Interactions between grape anthocyanins and pyruvic acid, with effect of pH and acid concentration on anthocyanin composition and color in model solutions

The formation of vitisin A, an anthocyanin formed naturally in small quanti ties in maturing port wines, was studied in model nine solutions at a range of pH values (2.0-4.5) and pyruvate concentrations [molar ratios of pyruvi c acid to total anthocyanins (PA/TA) ranging from 12.20 to 172.40]. Additio nally, the effect of vitisin A formation on the color changes of these mode l wines was evaluated. Vitisin A was formed through the interaction between malvidin 3-glucoside and pyruvic acid, and vitisin A in acylated forms, ha ving the 6-position of the sugar acylated with acetic acid (3-acetylvitisin A) and p-coumaric acid (3-p-coumarylvitisin A), formed through the interac tion between pyruvic acid and malvidin 3-acetylglucoside and malvidin 3-p-c oumarylglucoside, respectively; their identities were confirmed by spectral analysis and FABMS. The maximum formation of these new anthocyanin derivat ives was at pH 2.7-3.0, at the higher pyruvic acid concentration (PA/TA of 172.40 units). The vitisins A caused changes in the color of the solution a nd expressed about 11 times (pH 3) to 14 times (pH 2) more color than the n ormal anthocyanins. On aging, the model solutions changed from a bluish red , attributable to the main anthocyanins present, to a slightly more orange red, attributable to the vitisin compounds. The aged models containing viti sins A were all much redder than the more red-brown color of the models age d without pyruvic acid.