WATER-IN-TRIGLYCERIDE OIL-EMULSIONS - EFFECT OF FAT CRYSTALS ON STABILITY

The influence of low concentrations (0.1-5%) of fat crystals on the st ability of water-in-soybean oil emulsions was examined by light scatte ring and sedimentation experiments. Both the initial flocculation/coal escence rate and longterm stability against water separation were dete rmined. The initial flocculation/coalescence rate increased upon addit ion of small amounts of fat crystals. When the crystal concentration w as 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 wate r droplets by fat crystals. Fat crystal wetting by water is an importa nt criterion for this phenomenon to occur. Emulsion stabilization for crystal concentrations above critical is caused by a mechanical screen ing of water droplets. The presence of considerable amounts of crystal s in oil also lowered the density difference between droplet and mediu m, and enhanced viscosity. The degree of increase in viscosity depende d upon the emulsifier. Both a decrease in density difference and an in crease in viscosity play a role in hindering flocculation/coalescence of droplets. In long-term studies of water separation, all concentrati ons 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 c rystals up to 5%. For lecithin-stabilized emulsions, an optimal effect was achieved for fat crystal concentrations of 1-2%.