Relationship between the Protease and Amylase Systems of Aspergillus oryzae PRB-1 and the Physicochemical Properties of High-salt Diluted-state Soy Sauce
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Abstract:
Isolated Aspergillus oryzae PRB-1(AP) strain was applied in the manufacture of koji and high-salt diluted-state soy sauces. The results showed that the acid protease and neutral protease activities of AP koji were 398.53 U/g and 1539.98 U/g, which were increased by 71.79% and 59.93% when compared with those of Aspergillus oryzae 3.042(AO), respectively. The amylase activity of AP koji was slightly lower than that of AO. AP koji contained five neutral protease components, two acid protease components, and four amylase components, among which protease Rf6 and amylase Rf3 showed the highest activity. The total acid content of AP and AO moromi samples increased as the fermentation time was prolonged and the pH value decreased from neutral to acidic. Amino acid nitrogen continuously increased in moromi and the reducing sugar content showed a slow downward trend after the initial sharp increase. The amino acid nitrogen content of AP first filtrate was 0.86 g/100 mL after 55 days of fermentation. Meanwhile, the utilization ratio of raw material (81.97%) and the amino acid production rate (61.37%) of AP were higher than those of AO. The reducing sugar content of AP first filtrate was 4.82 g/100 mL, lower than that of AO. The neutral protease activity of koji was positively correlated with the amino acid production rate (p < 0.05), but had no significant impact on other indices (p > 0.05).
