Lingjun Ma and Andrew Waterhouse*
*Department of Viticulture and Enology, University of California, Davis, CA 95616 (alwaterhouse@ucdavis.edu)

Wine oxidation is a chemical process that changes the chemical and sensory profile of wines. A degree of oxidation is beneficial for red wine to enhance color and to reduce astringency, but overoxidation results in negative characteristics. In wine oxidation, phenolics are oxidized to quinones and these reactive compounds have a key impact on the outcome, degrading color and flavor. Antioxidants can prevent degradation by nucleophilic reactions with or reduction of the quinones. The A-ring on flavonoids is an important nucleophile and should arrest oxidation by quenching the quinone. However, when we attempted to quantify that reaction rate, we observed that electron transfer occurred more quickly between the quinone and B-ring of flavonoid, resulting mostly in the flavonoid quinone, extending rather than arresting the oxidation reaction. The flavonoid quinone is known as a precursor of browning products. The fact that the electron transfer reaction was faster than the nucleophilic reaction helps explain why flavonoids in wine can stimulate browning rather than arresting oxidation.

Funding Support: American Vineyard Foundation