Paper Chromatography of Phenolic Compounds from Grapes, Particularly Seeds, and Some Variety-Ripeness Relationships

¹ Department of Viticulture and Enology, University of California, Davis, California.

A simple standardized technique for two-dimensional paper chromatographic "mapping" and estimation of the relative amounts of the phenolic substances in grape extracts was presented. This technique was applied to the study of weekly harvests of 12 grape varieties. The berry pulp tended to reflect the juice and seeds in phenolic composition. The juice phenolics, as a rule, were predominantly blue-fluorescing substances resembling chlorogenic acid and its analogs. Calzin and one of its parents, Refosco, were unique among 34 varieties tested in having a considerable content of astringent tannin in the juice. Skin extracts were quite variable in qualitative phenolic composition by variety, especially considering, but in addition to, the presence or absence of anthocyanins.

The phenolic composition of the seeds, however, followed a similar pattern in red or white grapes and in varieties with parentage from two species of Vitis. Among a total of about 25 differentiated substances readily oxidized by FeCl₃-K₃Fe-(CN)₆ and considered as phenols, the majority were present in the seeds of all varieties at similar stages, and usually in roughly similar proportions. Varietal differences did occur with respect to the presence or absence of a few of the substances and the relative amounts of those present per unit of total phenol.

The nature of several of the substances was outlined, and, in particular, evidence was presented that one was catechin, one was epicatechin, and a third was epicatechin gallate. Although these flavanols have been reported in grapes (4, 6) previously, epicatechin gallate has not always been found in seeds (6).

A considerable metabolism of phenolic substances in seeds during ripening was found even up to the last stages, as shown by the appearance or increase of some and the decrease of others in relation to a unit of total phenol.

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