Colloidal properties of sugar particle dispersions in food oils with relevance to chocolate processing

The influence of oil-soluble surface-active components on the interactions between fine sugar particles dispersed in different triglyceride oils has been investigated at a range of volume fractions. Four techniques were applied: rheology. sedimentation, light microscopy and adsorption. Eight different types of food oil were used: sunflower oil, soybean oil, milk fat, lauric fat (palm kernel oil), cocoa butter, pure stearin, pure olein, and a combined fats mixture. Low concentration additions of the emulsifiers, soya lecithin (phosphatidylcholine), polyglycerol polyricinoleate (PGPR) or monoolein, were used to alter the interactions between the hydrophilic sugar particles. In a dispersion of 70 wt% sugar and 0.3% of lecithin, approximately 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. The maximum effect was achieved in presence of soya lecithin. 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. Confocal laser microscopy was used to image the different mixtures, but it was not possible to quantify the sugar particle interactions with this technique.