Screening and fermentation performance of Aspergillus oryzae in soy sauce brewing in the Chishui River Basin

In order to promote the excavation and utilization of traditional soy sauce brewing strain resources in the Chishui River Basin, after primary and secondary screening, molds were selected from the brewing environment and fermentation mash samples of the Chishui River. The selected strains were identified through morphological observation and molecular biology techniques. Using Aspergillus oryzae Huniang 3.042 (M3.042) as the control, the fermentation performance of the selected strains applied in soy sauce koji and sauce mash was investigated. The results showed that four strains with higher enzyme activity (numbered XS-15, XS-17, XS-33, and XS-34) were screened out and all were identified as A. oryzae. Compared with the strain M3.042, the activities of neutral protease, acidic protease, aminopeptidyl and carboxypeptidyl in the preparation of soy sauce koji by the four strains of A. oryzae increased by 59.74%-80.93%, 123.27%-184.69%, 128.74%-320.70% and 125.85%-175.47%, respectively. The content of amino acid nitrogen, total acid, free amino acids and volatile components in the sauce mash increased by 2.30%-15.87%, 8.51%-34.47%, 4.41%-15.20% and 26.19%-71.06%, respectively. Among them, the soy sauce koji prepared by strain XS-34 exhibits superior enzyme activity. The contents of total acid (1.44 g/100 g), amino acid nitrogen in the sauce mash (0.95 g/100 g), reducing sugar (3.50 g/100 g), free amino acid (27.74 g/kg), and volatile component (20.7 mg/kg) were all the highest. The types of key volatile flavor components (ROAV>1) were the most abundant (33 kinds), and it also contained the unique substance 2-nonenal.