Characterization of Physicochemical Properties, Volatile Compounds, and Microbial Community Structure in Five Sweet Rice Wine Starters.

Sweet rice wine starter (SRWS), a solid-state saccharification and fermentation starter, directly governs the fermentation efficiency and flavor profile of sweet rice wine (SRW). However, how Jiuqu characteristics, volatile compounds, and microbial communities collectively shape SRW flavor remains poorly understood, particularly with respect to carbon and nitrogen metabolism. In this study, five SRWS samples were comprehensively characterized through integrated physicochemical measurements, HS-SPME-GC-MS, high-throughput sequencing, and PICRUSt2 analysis. The five SRWSs exhibited significant differences in physicochemical properties (p < 0.05). Sixteen discriminatory volatile compound markers were identified in SRWS. Microbial community structures differed among SRWSs, with 24 differentially abundant species detected. Mantel test and correlation network analysis revealed that distinct microbial populations play critical roles in shaping and transforming flavor compounds. Functional prediction showed that fungi dominated carbon metabolism, nitrogen metabolism, and ethanol biosynthesis, whereas bacteria promoted lactic acid synthesis. Certain higher alcohols were produced through the concerted action of both fungal and bacterial metabolism. Collectively, these findings indicate that the biochemical characteristics of SRWS microbial communities are underpinned by a structured and complementary metabolic division of labor between bacteria and fungi. A systematic characterization framework was employed to understand the differential features of SRWS microbial communities in this work. It further establishes a theoretical basis for optimizing industrial SRW fermentation processes and rationally designing functional Jiuqu.