Integrated analysis of physicochemical properties, microbiome, and flavor profiles for differentiating two aroma grades of sauce-flavor Daqu

Aroma characteristics are critical indicators for evaluating sauce-flavor Daqu quality. This study systematically compared physicochemical properties, enzyme activities, microbiomes, and flavor profiles of first-grade (GF) and second-grade (GS) aroma Daqu . GF had higher total acidity, amino nitrogen content, acid protease activity, a lower pH, and was correlated with enrichment of bacteria potentially associated with flavor precursor production such as Kroppenstedtia guangzhouensis and Kroppenstedtia eburnea . GS showed higher liquefying/cellulase activities and pH, and was associated with dominance by hydrolytic fungi such as Paecilomyces variotii and off-odor-related Oceanobacillus . HS-SPME-GC–MS combined with VIP and OAV analyses identified 11 differential volatile compounds. Aldehydes were strongly correlated with positive aroma grading and may serve as potential indicators associated with grade differentiation, while GS accumulated dimethyl trisulfide correlating with off-odors. The findings reveal the relationships between multi-omics characteristics and aroma grade differentiation of Daqu , and provide theoretical support for Daqu quality evaluation and production regulation.