Insights into Microbial and Metabolite Profiles in Traditional Northern Thai Fermented Soybean (Tuanao) Fermentation Through Metagenomics and Metabolomics

Tuanao, a traditional Northern Thai fermented soybean product, was profiled with an integrated multi-omics workflow to clarify how microbes and metabolites co-evolve during household fermentation. Soybeans were fermented spontaneously for three days; samples from four time points were analyzed by shotgun metagenomics alongside 1H-NMR and UHPLC-ESI-QTOF-MS/MS metabolomics. <i>Bacillus</i> spp. (phylum Bacilliota) quickly supplanted early Enterobacterales and dominated the mature microbiome. The rise of <i>Bacillus</i> coincided with genes for peptide and carbohydrate utilization and with the accumulation of acetate, free amino acids (glutamine, leucine, alanine, valine) and diverse oligopeptides, whereas citrate and glucose-1-phosphate were depleted. This <i>Bacillus</i>-linked metabolic shift indicates that Tuanao is a promising source of probiotics and bioactive compounds. Our study provides the first system-level view of Tuanao fermentation and offers molecular markers to guide starter-culture design and quality control.