Colour effects of co-pigmentation of anthocyanins revisited—1. A colorimetric definition using the CIELAB scale

Abstract

This method is based on a spectral curve recorded and considered over the full range of visible light and a subsequent colorimetric specification (CIELAB system, L ∗ , C ∗ , h notation for the D65/10 ° illuminant/observer condition) using the three attributes of colour perception, hue, lightness and saturation for a complete definition of the colours of anthocyanin solutions. Spectral and colour measurements were performed on model solutions of pure and co-pigmented (by quercetin 3-rhamno-glucoside) cyanin (cyanidin 3,5-diglucoside) at pH from 2.5 to 5.5. Regarding the colour of anthocyanin solutions, major discrepancies were found between the results of this colorimetric analysis and those formerly reported which were only based on variations of the visible λ max. As their concentration increased, pure cyanin solutions exhibited huge variations of hue (from magenta to orange) in their colour, although their λ max. remained stable. Contrary to usual reports concerning ‘the blueing effect’ of a spectral bathochromic shift, it was observed that the colour of solutions, as their visible λ max. moved higher, shifted either yellower or bluer, depending on the pH and concentration. As for colour variations caused by absorbance changes, this study showed that the currently employed term ‘intensity’ was quite ambiguous, indistinctly representing variations of two attributes of colour, saturation and lightness. Consequently, a revision of the effects of some chemical parameters on the colour of anthocyanin pigments is presented.