Exploring the core microorganisms and mechanisms responsible for biogenic amines production during soy sauce fermentation

Hazardous levels of biogenic amines (BA) are frequently detected in soy sauce. However, the microorganisms and mechanisms responsible for BA formation in soy sauce are not well understood. In this study, we investigated the dynamic changes and metabolic pathways of BAs during soy sauce fermentation via metabolome and metagenomic analyses. Spermidine and putrescine were the main BAs detected during koji making, while putrescine, tyramine, phenylethylamine, and histamine were dominant during moromi fermentation. PCA analysis revealed that the soy sauce fermentation process could be divided into five representative stages based on the dynamics of BAs. Metagenomic analysis uncovered that a total of 15 genera were mainly involved in BAs formation, particularly, histamine was principally produced by Klebsiella, and Bacillus was the major tyramine-synthesizing bacteria. Correlation analysis showed that pH increase inhibited the spermidine production during koji making, whereas elevated NaCl concentration facilitated the phenylethylamine formation during moromi fermentation. Co-occurrence network analysis unveiled the associations between the BA-producing microorganisms and other genera. Overall, these results have improved our understanding of the mechanism of BA formation during soy sauce fermentation and guided the development of fermentation agents capable of degrading BA in industrial manufacture soy sauce production.