Antioxidant activity of flavone C-glucosides determined by updated analytical strategies

The antioxidant activity of flavone C-glucosides, namely orientin (OR), homoorientin (hOR), vitexin (VT) and isovitexin (iVT) in comparison to quercetin (Q) was measured against 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical cation (ABTS+), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), superoxide anion radical O2- whilst the reducing activity was determined by cyclic voltammetry (CV) method. The order of the antioxidant activity determined against ABTS+ and DPPH radicals was as follows: Q≥hOR>OR⋙iVT>VTQ≥hOR>OR⋙iVT>VT. Orientin (OR) and homoorientin (hOR) showed the highest ability to scavenge superoxide anion radicals whilst about threefold lower was found for VT and iVT. The order of the antioxidant activity determined against superoxide anion radicals was hOR > OR > Q > iVT = VT. The reducing activity of hOR and OR derived from CV experiments performed within the range from −100 to +1300 mV showed twofold higher values than those determined for VT and iVT. In contrast, when CV tracing was carried out from −100 to +800 mV, the order of the antioxidant activity was as follows: Q > hOR = OR, and no antioxidant activity of VT and iVT was noted.