Wheat-Surface Microbiota as a Key Driver of Daqu Quality: Evidence from Microbial Diversity and Volatile Flavor Analysis.

Traditional fermentation processes rely on complex microbial communities; however, the specific contributions of raw material-associated microorganisms to community assembly and flavor formation remain unclear. In this study, traditional Daqu (T) and surface-disinfected Daqu (S) were used as paired controls to decouple the contribution of raw material-associated microorganisms. By integrating community, flavor, and functional analyses, we revealed their ecological roles in driving deterministic assembly, reshaping fungal interactions, and associating with characteristic flavors. The results showed that T was dominated by Saccharopolyspora and Thermoascus, whereas S was dominated by mesophilic lactic acid bacteria such as Weissella. The selective pressure imposed by wheat-associated microorganisms drove deterministic community assembly and shifted fungal interactions from competition to positive mutualism. A total of 110 flavor compounds were identified, from which 21 potential contributing compounds and 25 differential markers were screened. The characteristic flavors of T were tetramethylpyrazine, dimethyl trisulfide, benzaldehyde, isovaleric acid, and 2-methoxy-4-vinylphenol, whereas those of S were mainly 1-octen-3-ol, 2-octanone, and phenylethyl alcohol. Functional prediction and correlation analysis showed that wheat-associated microorganisms were positively correlated with primary metabolic pathways such as those involving amylase and alcohol dehydrogenase, while Saccharopolyspora, Cutaneotrichosporon, and specific Bacillus species were positively correlated with secondary metabolism and characteristic flavor formation. This study deepens the understanding of the ecological roles of raw material-associated microorganisms and provides a scientific basis for process optimization and microbial community regulation in traditional fermented foods.