Sousa, DiogoBasílio, NunoOliveira, Joanade Freitas, VictorPina, Fernando2022-06-292023-01-052022-01-190021-8561PURE: 42244518PURE UUID: 7a6bf19d-5f74-4b74-ab86-c01a59f2d9a2Scopus: 85122756786PubMed: 34982560WOS: 000740952200001ORCID: /0000-0001-8529-6848/work/109596376http://hdl.handle.net/10362/141060Publisher Copyright: © 2022 American Chemical SocietyThe kinetics and thermodynamics of the pH-dependent reversible and irreversible processes leading to color fading of pelargonidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, and cyanidin-3-O-glucoside dyes in aqueous solutions are reported. Following the addition of base to the flavylium cation, the quinoidal bases disappear by three distinct steps: (i) in an acidic medium by a biexponential process, in which the faster step is controlled by the hydration reaction and the slower one by cis–trans isomerization; the degradation process occurs essentially from the anionic quinoidal base; (ii) in a basic medium (pH > 9.5), in which the disappearance of the anionic bases is monoexponential, with the rate proportional to the hydroxyl concentration (hydroxyl attack), leading to anionic chalcones (cis and trans) at equilibrium─the slower degradation step occurs from the di- and trianionic chalcones; and (iii) in the pH region circa 7.7 < pH < 9.5, in which hydration and hydroxyl attacks are much slower than anionic quinoidal base degradation (which is the rate-controlling step) and the equilibrium cannot be attained.134754885enganthocyaninsdegradation kineticsdirect and reverse pH jumpsstopped flowGeneral ChemistryGeneral Agricultural and Biological Sciencesjournal article10.1021/acs.jafc.1c06521https://www.scopus.com/pages/publications/85122756786