Intermolecular Copigmentation of Malvidin-3-O-glucoside with Caffeine in Water: The Effect of the Copigment on the pH-Dependent Reversible and Irreversible Processes

[Image: see text] Intermolecular copigmentation of malvidin-3-O-glucoside with caffeine was studied using a holistic procedure that includes the extension to basic pH values. In moderately basic solutions (7.5 < pH < 9.5) and independently of the copigment presence, there is a pH region where degradation of the quinoidal base and anionic quinoidal bases is faster than hydration and OH(–) nucleophilic addition, preventing the system from reaching the equilibrium. Intermolecular copigmentation with caffeine reduces significantly the degradation rate of quinoidal bases. In a more basic medium, the equilibrium is reached and degradation occurs from the anionic chalcones. In this case, the addition of caffeine also reduces the degradation rate in the interval 10 < pH < 11.5.