Effects of Mash Acidity on the Microbial Community Structure of Fermenting Grains during the Brewing of Daqu Baijiu
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Abstract:
Acidity is an important parameter in the brewing of Daqu baijiu. Acid stress plays a key role in the production of baijiu, as it reshapes the microbial community structure of the fermentation starter during the brewing process. To study the impact of acid stress on microbial community structure in fermenting grains during baijiu brewing, a solid-state model of baijiu brewing was constructed with three different acidity levels (low, medium, and high). The results showed that increasing acidity increased the relative abundance of acidogenic bacteria and acid-tolerant Bacillus bacteria, and decreased the relative abundance of acid-intolerant microbes. The dominant microbes were members of the Ascomycota fungal phylum, and their numbers initially increased with decreases in dissolved oxygen and increases in acidity in the mash before decreasing. According to the microbe numbers in the fermenting grains, increasing acidity decreased the number of aerobic bacteria and lactic acid bacteria. Caproic acid-producing bacteria were the most abundant when the acidity level was 15 mmol/100 g. Furthermore, the yeast population decreased with increasing acidity. The physicochemical analysis of fermenting grains showed that increasing acidity increased starch content in the grains and that high acidity resulted in low ethanol content. Overall, by analyzing how acidity reshapes the microbial bacterial structure of fermenting grains and the growth of desirable microbes under different levels of acidity, this study has identified the optimal conditions for the proliferation of desirable microbes and thereby provides scientific guidelines for the brewing of baijiu.
