Chemical changes in the volatile composition associated to the anoxic and oxidative storages of red wines

Sixteen red wines were stored for one month at 35 °C under anoxic conditions and with 35 mg/L of O₂ (over the stoichiometric to total SO₂). Major and minor volatile compounds, including Strecker aldehydes, total acetaldehyde, and acetals, were analysed. Both storage conditions led to qualitatively similar changes, although oxidation caused more pronounced effects, involving eight chemical processes. Three were time-dependent (hydrolysis of glycosidic precursors, esterification equilibria, and molecular rearrangements in acidic media) and not related to oxygen. Two processes (acetalization and Strecker degradation) occurred under both conditions but were more intense with oxidation. Additional oxidative effects included the oxidation of terpenols and methionol, the degradation of phenols (likely ferulic and sinapic acids) into vanillin and syringaldehyde, and the loss of non-polar compounds, such as esters and higher fatty acids, due, possibly, to adsorption. The most sensory-relevant changes were the accumulation of Strecker aldehydes, free acetaldehyde, and diethyl acetal in oxidised samples.