Enhancing the Quality of High-temperature Daqu in Northern China by Adding Exogenous Bacillus spores

In this study, the quality of high-temperature Daqu in Northern China was targeted for enhancement, with the aim of subsequently improving the quality of sauce-flavor liquor. This was achieved by incorporating No.1 Bacillus velezensis, No.2 Bacillus amyloliquefaciens and the control without exogenous spore addition during the Daqu production process. A comparative analysis of different Daqu samples was conducted using physicochemical index determination, high-throughput sequencing technology, and gas chromatography-ion mobility spectrometry (GC-IMS). The findings revealed that in Fortified Daqu No.2, the physicochemical indices including saccharification, liquefaction, fermentation, and esterification capabilities were significantly elevated compared to Fortified Daqu No.1 and the control Daqu. Additionally, a decrease in Daqu acidity was observed following spore addition. High-throughput sequencing and microbial counts showed that Bacillus populations in Fortified Daqu No.2 reached 4.2×10⁸ CFU/g, and the abundance ratio was 21.68%. In contrast, Fortified Daqu No.1 contained 2.3×10⁸ CFU/g Bacillus, and the abundance ratio was 18.92%, while the control Daqu exhibited 4.4×10⁷ CFU/g Bacillus and the abundance ratio was 7.48%. Analysis of the GC-IMS three-dimensional spectra indicated that both the content and variety of flavor compounds in the two Fortified Daqu samples were markedly higher than those in the control Daqu. Furthermore, multiple characteristic pyrazines were identified in Fortified Daqu No.2 based on fingerprint analysis. In brief, the addition of exogenous Bacillus subtilis has improved the physical and chemical indicators, microbial indicators, and volatile flavor compounds of the two types of Fortified Daqu, improving the quality of high-temperature Daqu in Northern China.