New insights into the chemical bases of wine color evolution and stability: the key role of acetaldehyde

The reactivity of malvidin-3-O-glucoside with acetaldehyde, pyruvic and p-coumaric acids, was separately studied in wine model solution in the presence and absence of catechin, by UV-Visible spectrophotometry, NMR and Mass spectrometry. These naturally occurring metabolites were selected on account of their role in determining the red wine color. The scientific bases underlying the wine color are far from being fully clarified. Nonetheless, understanding the factors that govern the wine color is a crucial prerequisite for winemakers to implement appropriate technological practices to produce naturally stable high-quality wines. Among the investigated wine metabolites, acetaldehyde turned out to be the most reactive towards malvidin-3-O-glucoside by forming, as major products, ethylene-linked polymeric pigments that affected chromatic properties of the wine-like model solutions. Pyruvic acid and p-coumaric acid did not react with malvidin-3-O-glucoside, but in combination with catechin, they both determined a significant hypsochromic effect. Unexpectedly, in our model solutions, the formation of pyranoanthocyanins was not observed.