Colour implications of self-association processes of wine anthocyanins

Copigmentation processes have been indicated to be crucial to stabilise coloured forms of the anthocyanins and explain colour expression in young red wines. Several studies exist about copigmentation between anthocyanins and different phenolics in model solutions, but little information is available about interactions among anthocyanins themselves. In this work, the process of self-association has been investigated in wine-like model solutions containing different grape anthocyanins (the 3-glucosides of malvidin, delphinidin and peonidin). The results obtained confirmed the existence of anthocyanin self-association and its influence on the apparent hydration constant of the anthocyanins with subsequent modification in the colour of the solutions. It was observed that the greater the degree of methoxylation of the anthocyanin B-ring the greater was the magnitude of the self-association. Colour analyses in the CIELAB space showed that self-association produces changes, which are more important in quantitative parameters (chroma, C-ab(*) and lightness, L-*) than in qualitative ones (hue, h(ab)). Self-association leads to an increase in C-ab(*), indicating a more intense colour of the solutions, and to a decrease in the psychometric index L-*, meaning that a darkening is produced. The effects on the colour were more pronounced with the passage of time of storage of the solutions.