Stability control of large oil droplets by layer-by-layer deposition using polyelectrolyte dietary fibers

O/W emulsion is desirable to control the stability of oil droplets for the protection of bioactive lipophilic components during the storage and their targeted release in a gastrointestinal tract. In this study, we modified the surface properties of oil droplets larger than 10 μm in size by electrostatic layer-by-layer multicoatings using polyelectrolyte dietary fibers, aiming to control their stability. Monodisperse large oil droplets were prepared by microchannel emulsification using modified-lecithin as emulsifier. Chitosan (CHI) as a cationic dietary fiber and carboxymethyl cellulose (CMC) as an anionic fiber were alternately coated onto oil droplet surface. The ζ-potential of oil droplets was alternately changed, depending on the net charge of droplets dominated by the electrostatic property of the outer fiber layer. Multicoated oil droplets did not aggregate or coalescence in an emulsifier-free aqueous medium after two weeks storage at room temperature. When CHI was modified outer layer, oil droplets were unstable at high pH value (pH > 6), due to loss of CHI charge. When CMC was outer layer, the oil droplets showed good stability to aggregation in between pH 5 and 9, but aggregated at lower pH value (pH < 5), due to loss of CMC charge. These findings indicated that large oil droplet stability can be controlled by layer-by-layer coating using food grade polyelectrolytes.