Antioxidant and antibacterial constituents of <i>Steganotaenia araliacea</i> stem bark

Abstract

Steganotaenia araliacea Hochst (Apiaceae/ Umbelliferae) is a small tree used in traditional medicine especially in tropical Africa and savannah where it is mostly found. It is used in ethnomedicine to treat pneumonia, asthma, peptic ulcer, sore throat, fever, as a diuretic agent and other diseases of microbial origin. The antioxidant and anti-bacterial activities of the hexane, dichloromethane and aqueous extracts obtained from the stem bark of Steganotaenia araliacea were evaluated in terms of capacity to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and to inhibit the growth of typed microorganisms used (namely Staphylococcus aureus, Salmonella typhi and E. coli). The hexane and dichloromethane extracts showed significant antioxidant activity, expressed as IC₅₀, 5.62μg/mL and 1.26μg/mL respectively. The antioxidant potential of the extracts, expressed as IC₅₀, ranged between 1.26 μg/mL and 5.62 μg/mL. (Ascorbic acid, gallic acid and rutin used as standard had 2.79 μM, 1.78 μM and 10.0 μM respectively). In the test for antibacterial activity, dichloromethane extract showed the highest inhibitory activity followed by hexane extract, especially against, Salmonella typhi. GC-MS analysis of the hexane and dichloromethane was carried out to determine their chemical constituents. Results revealed that both extracts contained similar compounds (including cumene, xylene, citronellol and long chain hydrocarbons). In addition the dichloromethane extract contains cadinanol, ar-curcumene and α-guaien, not found in hexane extract. These compounds may be contributing to the observed antioxidant activity of the extract.

Keywords: Steganotaenia araliacea; Antimicrobial; Antioxidant; GC-MS; Cadinanol; Citronellol