Application of Clostridium butyricum, Rummeliibacillus suwonensis, and Issatchenkia orientalis for Nongxiangxing baijiu fermentation: Improves the microbial communities and flavor of upper fermented grain

Ethyl hexanoate and ethyl butyrate are essential to the flavor compounds in Nongxiangxing baijiu, but low levels of these two esters in upper fermented grains (FG) decreases the quality of upper distilled baijiu, representing the main challenge in Nongxiangxing baijiu production. This paper enhanced fermentation by inoculating functional Clostridium butyricum, Rummeliibacillus suwonensis, and Issatchenkia orientalis strains into upper FG. The results showed that the ethyl butyrate content in the upper FG increased significantly and the content of ethyl hexanoate did improve from the results of many determinations. High-throughput sequencing indicated that the dominant phyla in the FG were Firmicutes, Actinobacteriota, Proteobacteria, Ascomycota, and Basidiomycota. The canonical correspondence analysis (CCA) and person correlation network revealed the relationship between the microbial community, physicochemical environment, and flavor compounds. The temperature, oxygen, and acidity were closely related to the microbial community, while most flavor compounds were positively correlated with Caldicoprobacter, Caproiciproducens, Delftia, Hydrogenispora, Thermoactinomyces, Issatchenkia Bacillus, and Aspergillus. These results helped improve the quality of Nongxiangxing baijiu.