Metatranscriptomic insights into the mechanism of 'Multiple Qu' utilization in Jian-flavor Baijiu fermentation

The unique process of "Multiple-qu fermentation" (MF) is essential for the formation of the Jian-flavor Baijiu, but the mechanisms behind its aroma development remain not fully understood. This study compared the effects of "Single-qu fermentation"(SF) and MF on Baijiu production to elucidate the microbial and metabolic interactions responsible for its distinct aroma. Firstly, significant differences were observed in the microbial communities of the two types of Daqu. Medium-temperature Daqu (MT-Daqu) had higher relative abundances of Bacillus, Thermoactinomyces, Thermoascus, and yeasts like Picha and Saccharomycopsis. In contrast, high-temperature Daqu (HT-Daqu) was dominated by thermophilic genera such as Kroppenstedtia, and Thermomyces. In MF, the addition of HT-Daqu promoted an increase in Acetilactobacillus, while simultaneously leading to a decline in Lactobacillus and Kazachstania. Metatranscriptomic analysis revealed that Acetilactobacillus, Lactobacillus, Kazachstania, and Saccharomyces were the primary transcriptionally active genera in Baijiu fermentation. In SF, elevated transcription levels of Lactobacillus promoted the synthesis of ethyl lactate, reaching a concentration of 19.32 µg/L, compared to 7.33 µg/L in MF. Conversely, in MF, elevated transcription levels of Acetilactobacillus, Saccharomyces, and Kazachstania enhanced the synthesis of acetate esters and medium-chain fatty acid (MCFA) ethyl esters, reaching 28.50 µg/L and 195.84 µg/L, compared to 15.77 µg/L and 148.73 µg/L in SF. These differences in microbial communities and transcriptional activity directly shape the synthesis of key flavor compounds, thereby enhancing the distinct sensory characteristics of Jian-flavor Baijiu. This study provides new insights into the microbial and metabolic dynamics driving MF's role in Jian-flavor Baijiu.