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Organic solvent residues are always a concern with the liposomes produced by traditional techniques. Our objectives were to encapsulate hydrophilic and lipophilic compounds in liposomes using a newly designed supercritical fluid process coupled with vacuum-driven cargo loading. Supercritical carbon dioxide was chosen as the phospholipid-dissolving medium and an ecofriendly substitute for organic solvents. Liposomal microencapsulation was conducted via a 1000-μm expansion nozzle at 12.41MPa, 90°C, and aqueous cargo loading rate of 0.25ml/s. Vitamins C and E were selected as model hydrophilic and lipophilic compounds encapsulated in the integrated liposomes. The average vesicle size was 951.02nm with a zeta potential of -51.87mV. The encapsulation efficiency attained was 32.97% for vitamin C and 99.32% for vitamin E. Good emulsion stability was maintained during storage at 4°C for 20days. Simultaneous microencapsulation in the liposomes was successfully achieved with this supercritical fluid process.

A new technique of liposomal microencapsulation, consisting of supercritical fluid extraction followed by rapid expansion of the supercritical solution and vacuum-driven cargo loading, was successfully developed. It is a continuous flow-through process without usage of any toxic organic solvent. For use as a coating material, the solubility of soy phospholipids in supercritical carbon dioxide was first determined using a dynamic equilibrium system and the data was correlated with the Chrastil model with good agreement. Liposomes were made with D-(+)-glucose as a cargo and their properties were characterized as functions of expansion pressure, temperature, and cargo loading rates. The highest encapsulation efficiency attained was 31.7% at the middle expansion pressure of 12.41MPa, highest expansion temperature of 90°C, and lowest cargo loading rate of 0.25mL/s. The large unilamellar vesicles and multivesicular vesicles were observed to be a majority of the liposomes produced using this eco-friendly process.

Background Liposomes are spherical phospholipid vesicles with the capability of versatile microencapsulation of hydrophilic and lipophilic compounds. Organic solvent residue has always been a concern in conventional methods of liposome generation. Scope and approach Dense gas techniques using supercritical carbon dioxide as the phospholipid-dissolving agent can provide a green solution for reduction or avoidance of organic solvent use. Key findings and conclusions In this review, conventional and dense gas processes of liposomal microencapsulation are evaluated. Comprehensively understanding the current progress of supercritical fluid techniques for liposomal microencapsulation will be helpful for development of a non-toxic continuous process of this application in the food and related industries.

The solubility of methyl anthranilate in supercritical carbon dioxide was determined using dynamic and static equilibrium systems. Three temperatures (40, 60 and 80 °C) and a pressure range between 160 and 340 atm were applied for the dynamic solubility measurements. The flow rate was maintained at 0.5 mL min−1 in the dynamic solubility measurements, where the solute solubility was claimed to be independent of the flow-rate factor. Two temperatures (40 and 60 °C) and the pressure range between 100 and 265 atm were used in the static equilibrium system. The crossover pressure region was observed between 220 and 240 atm in the static system, but was not seen in the dynamic system. The solubility of methyl anthranilate determined by the static system was consistently higher than the dynamic solubility measurement, indicating that the static technique provided more reliable solubility data for methyl anthranilate than the dynamic technique. The solubility data obtained with the static system were in good agreement with the predictive models based on the Chrastil equation and the Peng–Robinson equation of state with the Panagiotopoulos and Reid mixing rule. Copyright © 2006 Society of Chemical Industry