Microbial Community and Metabolite Dynamics During Soy Sauce Koji Making

Guiliang Tan; Min Hu; Xiangli Li; Xueyan Li; Ziqiang Pan; Mei Li; Lin Li; Yi Wang; Ziyi Zheng

doi:10.3389/fmicb.2022.841529

Microbial Community and Metabolite Dynamics During Soy Sauce Koji Making

Front Microbiol. 2022 Feb 25:13:841529. doi: 10.3389/fmicb.2022.841529. eCollection 2022.

Authors

Guiliang Tan¹, Min Hu², Xiangli Li³, Xueyan Li¹, Ziqiang Pan¹, Mei Li¹, Lin Li¹, Yi Wang¹, Ziyi Zheng¹

Affiliations

¹ School of Material Science and Food Engineering, Zhongshan Institute, University of Electronic Science and Technology of China, Zhongshan, China.
² School of Environmental and Safety Engineering, Changzhou University, Changzhou, China.
³ School of Health Industry, Zhongshan Torch Vocational and Technical College, Zhongshan, China.

Abstract

Koji making is a pre-fermentation stage in soy sauce manufacturing that impacts final product quality. Previous studies have provided valuable insights into the microbial species present in koji. However, changes in microbial community functional potential during koji-making are not well-known, nor are the associations among microbial populations and flavoring characteristics. In the present study, we investigated the succession of microbial communities, microbial community functional potential, metabolite profiles, and associations among microbial community members/functions with metabolites during koji making using shotgun metagenomic and metabolomic analyses. Firmicutes, Proteobacteria, and Ascomycota were identified as the most abundant microbial phyla in early koji making (0-12 h). Aspergillus (fungi) and Weissella (bacteria) exhibited marked abundance increases (0.98-38.45% and 0.31-30.41%, respectively) after 48 h of fermentation. Metabolite analysis revealed that aspartic acid, lysine, methyl acetate, isovaleraldehyde, and isoamyl alcohol concentrations increased ∼7-, 9-, 5-, 49-, and 10-fold after 48 h of fermentation. Metagenomic profiling demonstrated that koji communities were dominated by genes related to carbohydrate metabolism and amino acid metabolism, but functional profiles exhibited marked shifts after 24 h of fermentation. The abundances of genes within the categories of carbohydrate and amino acid metabolism all increased during koji making, except for pyruvate metabolism, glycolysis/gluconeogenesis, and the citrate cycle. Correlational analyses indicated that Aspergillus, Lactococcus, Enterococcus, Corynebacterium, and Kocuria abundances were positively correlated with 15 amino acid concentrations (all p < 0.05), while Weissella abundances were positively correlated with concentrations of volatile flavor compounds, including eight amino acids, phenylacetaldehyde, acetic acid, 2,3-butanediol, ethyl acetate, and ethanol (p < 0.05). These results provide valuable information for understanding the microbial-associated mechanisms of flavor formation during koji making.

Keywords: functional potential; koji making; metabolites; metagenome; microbial community structure.