Deciphering microbial community dynamics along the fermentation course of soy sauce under different temperatures using metagenomic analysis

Abstract

Fermented soy sauce consists of microorganisms that exert beneficial effects. However, the microbial community dynamics during the fermentation course is poorly characterized. Soy sauce production is classified into the stages of mash fermentation with koji (S0), brine addition (S1), microbial transformation (S2), flavor creation (S3), and fermentation completion (S4). In this study, microbial succession was investigated across stages at different temperatures using metagenomics analyses. During mash fermentation, Aspergillus dominated the fungal microbiota in all stages, while the bacterial composition was dominated by Bacillus at room temperature and by a diverse composition of enriched lactic acid bacteria (LAB) at a controlled temperature.Compared with a stable fungal composition, bacterial dynamics were mostly attributable to fluctuations of LAB, which break down carbohydrates into lactic acid. After adding brine, increased levels of Enterococcus and decreased levels of Lactococcus from S1 to S4 may reflect differences in salinity tolerance. Staphylococcus, as a fermentation starter at S0, stayed predominant throughout fermentation and hydrolyzed soybean proteins. Meanwhile, Rhizopus and Penicillium may improve the flavor. The acidification of soy sauce was likely attributable to production of organic acids by Bacillus and LAB under room temperature and controlled temperature conditions, respectively. Metagenomic analysis revealed that microbial succession was associated with the fermentation efficiency and flavor enhancement. Controlled temperature nurture more LAB than uncontrolled temperatures and may ensure the production of lactic acid for the development of soy sauce flavor.

Research Progress on Bioaugmentation Technology for Improving Traditional Chinese Fermented Seasonings

“…Koji fermentation, triggered by the introduction of molds like Aspergillus oryzae to steamed soybeans, is a fundamental stage in the creation of top-quality soy sauce. The fermentation of moromi, which comprises koji, sea salt, and brine, typically takes several months to finish [54]. During the koji fermentation stage, molds generate proteolytic enzymes that hydrolyze proteins into peptides and amino acids, as well as amylase to convert starch into fermentable sugars.…”