Water-in-triglyceride oil emulsions. Effect of fat crystals on stability

The influence of low concentrations (0.1-5%) of fat crystals on the stability of water-in-soybean oil emulsions was examined by light scattering and sedimentation experiments. Both the initial flocculation/coalescence rate and long-term stability against water separation were determined. The initial flocculation/coalescence rate increased upon addition of small amounts of fat crystals. When the crystal concentration was increased above a critical concentration (specific to a system), a decrease in the flocculation/coalescence rate occurred. The increased flocculation/coalescence rate is likely the effect of bridging of water droplets by fat crystals. Fat crystal wetting by water is an important criterion for this phenomenon to occur. Emulsion stabilization for crystal concentrations above critical is caused by a mechanical screening of water droplets. The presence of considerable amounts of crystals in oil also lowered the density difference between droplet and medium, and enhanced viscosity. The degree of increase in viscosity depended upon the emulsifier. Both a decrease in density difference and an increase in viscosity play a role in hindering flocculation/coalescence of droplets. In long-term studies of water separation, all concentrations of fat crystals stabilized the water-in-oil emulsions. The droplet size of these emulsions increased until the critical droplet size was approached where the screening effect of crystals on the droplets no longer stabilized the emulsions. The stabilizing effect for emulsions with monoolein was continuously improved by increasing the amount of crystals up to 5%. For lecithin-stabilized emulsions, an optimal effect was achieved for fact crystal concentrations of 1–2%.