Color stability and spectroscopic properties of deoxyvitisins in aqueous solution

Abstract

The color properties and stability of three types of 3-deoxyvitisins derived from peonidin (deoxyvitisin A, B and methyldeoxyvitisin) were studied using UV-Visible spectroscopy. Similarly to pyranoanthocyanins, the conjugated double bonds among pyranic rings C and D provide a higher electronic delocalization that prevents the nucleophilic attack of water at position 2 and the subsequent formation of the hemiketal and chalcone species. Consequently, besides the flavylium cation (AH⁺), neutral (A) and ionized bases (Aⁿ⁻) have been identified by increasing pH, and the respective acidity constants were determined. The acidity constant values for the formation of the neutral quinoidal base (pK_{a2(deoxyvit A)} = 4.8, pK_{a1(deoxyvit B)} = 4.7 and pK_{a1(methyldeoxyvitisin)} = 5.2) are slightly higher than the ones reported in the literature for their corresponding 3-glucosyl derivatives (vitisins). Given their higher stability, these pigments may be regarded as potential food colorants.