Dynamic Changes and Potential Correlations between Microbial Diversity and Volatile Flavor Compounds in Chinese Medium-Temperature Daqu during Manufacturing

To investigate the dynamic changes and potential correlations between microbial diversity and volatile organic compounds (VOCs) during Chinese medium-temperature Daqu (MTD) manufacturing at different key stages, in this study, high-throughput sequencing (HTS) and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to analyze the microbial diversity and VOCs of MTD, respectively. The results showed that <i>Weissella</i>, <i>Staphylococcus</i>, <i>Thermoactinomyces</i>, <i>Kroppenstedtia</i>, and <i>Lactobacillus</i> were the dominant bacterial genera, while <i>Aspergillus</i>, <i>Alternaria</i>, <i>Thermoascus</i>, <i>Thermomyces</i>, <i>Wickerhamomyces</i>, and <i>Saccharomyces</i> were the dominant fungal genera. A total of 61 VOCs were detected by GC-IMS, among which, 13 differential VOCs (VIP > 1) were identified, that could be used as potential biomarkers to judge the fermentation stage of MTD. <i>Kroppenstedtia</i> and <i>Saccharopolyspora</i> were positively correlated with 3-methyl-2-butenal and 2,2,4,6,6-pentamethylheptane-D, respectively, and both of these were positively correlated with butanal-D. <i>Acetobacter</i>, <i>Streptomyces</i>, and lactic acid bacteria (LAB) including <i>Leuconostoc</i>, <i>Pediococcus</i>, <i>Weissella</i>, and <i>Lactobacillus</i> were negatively correlated with their associated VOCs, while fungi were generally positively correlated with VOCs. <i>Wickerhamomyces</i>, <i>Saccharomyces</i>, and <i>Candida</i> were positively correlated with butan-2-one-M. This study provides a theoretical basis for explaining the mechanisms of MTD flavor formation and screening functional microorganisms to improve the quality of MTD.