Abstract: In this study, the outer, middle and inner layers of fermented grains in the 5th round of stacking fermentation of sauce-flavor baijiu were analyzed for physicochemical factors, organic acid contents and microbial community structure by high performance liquid chromatography (HPLC) and high-throughput sequencing technology. Moreover, the correlation of microbial community succession with physicochemical factors and organic acid contents was analyzed to reveal the key environmental factors affecting the microbial community in fermented grains. The results showed that during the 5th round of stacking fermentation, there were significant differences in the temperature and acidity among different layers of fermented grains (P < 0.05). With the prolongation of stacking time, the organic acid content in each layer of fermented grains generally showed an increasing trend, and at the late stage of stacking fermentation, the contents of all organic acids except fumaric acid significantly differed among the three layers (P < 0.05). The average content of lactic acid across all layers was the highest (34.910 mg/g), followed by formic acid, acetic acid, succinic acid, and malic acid, all of which were the main organic acids in the 5th round of stacking fermentation. Saccharomycopsis, Thermomyces, Aspergillus and Thermoascus were the dominant fungal genera in the early stage of stacking fermentation while Kazachstania, Pichia and Zygosaccharomyces were the dominant fungal genera in the middle and late stages. Kroppenstedtia and Virgibacillus were the dominant bacterial genera throughout the entire fermentation process. The structure of the fungal community varied greatly as stacking fermentation progressed, while the structure of the bacterial community remained stable. However, the microbial community was differentially distributed among the layers of fermented grains. Correlation analyses showed that starch, reducing sugar, lactic acid and formic acid were the key environmental factors affecting the microbial community in fermented grains. The interaction between organic acids and key microorganisms differed among different layers of fermented grains. This study provides a theoretical basis for the regulation of the stacking fermentation process of sauce-flavor baijiu and the production of high-quality baijiu.

Key words: sauce-flavor baijiu; stacking fermentation; microbial community structure; environmental factors; organic acids; correlation