Abstract: The physicochemical properties and microbial community structure of two grades of Nongxiangxing Daqu were analyzed, and the internal relationship between them was investigated. High-throughput sequencing was used to analyze the differences in the microbial community structure between the two grades of Daqu. Meanwhile, we determined their physicochemical properties. Redundancy analysis (RDA) was used to study the relationship between microbes and physicochemical properties. The results showed that the bacterial community structures in the two grades of Daqu were similar, and the dominant bacterial genus were Thermoactinomyces, Weissella, and Lactobacillus, Kroppenstedtia; the domininant fungi were Thermomyces, unclassified_f__Aspergillaceae, and Thermoascus. We found that the relative abundance of Thermoascus in the superior grade was significantly higher than the first grade through differential microbial analysis, while the reverse was observed for unclassified_f__Aspergillaceae. The differential bacteria were all low-abundance species (relative abundance less than 1%). In addition, the moisture content, pH, liquefaction power and saccharification power of the superior grade were significantly lower than the first grade, while the total acid content and esterification power were significantly higher than the first grade. However, there was no significant difference in fermentation power between them. RDA analysis showed that the baterial genera Lactobacillus, Staphylococcus, Weissella and the fungal genus Thermoascus were positively correlated with fermentability and pH, whereas Thermoactinomyces and Kroppenstedtia were negatively correlated with pH. These results may provide a theoretical basis for establishing a more scientific quality evaluation standard for Daqu.

Key words: Daqu quality; physicochemical properties; microbial community structure; correlation analysis