Effect of Fortified Daqu on the Microbial Community and Flavor in Chinese Strong-Flavor Liquor Brewing Process

Abstract

<i>Daqu</i>, an important fermentation starter for the production of Chinese liquor, as used in the current study included traditional <i>Daqu</i> and fortified <i>Daqu</i> inoculated with <i>Bacillus velezensis</i> and <i>Bacillus subtilis</i>. To evaluate the effect of fortified <i>Daqu</i> on strong-flavor liquor production, the differences of microbial communities among three inoculation patterns of fermented grains (FG) were analyzed by the Illumina MiSeq platform. A higher relative abundance of dominant genera including <i>Bacillus</i>, <i>Lactococcus</i>, <i>Aspergillus</i>, and <i>Candida</i>, and lower relative abundance of <i>Lactobacillus</i>, were observed in FG50, in which mixed <i>Daqu</i> (traditional: fortified <i>Daqu</i> = 1: 1, w/w, 50% fortified <i>Daqu</i>) was used as the starter. Then, volatile compounds of their distillations were also examined by HS-SPME-GC-MS. The results showed that the contents of skeleton flavor components, mainly including important esters and aromatic compounds, were higher in the corresponding liquor L50, which distillated from FG50. Moreover, most esters mainly positively correlated with <i>Lactobacillus</i> and <i>Candida</i> in the bottom layer of FG fermented with 50% fortified <i>Daqu</i> (FG50-B). Aromatic compounds were strongly positively correlated with <i>Bacillus</i> and <i>Aspergillus</i> in the middle layer of FG with 50% fortified <i>Daqu</i> used (FG50-M). In particular, hexyl hexanoate showed a positive correlation with higher abundances of <i>Ruminococcus</i> in the FG with addition of 100% fortified <i>Daqu</i> (FG100). This study observed microbial compositions in the FG with fortified <i>Daqu</i> addition, and it further revealed the correlations between pivotal microbes and main flavor compounds. These results may help to develop effective strategies to regulate microbes for the brewing process and further improve the flavors of Chinese liquor.