Spatially Resolved Experiments to Monitor the Singlet Oxygen Initiated Oxidation of Lipid Droplets in Emulsions

Abstract

AbstractPolyunsaturated fatty acids (PUFAs) are present in lipid systems ranging from cell membranes to food products. Reactive oxygen species (ROS) degrade PUFA‐based lipids, often resulting in undesired consequences. Thus, understanding mechanisms of ROS‐mediated lipid oxidation, including means to inhibit such oxidation, are important. Of significance are oxidation 1) at interfaces in heterogeneous samples, and 2) that may propagate from one lipid droplet to another in an emulsion. We used an optical technique to study spatially resolved aspects of lipid oxidation in oil‐in‐water emulsions. We initiated oxidation using two‐photon photosensitized production of singlet oxygen, O2(a1Δg), confined in a small volume either inside or outside a lipid droplet. The products initially formed (e. g. hydroperoxides) spawned the formation of other ROS (e. g. alkoxyl radicals) that propagated in time and space. We monitored these reactions in imaging experiments using fluorescent probes. Among our results, we demonstrated that the oxidation of one droplet did not appear to spread rapidly to a neighboring droplet. Our observations set the stage for a host of systematic studies.