Antioxidant Activity of Stem Bark of Thespesia populnea Soland ex Corr.

Objective: To evaluate the antioxidant activity of stem bark of Thespesia populnea. Materials and Method: Antioxidant activity of T. populnea stem bark was studied in four in vitro / ex vivo models, viz., DPPH radical scavenging activity, superoxide scavenging activity, reducing power assay and lipid peroxidation. Results: Preliminary phytochemical screening showed the presence of high amount of phenolics, tannins and flavonoids. Subsequent quantification by Folin Ciocalteau method showed the presence of high amount of total phenolics (10.11 % w/w, calculated as gallic acid). Methanolic extract of stem bark of T. populnea showed a very good DPPH radical scavenging activity (EC₅₀ of 12.08 μg) and superoxide scavenging activity (EC₅₀ of 73.53 μg) in a dose dependent manner. The reduction ability of the extract, (Fe³⁺ to Fe2+ transformation) was found to increase with increasing concentrations where a maximum absorbance of 1.012 was obtained at a concentration of 300 μg. It also inhibited lipid peroxidation in a dose dependent manner with an EC₅₀ of 20.76 μg, which was comparable to α-tocopherol (EC₅₀ of 27.35 μg). Conclusion: The methanolic extract of the stem bark of T. populnea showed very good free radical scavenging activity, including inhibition of lipid peroxidation and reducing power.