Superoxide and Singlet Oxygen in Milk Lipid Peroxidation

Abstract

The extent to which the excited state molecular oxygen species, singlet oxygen i 02, participates in milk lipid oxidation was considered. Light, copper, and enzyme catalyzed oxidative reactions were included in the study. The working hypothesis was that superoxide anion was produced in the copper and xanthine oxidase systems and that the anion once produced underwent chemical dismutation to singlet oxygen; light-catalyzed reactions produced singlet oxygen directly through mediation of a triplet sensitizer. In the presence of a singlet oxygen trapper (1,3-diphenylisobenzofuran) or a single oxygen quencher (1,4-diazabycyclo-[2-2-2] octane), lipid oxidation was inhibited. Too, superoxide dismutase acted as a protective agent against lipid oxidation by catalyzing superoxide dismutation to ground state oxygen, thus circumventing singlet-generating spontaneous dismutation. Singlet oxygen is the immediate source of the hydroperoxides that initiate lipid oxidation catalyzed by the three agents.