Investigating the Correlation between Different Daqu Qualities and Brewing Performance Based on Metagenomics Technology

To systematically analyze the quality characteristics of different types of Daqu and their fermentation efficiency under the same brewing process, and to elucidate the intrinsic correlation between Daqu quality parameters and baijiu flavour characteristics, this study systematically compared and analyzed the physicochemical indices, microbial community structures, and brewing effects of medium-, medium-high-, and high-temperature Daqu. Furthermore, the internal relationships among these three aspects were examined. The analysis of physicochemical indices revealed that medium-temperature Daqu exhibited the highest moisture content, saccharifying power, and liquefaction power, while high-temperature Daqu showed the highest acidity. In terms of microbial community structure, the main dominant genera in medium-temperature Daqu were Aspergillus (70.90% abundance), Thermomyces (10.74% abundance), Bacillus (32.54% abundance), and Staphylococcus (15.56% abundance). In medium-high-temperature Daqu, the dominant genera included Aspergillus (75.52% abundance), Saccharomycetales (14.97% abundance), and Weissella (16.65% abundance). High-temperature Daqu was primarily characterized by the presence of Aspergillus (33.84% abundance), Thermomyces (33.67% abundance), Virgibacillus (25.52% abundance), and Kroppentedtia (24.10% abundance). The analysis of the brewing effect showed nine different flavour substances in the three kinds of Daqu baijiu. The sensory experience of medium-temperature Daqu baijiu was sweet and harmonious. Medium-high-temperature Daqu baijiu had a pleasing grain aroma, and high-temperature Daqu baijiui had a rich aroma and pure aftertaste. The results of the correlation analysis indicated that acidity was positively correlated with the abundance of Thermoascus and Virgibacillus. Liquefaction power positively correlated with Wallemia, Staphylococcus, and Saccharopolyspora abundance. Additionally, saccharifying power was positively correlated with Pantoea, while fermentation power was positively correlated with Weissella abundance. The physicochemical properties of Daqu significantly influenced its microbial community composition. Aspergillus showed a negative correlation with the content of methanol and isobutanol. Bacillus, Staphylococcus, and Saccharopolyspora abundance were positively correlated with ethyl acetate and ethyl lactate, whereas Lactobacillus abundance was negatively correlated with ethyl acetate content. The various flavour types of Daqu differed significantly in the physicochemical and microbial compositions among the various flavour types of Daqu. Within the same process, the style of different flavour types of Daqu baijiu was primarily determined by the processing style. The physicochemical properties and microbial diversity of Daqu were closely linked to the quality of baijiu. This study demonstrated the influence of Daqu and processing methods on baijiu style, explored the relationship between Daqu's physicochemical and microbial aspects and baijiu flavour, and provided a theoretical foundation for enhancing the quality of different flavour baijiu and integrating various flavour types.