The Procyanidins of White Grapes and Wines

Procyanidin extracts were prepared from a Seyval white wine, from a Müller-Thurgau wine fermented partly on its skins, and from grape seeds. The extracts were studied chromatographically, showing a range of discrete procyanidin oligomers up to the pentameric and significant quantities of more polymeric and oxidized material. Semi-quantitative estimations showed that the level of total procyanidins was as low as 5-10 mg/l in the Seyval wine rising to 300 mg/1 in the Müller-Thurgau, but that the qualitative distribution patterns of the catechins and procyanidins showed no marked differences between the two. The Müller-Thurgau extract was examined by counter-current distribution between ethyl acetate and water, thus achieving a separation of different groups of oligomeric procyanidins and this was followed by further chromatographic treatment on Sephadex LH-20. The four main procyanidin dimers of white wines were isolated in the free state and were characterized by chromatography and their degradative behavior in the presence of acidic toluene-thiol as procyanidins B1-B4. A further procyanidin fraction was isolated and shown to consist of a mixture of two stereoisomeric trimers, one composed of three epicatechin units and the other of two epicatechins and a terminal catechin. The English-grown MüllerThurgau wine was found to contain negligible amounts of gallocatechins and of galloyl esters of catechins, either alone or in combination as procyanidins; this is in contrast to some previous reports.