Development of nanoemulsions by an emulsification-evaporation technique

The aim of this study was to investigate the preparation of oil-in-water (O/W) nanoemulsions using an emulsification–evaporation process. Nanoemulsions were formed by homogenizing 10 wt% of an organic phase composed by corn oil and hexane mixed at different ratios, and 90 wt% emulsifier solution containing 1.0 wt % of Tween 20 (T20) or β-lactoglobulin (β-Lg). Nanoemulsions were prepared using a two-step homogenization process. First, a coarse O/W emulsion was formed by homogenizing of the organic and aqueous phases with a high-speed blender. Then, the coarse O/W emulsions were passed 5 times through a high pressure homogenizer at 15,000 psi to produce fine O/W emulsions; later these samples were subjected to evaporation to remove their hexane content. Particle sizes and PDI (polidispersity index) were determined by dynamic laser light scattering and nanoemulsions appearance was evaluated using a Turbiscan instrument by means of the area under the backscattering curve (AUC). All measurements were determined before and after hexane evaporation. Before hexane evaporation, the Z-average diameters of nanoemulsions prepared with T20 ranged from 171 to 95 nm, while those using β-Lg ranged from 170 to 125 nm. However, after hexane evaporation, the smallest Z-average diameters obtained using T20 and β-Lg were 60 and 97 nm, respectively. Particle size of nanoemulsions decreased with increasing hexane content both T20 and β-Lg. As the hexane content in organic phase increased, the particle size distribution after hexane evaporation shifted indeed to smaller particles and distribution pattern narrowed. In all cases PDI values were ≤ 0.14, which reflects a good monodispersity of the nanoemulsions. The backscattered light intensity decreased with increasing the particle size. The smaller AUC were obtained after hexane evaporation, and by increasing the hexane content in organic phase. However, the smallest AUC was reached after hexane evaporation using T20 and the highest hexane content in organic phase, so the nanoemulsions looked transparent or translucent.