Encapsulation of lutein in liposomes using supercritical carbon dioxide

•Lutein-loaded liposomes were prepared using supercritical carbon dioxide (SC-CO2).•Liposomes have a small particle size and high encapsulation efficiency (EE).•High pressure and depressurization rate increase the EE and uniformity of liposomes.•Amphiphiles may be uniformly dispersed in an aqueous phase upon depressurization.•The SC-CO2 method showed great promise to produce liposomes to deliver bioactives.

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 ± 1.9 nm-195.4 ± 2.3 nm, an encapsulation efficiency of 56.7 ± 0.7%-97.0 ± 0.8% and a zeta potential of −54.5 ± 1.2 mV to −61.7 ± 0.6 mV. A higher pressure (200-300 bar) and depressurization rate (90-200 bar/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.

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