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

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Abstract
Summary It was found that the reaction between malvidin 3‐glucoside and added pyruvic 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 organic acids. The acylated forms of vitisin A (3‐acetylvitisin A and 3‐p‐coumarylvitisin A) were formed through the interaction of malvidin 3‐acetylglucoside and malvidin 3‐p‐coumarylglucoside. Disappearance of the three main anthocyanins (malvidin 3‐glucoside, malvidin 3‐acetylglucoside and malvidin 3‐p‐coumarylglucoside) from the model wine with time followed first order kinetics. Acetaldehyde had the effect of increasing the total amount of these losses but producing smaller amounts of vitisin A. During ageing model solutions developed some browness. The brownest solution was obtained without A and a reduced rate of browning was found in the presence of A. This latter result can be explained by the assumption of a superimposition of a blueing effect upon reactions of A with anthocyanins. In the presence of PA the formation of vitisin A compounds gave an intermediate colour, contributing a reddish hue to the solution. A good correlation (r2= 0.96) between the percentage of vitisin A, of the total anthocyanins and the hue angle was observed. The addition of large amounts of organic acids that are normally 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 anthocyanin was lost to form the new compounds.