A STUDY OF THE RHEOLOGICAL PROPERTIES OF CONCENTRATED FOOD EMULSIONS

The theological properties of oil-in-water emulsions stabilised by a variety of emulsifiers were investigated at oil phase volume concentrations ranging from 10 to 70%. Most emulsions exhibited Newtonian behaviour at lower oil concentrations and either pseudoplastic or plastic behaviour at higher concentrations. Oil concentrations for all emulsions were normalised using a normalisation factor which was dependent on shear rate. This resulted in shear-independent curves of relative viscosity of emulsion (mu(r)) against normalised oil concentration. These experimental shear-independent curves could be fitted with a mathematical empirical model lip to a normalised oil concentration of about 1.2. The model was successfully used to predict viscosities of other emulsion systems reported in the literature. It was also able to predict the theological behaviour of an emulsion at a given oil concentration provided the flow curve of the same emulsion was known at another oil concentration. A theoretical model based on the increase of the volume of the emulsion globule due to the emulsifier adsorbed on the globule surface and a flocculation reversible arrow deflocculation shear-dependent reaction was developed. This yielded an expression practically identical to the empirical model. Parameters of the theoretical model may be used to estimate the degree of aggregation and other microstructural characteristics of emulsions.