Phytochemical Investigation and In Vitro Antioxidant Activities of Tetracarpidium conophorum (African Walnut) Seeds

Tetracarpidium conophorum (African walnut) is an African plant with ethnobotanical uses. The purpose of this study was to evaluate the phytochemical screening and in vitro antioxidant activities of methanol extract and fractions (F) [n-hexane (HEX-F), dichloromethane (DCM-F) and, ethyl acetate (EA-F)] of T. conophorum seeds. Phytochemical screening and in vitro antioxidant activity study were carried out using DPPH, ABTs radical scavenging assays, nitric oxide inhibitory and reducing potential assays. Methanol extract and its fractions contain phenols, flavonoids, saponins, tannins, terpenoids, and alkaloids. The concentrations of total phenols and flavonoids content were significantly higher in EA-F and crude methanol extract compared to other fractions. Crude methanol and EA-F contain higher concentrations of tannin while hexane fraction had the lowest tannin content but relatively higher proanthocyanidin content compared to other fractions. The antioxidant activity study showed that both methanol crude extract and fractions of T. conophorum seeds have significant activities for DPPH radical scavenging, reducing power, ferric reducing antioxidant potential, nitric oxide inhibitory activities, ABTS and hydroxyl radical scavenging for. DPPH radical scavenging activities of EA-F showed the lowest IC50 of 33.11 µg/mL, followed by Hex-F, DCM-F and crude methanol extract with IC50 of 33.43, 42.09 and 45.44 µg/mL, respectively, when compared to ascorbic acid with IC50 of 17.08 µg/mL. The study showed that T. conophorum seed is a rich source of secondary metabolites, which may be responsible for its antioxidant activities