Vegetable oil-based nanoemulsions containing curcuminoids: Formation optimization by phase inversion temperature method

Abstract This study aimed to investigate the formation of curcuminoid-loaded nanoemulsions (NE) with a nonionic surfactant, PEG-40 hydrogenated castor oil (RH40) prepared by phase inversion temperature (PIT). Various vegetable oils were screened and the results showed that coconut oil provided the highest curcuminoid solubility, suitable PIT and the largest NE region in the ternary phase diagram for the formation of NE (droplets size 20–100 nm and polydispersity below 0.2). Curcuminoid-loaded NE comprising 8.3 wt% coconut oil with different curcuminoid and RH40 concentrations were prepared. The results revealed that at the RH40 concentration of ≤10 wt%, an increase in curcuminoid concentration resulted in the migration of curcuminoids towards the oil phase, affirmed by the observation of increases in droplet size. Contrarily, no significant changes ( p  > .05) in droplet size with increased curcuminoid concentration were observed with the NE of RH40 > 10 wt%, related to the migration of curcuminoid molecules from oil droplets into microemulsion droplets in the aqueous phase. All formulations were physically stable for at least two months. However, the degradation of curcuminoids increased with increased temperature and surfactant concentration. Based on our results, the suitable RH40 concentration and storage condition for curcuminoid-loaded NE were 10 wt% and 4 °C, respectively.