Changes in aliphatic ester composition of white wines during exposition to light. An HS-SPME-GC-MS study

The irradiation of four Italian white wines with a visible light comparable to that encountered in the market place showed a modification in the amount of aliphatic esters in the wines. Aliphatic esters are responsible for fruity aromas in wines. The first wine studied was the Gewürztraminer, a white wine from Alto Adige (Northern Italy). The amounts of the esters presents in the wine decreased. All the curves follow a pseudo-first-order kinetics. This behaviour can be explained assuming a photooxidation process catalysed by riboflavin. When Arneis Blangè was irradiated, ethyl acetate showed an increase after one day of irradiation; its content then decreased and after five days' irradiation its concentration reached a maximum. Conversely, the concentration of other aliphatic esters decreased after one day's irradiation and then increased progressively to reach a maximum after five days' irradiation. The same behaviour was observed with Pecorino wine. In this case, the concentration of the aliphatic esters decreased until the second day of irradiation but increased after five days' irradiation. In the case of the irradiation of Lighea Zibibbo all the esters showed an increase in concentration after one day of irradiation. The concentration decreased after two days' irradiation, and then increased to reach a maximum after seven days of irradiation. The increase in the amount of esters in some wines and, by contrast, the decrease in the same compounds in Gewürztraminer can be explained by considering that, during the irradiation, the pH of Gewürztraminer did not change, while the pH of Arneis Blangè changed following a curve similar to that showed by the concentration of esters. The pH change can be explained assuming the presence of a photocatalytic process induced by the presence of metals in the wines and influencing the amount of tartaric acid.