Dynamic changes of volatile substances and their driving factors during curing and fermentation of Hainan cigar

Air-curing and fermentation are pivotal for cigar flavor, shaped by moisture dynamics, enzymatic activity, and microbial metabolism. This study comprehensively characterized Hainan cigar tobacco leaves (CTLs) across these processes, integrating volatile metabolomics, enzyme assays, high-throughput microbial sequencing, functional prediction, and correlation analyses to unravel the regulatory network of water activity, microbial succession, and metabolite transformation. Water activity served as the core environmental regulator. Low water activity in stem-drying selected stress-tolerant Bacillus and Aspergillus; rehydration to 0.75 in fermentation activated microbial metabolism, enriching functional specialists (Pseudomonas and Aspergillus). Volatile metabolites exhibited stage-specific dynamics: terpenoids peaked in final fermentation, the terpenoid content reached its peak during the final fermentation stage, characterized by a marked enrichment of key volatile aroma compounds, including neophytadiene, β-damascenone, and β-ionone. Functional analyses revealed upregulated amino acid degradation, lipid metabolism, and terpenoid transformation in fermentation. Aspergillus drove carotenoid/terpenoid precursor cleavage via oxidative enzymes to generate key C13-norisoprenoid aromas. Pseudomonas synergistically promoted high-impact aromas through secondary metabolism (e.g., polyketide biosynthesis). Other microbes cooperated in lipid oxidation, nitrogen-containing heterocycle formation, and aroma integration. This study distinguishes dehydration-driven air-curing and aroma-producing fermentation, identifies Pseudomonas, Bacillus, and Aspergillus as core functional drivers, and provides a theoretical basis for optimizing cigar tobacco production and precision quality control.