Radical Scavenging Capacity of Wine Anthocyanins Is Strongly pH-Dependent

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Abstract
The radical scavenging capacity of red wine anthocyanins was quantified by the so-called TEAC assay with special emphasis on the influence of pH and conjugation on this activity. The pH appears to be a dominant factor in the radical scavenging capacity of wine anthocyanins, with higher pH values increasing this capacity significantly. On the basis of the pKa values for deprotonation and theoretical calculations, it could be concluded that the effect is due to an increase in intrinsic radical scavenging capacity upon deprotonation. The data also reveal that the reduction in radical scavenging activity of anthocyanins upon their conjugation can, at least in part, be ascribed to an increase in pKa values upon conjugation. Altogether, the results obtained provide molecular insight into factors that influence radical scavenging potential of anthocyanins and reveal that the radical scavenging-mediated supposed beneficial health effects of these wine pigments will be influenced by the pH of the surrounding matrix or tissue. Keywords: Anthocyanidins; anthocyanins; radical scavenging capacity; TEAC; pH; body fluids; pKa