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Copper(II)‐mediated oxidation of (+)‐catechin in a model white wine system
Author(s) -
CLARK ANDREW C.,
SCOLLARY GEOFFREY R.
Publication year - 2002
Publication title -
australian journal of grape and wine research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.65
H-Index - 77
eISSN - 1755-0238
pISSN - 1322-7130
DOI - 10.1111/j.1755-0238.2002.tb00255.x
Subject(s) - chemistry , pyrogallol , catechin , copper , glyoxylic acid , tartrate , wine , white wine , absorbance , browning , hydrogen peroxide , ethanol , nuclear chemistry , inorganic chemistry , organic chemistry , polyphenol , antioxidant , chromatography , food science
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.