The main Constituents of the Surface Waxes of Varieties and Species of the Genus VITIS

Abstract

Cuticular waxes from fresh grapes and leaves of Vitis vinifera, Vitis labrusca, Vitis rupestris, several Vitis hybrids, and Parthenocissus quinquefolia were extracted with cold chloroform. The main constituent of the waxes from grapes was oleanolic acid, which is present in the surface wax of leaves in only small amounts. The chloroform extracts were separated by extraction with petroleum ether into the insoluble "hard wax", consisting mainly of oleanolic acid, and the soluble "soft wax," which was fractionated by chromatography on aluminum oxide into hydrocarbons, an "ester-aldehyde" fraction, free alcohols, and free acids. The waxes of all grape vine varieties appeared to have a similar composition except V. labrusca var Isabella, which contained a much higher amount of hydrocarbons in the cuticular wax. The compositions of the hydrocarbons, free alcohols, and free acids were determined by gas-liquid chromatography. The following chain-length distributions were found: hydrocarbons, n-C₁₈ to n-C₃₅, with n-C₂₅, n-C₂₇, n-C₂₉ and n-C₃₁ as main constituents; alcohols, n-C₂₀ to n-C₃₄, with n-C₂₆ in grapes and n-C₂₈ and n-C₃₀ in leaves as main constituents; acids, n-C₁₄ to n-C₃₂, with n-C₂₆ as the main constituent. Except for the high content of paraffins in V. labrusca, the differences between the analyzed varieties and species of grape vines were small.