Trypsin Inhibitor Activity and Condensed Tannin Content in Bambara Groundnut (Vigna Subterranea (L.) Verdc) Grown in Southern Africa

Legumes are an important source of protein in many developing countries. However this protein is not readily available because of antinutrients. Farmers are being encouraged to grow bambara groundnut to meet food sufficiency, hence information on the content of antinutrients is required. The objective of the study was to compare antinutrients trypsin inhibitor activity and condensed tannin content in nine landraces of bambara groundnut grown in three Southern African countries, Botswana, Swaziland and Namibia respectively. Trypsin inhibitor activity was determined in raw seeds using the method developed by Kakade et al. (1974). Six landraces from Namibia (AHM 968, NC2, NC1, DIP C and GAB C and AHM753), three from Swaziland (OM1, NC2 and UR/SR) and two from Botswana (DIPC and UR/SR) had high trypsin inhibitor activity. DIPC had the highest overall trypsin inhibitor activity (units/mg protein) of 60.4 while AHM 753 had low trypsin inhibitor activity of 49.1 (p< 0.05). The trypsin inhibitor activity of each landrace differed from country to country with no simple pattern revealed but the landraces from Namibia had the highest activity and those grown in Botswana had the least. The trypsin inhibitor activity reported is higher than in soybean and pigeon pea. The condensed tannin content was determined using butanol-HCl method by Porter et al. (1986). It ranged from 0.02% in NC1 and OM1 grown in Swaziland and Namibia respectively to 0.49% in AHM 753 cultivated in Namibia. Thirteen out of the 27 samples analysed had tannin content below the allowed limit of 0.10%; three were cultivated in Botswana and five each from Namibia and Swaziland. Seeds that had the highest condensed tannin content were brown, tan and red while those with the lowest condensed tannin content were cream coloured are they are recommended to be used in weaning formula.