title: UV-visible spectroscopic investigation of the 8,8-methylmethine catechin-malvidin 3-glucoside pigments in aqueous solution: structural transformations and molecular complexation with chlorogenic acid.
abstract: The physicochemical properties of 8,8-methylmethine catechin-malvidin 3-O-glucoside isomers, commonly referred to as catechin-ethyl-malvidin 3-O-glucoside, have been studied in aqueous solutions and compared with those of the parent anthocyanin (malvidin 3-O-glucoside). The hydration and acidity constants (pKh and pKa) of the catechin-ethyl-malvidin 3-O-glucoside pigments and malvidin 3-O-glucoside were determined by UV-visible spectroscopic measurements. The ethyl-linked catechin-malvidin 3-O-glucoside pigments present higher stability toward hydration than the parent anthocyanin. The high resistance of these ethyl-linked pigments toward the hydration is related to the self-association that offers optimal protection from the nucleophilic attack of water. Moreover, the ethyl link may confer to the molecule enough flexibility to undergo intramolecular interaction, further protecting it from hydration and bisulfite discoloration. In the wine pH range (3.2-4.0), due to the low pKa and high pKh values, the ethyl-linked pigments are present as colored forms (flavylium cation and quinonoid bases).
authors.affiliation: INRA, UMR sciences pour l'oenologie, 2 Place Viala, 34060 Montpellier, France.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Dueñas
authors.forename: Erika
authors.initials: E
authors.lastname: Salas
authors.forename: Véronique
authors.initials: V
authors.lastname: Cheynier
authors.forename: Olivier
authors.initials: O
authors.lastname: Dangles
authors.forename: Hélène
authors.initials: H
authors.lastname: Fulcrand
mesh_terms: D000872:Anthocyanins / Q000032:analysis* / Q000737:chemistry; D002392:Catechin / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D002726:Chlorogenic Acid / Q000737:chemistry*; D005960:Glucosides; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010860:Pigments, Biological / Q000032:analysis* / Q000737:chemistry; D012996:Solutions; D013816:Thermodynamics; D014867:Water; D014920:Wine / Q000032:analysis
chemical_list: C508019:8,8-methylmethine catechin; D000872:Anthocyanins; D005960:Glucosides; D010860:Pigments, Biological; D012996:Solutions; D014867:Water; D002726:Chlorogenic Acid; C458419:malvidin-3-glucoside; D002392:Catechin