Understanding the contribution of ascorbic acid to the pigment development in model white wine systems using liquid chromatography with diode array and mass spectrometry detection techniques.

The present study investigated the contribution of ascorbic acid to the formation of coloured species in model white wine systems containing (+)-catechin as the oxidisable phenolic substrate. Reactions were carried out in the presence or absence of ascorbic acid in model wine systems buffered with either tartaric acid or formic acid. High performance liquid chromatography with diode array detector (HPLC-DAD) or mass spectrometry (HPLC-MS) analyses demonstrated that glyoxylic acid-derived xanthylium pigments were the main coloured species produced in all samples except those containing just (+)-catechin and formic acid. Higher concentrations of these pigments were detected in the tartaric acid based model system containing both (+)-catechin and ascorbic acid than in the corresponding formic acid model system. The inability of formic acid to form an aldehyde, unlike the known oxidative formation of aldehydes from tartaric acid, contributes to the lower colour development in the formic acid model system. Significantly, these observations imply that ascorbic acid must break down to provide an aldehyde, or ketone, capable of reacting with (+)-catechin to generate the glyoxylic acid-derived xanthylium cations.