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

Objective To investigate the material basis underlying the significant differences in color changes during the air-curing process of cigar tobacco leaves. Method 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. Result 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（L*），yellowness/blueness（b*），and browning index（BI）compared to Dexue No.1.The L* and b* 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. Conclusion 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.