent of hydrolysis during the ripening of FSR must be due to the serine proteases and the metal proteases from the viscera of sardine. These results showed that trypsin-like, chymotrypsin-like, and aminopeptidase-like enzymes in brine may hydrolyze fish meat during the ripening of FSR.