Abstract
The root bark of Osyris lanceolata was screened for its antioxidant potential using three variations of the DPPH radical scavenging method viz a TLC-autographic assay, a semi-quantitative TLC assay, and a spectrophotometric assay. The total phenolic content was evaluated as gallic acid equivalents (GAE) using the Folin-Ciocalteu method. The powdered root bark was extracted sequentially with n-hexane, chloroform, methanol and 90% methanol/water. A separate supercritical fluid extraction (SFE) of the root bark was also carried out. The radical scavenging ability, as measured by IC50 values, was found to be 48.4 ± 0.4 and 49.5 ± 1.9 μg/mL for the 90% methanol/water and methanol extracts respectively, while those of the chloroform, n-hexane, and SFE extracts were found to be < 250 μg/mL. Under the same conditions, the values for the standards, ascorbic acid and gallic acid, were found to be 38.70 ± 0.08 and 2.86 ± 0.01 μg/mL respectively. The radical scavenging power of the five extracts correlated positively with the total phenolic content and was ranked in the following decreasing order: 90% methanol/water > methanol > chloroform > SFE > n-hexane with total phenolic contents of 290.2 ± 3.3, 271.0 ± 3.7, 74.4 ± 0.8, 62.5 ± 0.4 and 49.5 ± 1.9 mg GAE/g of dry extract, respectively. The 90% methanol/water and methanol extracts showed several components with high antioxidant activity displaying fast kinetics in both TLC assays, while the chloroform, SFE, and n-hexane extracts exhibited slow kinetics antioxidant activity.