Antioxidant activity of polyphenols from solid olive residues of c.v. Coratina

The antioxidant profile of extracts from solid olive residue (SOR) of c.v. Coratina, a cultivar widely diffused in the south of Italy, using both cell-free and cell-based experimental models, was investigated. A total hydroalcoholic extract (polyphenols content 19.7%) and a purified extract (Oleaselect (TM)) (polyphenols content 35.1%) were tested for their ability to quench the stable free radical DPPH, the peroxyl radicals (ORAC assay), by monitoring the loss in fluorescence of R-phycoerythrin induced by the peroxyl radical generator AAPH and their ability to inhibit the cumene hydroperoxide-induced lysis of rat red blood cells (RBC). The total hydroalcoholic extract showed IC50 26.96 +/- 1.53 mu g/ml in the DPPH assay, that 10 mu g/ml were equivalent to 2.11 +/- 0.12 mu g/ml Trolox (ORAC assay) and IC50 1.7 +/- 0.20 mu g/ml in the RBC hemolysis. The Oleaselect (TM) extract was 4 to 5 folds more active than the hydroalcoholic extract in all the experimental models, with IC50 values of 7.36 +/- 0.38 mu g/ml in the DPPH test and of 0.38 +/- 0.03 mu g/ml in RBC; the antioxidant activity in the ORAC assay was slightly greater than that of Trolox (10 mu g/ml equivalent to 11.45 +/- 0.40 mu g/ml). The scavenging effect of the extract in the ORAC assay was compared to that of verbascoside (the main polyphenol component) and of caffeic acid (the basic constituent of verbascoside): the results indicate that caffeic acid (10 mu g/ml equivalent to 35.70 +/- 2.95 mu g/ml Trolox) is more potent than verbascoside (10 mu g/ml equivalent to 15.42 +/- 1.21 mu g/ml Trolox) in entrapping peroxyl radicals. Finally the antioxidant activity of the Oleaselect (TM) extract was confirmed in human umbilical endothelial cells (EC) exposed to the site-specific peroxyl radical inducer AAPH, where a massive lipid peroxidation process (marker the fluorescence probe BODIPY) takes place, paralleled by a marked loss of cell viability (calcein assay). The purified extract (1-20 mu g/ml) pre-incubated with EC for 1 h dose-dependently inhibited both the lipid-peroxidation damage and cell death. Taking into account the total polyphenol content, these results clearly indicate a greater antioxidant activity for the purified extract, due to a cooperative antioxidant interaction among its polyphenol constituent