Chromatic characterization of anthocyanins from red grapes—I. pH effect

Five anthocyanins (the 3-monoglucoside of delphinidin, cyanidin, petunidin, peonidin and malvidin), isolated from red grape skins, were subjected to a spectroscopic study to characterize their chromatic properties in a model solution imitating wine in the pH range 1.5–7.0. Tristimulus colorimetry (CIEXYZ, CIELUV and CIELAB colour spaces) proved to be a useful tool for the chromatic characterization of these anthocyanins. Significant colour differences were found among them, related to the number and type of substituents in their B rings. Two-substituted compounds were located in the area of orange hue, while three-substituted compounds were in the area of red–purple. As the methoxylation degree increased, a shift was observed toward purple. Also, a relationship was found between saturation and chroma and the number of hydroxy groups in the B ring. In all the anthocyanins studied, the increase in pH provoked a curve displacement in chromaticity, approaching that of the illuminant..