Condensed Tannins and Flavonols of Selected Forage Plants from Botswana
Keywords:
forage, isolation, condensed tannins, flavonolsAbstract
The characterization of the phenolic constituents of Viscum verrucosum, Tapinanthus oleifolius and Grewia flava forage plants, consisting of leaves and small stems, were investigated. The plants were harvested over two summers (February 2009 and 2010). Each plant sample was extracted and purified by a step (conventional) and linear gradient method on a Sephadex LH-20 column. The chemical composition of the condensed tannin (CT)-containing fractions in these plants was studied by the 13C-NMR spectroscopy. Further purification of the thiolysis products of the CT polymers from these plants led to the isolation of (-)epicatechin which was found to be the dominant compound in the extender units. Fractionation of the fractions from V. verrucosum and T. oleifolius yielded flavonols (kaempferol and quercetin derivatives), which were successfully purified and characterized by LC-ESI-MS/MS. The analytical techniques employed revealed that CT from V. verrucosum, T. oleifolius and G. flava were procyanidin (PC) and cis dominant, with variable chain lengths. In addition, low molecular weight phenolics were isolated and characterized.
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