Adsorption behavior of monoglycerides at the vegetable oil/water interface

Abstract

Knowledge of interfacial adsorption behavior of monoglycerides is important in the development and processing of a variety of food products. In this study two commercial oil blends were used, one of which (Blend-2) had a considerable amount of surface active impurities. For the oil blend which contained fewer impurities (Blend-1), interfacial tension (IFT) decreased with monoglyceride concentration as is normally expected. For Blend-2, however, it was found that the equilibrium IFT (in the presence of NaCl) increased with increasing monoglyceride concentration. This anomalous behaviour was explained on the basis of the formation of reverse micelles of monoglycerides in the oil phase. These reverse micelles can solubilize the impurities and thus remove them from the interface. Further evidence of micellization was obtained from experiments on purified versions of Blend-2 where the impurities were removed by adsorption on a Florisil/silica gel column. In this case, the IFT decreased with the monoglyceride concentration as expected, and a plot of equilibrium IFT versus monoglyceride concentration had a pronounced break, indicating the formation of reverse micelles beyond a critical concentration. Experiments at different temperature with soybean oil containing surface active impurities also support this hypothesis.