Encapsulation of lutein in liposomes using supercritical carbon dioxide

Liposomes loaded with lutein were prepared utilizing supercritical carbon dioxide (SC-CO₂). The effects of pressure, depressurization rate, temperature and lutein-to-lipid ratio on particle size distribution, zeta potential, encapsulation efficiency (EE), bioactive loading, morphology, phase transition and crystallinity were investigated. Liposomes prepared by the SC-CO₂ method had a particle size of 147.6±1.9nm-195.4±2.3nm, an encapsulation efficiency of 56.7±0.7%-97.0±0.8% and a zeta potential of -54.5±1.2mV to -61.7±0.6mV. A higher pressure (200-300bar) and depressurization rate (90-200bar/min) promoted a higher encapsulation of lutein whereas the lutein-to-lipid ratio had the dominant effect on the morphology of vesicles along with size distribution and EE. X-ray diffraction data implied a substantial drop in the crystallinity of lutein upon its redistribution in the liposome membranes. Differential scanning calorimetry indicated a broadened phase transition upon the simultaneous rearrangement of lutein and phospholipid molecules into liposomal vesicles. The SC-CO₂ method resulted in particle characteristics highly associated with the ability of CO₂ to disperse phospholipids and lutein molecules. It offers a promising approach to use dense phase CO₂ to homogenize hydrophobic or amphiphilic aggregates suspended in an aqueous medium and regulate the vesicular characteristics via pressure and depressurization rate. The SC-CO₂ method has potential for scalable production of liposomal nanovesicles with desirable characteristics and free of organic solvents.