Deciphering the mechanism of light quality regulating the quality of sun-cured yellow tobacco based on GC-MS non-targeted metabolomics

Sun-cured tobacco is cured by means of natural sunlight, a process that is highly susceptible to fluctuations in external environmental conditions, hindering standardized production and consequently leading to poor quality consistency. Therefore, light is a key environmental factor regulating the curing process of sun-cured tobacco, and as a core component of light, light quality can directly regulate the synthesis and accumulation of metabolites within sun-cured tobacco leaves, thereby governing the formation of their aromatic properties and core quality traits. However, existing studies have rarely explored the mechanisms underlying how light quality regulates aroma formation and core quality in sun-cured tobacco, leaving the intrinsic regulatory mechanisms largely unclear. To address this knowledge gap, the present study investigated how light quality regulates the aroma of sun-cured tobacco. Using the ‘Cun Sanpi’ variety, we applied three light treatments during the curing stage: natural light (NL), NL supplemented with red light (NL+R), and NL supplemented with blue light (NL+B). We analyzed leaf quality and metabolic dynamics through conventional chemical analysis, sensory evaluation, and GC-MS non-targeted metabolomics. The results indicated that light quality significantly altered tobacco quality. The NL+R treatment led to increased sugars, decreased nicotine, low mucosa irritation, and a pleasant aftertaste. In contrast, the NL+B treatment resulted in higher nitrogen and nicotine levels, which corresponded with poorer sensory quality. The NL treatment yielded leaves of intermediate quality. Metabolomic analysis identified 40 differential aroma-related metabolites, primarily carbohydrates and organic acids. These were significantly enriched in 23 metabolic pathways, with core pathways involving carbohydrate metabolism, amino acid metabolism, and secondary metabolite biosynthesis. We found that light quality drives differential metabolite accumulation by modulating metabolic rhythms and specific pathways: NL+R activated ubiquinone and terpenoid-quinone biosynthesis; NL+B regulated glycolysis/gluconeogenesis and propanoate metabolism; and NL influenced photosynthesis. This study identifies key metabolites, specific pathways, and their correlation with sensory traits in light-quality-mediated regulation of sun-cured tobacco. Our findings provide a theoretical foundation for optimizing light conditions during curing to improve tobacco quality in a targeted manner.