The adsorption isotherms of several emulsifiers to fat and sugar crystals dispersed in oils have been determined. Further, the influence of the emulsifiers on the interactions between the crystals has been estimated in sedimentation experiments, where an increased sediment volume due to adsorption corresponds to an increased adhesion between the crystals and vice versa. Most of the emulsifiers examined adsorb weakly to fat crystals and form tight monolayers, resulting in increased adhesion between the crystals at high concentrations. On the other hand, loosely packed layers are formed at low concentrations, and a decreased adhesion is observed. Unsaturated monoglycerides and phospholipids cause a decrease in adhesion for all concentrations examined.The emulsifiers adsorb more strongly to sugar crystals than to fat crystals and form tightly packed monolayers with hydrocarbon chains directed to the oil. The crystals are then stabilized sterically the adhesion between them is weaker and the sediments are more compact. At low concentrations, the opposite behavior often occurs. Monoglycerides interact in a specific way with sugar and cause increased adhesion between the crystals for all concentrations examined. Phospholipids reduce the adhesion between sugar crystals, resulting in much denser sediments. Saturated monoglycerides in amounts over the solubility limit tend to precipitate as a network between fat or sugar crystals, which causes bulky sediments and results in better stability against oiling out.

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) andChemistry 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.

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