Resumen de Cooper (II)-mediated oxidation of (+)-catechin in a model white wine system
Andrew C. Clark, Geoffrey R. Scollary
This study was undertaken to establish the role played by copper(II) in enhancing the rate of oxidation of flavanols. A model white wine system consisting of 12% (v/v) aqueous ethanol saturated with potassium hydrogen tartrate and adjusted to pH 3.2 was used to allow experimentation under well-defined conditions. (+)-Catechin was the oxidisable substrate and copper(II) concentrations up to 0.6 mg/L were employed. The model white wines were maintained at 45°C to induce the browning process. Under these conditions an increase in absorbance at 440 nm occurred provided the copper(II) concentration was 0.3 mg/L or greater. The coloured species responsible for the increase in absorbance were identified as xanthylium cations, formed by linkage of two (+)-catechin molecules. Glyoxylic acid acted as the bridge between the phloroglucinol-type moiety of the (+)-catechin molecules. The production of the xanthylium cations was inhibited by ethanol and also by mannitol and the implications of these observations for a free-radical induced mechanism are discussed.
