The composition of grape cuticle wax

Abstract

The cuticle wax of the grape is composed of a soft wax (30%) readily removed by light petroleum and a hard wax (30%), mainly oleanolic acid, removed by chloroform. The soft wax of the fresh grape is composed chiefly of long-chain alcohols together with smaller amounts of aldehydes, esters, fatty acids, hydrocarbons, oleanolic acid, and small amounts of high molecular weight substances. The soft wax of dried grapes is similar in composition but contains no aldehydes and larger amounts of high molecular weight substances and oxidation products. The aldehydes, unusual wax components, are straight chain and range from C16 to C32 with the even chain-lengths predominating. They were destroyed by neutral alumina but can be chromatographed on silicic acid.

The Surface Wax of Several Grapes in Japan

“…Since this type of surface structure is a strong barrier to the transpiration from berries, the chemical nature and fine structure of the wax have been investigated by many workers in `Thompson Seedless (Sultana)' , the most extensively grown raisin grape in the world (1,2,5,6,7,8,9,10,11). On the table grape cultivars, however, there have been hardly any detailed reports on them.…”

Cuticular Transpiration and Wax Structure and Composition of Leaves and Fruit of Vitis Vinifera

“…The chemical nature of the wax layer on the surface of grapes has been investigated by Radler and Horn (1965). They have shown the wax to consist of a "hard" wax component, oleanolic acid, together with a "soft" wax component, soluble in light petroleum vapour.…”

The Surface Waxes of the Sultana Vine (Vitis Vinifera Cv. Thompson Seedless)

“…The waxes and all fractions were also analysed by thin-layer chromatography, which was employed as a check of their uniformity. Since grape waxes have been shown to contain aldehydes, which are destroyed by chromatography on alumina (Radler and Horn 1965), this fraction of mature leaves and the corresponding ester fraction from young leaves were obtained by chromatography on silicic acid.…”

“…The surface area of leaves was estimated according to the method of Williams (1954), and the surface area of grapes was calculated from the berry volume, with the assumption that the berries are round. The methods of examination of the waxes were essentially as described by Radler and Horn (1965) g, 50 p.g of whole wax from young sultana grapes; h, 50 p.g of the light petroleum· soluble part of the wax from young sultana grapes; i, 50 p.g of whole wax from mature sultana grapes; j, 50 p.g of the light petroleum. soluble part of the wax from mature sultana grapes; k, 50 p.g of whole wax from young sultana leaves; l, 50 p.g of whole wax from mature sultana leaves; m,50 p.g of whole wax from sultana stems.…”

“…However, these lipids would have included, besides the surface waxes, those from the fruit flesh and from the grape-seed oil. Using chromatographic methods Radler and Horn (1965) have found that the surface waxes of ripe sultana grapes consist largely of oleanolic acid with lesser amounts of n-alcohols, n-aldehydes, esters, free acids, and n-hydrocarbons. An extension of this work has been the determination of the amount and composition of the surface waxes of different parts of the sultana vine at several developmental stages.…”