A New Insight into the Degradation of Anthocyanins: Reversible versus the Irreversible Chemical Processes

Diogo Sousa, Nuno Basílio, Joana Oliveira, Victor de Freitas, Fernando Pina

Research output: Contribution to journalArticlepeer-review

Abstract

The 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.

Original languageEnglish
Pages (from-to)656-668
Number of pages13
JournalJournal of Agricultural and Food Chemistry
Volume70
Issue number2
DOIs
Publication statusPublished - 19 Jan 2022

Keywords

  • anthocyanins
  • degradation kinetics
  • direct and reverse pH jumps
  • stopped flow

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