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Copper(II)‐mediated oxidation of (+)‐catechin in a model white wine system

Copper(II)‐mediated oxidation of (+)‐catechin in a model white wine system 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 45C 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Australian Journal of Grape and Wine Research Wiley

Copper(II)‐mediated oxidation of (+)‐catechin in a model white wine system

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Publisher
Wiley
Copyright
Copyright © 2002 Wiley Subscription Services, Inc., A Wiley Company
ISSN
1322-7130
eISSN
1755-0238
DOI
10.1111/j.1755-0238.2002.tb00255.x
Publisher site
See Article on Publisher Site

Abstract

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 45C 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.

Journal

Australian Journal of Grape and Wine Research – Wiley

Published: Oct 1, 2002

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