Phytochemical composition and antioxidant properties of methanolic extracts of whole and dehulled Bambara groundnut (Vigna subterranea) seeds (original) (raw)

The distribution of phytochemicals and their contribution to antioxidant potentials in whole and dehulled Bambara groundnut (BGN) seeds was evaluated. Whole BGN seeds were sorted using the testa and hilium colour and further grouped into whole and dehulled BGN seeds. Extractions of both whole and dehulled BGN seeds was done using methanol and the extracts assayed for total phenolics (TPC), flavanol, flavonol, anthocyanin content, oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP). Methanolic extract of whole BGN seed exhibited higher flavanol and flavonol content as well as significantly higher in-vitro antioxidant activities than dehulled BGN seeds. The TPC of whole BGN seed extract ranged from 3.6 to 11.0 GAE/g, while that of dehulled BGN ranged from 2.7 to 3.2 GAE/g. Identification of phenolics in whole and dehulled BGN seed extract using UPLC-qTOF-MS, revealed the presence of monoterpenoids (iridoids), phenolic acids, flavonoids and lignans. Bivariate correlations showed anthocyanin demonstrated weak positive correlation between flavanol, flavonol and ORAC for whole BGN seed extract; and negative correlation between flavanol, TPC, FRAP and ORAC for dehulled BGN. Aside the effect of dehulling, whole BGN seeds exhibited the presence of phytochemicals with beneficial properties for food and industrial application. Legumes are crops belonging to the Fabaceae family which due to the enormous protein and fibre available in their seeds, contributes a very significant and healthy portion to the human diet 1. Apart from their nutritive worth, legumes are rich in secondary metabolites 2 known for their contribution to a wide array of biological activities. One such legume is Bambara groundnut (BGN; Vigna subterranea), an underutilized neglected legume, grown for its seeds 3. Major producers of BGN in Africa are Nigeria, Niger, Ghana and Cote d'Ivoire; but widely grown in Eastern Africa and Madagascar 4. Likewise, in South Africa, major areas producing BGN seeds are Limpopo, Mpumalanga and KwaZulu-Natal Provinces. There are various opinions as to the origin of BGN in South Africa because the Vendas claim that they brought the legume to South Africa from Central Africa, while the people of Bolobedu also claim to have brought the seeds when they arrived in the south 5, 6. Nevertheless, the claim by the Vendas is supported by the name 'Nduhu-mvenda' meaning groundnut of Venda land and the traditional ritual, which is often performed during the harvest of BGN in Venda 7. Among the repository of underutilized crops, BGN has significant potential to ensure investment towards its improvement 8. Its seeds possess the ability to mitigate malnutrition and increase food security as they contain about 57-67% of carbohydrate and 15-27% of proteins, although lower concentrations of lipids (< 10%) have been reported 9-12. Bambara groundnut acts as a vital source of protein in the diets of a vast populace in Africa, especially to members of the populace that are unable to pay for animal protein. Besides, BGN is associated with diverse indigenous knowledge among cultures who depend on it for sustenance.