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[Display omitted] • P. pentosaceus , W. paramesenteroides , R. emersonii, B. spectabilis were dominant in Daqu. • Four Saccharopolyspora species were dominant in wheat Qu. • Flavor metabolic pathways in Qu microbiota were reconstructed. • The dominant microbes in Qu may not be the main functional microbes. Daqu and wheat Qu are saccharification and fermenting agents in Chinese huangjiu and baijiu production. This study aimed to investigate the difference between Daqu and wheat Qu in physicochemical indices, microbial communities, functional genes, and the metabolic network of key microbes responsible for flavor synthesis by whole-metagenome sequencing and metabolite analysis. Herein, physicochemical indices indicated that compared with wheat Qu , Daqu exhibited higher protease and cellulase activity and acidity, and lower glucoamylase and amylase enzyme activity. Metagenomic sequencing reveals that although Daqu and wheat Qu community composition have significant differences at species level, they have similar functional genes. Daqu were enriched in Pediococcus pentosaceus , Weissella paramesenteroides , Rasamsonia emersonii and Byssochlamys spectabilis (22.48% of the total abundance), while wheat Qu harbored greater abundances of Saccharopolyspora (54.78%, Saccharopolyspora rectivirgula , Saccharopolyspora shandongensis , Saccharopolyspora hirsuta , Saccharopolyspora spinose , and Saccharopolyspora erythraea). From a functional perspective, the important functions of Daqu and wheat Qu are both amino acid metabolism and carbohydrate metabolism. Meanwhile, a combined analysis among microbiota, functional genes, and dominant flavors indicated S. shandongensis , S. rectivirgula , and S. spinose might be the main contributor to the synthesis of flavor compounds in wheat Qu , while R. emersonii , W. paramesenteroides , Leuconostoc citreum , Leuconostoc mesenteroides , Weissella cibaria and P. pentosaceus may make the greatest contribution to flavor compounds synthesis in Daqu. This study reveals the microbial and functional dissimilarities of Daqu and wheat Qu , and helps elucidating different metabolic roles of microbes during flavor formation. [ABSTRACT FROM AUTHOR]

Aromatic alcohols (including β-phenylethanol, tyrosol and tryptophol) could contribute positively to the aroma flavor of huangjiu at an appropriate amount. In this study, it was found that the aromatic alcohols in huangjiu were predominantly synthesized by Saccharomyces cerevisiae HJ01. The Ehrlich pathway and shikimate pathway, including 31 genes, are responsible for aromatic alcohol biosynthesis in S. cerevisiae. During the first 120 h of huangjiu fermentation, the genes GAP1 HJ01 (permease), BAT2 HJ01 (transaminase), PDC1 HJ01 and PDC5 HJ01 (pyruvate decarboxylase), and ADH1 HJ01 (alcohol dehydrogenase) formed integrated Ehrlich pathway are responsible for aromatic alcohol biosynthesis. In S. cerevisiae HJ01, the mutations in the promoter region of genes GAP1 HJ01, BAT2 HJ01, PDC1 HJ01, and PDC5 HJ01 involved in the Ehrlich pathway increased the promoter strength and transcriptional levels of related genes. The addition of 20 U/g acid protease could substantially increase the expression levels of genes involved in the Ehrlich pathway, and therefore there were 34.7% increasing for the concentration of total aromatic alcohols. • Aromatic alcohols in huangjiu are synthesized by Saccharomyces cerevisiae. • Aromatic alcohols in huangjiu are mainly synthesized through the Ehrlich pathway. • Key genes and promoter mutations in Ehrlich pathway were identified. • Acid protease enhanced expression level of key genes. [ABSTRACT FROM AUTHOR]