Effect of acetaldehyde and several acids on the formation of vitisin A in model wine anthocyanin and colour evolution

It was found that the reaction between malvidin 3-glucoside and added pyruv ic acid (PA), leading to the formation of vitisin A in model wine solutions , was not prevented by the addition of either acetaldehyde (A) or several o rganic acids. The acylated forms of vitisin A. (3-acetylvitisin A and 3-p-c oumarylvitisin A) were formed through the interaction of malvidin 3-acetylg lucoside and malvidin 3-p-coumarylgIucoside. Disappearance of the three mai n anthocyanins (malvidin 3-glucoside, malvidin 3-acetylglucoside and malvid in 3-p-coumarylglucoside) from the model wine with time followed first orde r kinetics. Acetaldehyde had the effect of increasing the total amount of t hese losses but producing smaller amounts of vitisin A. During ageing model solutions developed some browness. The brownest solution was obtained with out A and a reduced rate of browning was found in the presence of A. This l atter result can be explained by the assumption of a superimposition of a b lueing effect upon reactions of A with anthocyanins. In the presence of PA the formation of vitisin A compounds gave an intermediate colour, contribut ing a reddish hue to the solution. A good correlation (r(2) = 0.96) between the percentage of vitisin A, of the total anthocyanins and the hue angle w as observed. The addition of large amounts of organic acids that are normal ly found in wine into the model solutions did not lead to the formation of new anthocyanins. The linear loss of PA in all model systems indicates that a first order reaction occurs and 35.35 times more PA than total anthocyan in was lost to form the new compounds.