Copigmentation effect and mechanism of α-cyclodextrin on wine color quality and stability: Combining dynamics, thermodynamics, structural characterization and quantum mechanics

This study was aimed to explore the effect of α-cyclodextrin (α-CD) on color quality and stability of red wines, and to dissect the mechanism of copigmentation at molecular level. Firstly, α-CD was added to real wine before fermentation and aging dynamics were monitored. This study found that α-CD enhanced visual quality by strengthening anthocyanins maceration during fermentation, yet α-CD improved color stability by promoting formation of color-stable polymeric anthocyanins during aging. Secondly, the thermodynamics and dose-effect relationships in model wines revealed that binding between α-CD and malvidin-3-O-glucoside (Mvd-G) was a spontaneous exothermic reaction driven by enthalpy, with an optimal molar ratio of 1:5. Finally, structural characterization of host-guest complex and electronic effects of intermolecular interactions revealed that Mvd-G successfully formed host-guest complex with α-CD through hydrogen bonding and dispersion. The hydroxyl group and glucoside in the anthocyanin C ring, as well as the primary hydroxyl group of the α-CD were the key structures for forming hydrogen bonds. The results of this study provided an experimental and theoretical basis for the applications of α-CD as copigment to enhance the color quality and stability.