Mildew invasion: Deciphering its influence on primary metabolites and microbial dynamics in fermented cigar tobacco ecosystems

This study aimed to elucidate the impact of mildew on the quality of fermented cigar tobacco leaves (CTLs) and identify potential biomarkers. Chemical constituents, microbial communities and metabolites in healthy CTLs (HCTLs) and mildewed CTLs (MCTLs) were systematically analyzed. Compared with HCTLs, the moisture, reducing sugar and total nitrogen contents of MCTLs increased, but the levels of starch, protein, total sugar and carbon-nitrogen ratio decreased. Mildew significantly altered flavor profiles, with 31 volatile flavor compounds (VFCs) and 9 free amino acids (FAAs) showing significant differences. Furthermore, the richness and diversity of bacterial and fungal communities decreased with mildew. The core functional microorganisms, including Pseudomonas, Pectobacterium, Aerococcus, Aspergillus, Alternaria, and Colletotrichum were screened. Notably, 2 chemical components (total acid, reducing sugar), 3 VFCs (2-undecanone,6,10-dimethyl, myosmine, 1-(5-methylfuran-2-yl)ethenone), and 4 FAAs (Asp, Ile, Val, Gly) were proposed as biomarkers indicating mildew tendency in fermented CTLs. These findings provide theoretical foundation for optimizing cigar production.