Estimation of procyanidin chain length.
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Biflavonoids↗
Biomedical subjects
B Labarbe
Publications and source records attributed to B Labarbe.
Phenolic composition of grape stems.
Grape stems contain significant amounts of polyphenolic compounds, especially phenolic acids, flavonols, and flavanonols such as astilbin. The tannin content was characterized after the depolymerization reaction thiolysis. Tannins consisted of polymeric proanthocyanidins (up to 27 units) mainly consisting of (-)-epicatechin units along with smaller amounts of (+)-catechin, (-)-epicatechin gallate, and (-)-epigallocatechin. Flavanonols (astilbin) have been identified for the first time in stem and characterized by LC/MS and NMR. All phenolic compounds in grape stems were quantified by HPLC: quercetin 3-glucuronide was the most important, followed by catechin, caffeoyltartaric acid, and dihydroquercetin 3-rhamnoside (astilbin). Comparison was made of proanthocyanidin characteristics in different white and red grape varieties and also among parts of the cluster (skin, seed, and stem). Stem-condensed tannins were qualitatively intermediate between seed and skin but could not be differentiated between red and white varieties.
Flavonoids↗
Quantitative fractionation of grape proanthocyanidins according to their degree of polymerization.
A method was developed for the fractionation of grape (seed or skin) proanthocyanidins according to their degree of polymerization. After precipitation in chloroform/methanol (75:25, v/v), the grape proanthocyanidins were deposited onto an inert glass powder column and sequentially dissolved in several fractions by increasing proportions of methanol in the solvent. Each fraction from each proanthocyanidin source was quantified and characterized after acidic degradation with phenylmethanethiol (i.e., thiolysis). The comparison of data from total extract and successive fractions showed that a quantitative separation was achieved so that estimation of polymer size distribution 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 of grape proanthocyanidins according to their degree of polymerization because it gives both qualitative and quantitative information especially on the highly polymerized forms, which were not fractionated by previous techniques.
Anthocyanins↗