Evaluation of in vitro Antioxidant Properties of Methanol Extract and Fractions of Cola rostrata (K. Schum) Leaves

Abstract

Background and Purpose: Medicinal plants are used for the treatment of diseases because of the presence of therapeutic phytochemical constituents. Antioxidants play important roles in preventing and mitigating diseases. The plant Cola rostrata K. Schum (Sterculiaceae) is used in traditional medicine for pain relief, diabetes, erectile dysfunction, dental hygiene, and other conditions. The objective was to evaluate the total phenolic content and in vitro antioxidant properties of C. rostrata leaf extract and fractions. Methods: The dried and pulverized leaves of the plant were soaked in methanol for 72 h for extraction. Fractionation of the methanol extract was done using n-hexane, ethyl acetate, and methanol in a column. The extract and fractions were screened for phytochemical constituents. The total phenolic content was determined using the Folin-Ciocalteu assay. In vitro antioxidant properties were evaluated using the 2,2-diphenyl-1-picyhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and hydroxyl radical scavenging assay against ascorbic acid (standard). Results: The phytochemical screening revealed the presence of alkaloids and flavonoids among others. The total phenolic content was higher in the extract (1.34 mg/g GAE) compared to the fractions. In the DPPH assay, the n-hexane fraction had lower IC50 (0.93 µg/mL) than the standard (3.44 µg/mL). In the FRAP assay, the ethyl acetate fraction had EC50 of 0.71 µg/mL which was lower than that of the standard (1.34 µg/mL). In the hydroxyl radical scavenging assay, the n-hexane had lower IC50 (0.37 µg/mL) than the standard (1.45µg/mL). Conclusion: The findings suggest that the leaves of C. rostrata have potential antioxidant properties which may be due to the high phenolic content.