Ability of Different Flavonols and Commercial Mannoproteins to Enhance Wine Colour through Copigmentation

Copigmentation is a noncovalent interaction between anthocyanins and colourless copigments that stabilises the anthocyanin-coloured forms by protecting them against water attack. Copigmentation can be responsible for almost half of the colour observed in young red wines. It has been reported that flavonols are the most effective wine copigments, but studies on the influence of the structure of these copigments on the magnitude of copigmentation are scarce. However, flavonol profiles change with grape variety and can condition the colour of the resulting wines. In addition, mannoproteins (MPs) have been reported to interact with flavonoids, which, consequently, might affect the flavonol-anthocyanin interaction. The objective of the present study was to evaluate the ability of five grape flavonols (isorhamnetin, kaempferol, quercetin, syringetin, and myricetin 3-O-glucosides: I-3-glc, K-3-glc, Q-3-glc, S-3-glc, and My-3-glc) by conventional spectrophotometric measurements and CIELAB analysis to copigment with malvidin 3-O-glucoside (mv-3-glc) in the absence or presence of five different MPs (binary and ternary model systems). Among the tested flavonols, I-3-glc was the most effective copigment, whereas K-3-glc was the least one. S-3-glc and Q-3-glc showed intermediate effectiveness, but that of S-3-glc was closer to I-3-glc and that of Q-3-glc to K-3-glc. These results point out that the presence of methoxyl groups in the B-ring of the flavonol increases copigmentation magnitude. The participation of My-3-glc in copigmentation interactions seemed to be hindered by its colloidal instability. Regarding the tested MPs, they did not provoke a direct copigmentation effect, but were able to modify the magnitude of the interaction between the flavonols and the anthocyanin and, in some cases, the colloidal behaviour of coloured aggregates formed over time. Finally, the results of the additional HPLC-DAD analyses point to a greater protection of the anthocyanin against degradation in the model systems where the magnitude of copigmentation was greater.