WETTING OF FAT CRYSTALS BY TRIGLYCERIDE OIL AND WATER .2. ADHESION TOTHE OIL WATER INTERFACE/

Fat crystals influence the stability of food emulsions, such as margar ine, butter, or cream, if adsorbed to the oil/water interface. During the adsorption process, a new fat crystal/water interface is created, while the oil/water interface is lost. The driving force for adsorptio n is therefore the difference between the interactions between fat cry stal/water and oil/water. In this work, we have estimated this interac tion difference and compared it to the displacement energy for fat cry stals from the oil/water interface to the oil. Our calculations have s hown that fat crystal adsorption to the oil/water interface (expressed by contact angle theta) is determined by polar energy, excess of fat crystal/water over oil/water (I-SW - I-OW). The interfacial tension co nstitutes the resistance force for crystal adsorption to the interface . Polar interaction energy for fat crystal/water is stronger than the polar interaction energy for oil/water in all cases examined (I-SW - I -OW > 0). The difference corresponds to about 10(4)-10(6) hydrogen bon ds for a hypothetical fat crystal with a diameter of 1 mu m The displa cement energy for fat crystals to oil is lower than the polar energy e xcess in most cases examined. Thus, an additional interaction between fat crystals and oil makes it easy to displace the crystals to the oil . There is also a relationship between the adhesion tension (-gamma(OW ) . cos theta) for the crystals at the oil/water interface and the int erfacial tension gamma(OW). A straight line of slope -1 is achieved fo r systems with low interfacial tensions (gamma(OW)) and low polar ener gy excess (I-SW - I-OW).