Metabolomic analysis of color variation during air-curing in different cigar tobacco varieties

<bold>Objective</bold> To investigate the material basis underlying the significant differences in color changes during the air-curing process of cigar tobacco leaves. <bold>Method</bold> Using middle leaves of cultivars Chuanxue No.5 and Dexue No.1 as experimental materials，changes in leaf images，color parameters，and cellular ultrastructure during curing were recorded.Ultra-high-performance liquid chromatography coupled with orbitrap mass spectrometry（UHPLC-OE-MS）was employed for metabolomic analysis of leaves on day 9 of curing. <bold>Result</bold> As curing progressed，yellowing and browning occurred faster in Chuanxue No.5 than in Dexue No.1.In the early curing stage，Chuanxue No.5 exhibited higher values for lightness（<italic>L</italic>^*），yellowness/blueness（<italic>b</italic>^*），and browning index（BI）compared to Dexue No.1.The <italic>L</italic>^* and <italic>b</italic>^* values of Chuanxue No.5 declined sharply after day 9，while BI differences diminished in mid-to-late curing.Ultrastructural analysis revealed earlier membrane rupture，chloroplast disintegration，and an increasing number of plastoglobules formation in Chuanxue No.5.Metabolomic profiling on day 9 identified significant inter-cultivar differences：Chuanxue No.5 showed higher overall relative content of lipids and lipid-like molecules.Further screening identified 40 significantly differential metabolites，primarily fatty acids，flavonoids，and terpenoids.KEGG enrichment analysis indicated that differentially abundant metabolites were most prominently enriched in linoleic acid metabolism and α-linolenic acid metabolism pathways.Among these，9（S）-HODE—a metabolic derivative of linoleic acid—exhibited higher relative abundance in Chuanxue No.5 leaves. <bold>Conclusion</bold> The differential progression of color changes during curing may be attributed to variations in the relative content of metabolites such as fatty acids and flavonoids.