Engineering liposomes of leaf extract of seabuckthorn (SBT) by supercritical carbon dioxide (SCCO2)-mediated process

Seabuckthorn (SBT; Hipphophae rhamnoides) leaf extract obtained by supercritical carbon dioxide (SCCO(2)) using ethanol as an entrainer, containing mainly flavanoids as bioactive principles with antioxidant and antibacterial properties, was used for the preparation of liposomes. Liposomes are promising drug carriers with sustained release because they can enhance the membrane penetration of drugs, deliver the entrapped drugs across cell membranes, and improve extract stability and bioavailability. The aim of the present study was to compare the two different methods of liposome production: the Bangham thin-film method and SCCO(2) gas antisolvent method (SCCO(2) GAS) for the incorporation of SBT leaf extract in terms of particle size, morphology, encapsulation efficiency, antioxidant activity, and thermal stability. Liposomes obtained with the thin-film method were multilamellar vesicles with average particle size (3,740 nm), encapsulation efficiency (14.60%), and particle-size range (1.57-6.0 µm), respectively. On the other hand, liposomes by the SCCO(2) GAS method were nanosized (930 nm) with an improved encapsulation efficiency (28.42%) and narrow range of size distribution (0.48-1.07 µm), respectively. Further, the antioxidant activity of leaf extract of SBT was determined by the 2 diphenyl-1-picrylhydrazyl method and expressed as Trolox equivalents as well as of the intercalated extract in liposomes. The oxidative stability of SBT encapsulated in liposomes was again estimated using differential scanning calorimetry (DSC). Thermal-oxidative decomposition of the samples (i.e., pure liposomes and encapsulated extracts) and the modification of the main transition temperature for the lipid mixture and the splitting of the calorimetric peak in the presence of the antioxidants were also studied by DSC. After encapsulation in liposomes, antioxidant activity proved to be higher than those of the same extracts in pure form.