Surface Interactions in Oil Continuous Food Dispersions

We have previously shown that in an oil continuous system, emulsifiers adsorb to fat or to, the more polar, sugar crystals and thereby influence their properties. The adsorption has been measured with about 10 different common food emulsifiers and has been directly measured by the serum displacement method.A simple way to evaluate the consequence of the adsorption is sedimentation experiments where an increased sediment volume indicates an increased adhesion. Sedimentation experiments have shown that the adsorbed layers both can increase or decrease the adhesive forces between sugar and fat crystals. We also observed large differences between sugar and fat crystals. In experiments with trace amounts of water present we have found the adsorption and the interaction very sensitive to the water content in the system. The adsorption isotherms are compared with contact angle measurements in the three phase contact water/crystal/oil. A strong correlation is found in both the receding and the advancing contact angles.An increased adhesion causes an increased viscosity and rigidity and a reduced adhesion results in a much more liquid oil dispersion. A satisfying correlation between the sedimentation experiments and rheological experiments was found. Through a comparison with a network model the character of the force is compared with different interaction models (water bridges and van der Waals forces).The influence of the adsorbed emulsifiers on the sintering of fat crystals is also studied in a set of preliminary experiments.