SURFACE-PROPERTIES OF OIL-IN-WATER EMULSION DROPLETS CONTAINING CASEIN AND TWEEN-60

Studies have been made of changes in the surface properties (thickness of the adsorbed protein layer, xi-potential) of droplets formed when Tween 60 was incorporated into emulsions prepared from sodium caseinat e and soy oil. At molar ratios of surfactant/protein of up to 90:1, Tw een displaced some, but not all, of the casein from the interface, the amount depending on the relative concentrations of the two surfactant s. Both the thickness of the adsorbed layer of casein and the xi-poten tials of the particles depended strongly on the amount of Tween presen t, both of these properties becoming smaller in magnitude as the conce ntration of Tween increased. However, in addition, the layer thickness and the xi-potential depended on the overall concentration of protein , not simply on the actual amount adsorbed, so that emulsions with the same protein load but different protein concentrations did not show t he same surface properties. This behavior can be explained if the Twee n not only competes with protein for the interface but causes conforma tional changes in the protein molecules already adsorbed.