Formulation, characterization and stability of o/w nanoemulsion containing rice bran oil prepared by emulsion phase inversion

Rice bran oil (RBO) contains naturally occurring antioxidants such as carotenoids, tocopherol, and γ-oryzanol. The aim of this research was to formulate and evaluate the characteristics of nanoemulsion which was prepared using RBO containing naturally occurring antioxidants. The RBO-in-water nanoemulsion was prepared by the emulsion phase inversion method. The oil phase of the nanoemulsion was prepared by either virgin coconut oil (VCO) or palm oil (PO) combined with RBO with the ratio of 5:5; 4:6, 3:7, 2:8 and 0:10. Tween 80 was used as a surfactant. The surfactant to oil ratios was predetermined at 2.5:1.0 and 3.0:1.0. The aqueous phase (80% w/w) was titrated into an organic phase that consisted of Tween 80 and oil phase (approximately 20% w/w). Droplet size, zeta-potential and polydispersity index of the nanoemulsion were used as the main parameters. The results showed that the smallest droplet (<100 nm) of the nanoemulsion was obtained when the ratio of VCO: RBO at 3:7 and the ratio of PO: RBO at 4:6 with the surfactant to oil ratio (SOR) was 2.5. Nanoemulsion with a relatively small polydispersity index of 0.3 was achieved when the ratio of PO: RBO was 3:7 and SOR at 3. All of the freshly prepared RBO containing nanoemulsion have good stability with zetapotential values of < -30 mV. Nanoemulsions were stable against centrifugation at 2300 rpm for 15 mins, but they were not stable against heating at 105°C for 5 hrs. The RBO-inwater nanoemulsion could be successfully prepared by phase inversion method, by combining RBO with either VCO or PO at different ratios.