Phytochemical constituents and antioxidant activities of aqueous and methanol stem extracts of Costus afer Ker Gawl. (Costaceae)
Medicinal plants contain bioactive compounds capable of preventing and fighting oxidative related diseases. These compounds must be screened and assayed before effective drugs are developed. Thus, phytochemical constituents and antioxidant activities of aqueous and methanol stem extracts of Costus afer Ker-Gawl were evaluated. C. afer contained flavonoids, phenols, anthraquinones, cardiac glycosides, terpenoids, alkaloids and tannins. Preliminary screening of free radical scavenging activity of extracts with 2,2-Diphenyl-1-picrylhydrazyl (DPPH) using thin layer chromatography tested positive. The aqueous extract had a higher free radical scavenging activity with IC50 (concentration of samples required for 50% inhibition of DPPH radical activity) value of 64.42 g/ml than methanol extract (92.33 g/ml). Furthermore, total phenolic content in aqueous extract (0.66 ± 0.02 mg gallic acid equivalent/g) was significantly higher (p < 0.05) than methanol extract (0.52 ± 0.01 mg gallic acid equivalent/g). In addition, inhibition of lipid peroxidation by aqueous extract (80.60 ± 0.28%) was significantly higher (p < 0.05) than methanol extract (77.00 ± 0.84%). Nevertheless, methanol and aqueous extracts of C. afer possess anti-oxidative properties as well as bioactive metabolites. Thus, stem extracts of C. afer could serve as sources of antioxidants and bioactive compounds for nutrition and therapeutic purposes.
Key words: Costus afer, phytochemicals, antioxidant, phenol, nutrition, therapeutic.