Rheological properties of soybean protein isolate gels containing emulsion droplets

Rheological properties of soybean protein gels containing various volume fractions oil droplets have been studied at small and large deformations. Dynamic viscoelastic properties of soybean protein isolate gels were determined as a function of the volume fraction of oil droplets stabilised by the same protein, both in absence and presence of 0.2 M sodium chloride (NaCl). The storage and loss moduli were higher if NaCl was added. For both conditions, they increased with increasing oil volume fraction during the heating as well as the cooling stage. Furthermore, gel formation started at a lower temperature with increasing oil volume fraction. The increase in the moduli with increasing volume fraction of oil droplets was stronger than predicted by Van der Poels theory for a simple filled gel containing single interacting stiff emulsion droplets. This effect was attributed to aggregation of the emulsion droplets. Fracture properties of gels with different oil volume fraction and oil droplet size were determined at pH 7.0, in the presence of 0.2 M NaCl, by a uniaxial compression test. Compressive stresses of the gels containing oil droplets of 1.17 μm were higher than those containing droplets of 2.70 μm, especially at higher volume fractions of oil droplets. The fracture strain did not depend on the volume fraction of oil droplets.