Liposomes incorporating essential oil of Brazilian cherry (Eugenia uniflora L.): Characterization of aqueous dispersions and lyophilized formulations

Multilamellar liposomes incorporating essential oil of Brazilian cherry (Eugenia uniflora L.) leaves were produced by dry film hydration. Gas chromatography demonstrated the compounds found in the essential oil were effectively incorporated in the aqueous dispersions of liposomes. Differential scanning calorimetry analyses revealed the incorporation of the essential oil did not cause phase separation in the membrane structure; the gel-liquid crystalline transition temperature (main transition) remained the same despite the higher heterogeneity indicated by the transition peak broadening. Different cryoprotectors (sucrose and trehalose) were added to the liposomal formulations to be tested in their ability to protect the liposomal structure during the lyophilization. The morphological aspect of the lyophilized powders analysed by scanning electron microscopy showed significant differences among the samples with and without cryoprotectors. Fourier-transform infrared spectroscopy indicated the cryoprotectors interacted effectively with the polar heads of phospholipids in the bilayer. In terms of water absorption, trehalose was identified as a much more effective protector agent against it than sucrose. The cryoprotectors showed different degrees of effectiveness of preservation of the liposomal structure when the rehydration assays of lyophilized liposomes were carried out, as particle size measurements indicated a moderate process of fusion when the formulations with sucrose were rehydrated.