Microbial diversity, functional properties, and flavor characteristics of high-temperature Daqu with different colors

High-temperature Daqu (HTD) plays a crucial role in the quality of sauce-flavor baijiu. Daqu of different colors serves distinct functions in the baijiu brewing process. However, indicators for distinguishing among different-colored Daqu remain insufficient. This study investigated the microbial community structures, physicochemical properties, and E-sensory characteristics of different-colored HTD from Shandong Province. The results revealed significant differences in microbial communities among the three HTD types (P < 0.05). Kroppenstedtia eburnea, three Bacillus species, and Weizmannia coagulans were significantly enriched in white Daqu; an unclassified Staphylococcus species dominated in black Daqu; and Aspergillus oryzae, Aspergillus fumigatus, and Proteus mirabilis were highly abundant in yellow Daqu. Compared to HTD from Guizhou and Hubei, Shandong HTD was characterized by microbial species such as Proteus mirabilis and Bacillus velezensis. Using metagenomic analysis, we, for the first time, identified Thermomyces lanuginosus, Lentibacillus daqui, and an unclassified Thermoascus species as potential major contributors to pyrazine synthesis in HTD. The primary differences among the three colored Shandong Daqu types lay in their aroma profiles rather than taste. Electronic nose and electronic tongue analyses demonstrated that the W6S and W3S sensors effectively distinguished black and white Daqu, respectively, marking a novel application of these technologies in Daqu analysis. Acidity was identified as a key factor influencing microbial community structure, flavor characteristics, and enzyme activities, with a nonlinear relationship observed between acidity and enzyme activities. This study highlights the microbial and sensory distinctions among different-colored HTD and provides effective indicators for distinguishing these three types of Daqu.