Electron spin resonance spectroscopic measurement of antioxidant activity of organic solvent extracts derived from the methanolic extracts of Sri Lankan thebu leaves (<i>Costus speciosus</i>)

Abstract

In this study, the antioxidant effects of different solvent soluble fractions derived from the methanolic extracts of the Sri Lankan thebu plant (Costus speciosus) leaves were assessed. For the antioxidant activity of the extracts, 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl and alkyl radical scavenging potentiality were measured using electron spin resonance (ESR) spectroscopy compared to the standard antioxidant ascorbic acid. Among the extracts, ethyl acetate fraction (T-EA) indicated the strongest scavenging activity against hydroxyl and alkyl radicals with the IC50 values 0.046 +/- 0.002 and 0.055 +/- 0.004 mg mL(-1), respectively. The aqueous fraction (T-WE) indicated the highest DPPH radical scavenging activity (IC50 value 0.110 +/- 0.01 mg mL(-1)). The total phenolic content in thebu extracts was the highest in T-EA fraction with 6.57 %. Moreover, both T-EA and T-WE fractions did not show any significant cytotoxic effect against vero cells in vitro assays. These results indicated the profound antioxidant effects of the Sri Lankan thebu leaf extracts for the first time. Isolation of antioxidative compounds from T-EA and T-WE fractions and in vitro antioxidant effects can be considered in further studies.