The experimental conditions used in this thesis, i.e., reaction temperature, ascorbic acid concentration and model wine system components, were found to impact on the kinetics of the degradation of ascorbic acid and on the kinetics of formation of its degradation products. Importantly, the chemical identity of the degradation compounds was not affected by the reaction conditions and this allowed further experiments to be performed at elevated temperatures, often referred to as accelerated ageing' conditions. Ascorbic acid enhanced the colouration of phenolic solutions, not through hydrogen peroxide production, but rather via one of its carbon-based degradation products. The latter was identified as L-xylosone which was found to form two isomeric addition products with (+)-catechin. These (+)-catechin-based isomers were determined to be pigment precursors to the glyoxylic acid-derived xanthylium cations under model wine conditions. Although not identified in model wine systems itself, L-xylosone was therefore established as another degradation product of ascorbic acid in wine media, and was added to the list of compounds able to react with (+)-catechin to form glyoxylic acid-derived xanthylium cations. Ascorbic acid and sulfur dioxide offered some protection towards the L-xylosone-derived (+)-catechin isomers while metal ions enhanced their conversion to the coloured xanthylium cations.
|Qualification||Doctor of Philosophy|
|Award date||01 Mar 2011|
|Place of Publication||Australia|
|Publication status||Published - 2011|