INFLUENCE OF WATER-SOLUBLE NONIONIC EMULSIFIER ON THE RHEOLOGY OF HEAT-SET PROTEIN-STABILIZED EMULSION GELS

The influence of nonionic emulsifier Tween 20 [polyoxyethylene (20) sorbitan monolaurate] on the small-deformation shear theological behavior of beta-lactoglobulin emulsion gels has been investigated. Measurements are reported for heat-set oil-in-water emulsion gels (5-10 wt % protein, 38 wt % oil, pH 7) containing surfactant added after homogenization but prior to heat treatment (30 min at 90 degrees C). Storage and loss moduli (frequency 1 Hz) and protein surface coverages of emulsion gels containing 6, 7, and 8 wt % protein have been determined at 30 degrees C. Comparison with results from the equivalent theological experiments on pure beta-lactoglobulin systems (12-14 wt %, pH 7) shows that the incorporation of fine emulsion droplets greatly reduces the overall concentration of protein required to make a self-supporting gel. For constant oil content and thermal gelation conditions, the emulsion gel strength is very sensitive to protein content and surfactant/protein molar ratio R. In particular, the storage modulus has been shown to increase at low emulsifier contents (R approximate to 1), to decrease at intermediate emulsifier contents (R approximate to 2), and then at high emulsifier contents (R greater than or equal to 4) either to increase again or to remain low depending on the protein content. This behavior can be explained in terms of the effect of system composition on the balance between the different kinds of interfacial and bulk protein-surfactant interactions.