Fabrication of vitamin E-enriched nanoemulsions by spontaneous emulsification: Effect of propylene glycol and ethanol on formation, stability, and properties

Oil-in-water nanoemulsions are finding increasing application within pharmaceutical and functional food products as delivery systems to encapsulate lipophilic bioactive components, such as drugs, vitamins, and nutraceuticals. We investigated the influence of two water-soluble cosolvents, propylene glycol (PG) and ethanol, on the formation, stability, and properties of vitamin E acetate-loaded nanoemulsions (VE-NEs) prepared by spontaneous emulsification. This method simply involves titrating an organic phase (VE + surfactant) into an aqueous phase (water + cosolvent). The particle size and optical clarity of the nanoemulsions (10% VE + 10% surfactant + 80% aqueous phase) depended strongly on cosolvent type and concentration. The smallest droplets (d < 50 nm) and highest transparency were observed when either 30% PG or 20% ethanol was present in the aqueous phase. However, these nanoemulsions were highly unstable to droplet growth during storage, especially at elevated temperatures, which was attributed to coalescence and Ostwald ripening. Dilution of the nanoemulsions (100 x with water) prior to storage considerably improved their long-term stability especially at higher storage temperatures. Undiluted nanoemulsions exhibited a sharp and irreversible increase in turbidity upon heating: approximate to 53 degrees C for the system containing 30% PG and approximate to 38 degrees C for the system containing 20% ethanol. Diluted nanoemulsions had much better thermal stability, with a steep increase in turbidity occurring at approximate to 75.5 degrees C for both systems. This study provides important information about the effect of cosolvents on the formation, stability, and physical properties of VE-NEs suitable for use in pharmaceutical and food products. (C) 2013 Elsevier Ltd. All rights reserved.