Antioxidative and antimicrobial activities of the extracts from the seed coat of Bambara groundnut (Voandzeia subterranea)

Abstract

Antioxidative and antimicrobial activities of extracts from Bambara groundnut seed coat, prepared using water, ethanol and acetone as the media at various temperatures (30, 60, 90 °C) were investigated. Extraction yields and phenolic contents of Bambara groundnut seed coat extracts (BGSEs) varied from 5.21 to 13.23% and from 169 to 569 mg GAE per g dry extract, respectively. BGSEs showed varying antioxidative activities including DPPH, ABTS, hydroxyl and superoxide anion radical scavenging activities, ferric reducing antioxidant power and metal chelating activity, depending on extraction conditions (p < 0.05). Antioxidative activities of BGSE prepared using ethanol at 60 °C (BGSE_E60) were stable in a wide pH range and with heat treatment. BGSE_E60 exhibited antioxidative activities in the lecithin liposome system and steamed chicken mince as evidenced by the retarded formation of conjugated diene, peroxide value and thiobarbituric acid reactive substances (TBARS) (p < 0.05). Additionally, the BGSE_E60 (2.5–30 mg ml⁻¹) possessed antimicrobial activities against bacteria (Staphylococcus aureus, Escherichia coli, Bacillus cereus), yeast (Candida albicans) and mold (Aspergillus niger), in a dose-dependent manner. Scanning and transmission electron microscopic studies also revealed the damage of microbial cells after being treated with BGSE_E60. No cytotoxicity of BGSE_E60 against the primate cell line (Vero) was observed. Therefore, extraction yields, total phenolic contents and antioxidative activities of BGSEs were governed by the extracting solvents and temperatures used. Additionally, BGSEs could be used as natural antioxidants and antimicrobial agents without cytotoxicity.