Effect of vegetable oil unsaturation and minor polar components on the physical properties of rice bran wax oleogels

For the practical application of oleogels and to produce oleogels with consistent properties, a full understanding of the factors affecting properties of oleogels is necessary. This study aimed to understand the effects of type of oil and minor components in oils on the properties of 3% and 7% rice bran wax (RBW) oleogels, which were prepared with 12 vegetable oils with different degrees of unsaturation as well as the same oils where polar compounds were removed (stripped oils). Correlation coefficients of iodine values (IVs) of oils with the firmness of 3% and 7% RBW stripped oil oleogels were -0.632 and -0.499, respectively, indicating that the gel strength decreased with increasing unsaturation of oil. The gel strength increased after removing polar compounds in oil for all the oleogel samples. Higher unsaturation of oil resulted in higher solid wax contents (SWCs) in 7% RBW stripped oil oleogels (r = 0.617), which, however, did not affect the gel strength. Very thin, large platelet wax crystals were observed under phase-contrast microscopy, which were almost identical across the oleogel samples. The permeation of dyed oil through oleogels was faster with unstripped oil oleogels than stripped oil oleogels, and the negative correlation between the color permeation rate and the firmness of oleogels was significant (r = -0.602 at Day 28) indicating that defects in the three-dimensional crystal network is an important factor for the gel strength. This study found several important factors affecting the physical properties of RBW oleogels, which can be applied to their practical applications. PRACTICAL APPLICATION: For the practical application of oleogels, factors affecting properties of oleogels must be fully understood so that the quality of oleogel-containing food products could be well controlled. Although oil is the major component of oleogels, the effect of the type of oil on oleogel properties was not well understood to date, and this study revealed very important relationships between oil properties and oleogel properties, which can be applied to the production of oleogel-containing products. The major findings are that gel strength was higher with lower unsaturation of oil and less polar compounds in oil and that melting temperature was higher with higher unsaturation of oil.