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

Fat crystals influence the stability of food emulsions, such as margarine, 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 adsorption is therefore the difference between the interactions between fat crystal/water and oil/water. In this work, we have estimated this interaction difference and compared it to the displacement energy for fat crystals from the oil/water interface to the oil. Our calculations have shown 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 constitutes 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 bonds for a hypothetical fat crystal with a diameter of 1 mu m The displacement energy for fat crystals to oil is lower than the polar energy excess 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 interfacial tension gamma(OW). A straight line of slope -1 is achieved for systems with low interfacial tensions (gamma(OW)) and low polar energy excess (I-SW - I-OW).