Abstract: This study investigated the changes in microbial community structure and flavor substances of high-temperature Daqu before and after the turning over as the key step in the production process. The results showed that during the turning over stage, the composition and abundance of the microbial community underwent significant changes. The abundance of the fungal genera Thermoascus and Thermomyces and the abundance of the bacterial genera Virgibacillus, Oceanobacillus, Saccharopolyspora, and Kroppenstedtia increased after two cycles of turning over. Gas chromatography-mass spectrometry (GC-MS) identified 49 volatile compounds, including 12 esters, 9 pyrazines, 6 alcohols, 6 aldehydes, 5 ketones, 3 phenols, 2 ethers, 2 furans, 1 alkene, 1 acid, and 2 other substances, with increased levels of ethyl caproate, ethyl octanoate, 2-phenylethanol, and 2,3,5,6-tetramethylpyrazine being observed after turning over. In addition, correlation analysis revealed potential associations between microbial community and flavor substances, with Virgibacillus, Oceanobacillus, Saccharopolyspora, Kroppenstedtia, Thermoascus, and Thermomyces showing positive correlations with ester compounds, and Bacillus and Pichia showing positive correlations with 2,3,5,6-tetramethylpyrazine. This study provides basic data for exploring the root causes of variations in the biological characteristics of high-temperature sauce-flavor Daqu and the principles governing the formation of flavor substances in sauce-flavor baijiu brewing, and offers important references for formulating effective process strategies to improve the quality stability of high-temperature Daqu.

Key words: sauce-flavor Daqu; microbial community; turning over; volatile flavor substances; correlation analysis