Phenolic content and antioxidant property of the bark extracts of Ziziphus mucronata Willd. subsp mucronata Willd

Background: Several plants traditionally used in treatment of a variety of infections in South Africa are reported in ethnobotanical surveys. Many of these plants including Ziziphus mucronata subsp. mucronata lack scientific reports to support their medicinal importance. Methods: The antioxidant activities and phenolic contents of the acetone, ethanol and aqueous extracts of the stems of Z. mucronata subsp. mucronata were evaluated using in vitro standard methods. The total phenol, total flavonoids and proanthocyanidin content were determined spectrophotometrically. Quercetin, Tannic acid and catechin equivalents were used for these parameters. The antioxidant activities of the stem bark extracts of this plant were determined by ABTS, DPPH, and ferrous reducing antioxidant property (FRAP) methods. Results: The quantity of the phenolic compounds, flavonoids and proanthocyanidins detected differ significantly in the various extracts. The phenolics were significantly higher than the flavonoids and proanthocyanidin contents in all the extracts investigated. The ferric reducing ability and the radical scavenging activities of the extracts were very high and dose-dependent. The ethanol extract had the highest antioxidant activity, followed by the acetone extract while the aqueous extract was the least active. Reacting with ABTS, the 50% inhibitory concentrations (IC50) were (0.0429 +/- 0.04 mg/ml) for aqueous, (0.0317 +/- 0.04 mg/ml) for acetone and (0.0306 +/- 0.04 mg/ml) for ethanol extracts while they inhibited DPPH radical with 50% inhibitory concentration (IC50) values of 0.0646 +/- 0.02 mg/ml (aqueous), 0.0482 +/- 0.02 mg/ml (acetone) and 0.0422 +/- 0.03 mg/ml (ethanol). Conclusions: A correlation between the antioxidant activity and the total phenolic contents of the extracts indicated that phenolic compounds were the dominant contributors to the antioxidant activity of the plant. This study, therefore, demonstrated that Z. mucronata subsp. mucronata has strong antioxidant property and free radical scavenging capability.