Virgibacillus halodenitrificans ST‐1 for fermentation of shrimp paste and hydrolysates of its protease

The nutrition and flavor of shrimp paste came from hydrolyzation by enzymes that were produced by microorganisms. The salt‐tolerant strain Virgibacillus halodenitrificans ST‐1 isolated from shrimp paste was studied and used in the fermentation of shrimp paste. The strain and the protease produced by ST‐1 were investigated. The optimum pH of the protease was 8.0, and the reaction temperature was 30°C. The protease showed high activity in the range of pH (5.0–11.0) and NaCl concentration (1%–15%). Divalent cations such as Ba(2+), Ca(2+), Mg(2+), Mn(2+), and Si(2+) could enhance the protease activity. Residual activity of protease was more than 90% when it was incubated with PMSF and H(2)O(2). Also, the enzyme retained more than 90% of initial activity after it was incubated with organic solvents. Variety of natural proteins could be substrates of the protease. By analyzing the release rate of free amino acids, it was predicted that the cleavage sites of the protease were mainly Glu, Asp, Gly, Leu, and Lys. Moreover, the hydrolysates of the protease had antioxidant activity, especially for DPPH and superoxide anion radical scavenging. The strain ST‐1 and the protease both were excellent candidates for food industries.