Antioxidant Activity of the Main Bioactive Derivatives from Oleuropein Hydrolysis by Hyperthermophilic β-Glycosidase

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Abstract
The main reaction products obtainable by the hydrolysis of commercially available oleuropein by hyperthermophilic β-glycosidase were purified and structurally characterized by UV and 1H and 13C NMR analyses. Their antioxidant activity, in particular their capacity to inhibit the fatty acid peroxidation rate, was studied. The molecular structures assigned revealed the presence of two elenolic acid forms presenting different antioxidant abilities closely correlated to their molecular structures, as well as an unstable elenolate which is a rearrangement product of the oleuropein aglycon. This molecule, under the reaction conditions (pH 7.0, 60 °C) required for β-glycosidase activity, rapidly gives rise to 3,4-dihydroxy-phenylethanol (hydroxytyrosol). Keywords: Oleuropein; 3,4-dihydroxy-phenylethanol; elenolic acid; β-glycosidase; antioxidant activity