Acid complexation of iron controls the fate of hydrogen peroxide in model wine.

At a key branchpoint in wine oxidation, hydrogen peroxide reacts either with iron(II), leading to the Fenton oxidation of ethanol, or with sulfur dioxide, precluding oxidation. The fate of H2O2 was investigated in anoxic model wines with different pH and acid buffers. In the absence of SO2, anoxic conditions allowed the stoichiometric production of acetaldehyde from H2O2 despite iron(II) being limiting, indicating efficient iron redox cycling. Acetaldehyde production was faster at pH 4.0 than at pH 3.0, attributable largely to increased iron complexation. Citrate allowed the most rapid acetaldehyde formation, while the comparative effects of tartrate and malate were pH-dependent, likely due to differences in their iron-chelating abilities. The inclusion of SO2 greatly diminished acetaldehyde formation, but did not prevent it, and reduced the differential effects of pH and acid composition. Findings overall suggest management of wine acidity can significantly affect the rate and outcome of oxidation.