Phenolic content, antioxidant, cytotoxic and antiproliferative effects of fractions of Vigna subterraenea (L.) verdc from Mpumalanga, South Africa

Jane N C Okafor; Fanie Rautenbauch; Mervin Meyer; Marilize Le Roes-Hill; Taahir Harris; Victoria A Jideani

doi:10.1016/j.heliyon.2021.e08397

Phenolic content, antioxidant, cytotoxic and antiproliferative effects of fractions of Vigna subterraenea (L.) verdc from Mpumalanga, South Africa

Heliyon. 2021 Nov 14;7(11):e08397. doi: 10.1016/j.heliyon.2021.e08397. eCollection 2021 Nov.

Authors

Jane N C Okafor^{1

2}, Fanie Rautenbauch³, Mervin Meyer⁴, Marilize Le Roes-Hill⁵, Taahir Harris¹, Victoria A Jideani¹

Affiliations

¹ Food Science and Technology Department, Cape Peninsula University of Technology, Bellville, 7535, South Africa.
² Nutrition and Toxicology Division, Federal Institute of Industrial Research, Oshodi (FIIRO), P.M.B 21023, Ikeja, Lagos, Nigeria.
³ Applied Microbial and Health Biotechnology Institute, Cape Peninsula University of Technology, Bellville, 7535, South Africa.
⁴ Nanotechnology Innovation Centre, Department of Biotechnology, University of the Western Cape, Private Bag x17, Bellville, 7535, Cape Town, South Africa.
⁵ Biocatalysis and Technical Biology Research Group, Institute of Biomedical and Microbial Biotechnology, Cape Peninsula University of Technology, Bellville, 7535, South Africa.

Abstract

Consistent intake of legumes has been correlated with decreased possibility of developing colorectal cancer (CRC) due to the content of some phytochemicals like polyphenols. Bambara groundnut (BGN) is an underutilized crop with a rich nutritional profile, but have not been exploited for its nutraceutical and medicinal benefits. In this study, total polyphenol, flavonoid (flavonol and flavanol) content, antioxidant activity and cytotoxicity/antiproliferative properties of 70% ethanolic extracts of whole BGN, cotyledon and seed coat on Caco-2 and HT-29 colon cancer cells were evaluated. Seed coat had a significantly (p < 0.05) higher composition of total polyphenol, flavonol and flavan-3-ol (flavanol) compared to whole seed and cotyledon. Antioxidant activity determined with ferric reducing antioxidant power (FRAP), 2,2- azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and oxygen radical absorbance capacity (ORAC) assays, showed that seed coat with higher polyphenolic content had significantly (p < 0.05) greater antioxidant activity. BGN fractions demonstrated cytotoxic and antiproliferative effects against HT-29 and Caco-2 colon cancer cells in a dose-dependent manner, with seed coat and whole seed exhibiting greater cytotoxicity and higher antiproliferative activity and colon cancer cell inhibition. Extracts of the cotyledon also showed cytotoxic activity and hindered cancer cell growth/division but to a significantly (p < 0.05) lower magnitude. BGN parts indicated a greater cytotoxic effect and potential to slow down Caco-2 colon cancer cell growth and division over HT-29. This result provides new knowledge on the possible health benefits of BGN, as well as the potential for product development and may influence its consumption and utilisation.

Keywords: Antioxidant activity; Antiproliferation; Bambara groundnut; Colon cancer; Cotyledon; Cytotoxicity; Phenolic; Seed coat.