Preparation and invitro diffusion study of essential oil Pickering emulsions stabilized by silica nanoparticles

In the field of essential oil research, the low water solubility of essential oils (EOs) causes several problems, not only in pharmaceutical applications, but also in microbiological experiments. The aim of our work was to prepare Pickering emulsions with tea tree, thyme, and anise EOs stabilized with silica nanoparticles, in order to enhance their availability for microbiological tests. We have examined the influence of surface properties and concentration of silica nanoparticles and dispergation energy on emulsion stability and droplet size. In vitro diffusion experiments have been performed on model agar gel membranes, with the stable Pickering emulsions and conventional emulsions of EOs stabilized with Tween80 surfactant. We have examined the influence of surface modifying group type, surface coverage of silica nanoparticles, and droplet size of the emulsions on the diffusion properties of the EOs. Our results show that highly stable Pickering emulsions can be prepared with silica nanoparticles of 20 nm diameter and 20% of surface covered with ethyl groups, in a wide EO concentration range. The cumulative amount of the EO was more effective in Pickering emulsions than in conventional emulsions for tea tree and thyme EOs, whereas the opposite case was true for anise EO. As the droplet size of the Pickering emulsion decreases, the cumulative concentration of the EO increases. In this work, we have shown that the Pickering emulsions of EOs are a suitable form for EO transport through complex membranes, and hopefully can be effectively applied in microbiological and pharmaceutical experiments.