Proanthocyanidins and other phenolics in Acacia leaves of Southern Africa

Abstract

Four provenances each of Acacia karroo, Acacia nilotica, Acacia tortilis, Acacia senegal, Acacia erioloba and Faidherbia albida were sampled at Cyrene, Lucydale and Mahiye in the Matopos Research Station. Provenances were not replicated within site. The leaves and leaf stalks sampled were dried at 55°C and then analysed for total phenolics and proanthocyanidins (PAs). Variations in content of PAs and total phenolics of the Acacias were studied. Three assay methods for phenolics were evaluated. Total phenolics were estimated by precipitation with trivalent ytterbium after extraction with acetone:water (7:3 v/v) or colorimetrically by the Folin–Ciocalteu method. PAs were estimated colorimetrically by the butanol–HCl method. The results from the colorimetric methods are reported as absorbance units (au). A. senegal contained the lowest level of ytterbium precipitated phenolics (Ybppt) ( mean=47 g/kg DM), while A. nilotica contained the highest ( mean=298 g/kg DM). Amounts of Ybppt for A. karroo, A. erioloba and F. albida were not significantly different ( P>0.05) from one another. The amount of Ybppt for A. tortilis was significantly different ( P<0.05) from the amount for A. karroo but not different from the amount for F. albida and A. erioloba ( P>0.05). A. senegal was again the lowest in total phenolics detected by the Folin–Ciocalteu method ( A 675=0.370 au/g DM), while A. nilotica was the highest ( A 675=5.261 au/g DM). A. karroo, F. albida and A. tortilis were not significantly different ( P>0.05) from one another. PAs were lowest for A. senegal ( A 550=0.040 au/g DM) and highest for A. karroo ( A 550=2.011 au/g DM). Values for A. tortilis, F. albida and A. erioloba were not significantly different ( P>0.05) from one another. For all the three assay methods, there were no significant differences ( P>0.05) between Cyrene and Mahiye sites. The regression analysis of PAs on Ybppt showed the relationship to be highly significant ( P<0.05) for A. karroo, F. albida and A. erioloba ( R 2=0.904, 0.892, 0.884, respectively, and significant for A. tortilis ( R 2=0.680). It was poor for A. senegal and A. nilotica ( R 2=0.347 and 0.460, respectively). The relationship between total phenolics and Ybppt was similarly good for F. albida, A. erioloba, A. nilotica and A. karroo ( R 2=0.957, 0.808, 0.792, and 0.725, respectively) but poor for A. senegal, and A. tortilis ( R 2=0.413 and 0.004, respectively).