Grape catechins—natural antioxidants

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Abstract
Catechin monomers and procyanidin dimers of group B are constituents of grapes, with grape seeds the natural reservoir of these polyphenols. The antioxidant properties of these natural compounds is well established. In this research the mass fractions of catechin monomers (+)‐catechin and (‐ )‐epicatechin, and of procyanidin dimers B1, B2, B3 and B4, were determined in the grape skin extracts of 10 different grape cultivars. Fractionation of neutral phenolics was carried out on Sep Pak C18 cartridges. Separation and quantification of catechin monomers and procyanidin B dimers were undertaken using the high‐performance liquid chromatography reversed‐phase technique. The results confirmed the presence of catechin monomers in almost all the grape skin extracts analysed from the 1990, 1991 and 1992 vintages. The dominating catechin monomer was (+)‐catechin, except for grape skin extracts of Cabernet Sauvignon cv. (vintage 1992). The dominating procyanidin dimer was procyanidin dimer B1. According to the results obtained, the amounts of catechin monomers and procyanidin dimers of group B in the grape skin extracts are not sufficiently high to consider the grape skin a rich source of these polyphenolic compounds.