Thrombolytic Activities of Nattokinase Extracted from Bacillus Subtilis Fermented Soybean Curd Residues

To recycle food wastes, soybean curd residue (SCR) was used as substrate in Bacillus subtilis fermentation to extract nattokinase (NK). In researches, the extract conditions of Natto-NK, as well as the fibrinolytic activities of SCR-NK were investigated. In fibrinolytic activities, Natto-NK and wet corn distillers’ grain (WDG)-NK were regarded as comparisons. It was showed that the highest Natto-NK yield could reach 0.108 g per 150 g Natto (wet), when extract conditions were involved with saline (0.9%) 375 ml, (NH4)2SO4 30 g and the ratio of 3/4 of ethanol to saline. After fibrin hydrolysis for 4 h, hydrolyzed areas of SCR-NK were 49 mm in one hole, consistent with that of Natto-NK. Apart from this, as a result calculated according to the dried substrate, the SCR-NK yields (0.415 g/150 g) were significantly (p<0.05) higher than Natto-NK yields (0.270 g/150 g), although in activities, SCR-NK (1.3 fibrinolytic unit/ml (FU/ml)) showed slight superiorities to that of Natto-NK. It suggested that SCR could be regarded as a promising fermentation source for NK production.