Abstract
The metabolism and accumulation of flavor compounds in Chinese Baijiu are driven by microbiota succession and their inter-related metabolic processes. Changes in the microbiome composition during Baijiu production have been examined previously; however, the respective metabolic functions remain unclear. Using shotgun metagenomic sequencing and metabolomics, we examined the microbial and metabolic characteristics during light-flavor Baijiu fermentation to assess the correlations between microorganisms and their potential functions. During fermentation, the bacterial abundance increased from 58.2% to 97.65%, and fermentation resulted in the accumulation of various metabolites, among which alcohols and esters were the most abundant. Correlation analyses revealed that the levels of major metabolites were positively correlated with bacterial abundance but negatively with that of fungi. Gene annotation showed that the Lactobacillus species contained key enzyme genes for carbohydrate metabolism and contributed to the entire fermentation process. Lichtheimia ramosa, Saccharomycopsis fibuligera, Bacillus licheniformis, Saccharomyces cerevisiae, and Pichia kudriavzevii play major roles in starch degradation and ethanol production. A link was established between the composition and metabolic functions of the microbiota involved in Baijiu fermentation, which helps elucidate microbial and metabolic patterns of fermentation and provides insights into the potential optimization of Baijiu production.
Highlights
Baijiu, a traditional fermented alcoholic beverage, is very popular in China
The culture-based microbial abundance estimates and physicochemical properties of fermented grain provided the first insights into the microbial composition and metabolic changes, which offered a basis for further omics analyses
During light-flavor Baijiu fermentation, the grain was transformed from loose, large sorghum particles to a watery, sticky substance (Figure 1a)
Summary
As is the case with all naturally fermented food products, changes in the microbiome composition during fermentation are essential for the development and final quality of Baijiu [1,2]. It is important to elucidate the structure and metabolic function of the microbiome so as to better understand the mechanisms underlying fermentation. Light-flavor Baijiu is famous for its pure, pleasantly fruity, and mild taste, and for its refreshing aftertaste [7], which have made it the predominant type of Baijiu in the Chinese liquor market [1,8]. Light-flavor Baijiu is produced in an open solid-state fermentation process. During light-flavor Baijiu fermentation, microorganisms originating from Daqu and from the environment, such as Bacillus, Lactobacillus, Pediococcus, Saccharomycopsis, Saccharomyces, Pichia, Wickerhamomyces, and Aspergillus, were found to be predominant [9,10]
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