Ostwald Ripening Stability of Curcumin-Loaded MCT Nanoemulsion: Influence of Various Emulsifiers

Curcumin is a flavonoid found in the rhizome of the turmeric plant (Curcuma longa L.) and has recently attracted interest because it has numerous biological functions and therapeutic properties. In the present study, we attempted to incorporate curcumin into medium-chain triglyceride (MCT) nanoemulsions (0.15 wt% curcumin, 10 wt% MCT oil, and 10 wt% emulsifiers) with various emulsifiers [polyoxyethylene (20) sorbitan monolaurate (Tween-20), sorbitan monooleate (SM), and soy lecithin (SL)]. The physicochemical properties of the nanoemulsions including the Ostwald ripening stability were investigated. The initial droplet size was found to be 89.08 nm for the nanoemulsion with 10 wt% Tween-20 (control), and when Tween-20 was partially replaced with SM and SL, the size decreased: 73.43 nm with 4 wt% SM+6 wt% Tween-20 and 67.68 nm with 4 wt% SL+6 wt% Tween-20 (prepared at 15,000 psi). When the nanoemulsions were stored for 28 days at room temperature, the droplet size increased as the storage time increased. The largest increase was observed for the control nanoemulsion, followed by the 4 wt% SL+6 wt% Tween-20 and 4 wt% SM+6 wt% Tween-20 systems. The Turbiscan dispersion stability results strongly supported the relationship between droplet size and storage time. The time-dependent increase in droplet size was attributed to the Ostwald ripening phenomenon. Thus, the Ostwald ripening stability of curcumin-loaded MCT nanoemulsions with Tween-20 was considerably improved by partially replacing the Tween-20 with SM or SL. In addition, curcumin may have acted as an Ostwald ripening inhibitor.