Color and stability of pigments derived from the acetaldehyde-mediated condensation between malvidin 3-O-glucoside and (+)-catechin

pigment derived from the acetaldehyde-mediated condensation between (+)-cat echin and malvidin 3-O-glucoside has been prepared and isolated by semiprep arative HPLC, and its characteristics of color and stability have been stud ied and compared with that of malvidin glucoside in aqueous solutions. When the pH was increased from 2.2 to 5.5, the solution of the pigment became p rogressively more violet (lambda (max) = 560 nm at pH 5.5), whereas similar solutions of the anthocyanin were almost colorless at pH 4.0. This behavio r indicated that the anthocyanin moiety of the pigment was more protected a gainst water attack, and thus the formation of its quinonoidal forms was fa vored. The color of the pigment also showed; more stability with regard to bleaching by SO2 than that of malvidin glucoside. Nevertheless, the pigment was more sensitive to degradation in aqueous solution than the anthocyanin . The cleavage of the ethyl bridge that links the anthocyanin and the catec hin constituted the first step in its degradation, as demonstrated by the f ormation of malvidin glucoside as a major product.