ISOLATION OF TANNINS FROM LEAVES OF SOME TREES AND SHRUBS AND THEIR PROPERTIES

Tannins extracted from leaves of five trees/shrubs (Acioa barteri, Dichostachys cinerea, Guiera senegalensis, Quercus incana, and Piliostigma reticulatum) in aqueous acetone containing ascorbic acid were isolated using Sephadex LH-20. There was no significant difference detected between ascorbic acid containing preparations and preparations in which ascorbic acid was removed, based on the vanillin-HCl (VA), butyl alcohol-HCl-Fe3+ (BHF), and protein precipitation assays, suggesting that the removal of ascorbic acid from the tannin preparation did not oxidize the tannins studied. The lambda(max) of the preparations free of ascorbic acid was between 270 and 280 nm. The protein precipitation capacity (PPC) was from 3 to 10 g of bovine serum albumin precipitated/g of tannins. The poor correlations of PPC with condensed tannins (r = 0.58 and 0.51, respectively) with the VA and BHF values and a high correlation (r = 0.95) with total phenolic content suggested the preparations to be a mixture of condensed and hydrolyzable tannins, which was substantiated by the detection of gallic acid on hydrolysis of these tannins. These preparations should be used as a standard with caution. The PPC of isolated tannins was almost the same as that for those present in the extract, indicating that the biological activity of the isolated tannins is similar to those present in the plant.