Bacillus subtilis B-2 Improved the Quality of Low-Salt Fermented Fish Sauce through Regulating the Microbial Community

In this study, the effect of fermentation with Bacillus subtilis B-2, a salt-tolerant strain capable of producing high yield of protease, on the microbial community and the contents of biogenic amines and amino acid nitrogen (AAN) during the fermentation of low-salt fish sauce. The results of high-throughput 16S rRNA gene sequencing showed that fermentation with B-2 reduced the richness and evenness of the microbial community, Bacillus was dominant throughout the fermentation process and the abundance of spoilage microorganisms significantly decreased. B-2 significantly inhibited the formation of histamine, putrescine, cadaverine, and tyramine, and their contents at the end of fermentation decreased by 25.9%, 35.6%, 23.6% and 9.3%, respectively, compared with those in naturally fermented fish sauce. The content of AAN in low-salt fish sauce was significantly improved by inoculated fermentation, reaching 1.23 g/100 mL after 15 days of fermentation, which was significantly higher than that of naturally fermented fish sauce (0.79 g/100 mL). The correlation network map showed that the decrease in the abundance of Brevibacterium, Dietzia, Paracoccus, Aequorivita, and Brachybacterium was the major reason for the decrease in microbial diversity at the late stage of fermentation of naturally fermented fish sauce. The abundance of Stenotrophomonas showed a significantly positive correlation with the contents of many biogenic amines in naturally fermented and B-2 fermented fish sauce, suggesting its important role in the formation of biogenic amines in low-salt fish sauce. Comparative analysis of the microbial community and quality attributes at the end of fermentation showed that the metabolism of B-2 was the main reason for the decrease in the species and abundance of spoilage microorganisms, the increase in AAN content, and the decrease in the contents of key biogenic amines. B. subtilis B-2 is expected to be developed as a special fermentation starter for fish sauce to improve the quality and safety of rapidly fermented low-salt fish sauce.