Impact of Ascorbic acid on the Oxidative Colouration and Associated Reactions of a Model Wine Solution Containing (+)-Catechin, Caffeic acid and Iron

Aim: The aim of this study was to examine the oxidative reactions and associated colouration changes relevant to white wine in a synthetic wine system consisting of different combinations of 200 mg/L caffeic acid, 150 mg/L (+)-catechin and 1000 mg/L ascorbic acid, in the presence of 1.5 mg/L iron(II).Method and Results: Reactions were monitored by UV/VIS, CIELab, LC-DAD and LC-MS techniques. When ascorbic acid was less than 90% depleted in samples it induced yellow/green colouration but prevented brown colouration that would otherwise result from catechin- and caffeic acid-derived yellow and red pigments. However, during the loss of ascorbic acid, in the presence of either catechin and/or caffeic acid, reactions were still occurring to 'prime' the system for rapid colour formation. When the ascorbic acid was more than 90% depleted, the samples with catechin and/or caffeic acid had an increased rate of brown colouration compared to those to which ascorbic acid was not added.Conclusion: Ascorbic acid is efficient at preventing the production of pigmented phenolic compounds, but once depleted, induces their production.Significance of the Study: This study demonstrates that ascorbic acid is an effective anti-browning agent provided it persists in the wine after bottling, but if depleted, serious brown colouration ensues.