Influence of a shear post-treatment on rheological properties, microstructure and physical stability of emulgels formed by rosemary essential oil and a fumed silica

Nanoemulsions containing rosemary essential oil, a natural food preservative, were developed by the microfluidization technique and emulgels were formed by adding a fumed silica (Aerosil 200). The influence of homogenization pressure on droplet size was examined. The nanoemulsion prepared at 5000 psi in Microfluidizer showed the lowest Sauter diameter and it was selected as the starting point. The influence of shear on rheological properties, stability and microstructure was studied for both the nanoemulsion and the emulgel formed. The emulsion showed recoalescence induced by shear, while the emulgel exhibited an alignment of a 3D-network. In addition, the prepared emulgel exhibited time-dependent behaviour. In spite of the fact that the viscoelastic functions of the emulgel decreased as a result of shear, a significant improvement in physical stability was detected by means of the Multiple Light Scattering technique.