Spectroscopic characterization of aliphatic moieties in four plant cuticles

Aliphatic components of tomato, pepper, and apple fruit cuticles, and the leaf cuticles of mature olive trees, were characterized using elemental analysis, 13carbon (C) nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR). Cuticular fractions isolated for analyses included bulk, dewaxed, nonsaponifiable, and nonhydrolyzable cuticles. Results from 13C NMR and FTIR spectra indicate that the cuticles of all the plant materials studied are comprised of extractable lipids, polysaccharides, and cutin, whereas the cuticles extracted from the olive leaf, pepper fruit, and apple fruit also contained nonsaponifiable, nonhydrolyzable residues, likely to be cutan. Hydrogen (H)/C and [oxygen (O)+nitrogen(N)]/C atomic ratios for the olive leaf, pepper fruit, and apple fruit cuticle fractions indicate that their bulk cuticle, dewaxed cuticle, and lipid fractions are more aliphatic than but have a similar polarity to their respective cutan-like fraction. These results provide evidence that pepper fruit, apple fruit, and olive leaf cuticles each contain a cutan-like fraction, but in the olive leaf and apple fruit, this fraction has a slightly different chemical structure from that of the pepper fruit and makes up a smaller percent of the total cuticle.