Characterization of peroxides formed by riboflavin and light exposure of milk. Detection of urate hydroperoxide as a novel oxidation product.
Characterization of peroxides by size exclusion chromatography (SEC) of milk following exposure to riboflavin and light showed that hydrogen peroxide was the most abundant peroxide formed since it could be removed by catalase. Formation of peroxides after separation by SEC showed that hydrogen peroxide formation was primarily increased in the presence of caseins and ascorbate, although whey proteins also were found to contribute. Caseins and beta-lactoglobulin also formed catalase-resistant peroxides, presumably protein hydroperoxides. A catalase-resistant and unstable peroxide was observed in fractions containing urate. Experiments performed with pure urate suggested that urate radicals reacted further with superoxide leading to a urate hydroperoxide. Electron paramagnetic resonance spectroscopy using spin-traps showed that the presence of oxygen was required for urate radical formation, which could be assigned as nitrogen-centered radicals. These results suggest a new route during light-induced oxidation sensitized by flavins, in effect making urate pro-oxidative.
Clausen
Morten R
MR
Department of Food Science, Faculty of Agricultural Sciences, Aarhus University, DK-8830 Tjele, Denmark.
Huvaere
Kevin
K
Skibsted
Leif H
LH
Stagsted
Jan
J
D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D005260:Female; D006861:Hydrogen Peroxide / Q000737:chemistry*; D008027:Light; D008892:Milk / Q000737:chemistry* / Q000528:radiation effects*; D010084:Oxidation-Reduction / Q000528:radiation effects; D010545:Peroxides / Q000737:chemistry*; D012256:Riboflavin / Q000737:chemistry*; D014527:Uric Acid / Q000737:chemistry*
D010545:Peroxides; D014527:Uric Acid; D006861:Hydrogen Peroxide; D012256:Riboflavin