Dose-effect study on the antioxidant properties of leaves and outer bracts of extracts obtained from Violetto di Toscana artichoke

Artichoke (Cynara scolymus L.) is an edible vegetable largely used in the Mediterranean diet and in folk medicine. The present paper discusses the analysis of the polyphenol content of leaves and outer bracts of Violetto di Toscana artichoke using different extraction procedures with the aim of establishing a correlation between polyphenol subclasses and antioxidant activity measured on human LDL oxidized by copper ions. HPLC/DAD and HPLC/MS analyses revealed that both the matrixes contain identical polyphenol subclasses, with mainly quantitative differences. The antioxidant effect of four artichoke extracts decreases in the following order when the sum of total phenolic compounds was considered: ethanolic extract from leaves (IC50 = 2.92 +/- 0.46 mu M); ethanolic extract from outer bracts (IC50 = 4.04 +/- 0.21 mu M); ethyl acetate extract from leaves (IC50 = 4.91 +/- 0.11 mu M); ethyl acetate extract from outer bracts (IC50 = 10.18 +/- 1.6 mu M). IC50 were also calculated considering the concentrations of single polyphenol subclasses. In both cases, the potency of antioxidant properties was not related to the amount of total polyphenols or the single subclasses. (c) 2006 Elsevier Ltd. All rights reserved.