Effects of unsaturation and other properties of vegetable oils on the properties of rice bran wax oleogels

Authors: Hwang, Hong-Sik; Kim, Sanghoon; Moser, Jill; Liu, Sean

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2024
Publication Date: 12/19/2024
Citation: Hwang, H., Kim, S., Moser, J.K., Liu, S.X. 2024. Effects of unsaturation and other properties of vegetable oils on the properties of rice bran wax oleogels. Journal of Food Science. https://doi.org/10.1111/1750-3841.17613.
DOI: https://doi.org/10.1111/1750-3841.17613

Interpretive Summary: Food products such as margarines, spreads, shortenings, and related foods need solid fats that are semi-solids at room temperature for their desired textural properties. However, since these fats contain highly saturated fats such as animal fats, palm oil, coconut oil, and fully hydrogenated oils, which are known to be associated with health problems including cardiovascular disease, hypertension, and raised LDL cholesterol concentrations, efforts are being made to replace these fats with healthier fats. Oleogels are made of a small amount of gelator and healthy oils such as vegetable oils or fish oils, of which the physical properties are similar to those of conventional fats. Several studies proved the potential health benefits of oleogels. Among many gelators discovered, natural waxes have been studied the most as gelators because they make strong oleogels and are safe to use as food ingredients, widely available, and inexpensive. Since it is very recent that wax oleogels have been studied for food application, the effects of oil on the properties of wax oleogels are not well understood. In this study, the effects of twelve vegetable oils on rice bran wax (RBW) oleogels were investigated. Detailed compositions of oils were determined, and relationships between the composition of oil and RBW oleogel properties were examined. Less amounts of minor components in oil are desired for higher gel strength because it was found that minor components negatively affected the strength of oleogels. Oils with higher unsaturation provided softer oleogels with a higher melting temperature. Crystal shape and size of RBW were not the factors determining the gel strength. Instead, defects in the three-dimensional network of these crystals were found to be an important factor for the gel strength. This study identified several important factors affecting the properties of RBW oleogels, which provide valuable information for the practical application of these oleogels.

Technical Abstract: 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 kind of oil and minor components in oils on the properties of 3% and 7% rice bran wax (RBW) oleogels, which were prepared with twelve vegetable oils as well as the same oils where polar compounds were removed (stripped oils). Correlation coefficients of iodine values (IV) of oils with the firmnesses 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 (SWC) 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.