EXPLORING THE ROLE OF TRANSITION METAL IONS IN THE EVOLUTION OF ESTERS COMPOSITION OF YOUNG WHITE WINE DURING AGEING

Abstract

Young white wines are typically released to the market a few months after harvest, to be consumed within a year, when their fresh fruity aromas are still dominant and appealing to modern consumers. Esters, particularly higher alcohol acetates (HAAs) and ethyl esters of fatty acids (EEFAs), play a central role in the fruity expression of young white wines [1]. However, these esters are known to undergo significant hydrolysis during the first months of aging [1, 2]. Therefore, understanding the factors that affect the hydrolysis of esters is crucial for wine producers. Although the hydrolysis of esters in wine matrices has been extensively studied for decades [3], the role of transition metal ions on the fate of esters in wines is still poorly documented.

This study aimed to explore the influence of Fe, Mn and Cu on the evolution of the ester composition of young white wines after 8-weeks of artificial ageing at 30 ºC under different conditions. Young white wines were spiked with different mixtures of Fe, Mn and Cu, to reach final concentrations of 5 mg/L, 4 mg/L and 1 mg/L of metal ions, respectively. Wines were then aged in 20 mL SPME vials, full and half-full (oxidative conditions).

The presence of gallic acid was also tested in interaction with metal ions added.

The presence of the Fe, Mn, and Cu mixture, described, above significantly increased the hydrolysis of HAAs and EEFAs in two different wine samples, with an 18% and 25% drop in HAAs and a 12% and 15% drop in EEFAs, respectively, compared to the same wine samples without the addition of metal ions. The oxidative aging did not affect this trend, except for EEFAs with long carbon chains (C10 and C12), which showed a decrease in concentration when the vial was half-full in comparison to full vial.

In contrast, the presence of gallic acid at 50 mg/L limited the effect of the metal ion mixture on esters hydrolysis. Each metal ion was also tested individually. Fe alone or in association with Cu had the same impact as the mixture of the three metal ions. Surprisingly, esters hydrolysis was significantly boosted with the addition of Cu and Mn alone or in mixture, but also when Fe was mixed with Mn. The addition of Mn alone had the strongest impact with a drop of 40% and 30% of HAAs and EEFAs concentration, respectively.

This work opens new research perspectives on how transition metal ions can shape the evolution of wine esters and, more broadly, the aromatic composition of wine.