Contrasting the microbial community and non-volatile metabolites involved in ester synthesis between Qing-flavor Daqu and Nong-flavor Daqu

Daqu, a fermentation starter, was important source of key flavors of Chinese Baijiu. The quality of Chinese Baijiu could be significantly affected by the ester-synthesis microorganisms. In order to clarify the microbial community that promoted the ester formation in Daqu, the dynamic changes of microbial community and non-volatile profiles of Qing-flavor Daqu and Nong-flavor Daqu samples through the whole making process were investigated by Illumina MiSeq platform and liquid chromatograph-mass spectrometry (LC-MS). The non-volatile compounds related to ester synthesis were identified by comparing with ester synthesis pathway and partial least squares discriminant analysis (PLS-DA). Correlations between microbial community and non-volatile metabolites involved in ester synthesis of two types of Daqu were disclosed by Pearson correlation analysis. Results showed that a total of 50 key compounds involved in ester synthesis were identified and 25 primary functional microorganisms were screened in 39 samples. Among them, in Qing-flavor Daqu, the top three primary functional microorganisms that had strong correlations with ester-formation precursors were Lactobacillus, Pantoea, and Sphingomonas; Lactobacillus and Pantoea had significantly positive interactions with various microorganisms, but Sphingomonas did not interact with others. In Nong-flavor Daqu, the top three primary functional microorganisms that had strong correlations with ester-formation precursors were Candida, Apiotrichum, and Cutaneotrichosporon. Candida showed strong positive correlation with other microorganisms, whereas Apiotrichum and Cutaneotrichosporon had no interaction with other microorganisms. The study could help our understanding of the microbial metabolism process in Daqu and provided a scientific basis for a controllable and feasible fermentation system.