A colorimetric study of oenin copigmented by procyanidins

A colorimetric method was used to analyse the influence of procyanidin structure on colour changes of malvidin 3‐O‐glucoside (oenin) solution resulting from copigmentation. The study was performed in hydroalcoholic citrate/phosphate buffer solution (120 g L^?1) at pH 3.6 and ionic strength 0.2 mol L^?1. Chromatic L*, a* and b* coordinates (CIELAB, D65/10° illuminant/observer condition) obtained from spectral curves recorded between 360 and 830 nm allowed the calculation of lightness L*, chroma C* and hue angle h_ab. In general, addition of copigment induced colour enhancement (loss of lightness and increased chroma). The prevailing parameters affecting colour changes were lightness and chroma for monomers and lightness and hue for procyanidins B5 and B8 (C4–C6 dimers). A small blueing effect was observed only for catechin monomer‐copigmented solutions. For procyanidin copigments, as the structural complexity of the copigment increased, the hue angle moved to yellower values. The ester gallate of dimer B2 produced the strongest modification of colour attributes of oenin solution. Copyright © 2006 Society of Chemical Industry