Preparation of fine W/O/W emulsion through membrane filtration of coarse W/O/W emulsion and disappearance of the inclusion of outer phase solution

A water-in-oil-in-water (W/O/W) emulsion was prepared as a carrier system for the daily uptake of a bioactive compound using decaglycerol monolaurate and hexaglyceryl condensed ricinolate as hydrophilic and lipophilic surfactants, respectively. 1,3,6,8-Pyrenetetrasulfonic acid tetrasodium salt (PTSA) was used as a hydrophilic model compound of a bioactive substance. Membrane filtration of a coarse W/O/W emulsion prepared with a rotor/stator homogenizer produced a fine emulsion which had a mean oil-droplet diameter of < 1 μm. The emulsions were stable for 1 week at 4 °C. The encapsulation efficiency of PTSA was >90%. Microscopic observations revealed that the fluorescent material in the outer-phase solution was included into the oil phase during rotor/stator homogenization. It was suggested that because the rotor/stator homogenizer was used to produce both O/W and W/O/W emulsions, some part of the outer phase solution would be included in the oil phase during the second homogenization. The fluorescence shown in the oil droplets of the coarse W/O/W emulsion was diminished after membrane emulsification. This phenomenon suggested that the included outer-phase solution was released to the outer-phase solution from the interior of the W/O/W oil droplets during the membrane emulsification.