Superoxide and Singlet Oxygen in Milk Lipid Peroxidation

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Abstract
The extent to which the excited state molecular O species, singlet 1O2, participates in milk lipid oxidation was considered. Light, Cu and enzyme catalyzed oxidative reactions were included in the study. The working hypothesis was that superoxide anion was produced in the Cu and xanthine oxidase systems and that the anion once produced underwent chemical dismutation to singlet O; light-catalyzed reactions produced singlet O directly through mediation of a triplet sensitizer. In the presence of a singlet O trapper (1,3-diphenylisobenzofuran) or a single O quencher (1,4-diazabycyclo-[2-2-2]octane), lipid oxidation was inhibited. Superoxide dismutase acted as a protective agent against lipid oxidation by catalyzing superoxide dismutation to ground state O, circumventing singlet-generating spontaneous dismutation. Singlet O is the immediate source of the hydroperoxides that initiate lipid oxidation catalyzed by the 3 agents.