Abstract

Methanolic extract of Colebrookia oppositifolia Smith. was dissolved in distilled water and partitioned with n-hexane, chloroform, ethyl acetate and n-butanol sequentially. Phytochemical screening showed the presence of phenolics, flavonoides and cardiac glycosides in chloroform, ethyl acetate and n-butanol fraction. The antioxidant potential of all these fractions and remaining aqueous fraction was evaluated by four methods: 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity, total antioxidant activity, Ferric Reducing Antioxidant Power (FRAP) assay and ferric thiocyanate assay along with determination of their total phenolics. The polar fractions showed noteworthy antioxidant potential. The results revealed that ethyl acetate soluble fraction showed the highest value of percentage inhibition of DPPH (83.43 ± 1.27) at concentration of 60 µg/ml. The IC₅₀ of this fraction was 27.2 ± 0.23 µg/ml, relative to butylated hydroxytoluene (BHT), having IC₅₀of 12.1 ± 0.92 µg/mL. It also showed highest FRAP value (172.23 ± 1.66 µg of trolox equivalents), as well as highest value of inhibition of lipid peroxidation (57.61 ± 1.1%) as compared to the studied fractions. The chloroform fraction showed highest total antioxidant activity (0.711 ± 0.031), as well as highest total phenolic contents (72.5 ± 0.34). 

Key words: Colebrookia oppositifolia Smith, DPPH assay, total antioxidant activity, FRAP value, total phenolics, Inhibition of lipid peroxidation (%).