New findings on the incorporation of essential oil components into liposomes composed of lipoid S100 and cholesterol

The encapsulation of essential oil components into liposomes was demonstrated to improve their solubility and chemical stability. In this study, we investigated the effect of chemical structure, Henry's law constant (H-c), and aqueous solubility of essential oil components on their liposomal encapsulation. Estragole, eucalyptol, isoeugenol, pulegone, terpineol, and thymol were encapsulated in lipoid S100-liposomes using the ethanol injection method. The H-c values were determined. The incorporation in liposomes was more efficient (encapsulation efficiency > 90%) for the essential oil components exhibiting low aqueous solubility (estragole, isoeugenol, and pulegone). Moreover, efficient entrapment into vesicles (loading rate > 18%) was obtained for isoeugenol, terpineol, and thymol. This result suggests that the presence of a hydroxyl group in the structure and a low H-c value enhance the entrapment of essential oil components into liposomes. Furthermore, drug release rate from liposomes was controlled by the loading rate of essential oil components into liposomes, the size of particles, the location of essential oil components within the lipid bilayer, and the cholesterol incorporation rate of liposomes. Finally, considerable concentrations of isoeugenol, pulegone, terpineol, and thymol were retained in liposomes after 10 months with respect to the initial concentration.