Separation, Analysis, and Degradation of Cembranoids in Flue-Cured Tobacco Leaves

Cembranoids are significant flavor precursors found in flue-cured tobacco leaves. The degradation products can serve as important aromatic compounds. In this study, 16 cembranoids were discovered in flue-cured tobacco leaves by liquid chromatography–mass spectrometry (MS), and 1 cembranoid featuring both oxidation and dehydrogenation from α/β-cembranoid was identified for the first time. α- and β-cembranoids were confirmed to be precursors to various degradation products. Additionally, β-cembranoid was prone to epimerize into α-cembranoid while simultaneously undergoing allylic rearrangement, with the hydroxyl group undergoing migration. During the aging and curing processes, cembranoids can easily add oxygen atoms to the carbon–carbon double bonds, whereas the hydroxyl group in the structure may form epoxides, oxidize into ketones, or undergo dehydration reactions. Additionally, the microwave plasma torch interfaced with an MS was used to create and detect the pyrolysis and oxidized products of cembranoids. More degradation products were discovered, including oxidation products with the addition of one to three oxygen atoms, as well as a series of aromatic compounds such as 1,3,5-heptatriene and its range of homologs. This research presented the different degradation pathways of cembranoids in flue-cured tobacco during aging and curing processes, offering valuable insights for the enhancement of tobacco production techniques and quality control.