Decoding the thermocyclic solar-driven fermentation: Multi-omics insights into microbial and metabolic dynamics of...

Traditional Chishui River Basin soy sauce is produced through prolonged solar-cycle fermentation under diurnal temperature fluctuations and moisture absorption. Here, we employed integrated metagenomic and metabolomic analyses to investigate microbial and metabolic dynamics throughout fermentation. Results revealed a three-phase microbial succession: initial fungal-hydrolytic phase dominated by Aspergillus oryzae (82.28%), marked by proteolysis and amino acid accumulation; transitional phase enriched with Weissella (23.45%) and Zygosaccharomyces rouxii (5.85%), producing organic acids, esters, and maillard intermediates; maturation phase dominated by Bacillus (86.48%), associated with sharp increases in umami-enhancing peptides, pyrazines (e.g., tetramethylpyrazine), and phenolic compounds (e.g., 4-ethylguaiacol). Extended sun exposure selects for Bacillus dominance, allows sufficient time for slow chemical reactions, and enriches the volatile profile with stable pyrazines and phenolic compounds. These findings validate the flavor and mechanisms of traditional Chishui River Basin soy sauce and offer strategies for fermentation optimization via environmental and microbial regulation while maintaining product authenticity.