LC-MS and GC-TOF-MS metabolomics elucidate quality and metabolite variations of medium-grade Yunyan 87 (C4F) tobacco under stage-specific curing process

To investigate the impact of flue-curing parameters on the intrinsic quality of medium grade tobacco ( Nicotiana tabacum L.) leaves, this study uses C4F grade leaves of the Yunyan 87 variety as the experimental material. Based on the conventional curing process (Z4C), the parameters are adjusted at different stages to establish three optimized treatments: Z4G (yellowing + color-fixing stages), Z4S (color-fixing stage only), and Z4W (stem-drying stage). Metabolomics integrating LC-MS and GC-TOF-MS is employed to decipher the quality changes of C4F leaves under different curing process. The results show that the Z4G process promotes starch degradation and soluble sugar accumulation in tobacco leaves, achieving the optimal performance in aroma content, aroma quality, and overall sensory score. Z4S shortens the curing duration, elevates cinnamic acid content, and suppresses indole synthesis, but yields the lowest comprehensive score. Z4W, through low temperature and prolonged treatment, reduces the degradation of thermosensitive compounds, thereby minimizing the loss of flavonoids, phytol, geraniol, and other substances, while also decreasing the accumulation of alkaloids and their derivatives. This study elucidates the metabolic mechanism by which stage-specific curing regulation of the curing process modulates the quality formation of medium grade flue-cured tobacco, providing a theoretical basis and data support for the precise optimization of the curing protocol for C4F leaves and for enhancing their industrial usability.