Abstract: Bacillus, a common microorganism in traditional fermented foods, has good tolerance and the secretion ability of protease and amylase. It promotes the degradation of raw materials and enhances the flavor of fermented food during the fermentation process. 56 strains were separated with good protease activity from high-salt liquid-state moromi by casein plate method, and the enzyme activity were determined by koji-making after the Oxford-cup method rescreening. The strain CS1.11 with the highest amylase activity and CS1.13 with the highest protease activity and CS1.17 with the highest cellulase activity were screened. According to the sequence analysis of 16S rRNA and morphological, CS1.11, CS1.13, CS1.17 were identified as Bacillus velezensis, Bacillus methylotrophicus and Bacillus subtilis, respectively. 3 strains test bacteria and the control bacterium Bacillus subtilis CS1.03 were separately subjected to salt brine fermentation after koji-making. It was found that the fermented soy sauce inoculating CS1.13 had the highest ammonia nitrogen content (5.12 g/L). and the fermented soy sauce inoculating CS1.11 had the highest reducing sugar content (27.20 g/L). The results were consistent with the enzyme activity. In addition, 4 strains have little effect on the total acid content of soy sauce. The SPME-GC-MS internal standard method was used to qualitatively and quantitatively analyze the fermentation soy sauce. It was found that the 3 strains test bacteria and control bacterium had the advantages of producing pyrazines and their precursors acetoin and 2,3-butanediol. 3 strains test bacteria are better than the control bacterium. Pyrazines can give good flavor and health factors to soy sauce, and are characteristic flavor substances of Bacillus fermented soy sauce. Bacillus CS1.11, CS1.13, CS1.17 screened from high-salt liquid-state moromi have the potential of promoting moromi fermentation, riching flavor of soy sauce and increasing the health factors, and they will have good application prospects.

Key words: Bacillus spp., Promoting moromi fermentation, Screening of Oxford-cup method, Protease activity, Pyrazines