Bacteria‐induced amino acid metabolism involved in appearance characteristics of high‐temperature Daqu

BACKGROUND Significant changes occurd in Daqu bricks on the 15th day of incubation, and brick color (yellow, brown, or dark) is generally used as a standard for quality evaluation by experienced workers. This study aimed to explore the basis behind the phenomenon through multi‐omics studies. The physicochemical properties of different high‐temperature Daqu were compared. Furthermore, PacBio sequencing and the ultra‐high‐performance liquid chromatographic–Q‐exactive–mass spectrometric approach were employed to analyze the differences in the microbiome and metabolome among different Daqu samples. RESULTS Bacillus was the biomarker of yellow Daqu, Thermoactinomyces and Thermoascus were the key genera in brown Daqu, and Burkholderiales, Sphingomonas, and Ralstonia were biomarkers in dark Daqu. The physicochemical characteristics (especially the color values) of different high‐temperature Daqu showed strong correlations with the bacterial alpha diversity and the relative abundance of dominant bacterial genera. Amino acid metabolism pathways including tryptophan metabolism, β‐alanine metabolism, and arginine biosynthesis were the key factors resulting in the characteristic differences where Bacillus, Burkholderia, Ralstonia, and Sphingomonas were pivotal bacterial genera. The relative abundance of Bacillus had a positive correlation with the content of 3‐hydroxykynurenamine, l‐glutamic acid, and pantothenic acid, while it showed a negative correlation with indoleacetic acid, l‐tryptophan, N‐acetylserotonin, l‐histidine, l‐aspartic acid, phosphatidylserine, 5‐methoxyindoleacetate, and L‐serine. Burkholderia, Ralstonia, and Sphingomonas had the opposite effects. CONCLUSION Microbes play different roles in amino acid metabolism pathways, producing different metabolites, contributing to the differences in Daqu appearance and quality. © 2022 Society of Chemical Industry.