Interaction of Sulfur Dioxide, Polyphenols, and Oxygen in a Wine-Model System: Central Role of Iron and Copper

The effect of 4-MeC concentration on the reaction rate of SO₂ in the presence of Fe (5 mg/L) and Cu (0.15 mg/L) in the wine-model system.

The relationship between 4-MeC concentration and the initial rate of SO₂ reaction derived from Figure 2.

The effect of Fe and Cu concentration on the reaction rate of SO₂ in the presence of 4-MeC (1.2 g/L) in the wine-model system.

The effect of different polyphenols (9.67x 10⁻³ M) on the reaction rate of SO₂ in the presence of Fe (5 mg/L) and Cu (0.15 mg/L) in the wine-model system.

Uptake of SO₂ by a red wine (Mouton Cadet, Bordeaux) under the model-wine conditions. Mean of duplicate determinations. The average difference of any determination from the mean was 0.92% with a maximum difference of 1.96%.

Formation of sulfite radicals: radical chain initiation and redox cycling of iron.

Radical chain propagation in bisulfite oxidation. One oxygen molecule and a total of two bisulfite ions react on each turn of the cycle.

Possible mechanism for the reaction of SO₂ with hydrogen peroxide.

Oxidation of a catechol by Fe(III).

The Fenton reaction: oxidation of ethanol.

The scavenging of hydrogen peroxide formed by the oxidation of catechols by SO₂, so preventing oxidation of ethanol by the Fenton reaction.

Scavenging of peroxomonosulfate radicals by catechols so preventing radical chain propagation, which results in inhibition of SO₂ autoxidation.

Redox cycling of copper and iron while catalyzing the oxidation of catechols to produce quinones and hydrogen peroxide.