Composition and ultrastructure changes of leaf cuticle wax during the air-curing process in cigars

The quality of cigar tobacco leaves (CTLs) is considerably influenced by color changes that occur during the air-curing process, which are mainly regulated by polyphenols and membrane lipid peroxidation. Cuticular waxes form the outermost lipid layer covering the surface of plants, and their specific responses during CTL air-curing remain unclear. This study comprehensively investigated the changes in the morphology, appearance, and chemical composition of cuticular waxes. The contents of different lipids in CTLs changed significantly during air-curing, and the contents of ceramide, hexosylceramide and fatty acids in CTLs increased significantly, and cuticular wax was an important part of plant lipids. In terms of microstructure, as the air-curing process progressed, the cuticular wax structure of the CTL collapsed and fragmented, and the volume and density of wax crystals increased. In terms of chemical composition, long-chain fatty acids and esters in fatty compounds and sterols and tocopherols in cyclic components decreased. The results showed that the cuticular wax gradually degraded during the air-curing process, and the changes in the microstructure and chemical composition of cuticular waxes corresponded to the color changes of the CTLs throughout this process. Therefore, cuticular waxes may have an indirect effect in regulating color changes during the tobacco air-curing process. These findings underscore the indirect influence of cuticular wax dynamics on CTL quality during air-curing, offering valuable insights to guide improvements in tobacco leaf processing and product refinement. • The contents of different lipids in the cigar tobacco leaves changed significantly during air-curing. • The surface microstructure was modified in parallel with the cigar tobacco leaves during the air-curing process. • Alkanes, fatty acids and esters were reduced in wax during air-curing. • The change of epidermal wax was proposed to deal with the air-curing process of cigar tobacco leaves.