Microstructure and dynamics in protein stabilized emulsion gels under shear

The rheological properties of emulsions stabilized with plant proteins are very different to those formed with other stabilizers. It is useful to relate the microstructure to stability and rheological properties under shear to obtain a clearer understanding of the mechanisms governing shear stability. This study uses rheology-coupled small angle x-ray scattering (rheo-SAXS) to study pea protein dispersions and pea protein stabilized oil-in-water emulsions for various compositions and pH. Rheo-SAXS experiments show that emulsions have isotropic scattering even at shear rates up to 1000 s−1, thus have an excellent resilience to droplet elongation. The observed increase in scattered intensity with time at low momentum transfer corresponds to droplet breakage under shear that is irreversible when the shear rate is reduced. The simultaneous rheological results show shear-thinning and thixotropic behavior with shear stress dependent on both time and the applied shear rate. This is due to a dense network formed by protein in the continuous phase. X-ray photon correlation spectroscopy (XPCS) measurements demonstrate that the relaxation dynamics are mainly translational diffusion with different mobility at different length scales. This complements the rheo-SAXS results that identify the importance of the viscosity and elasticity of the protein network formed in the continuous phase for stability. The low capillary number caused by the high interfacial tension and low shear stresses when flowing provides good routes to droplet formation and eventual emulsion stability.