Enhancing rosemary oil-in-water microfluidized nanoemulsion properties through formulation optimization by response surface methodology

Nanoemulsions formulated with rosemary essential oil and a mixture of food-grade surfactants were prepared by microfluidization. The influence of HLB values and surfactant/oil ratio (R) on mean droplet sizes and polydispersity have been studied and analysed by response surface methodology. The optimum was found for HLB = 10.5 and R = 1, obtaining the lowest volumetric mean diameter (d(v) = 2.88 nm). Taking into account these results, the effect of rosemary oil concentration on the droplet size distributions and physical stability of the nanoemulsions was investigated. All emulsions with dispersed phase concentrations in the 1-10 g/100 g range showed destabilization by Ostwald ripening. The nanoemulsions that presented better physical stability were those formulated with 5 and 7.5 g/100 g of rosemary essential oil. This work demonstrates the capacity of rosemary oil to form stable nanoemulsions with potential applications as delivery systems and food preservatives.