Anthocyanin-derived pigments and colour of red wines

The colouring material of a red wine was fractionated by medium pressure liquid chromatography (LC) on a C18 reversed-phase column. Three fractions were collected and studied by liquid chromatography-diode array detection-mass spectrometry (LC-DAD-MS) and spectrophotometry in order to evaluate their pigment composition and colour characteristics. Fraction 1 represented 31% of the dry material (DM) of the wine and contained grape anthocyanins. Fraction 2 (6 1% DM) also contained anthocyanins together with several vitisin-like pigments, which appeared as very minor peaks in the liquid chromatograms. Fraction 3 (8% DM) exclusively showed anthocyanin-derived pigments. Diverse anthocyanin-derived pigments present in fractions 2 and 3 were identified by their mass spectra. It was shown that an erroneous notion about the components with influence on the colour of the wine is obtained if only the liquid chromatographic profiles are taken into account. At pH 4 the major contribution to the colour was made by the anthocyanin-derived pigments, which were hardly detected in the chromatograms, where the anthocyanins greatly predominated. An explanation is that the chromatograms are obtained in very acidic conditions at which the anthocyanins exist in the highly coloured flavylium form; however, at the usual pH value of the wine (3.2-4.0) they exist mainly as colourless hemiacetal structures. In contrast, the colour of the new pigments is much less affected by the pH and even if they may have lower molar absorptivity at 520 mu at very acidic pH values, their colour expression at the pH of the wine is higher than that of the anthocyanins. (C) 2002 Elsevier Science B.V. All rights reserved.