title: Grape anthocyanin oligomerization: a putative mechanism for red color stabilization?
abstract: The equilibrium forms of malvidin-3-O-glucoside trimer present in grape skins were studied in aqueous solution at different pH values through UV-Visible spectroscopy. It was observed that the reactivity of this compound is strongly dominated by acid-base chemistry (pKa1=3.61±0.03; pKa2=6.83±0.06), with the reaction sequence hydration-tautomerization-isomerization accounting less than 10% of the overall reactivity. The decrease of hydration of this flavylium cation derivative when compared to the original anthocyanins results from the formation of a cluster of the pigment with a high-energy of solvation that inhibits the access of water molecules to the flavylium cation core preventing by this way the hydration reactions. Overall of these results raise the hypothesis that polymerization may be a natural stabilization mechanism for the red color of anthocyanins.
authors.affiliation: Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Oliveira
authors.affiliation: REQUIMTE, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
authors.forename: Natércia F
authors.initials: NF
authors.lastname: Brás
authors.affiliation: Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
authors.forename: Mara Alhinho
authors.initials: MA
authors.lastname: da Silva
authors.affiliation: Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Mateus
authors.affiliation: REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. Electronic address: ajp@fct.unl.pt.
authors.forename: A Jorge
authors.initials: AJ
authors.lastname: Parola
authors.affiliation: Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal. Electronic address: vfreitas@fc.up.pt.
authors.forename: Victor
authors.initials: V
authors.lastname: de Freitas
mesh_terms: D000465:Algorithms; D000872:Anthocyanins / Q000737:chemistry* / Q000378:metabolism; D005960:Glucosides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D010860:Pigments, Biological / Q000737:chemistry* / Q000378:metabolism; D027843:Vitis / Q000737:chemistry*; D014867:Water
chemical_list: D000872:Anthocyanins; D005960:Glucosides; D010860:Pigments, Biological; D014867:Water; C458419:malvidin-3-glucoside
keywords: Hydration; Ionization reactions; Malvidin-3-O-glucoside trimer; Molecular dynamics simulations; Stacking