Deciphering the characteristics of strong-flavor Daqu at different grades through integrated microbiome and metabolome analysis

In strong-flavor <i>Baijiu</i> production, <i>Daqu</i> quality is crucial, yet grading often relies on subjective evaluation. This study compares physical and chemical properties, metal content, microbial composition, and metabolic profiles of three <i>Daqu</i> grades (P90, F90, S90) using a multi-omics approach. P90 exhibits superior esterification power and is dominated by <i>Bacillus</i>, <i>Thermoactinomyce</i>, and <i>Thermomyces</i>, with enhanced ester formation and aromatic precursor accumulation. Although S90 has higher microbial diversity, its lower abundance of key functional strains may limit fermentation efficiency and flavor compound production. PICRUSt analysis reveals grade-specific differences in carbohydrate, amino acid, and nucleotide metabolism pathways. Metabolomic profiling identifies 23 amino acids and derivatives enriched in <i>Daqu</i>, primarily mapping to tryptophan, phenylalanine, and arginine-proline pathways. These likely contribute to aroma precursor synthesis and microbial stability. Overall, these findings elucidate the microbiome-metabolome interactions underlying <i>Daqu</i> quality grading and inform strategies for <i>Daqu</i> quality evaluation and improvement in <i>Baijiu</i> fermentation.