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

Bukola C Adedayo,Marilize Le Roes-Hill,Tonna A Anyasi,Fanie Rautenbauch,Victoria A Jideani,Malcolm J C Taylor

doi:10.1038/s41598-021-93525-w

Abstract

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.

Highlights

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]
Extracts from the different Bambara groundnut (BGN) seeds used in this work showed varying antioxidant capacities in terms of the oxygen radical absorbance capacity (ORAC) values with the whole seed extracts exhibiting higher ORAC values
The distribution of phytochemicals and antioxidant activities in the BGN methanolic extracts varied with the testa and hilium colour

Summary

Introduction

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. In South Africa, major areas producing BGN seeds are Limpopo, Mpumalanga and KwaZulu-Natal Provinces. The phytochemical composition and the antioxidant activity of BGN from Limpopo Province of South Africa has not been reported. The objective of this work, was to determine the distribution of phytochemicals in BGN seeds obtained from the Limpopo Province of South Africa and their contribution to antioxidant activities

Methods

Results

Conclusion