Development of rosemary essential oil nanoemulsions using a wheat biomass-derived surfactant

In the present work aqueous-based emulsions formulated with bio-based solvents and surfactants were studied. The droplet size distribution, rheology and physical stability of rosemary essential oil/water emulsions formulated with an emulsifier derived from wheat waste (alkyl polypentoside) were investigated as a function of the dispersed phase concentration (10-50 wt%) by means of laser diffraction, multiple light scattering and rheology measurements. Subsequently, processing variables, such as the pressure and the number of microfluidization passes, were studied to the best formulation (20 wt% rosemary oil). The laser diffraction technique revealed that monodispersed submicron emulsions were obtained for oil phase concentrations below 20 wt%. All emulsions showed Newtonian behavior, except for the emulsion containing 50 wt% oil, which exhibited shear-thinning properties. Moreover, the main destabilization mechanism of all the emulsions was creaming. The combination of techniques used demonstrated that the emulsion containing 20 wt% rosemary essential oil (REO) and prepared by microfluidization at 2500 psi (17.2 MPa) exhibited the longest physical stability and the smallest droplet size after 3passes. This research is a contribution to sustainable development not only by using chemicals derived from renewable raw materials but also by achieving stable emulsions with a low surfactant/oil mass ratio.