2007/03/01 by John C. Danilewicz
Agricultural and Biological Sciences · Medicine · #Fermentation and Sensory Analysis #Horticultural and Viticultural Research #Phytochemicals and Antioxidant Activities
paper · pdf · doi:10.5344/ajev.2007.58.1.53
crossref issued 2007/03/01 · crossref published 2007/03/01 · crossref published-online 2007/03/01 · crossref published-print 2007/03/01 · openalex publication_date 2007/03/01 · crossref created 2022/09/30 · crossref deposited 2022/11/18 · openalex created_date 2025/10/10 · crossref indexed 2026/07/24 · openalex updated_date 2026/07/25
The rate of oxidation of SO<sub>2</sub> was studied in a wine-model system under aerial oxygen saturation conditions to gain further insight into its mechanism of action in wine. When SO<sub>2</sub> was studied alone, no significant oxidation was observed unless iron and copper were introduced. When these metals were added a slow oxidation was observed and bound SO<sub>2</sub> also increased to a small but significant extent. These results are consistent with a radical chain mechanism initiated by metal catalysis, in which powerful oxidizing radicals, capable of oxidizing ethanol to acetaldehyde, are produced. This increase in bound SO<sub>2</sub> is prevented by 4-methylcatechol (4-MeC) in keeping with the known ability of polyphenols to scavenge these intermediate radicals and thus to inhibit SO<sub>2</sub> autoxidation, which consequently should not occur in wine. When 4-MeC was introduced at a concentration that simulated the reducing capacity of red wine, again no significant SO<sub>2</sub> oxidation was observed without addition of iron and copper. Had the catechol been oxidized, hydrogen peroxide would have been generated and reacted with the SO<sub>2</sub>. In the presence of both metals the rate of SO<sub>2</sub> oxidation was markedly increased compared to SO<sub>2</sub> alone and then was dependent on the concentration of the catechol. These results demonstrate the crucial importance of metals in allowing polyphenol oxidation and that the rate of SO<sub>2</sub> consumption is dependent on the rate of catechol oxidation. When iron and copper were added separately, only a modest increase in rate of catechol oxidation resulted. However, when combined, marked synergism was observed and the rate then became very sensitive to copper concentration. It is proposed that copper, by interacting with oxygen, facilitates redox cycling of iron. Exposure of a red wine to the conditions used in this study produced similar results regarding SO<sub>2</sub> oxidation to those observed.