Quantitative fractionation of grape proanthocyanidins according to their degree of polymerization

A method was developed for the fractionation of grape (seed or skin) proant hocyanidins according to their degree of polymerization. After precipitatio n in chloroform/methanol (75:25, v/v), the grape proanthocyanidins were dep osited onto an inert glass powder column and sequentially dissolved in seve ral fractions by increasing proportions of methanol in the solvent. Each fr action from each proanthocyanidin source was quantified and characterized a fter acidic degradation with phenylmethanethiol (i.e., thiolysis). The comp arison of data from total extract and successive fractions showed that a qu antitative separation was achieved so that estimation of polymer size distr ibution in relation to other compositional characteristics (proportions of prodelphinidin units, galloylation rate) was thus possible. Mean degree of polymerization of separated proanthocyanidins ranged increasingly from 4.7 to 17.4 in seed (8.1 for total extract) and from 9.3 to 73.8 in skin (34.9 for total extract). The method proposed is very interesting for the study o f grape proanthocyanidins according to their degree of polymerization becau se it gives both qualitative and quantitative information especially on the highly polymerized forms, which were not fractionated by previous techniqu es.