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

Ambrósio Camuenho; André Seco; A Jorge Parola; Nuno Basílio; Fernando Pina

doi:10.1021/acsomega.2c02571

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

ACS Omega. 2022 Jul 12;7(29):25502-25509. doi: 10.1021/acsomega.2c02571. eCollection 2022 Jul 26.

Authors

Ambrósio Camuenho¹, André Seco¹, A Jorge Parola¹, Nuno Basílio¹, Fernando Pina¹

Affiliation

¹ LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica 2829-516, Portugal.

Abstract

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.