This spectrophotometric assay uses the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a reagent (Yadegarinia et al., 2006). The model of scavenging stable DPPH-free radicals can be used to evaluate the antioxidative activities in a relatively short time (Conforti et al., 2006). The samples are able to reduce the stable free DPPH radical to 1,1-diphenyl-2-picrylhydrazyl that is yellow colored. The hydrogen or electron donation abilities of the samples are measured by means of the decrease of the absorbance resulting in a color change from purple to yellow (Gutierrez et al., 2006). Another procedure can be applied for an EO. A dilution of the EO in toluene is applied onto a thin-layer chromatography (TLC) plate and toluene-ethyl-acetate is used as a developer (Sokmen et al., 2004a). The plates are sprayed with 0.4 mM DPPH in methanol. The active compounds were detected as yellow spots on a purple background. Only those compounds, which changed the color within 30 min, are taken as a positive result.
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