| 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 aqueoussolutions and compared with those of the parent anthocyanin (malvidin 3-O-glucoside). The hydrationand acidity constants (pKh and pKa) of the catechin-ethyl-malvidin 3-O-glucoside pigments and malvidin3-O-glucoside were determined by UV−visible spectroscopic measurements. The ethyl-linkedcatechin-malvidin 3-O-glucoside pigments present higher stability toward hydration than the parentanthocyanin. The high resistance of these ethyl-linked pigments toward the hydration is related tothe 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 tothe low pKa and high pKh values, the ethyl-linked pigments are present as colored forms (flavyliumcation and quinonoid bases). Keywords: Malvidin 3-O-glucoside; ethyl-linked pigments; hydration and transfer proton constants;intramolecular interaction and self-association
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