Oxygen dependency of one-electron reactions generating ascorbate radicals and hydrogen peroxide from ascorbic acid

• Published in: Food chemistry Vol. 196; pp. 1361 - 1367
• Main Author: Boatright, William L.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2016
• Subjects: Ascorbate radical; Ascorbic acid; Ascorbic Acid - pharmacology; Ascorbyl radical; Dehydroascorbate; Dehydroascorbic Acid; Electrons; Free Radicals; Hydrogen peroxide; Hydrogen Peroxide - pharmacology; Oxidation-Reduction; Oxygen - chemistry; Ascorbic acid; Hydrogen peroxide; Ascorbyl radical; Ascorbate radical; Dehydroascorbate
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2015.07.141

•Both one-electron oxidation reactions of ascorbic acid are dependent on oxygen.•The time-course of H2O2 generation from ascorbate oxidation is quantified.•Optimum levels of ascorbic acid for generation of H2O2 are presented.•These findings address conditions that relate to food products from pH 6.5 to 9.0. The effect of oxygen on the two separate one-electron reactions involved in the oxidation of ascorbic acid was investigated. The rate of ascorbate radical (Asc−) formation (and stability) was strongly dependent on the presence of oxygen. A product of ascorbic acid oxidation was measurable levels of hydrogen peroxide, as high as 32.5μM from 100μM ascorbic acid. Evidence for a feedback mechanism where hydrogen peroxide generated during the oxidation of ascorbic acid accelerates further oxidation of ascorbic acid is also presented. The second one-electron oxidation reaction of ascorbic acid leading to the disappearance of Asc− was also strongly inhibited in samples flushed with argon. In the range of 0.05–1.2mM ascorbic acid, maximum levels of measurable hydrogen peroxide were achieved with an initial concentration of 0.2mM ascorbic acid. Hydrogen peroxide generation was greatly diminished at ascorbic acid levels of 0.8mM or above.