New phenolic compounds formed by evolution of (+)-catechin and glyoxylic acid in hydroalcoholic solution and their implication in color changes of grape-derived foods

The reaction between (+)-catechin and glyoxylic acid in model solution syst em was investigated by LC/DAD and LC/ESI-MS analyses. The formation of phen olic compounds exhibiting absorption maxima near 300 nm and presenting a sh oulder around 350 nm was observed. Their structures consisted of a (+)-cate chin unit with one or two aldehyde groups linked at positions 6, 8 or 6 and of the A ring. In addition, new yellow pigments exhibiting UV-visible spec tra similar to those of xanthylium salts with absorption maxima at 450 and 280 mm were also detected. The major yellow compound was isolated and ident ified by ESI-MS and 1D and 2D NMR spectroscopy. The implication of these co mpounds in color change and browning observed during aging of grape-derived beverages is also discussed.