Waxes, grape skin

Grapes release numerous hydrocarbons in the adjacent gas volume. We have found alkanes, alkenes, and aromatic hydrocarbons (II). Accordingly, we extracted the skin waxes of the grapes with n-pentane and investigated the extracts by using a combination GLC-mass spectrometer. The total amounts of the wax extracts contained about 0.5% paraffins, 89% of which were saturated hydrocarbons ranging from Ci3 to C3i. 

The polyphenol oxidase was obtained from extracts of the pressed grape juice sediment by acetone precipitation, purified on Sephadex G 25 and DEAE-Sephadex A 25, and further concentrated by ultrafiltration. Model experiments were done in a Warburg apparatus (10). The grape skin waxes were extracted with pentane. The resulting extracts were analyzed by a GLC (Varian Aerograph, model 1201) which was coupled via a helium separator according to Watson and Bieman (19) to a mass-... 

Because of the varied nature of the plant tissues from which the proanthocyanidin extracts are derived, it is difficult to anticipate the expected outcome. As an example of how these procedures can be adapted to specific tissues and analyses, using grape tissues, fruit is harvested and the tissues of interest (e.g., skins and seeds) are removed from the remainder of the berry. They are rinsed well and then extracted as whole tissues using the conditions described in these protocols. For grape skins, aliquid-liq-uid extraction with chloroform has been successful in the removal of chlorophyll and waxes, yet no extraction with ethyl acetate has been performed because of the small proportion of flavan-3-ol monomers (Kennedy et al., 2001). For grape seeds, these protocols have... 

Biokinetic studies on grape berries show fludioxonil to be non-systemic (Table 15.2.3). After application, the major part of the applied fludioxonil was recovered from the surface. A small percentage of the applied fludioxonil (approx. 10%) was detected in the wax layer up to 14 days after application. No uptake of active ingredient into the skin or pulp was detected [38]. 

Other sterols and long-chain fatty acids share most of the properties of ergosterol. Some are constituents of grape bloom and cuticular wax, such as oleanoUc acid—especially when associated with oleic acid (Figure 3.5). These constituents explain the results of past experiments, indicating an acceleration of the fermentation speed of grape must in complete anaerobiosis when grape skins and seeds were added in suspension. 

The ripe grape skin also contains considerable amounts of aromatic substances and aroma precursors. In certain muscat varieties, the skin can contain more than half of the free terpenols of the berry (Bayonove, 1993). Other chemical families of aromatic snbstances may also be contained in the skin. Finally, the skin is covered by epicuticu-lar wax, essentially constituted of oleanolic acid. 

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