Analysis of the microbial community and the metabolic profile in medium-temperature Daqu after inoculation with Bacillus licheniformis and Bacillus velezensis
Boyang Xu, Shanshan Xu, Jing Cai, Wei Sun, Dongdong Mu, Xuefeng Wu, Xingjiang Li
Abstract
Daqu, an important fermentation and saccharifying agent, plays a crucial role in providing enzymes, flavoring substances, and precursors in the brewing process of Chinese liquor. To evaluate the effect of fortification (inoculation with Bacillus licheniformis and Bacillus velezensis) in the different layers of Daqu, we analyzed the microbial community structure, physicochemical index, enzyme activity, and flavor component of Daqu in this study. Fortification mainly changed the relative abundance of 22 genera in four layers of Daqu (surface, fire circle, middle, and center), including an increase in the abundance of Bacillus and Aspergillus, and a decrease in the abundance of Thermoascus, Lactobacillus, and some other genera. Notably, the esterification power of the fire circle and surface layer was significantly improved after inoculation. Moreover, the contents of flavor compounds, including alcohols, acids, and ketones (except esters), were all improved. In conclusion, we found that fortification controls microbial metabolism by altering the abundance of certain microorganisms, thereby enhancing the production of flavor substances.