Quantitative analyses of structural stabilization of oleogels by focusing on strain accumulated in crystalline domains

Abstract: Oleogel is a structure in which a small amount of gelling agent, such as vegetable waxes, forms a solid particle network structure that can maintain a large amount of liquid oil. However, it is quite difficult to manufacture the oleogels with high stability, leading to difficulties in the application of oleogels to actual food products. It was previously believed that the origin in the unstability of oleogels is attributed to an increase in the free energy of crystalline domains due to the size effect, which is known as Gibbs-Thomson effect. In the present study, we observed the structural stability of oleogels made of unrefined and refined rice bran wax (RBX) and olive oil by using polarized light microscope, scanning electron microscope and synchrotron radiation wide-angle and small angle X-ray diffraction techniques. To investigate the structural changes and stability of the manufactured oleogels, a duration of liquid oil leakage was also measured. In all the experiments, the oleogels were subjected to the storage at 20 ºC for 40~50 days. It was clarified that the unstability of oleogels is predominantly caused by the strain accumulated in the solid particle networks of oleogels, rather than the size effect of crystalline domains, as revealed in the X-ray diffraction peak intensities. Moreover, it was also indicated that the control of the strain accumulated in the solid particle networks of oleogels can largely be changed by the purification of RBX samples. This technique focusing on the control of the strain accumulated in the solid particle networks of oleogels may have the high potential to manufacture the oleogel with high stability.