EFFECTS OF SALT, TEMPERATURE, AND SURFACTANTS ON THE INTERFACIAL-TENSION BEHAVIOR OF A VEGETABLE OIL-WATER SYSTEM

The effects of salt and temperature on the interfacial tension (IFT) behavior of soybean oil/water interface were investigated. Salt led to a considerable reduction in the IFT of a commercial soybean oil/water system. The difference in the IFT in the absence and presence of salt increased with the temperature. As far as the dependence of the IFT on the temperature is concerned, opposite trends were observed for commercial and purified soybean oil systems due to the presence of surface active impurities in the commercial oil. Reduction in the IFT for the commercial soybean oil/water system was independent of the nature of the salt. Finally, the effect of salt on the IFT behavior of purified soybean oil containing various surfactants was investigated with a view to determine the nature of the impurities in the commercial oil. Both ricinoleic acid and ricinolein exhibited a behavior analogous to that of the impurities, especially in the presence of the salt, thereby indicating that ricinoleic-type surfactant molecules may be responsible for the peculiar interfacial tension behavior observed in the case of the commercial soybean oil. © 1992.