Application of Flow Cytometry As Novel Technology in Studying the Effect of Droplet Size on Lipid Oxidation in Oil-in-Water Emulsions

Despite several published studies, the impact of emulsion droplet size on lipid oxidation rates is unclear. This could be because oil-in-water emulsions are typically polydisperse and the oxidation rate of individual droplets is difficult to discern. Flow cytometry is a technique for studying individual cells and their subpopulations using fluorescence technologies, which is possible to be used in studying individual emulsion droplets. Typical emulsion droplets are too small to be visualized by flow cytometer so emulsions were prepared to have droplets >2 μm that were stabilized by weighting agent and xanthan gum to minimize creaming during storage. A radical-sensitive fluorescence probe (BODIPY) was added to the lipid used to prepare the emulsion so that the susceptibility of individual emulsion droplets could be determined. The results showed that in a polydisperse emulsion system, small droplets were oxidized faster than large droplets. A conventional method was also carried out by blending two emulsions with different droplet sizes and oil densities, and results were in agreement with the observation obtained from flow cytometry. As a new approach, flow cytometry could be utilized in emulsion studies to reveal insights of lipid oxidation mechanisms in individual droplets.