Structure and dynamics of reconstituted cuticular waxes of grape berry cuticle (Vitis vinifera L.)

Cuticular waxes from grape berry cuticle of Vitis vinifera L. have been investigated by X-ray diffraction, differential scanning calorimetry and gas chromato-graphy. The waxes were mainly composed of n-alcohols and n-fatty acids and a considerable amount (about 30%) of the cyclic terpenoid oleanolic acid. The physical techniques used showed that the waxes have a high degree of molecular order in spite of the presence of the cyclic component. Molecular dynamics of the reconstituted waxes were measured to characterize the transport properties of the cuticular waxes that form the transport-limiting barrier of plant cuticles. For this purpose, the diffusion coefficient of labelled cholesterol, imitating the terpenoic acid, was measured. The value obtained was around 10−21 m2 s−1 indicating a low mobility of the cyclic part of the reconstituted waxes. Temperature dependence of the diffusion coefficient was studied in the range of 5–45 °C. Arrhenius plot analysis yielded a high activation energy, 196.4 kJ mol−1, of the diffusion process. This indicates dense molecular packing of reconstituted cuticular waxes.