Interactions in dispersions of sugar particles in food oils: influence of emulsifier

The influence of oil-soluble surface-active components on the interactions of fine sugar particles dispersed in triglyceride oils has been investigated at different volume fractions by a combination of rheological and sedimentation experiments. Four different types of food oil were investigated: soybean, milk fat, lauric fat (palm kernel oil) and cocoa butter. The addition of a low concentration of emulsifier, soya lecithin (phosphatidylcholine) or monoolein, was used to adjust the nature of the interactions between the hydrophilic sugar particles. In a dispersion of 70 wt% sugar and 0.3% of lecithin, around 30–40% of the emulsifier present was found to be adsorbed at the surface of the sugar particles. The viscosities of the dispersions in the different oils were found to be similar up to 30 wt% sugar content. At high sugar contents (30–60 wt%), however, differences between the oil samples were evident. Lauric fat generated the highest viscosity amongst the different oils whereas cocoa butter exhibited the lowest. The presence of the emulsifier lowered the viscosity of the dispersions to differing extents. Gravity settling observations were made for dispersions of 10 wt% sugar particles in the different oils in the presence and absence of emulsifier. The emulsifiers were effective in reducing the volume of sediment and hence in increasing the sediment particle packing density. This implies that the adsorbed surface-active species reduce the strength of the attractive interactions between the sedimenting sugar particles, in good agreement with the rheological data at high sugar contents.