Dynamic interplay between core functional microbial succession and flavor metabolite formation in naturally fermented sufu: A multi-omics perspective

Sufu, a traditional Chinese fermented soybean product, has a diverse flavor profile influenced by fermentation methods and starter cultures. This study aimed to elucidate the dynamic interplay among microbial communities, quality, and flavor formation in naturally fermented sufu using multi-omics approaches. Through the characterization of flavor substances, a total of 78 volatile flavor compounds and 23 free amino acids (FAAs) were identified. Among them, 9 volatile flavor compounds (phenylethyl alcohol, odor activity value (OAV) = 3.11; 1-octen-3-ol, OAV = 34.83; ethyl valerate, OAV = 1.97; ethyl isobutyrate, OAV = 3.87; ethyl hexanoate, OAV = 1.17; phenylacetaldehyde, OAV = 3.90; 3-octanone, OAV = 3.84; 2-methoxy-4-vinylphenol, OAV = 2.94; and 2-pentylfuran, OAV = 21.15) and 11 FAAs (glutamic acid, alanine, glycine, proline, histidine, leucine, methionine, phenylalanine, tyrosine, valine, and isoleucine) were determined as key flavor substances in sufu. Additionally, three bioactive FAAs (Citrulline, Ornithine, and γ-Aminobutyric Acid) were identified. Metagenomic analysis revealed Actinomucor, Enterobacter, and Tetragenococcus as core functional microbiota, showing significant positive correlations (P < 0.05) with these key flavor compounds. These microbial genera played pivotal roles in quality development, as evidenced by their association with peak enzyme activities (protease: 34.35 U/g; esterase: 20.08 U/g at 14 d), which drove texture softening (hardness reduction from 1840.71 to 543.13 g) and FAA accumulation (glutamic acid reached 3076.39 mg/100 g). The study establishes a microbial-enzyme-flavor network where protease initiates precursor release, esterase determines complexity, and lipase modulates specificity. The results provide scientific evidence for enhancing sufu fermentation to boost quality and flavor.