Analysis of the effect of variable frequency fan on tobacco metabolites during curing via untargeted metabolomics

The Variable-frequency (VF) fan regulation is a promising technique for flue-curing of tobacco (Nicotiana tabacum L.), and exploring its mechanism is of great significance for improving the curing quality. The middle leaves of “Yunyan 87” were used as experimental materials for exploring the changes of metabolic components by untargeted metabolomics and monitoring dynamic changes of key physiological indicators during flue-curing, VF curing (dynamic frequency: 35–40–45–40 Hz) and constant-frequency curing (50 Hz, CK). VF treatment resulted in a more uniform yellowing process, reduced leaf browning, and improved color retention compared with the control. Leaves under VF treatment showed enhanced superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) activities, accompanied by lower malondialdehyde (MDA) accumulation. At 48 h, Pathway enrichment analysis revealed the glyoxylate and dicarboxylate metabolism pathway was most affected, with significantly enriched metabolites including isocitrate, citric acid, and glyoxylate. At 120 and 168 h, the most significant metabolic pathways affected by variable frequency fan were flavonoid and flavanol biosynthesis, accompanied significantly enrichment of kaempferol, quercetin, and quercetin. Notably, total aroma substances were reduced under VF (Neophytadiene − 42%, benzaldehyde − 28%). This study provided a metabolomics-based framework for improving intensive curing processes.