Effects of wheat-surface microorganisms on community assembly and characteristic flavor formation in high-temperature Daqu

Wheat serves as a vital initial inoculum for high-temperature Daqu microbiota, yet the functional roles of its indigenous microorganisms in Daqu quality formation remain poorly understood. Here, high-temperature Daqu was prepared using sterilized (Daqu_S) and non-sterilized wheat (Daqu_T). Combining high-throughput sequencing, flavoromics, and metabolomics, this study investigated how wheat-surface microorganisms shape Daqu microecology, community assembly, and flavor metabolism. Wheat-surface sterilization removed most of the epiphytic microbes and reshaped microbiome succession, whereby Kroppenstedtia and Thermoascus declined while Saccharopolyspora , Weissella , and Thermomyces were enriched. Co-occurrence network and neutral community model analyses revealed that sterilization increased network scale but decreased the proportion of positive correlations, and Daqu_S displayed a greater contribution of stochastic assembly processes. OPLS-DA models identified 19 differential volatiles (of 76 total) and 30 differential non-volatile metabolites (of 252 total). Daqu_T accumulated key amino-acid precursors and signature pyrazines including tetramethylpyrazine and trimethylpyrazine, whereas Daqu_S showed flavor imbalance with abnormal accumulation of lipids, amines, and aromatics. Multi-omics analysis indicated that bacteria enriched in Daqu_T encoded predicted key enzymes (e.g., EC:2.2.1.6, EC:1.4.1.2), which were putatively critical for carbon-nitrogen metabolism and characteristic pyrazine biosynthesis. Collectively, wheat-surface microorganisms appear to underpin microecological establishment, metabolite accumulation, and typical flavor development in high-temperature Daqu, offering new insights for targeted Daqu quality modulation.