Wetting of fat crystals has been extensively examined in this work by contact angle (0) measurements of fat crystal, oil, and water in three-phase contact. Contact angle was measured in oil. The crystals were nonpolar and wetted by oil for a contact angle equal to 0 °, and polar and wetted by water for an angle equal to 180 °. Fat crystals are expected to contribute to the stability of margarine emulsions if they are preferentially wetted by the oil phase (0 ° < 0 < 90°), but result in instability if they are preferentially wetted by the water phase (90 ° <0 <180°). In the absence of oil and water additives, fat crystals in c~ and L3' polymorphs were introduced to the oil/water interface from the oil side (contact angle 0 -30°). [3 Polymorphs were completely wetted by oil (0 = 0°). The contact angle for [3' crystals decreased with increasing temperature and was slightly lower in butter oil than in soybean oil. Emulsifiers in the oil phase (lecithins, monoglycerides and their esters, ethoxylated emulsifiers) and surface-active proteins in the water phase (milk proteins) made the crystals more polar (higher 0). Nonsurfaceactive proteins, sugar, and citric acid had no significant effect, although concentrations of salt lowered 0. Contact angle increased with temperature for emulsifiers of limited solubility in the oil, e.g., saturated monoglyceride. JAOCS 72, 921-931 (1995).

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 longterm 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 fat crystal concentrations of 1-2%.JAOCS 72, 939-950 (1995).

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