Stabilization of vitamin E-enriched nanoemulsions: influence of post-homogenization cosurfactant addition

Oil-in-water nanoemulsions are being used in the food, beverage, and pharmaceutical industries to encapsulate, protect, and deliver lipophilic bioactive components, such as drugs, vitamins, and nutraceuticals. However, nanoemulsions are thermodynamically unstable systems that breakdown over time. We investigated the influence of posthomogenization cosurfactant addition on the thermal and storage stability of vitamin E acetate nanoemulsions (VE-nanoemulsions) formed from 10% oil phase (VE), 10% surfactant (Tween 80), 20% cosolvent (ethanol), and 60% buffer solution (pH 3). Addition of a nonionic cosurfactant (0.5% Tween 20) caused little change in droplet charge, whereas addition of anionic (0.5% SDS) or cationic (0.5% lauric arginate) cosurfactants caused droplets to be more negative or positive, respectively. Tween 20 addition had little impact on the cloud point of VE-nanoemulsions, but slightly decreased their isothermal storage stability at elevated temperatures (37 °C). Lauric arginate or SDS addition appreciably increased the cloud point, but did not improve storage stability. Indeed, SDS actually decreased the storage stability of the VE-nanoemulsions at elevated temperatures. We discuss these effects in terms of the influence of surfactants on droplet growth through Ostwald ripening and/or coalescence mechanisms. This study provides important information about the effect of cosurfactants on the stability of VE-nanoemulsions suitable for use in pharmaceutical and food products.