THE INFLUENCE OF FOOD EMULSIFIERS ON FAT AND SUGAR DISPERSIONS IN OILS .2. RHEOLOGY, COLLOIDAL FORCES

The influence of food emulsifiers on the viscoelastic properties (storage modulus and yield value) of fat and sugar dispersions in vegetable oils has been investigated. It was found that almost all of the emulsifiers tested influence the rheology of the dispersions. The magnitude and the direction of the rheological changes depend on both the type and the amount of emulsifier. In most cases the changes are relatively small, especially for fat crystals. Generally speaking, the largest changes are caused by lecithins and saturated monoglycerides. The magnitudes of colloidal forces and equilibrium distances between the particles have been estimated from the rheological network model of van den Tempel [J. Colloid Sci. 16:284 (1964)] and from the correlation of the yield value to the interaction energy by Gillespie [J. Colloid Sci. 15.219 (1960)] and Tadros [Langmuir 6:28 (1990) and Chemistry and Industry 7.210 (1985)]. The results indicate that van der Waals forces alone cannot be responsible for the interparticle interaction in fat or sugar dispersions. The formation of water bridges is discussed as a probable source of interaction in both cases. Furthermore, the validity of the network model for fat and sugar dispersions in oils is questionable.