Dissecting the division of labor among five jiuqu starters in sesame-flavor baijiu fermentation

Sesame-flavor baijiu employs a unique multi-jiuqu co-fermentation system involving five functionally specialized starters: high-temperature daqu (HT-daqu), medium-temperature daqu (MT-daqu), Aspergillus -enriched fuqu ( Asp -fuqu), Bacillus -enriched fuqu ( Bac -fuqu), and Wickerhamomyces -enriched fuqu ( Wic -fuqu). However, their functional differentiation and synergistic mechanisms remain unclear. This study systematically investigated the enzymatic activities, microbial transmission patterns, and compound evolution patterns of these starters throughout fermentation. All five jiuqu starters exhibited amylase, neutral protease, and cellulase activities. Asp -fuqu showed the highest protease (1032.84 U/g) and cellulase (158.48 CU/g) activities, followed by Bac -fuqu, while all except Bac -fuqu contributed higher amylase to fermentation initiation. HT-daqu and MT-daqu contributed relatively low microbial biomass, whereas the three fuqu exhibited stronger inoculation capacity. Asp -fuqu predominantly supplied Aspergillus tubingensis and contributed key bacteria such as Weissella confusa and Bacillus subtilis , Bac -fuqu provided over half of the bacterial such as Bacillus licheniformis input forming the early fermentation bacterial framework, and Wic -fuqu served as the main yeast source dominated by Wickerhamomyces anomalus . Among the 13 jiuqu-derived aroma-active compounds (OAV >1), HT-daqu and MT-daqu primarily contributed ethyl hexanoate, phenylacetaldehyde, and 3-methylbutanal (formulation-weighted contribution ratios 40.64-50.54 % and 39.80-49.14 %, respectively), with HT-daqu also dominating 2,5-dimethylpyrazine (66.20 %). Wic -fuqu mainly supplied hexanal (45.57 %) and 2-pentylfuran (68.47 %). Asp -fuqu overwhelmingly dominated ethyl acetate, acetoin, and ethyl linoleate, and co-contributed isoamyl alcohol and nonanal with HT-daqu and MT-daqu. This study reveals how multi-jiuqu systems achieve functional complementarity via distinct enzymatic, microbial, and metabolic contributions, providing a basis for quality control and process optimization in sesame-flavor baijiu production.