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

Abstract

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.

Unveiling the microbiota of sauce-flavor Daqu and its relationships with flavors and color during maturation

“…Notably, all three types reached a final moisture content below 9%, adhering to the standard for qualified Daqu , preserving enzymatic and microbial activities ( Paredes-López et al, 1988 ; Xia et al, 2022 ). While the dropping trend of acidity during maturation was similar across the three colored Daqu , black Daqu exhibited the highest acidity, white Daqu the lowest, and yellow Daqu intermediate, consistent with findings in Zhang’s study ( Zhang et al, 2022 ). At the end of the maturation period, the acidity values for these three types of Daqu were 1.03, 0.56, and 0.35 mmol/10 g, respectively ( Figure 2B ), which were lower than those in previous studies ( Deng et al, 2020 ; Zhang et al, 2022 ).…”

“…While the dropping trend of acidity during maturation was similar across the three colored Daqu , black Daqu exhibited the highest acidity, white Daqu the lowest, and yellow Daqu intermediate, consistent with findings in Zhang’s study ( Zhang et al, 2022 ). At the end of the maturation period, the acidity values for these three types of Daqu were 1.03, 0.56, and 0.35 mmol/10 g, respectively ( Figure 2B ), which were lower than those in previous studies ( Deng et al, 2020 ; Zhang et al, 2022 ). In terms of reducing sugar, initial content varied significantly among the Daqu types but showcased an overall dropping trend, stabilizing at a low level of approximately 1.40% by the end of maturation ( Figure 2C ).…”

“…As for fungal composition, the predominant phyla included Ascomycota, Mucoromycota, Basidiomycota, Mortierellomycota, Chytridiomycota, and Rozellomycota (Figure 5B). Ascomycota was the most dominant phylum, collaborating with previous studies (Deng et al, 2020;Zhang et al, 2022). The abundance of Ascomycota in black Daqu maintained above 94.29%, yellow Daqu exhibited fluctuations ranging from 80.51 to 99.77%, and white Daqu displayed an initial increase followed by a decrease (80.03 to 97.43 to 74.23%) (Figure 5B).…”

“…Deng’s research shed light on the discrepancies in microbial composition among colored Daqu ( Deng et al, 2020 ). In addition, several studies unveiled the potential factors contributing to color formation in the three types of Daqu , highlighting the significant roles played by amino acid metabolism and the Maillard reaction ( Zhang et al, 2022 ; Zhu Q. et al, 2023 ).…”

Differential Characteristics of the Metabolic Profiles and Microbial Community between Superior and Normal Grades of Nongxiangxing-daqu

“…Based on commercial databases of KEGG and MetaCyc [ 26 ], the metabolic pathway enrichment was analyzed. A total of three hundred and ninety-nine bacterial metabolic pathways and seventy-four fungal metabolic pathways were obtained in the context of MetaCyc analysis.…”