Phytochemical composition, total phenolic content and ferric reducing antioxidant power determination of the antioxidant activity of leaf, stem and root bark extracts of Strophanthus sarmentosus DC

Abstract

Research into medicinal plants globally has led to major breakthroughs in drug discovery. Extracts from plant organs contain interesting secondary metabolites which have various medicinal applications in ethnomedicine. Strophanthus sarmentosus DC commonly called arrow poison or spider tresses is a very popular plant among traditional medical practitioners in Africa. S. sarmentosus has been reported to be effective in the treatment of arthritis, wound infections, gastrointestinal disorders and cardiac arrest in ethnomedicine. The increased interest in discovering drugs from natural source led to the investigation of the phytochemical composition, the total phenolic content (TPC) and ferric reducing antioxidant power (FRAP) of leaf, stem and root bark extracts of S. sarmentosus DC. The total phenolic content of the extracts were examined using the Folin-Ciocalteau method, while the ferric reducing antioxidant power is based on the presence of reducing agents in the different S. sarmentosus extracts and their abilities to reduce Fe³⁺ to Fe²⁺ by donating an electron. Both the TPC and FRAP assays were conducted at varying concentrations of the extracts using garlic and ascorbic acid as standards respectively. The phytochemical analysis revealed the presence of alkaloids, flavonoids, saponins, tannins, terpenoids and glycosides in varying proportions. The TPC is expressed as garlic acid equivalent (GAE) and the FRAP expressed as ascorbic acid equivalent (AAE). The leaf had the highest TPC value of the three extracts close to that of the reference garlic acid standard and the root bark extract also showed considerable TPC value slightly higher than the stem extracts. The leaf extract also gave the highest FRAP value, with the root bark extract having the least value and at the lower concentrations of 0.2 and 0.4 mg/cm³ there was no significant reducing abilities exhibited by the root bark extract. The stem showed low FRAP value particularly at the lower concentrations but showed higher values with increasing concentration. Both TPC and FRAP assay can be used to determine antioxidant activities in plants. The TPC and FRAP values in all the extracts is an indication of the antioxidant potentials of S. sarmentosus plant with the leaves having the highest FRAP and TPC values, making it a better antioxidant than other plant parts. This study therefore reports the phytochemical composition and high antioxidant activities of the total phenolic content and ferric reducing antioxidant power of the extracts of S. sarmentosus and also provides some scientific basis for its utilization in ethnomedicine.

Keywords: Strophanthus sarmentosus DC, Phytochemical, Folin-Ciocalteau assay, Total phenolic content, Ferric reducing antioxidant power