Condensed tannins and saponin content in different plant parts of Stylosanthes scabra (Fitzroy) plants harvested from agro-ecologically different sites in Zimbabwe

Abstract

The objective of this study was to determine the proanthocyanidin (PA; condensed tannin) and saponin contents of different parts of Stylosanthes scabra (Fitzroy) plants harvested from five agro-ecologically different sites in Zimbabwe. Condensed tannins and saponin content of S. scabra leaves and twigs were determined by the n-butanol HCl method and haemolysis test, respectively. Mimosa tannins were used as the stable reference standard for the condensed tannin analysis, although it is accepted that this has some failings. There were significant differences (p < 0.05) between species in the contents of extractable(soluble) and unextractable, both protein and neutral detergent fibre (NDF)-bound tannins. In all the samples, the concentration of bound tannins (protein and NDF bound) was significantly (p < 0.05) higher than that of the extractable tannins. Most of the bound tannins were bound to proteins. Total proanthocyanidin (sum of extractable and total residue tannins) concentration in the leaf and twig samples harvested at pre-anthesis, anthesis and post-anthesis stages of growth of Fitzroy was higher (p < 0.01) in the leaves than in the twigs. Condensed tannin contents were higher (p < 0.01) in S. scabra samples harvested at Chivhu than in those from Henderson Research Station and Mhondoro, which receive higher rainfall than at Chivhu. This study showed that the agro-ecological site and plant part affects proanthocyanidin concentrations in S. scabra.

African Journal of Range & Forage Science 2007, 24(3): 149–154