Crystallization and Gelation Behavior of Low- and High Melting Waxes in Rice Bran Oil: a Case-Study on Berry Wax and Sunflower Wax

Abstract

Low-melting berry wax (BEW) has proven to be a good oil gelator with a positive contribution to the consistency and flexibility of the structured oil. Nevertheless, the properties of BEW and the corresponding oleogel have not yet been investigated in-depth. In this research, the difference in crystallization and gelling behavior between sunflower wax (SW), a high melting wax, and BEW, a low-melting wax, in rice bran oil (RBO) was investigated. The difference in melting and crystallization temperatures can be explained by the different chemical composition (long-chain wax esters in SW and short-chain fatty acids in BEW). The heterogeneity in crystal habits (unidirectional platelets versus microcrystalline particles) and polymorphism (orthorhombic versus hexagonal) are responsible for the varying gel strength and hardness of the respective SW- and BEW-oleogels. The microcrystalline BEW particles aligned and reorganized during 1-month storage at 5 °C, which leaded to an increase in the gel strength and hardness of BEW-oleogel. The gelling property of SW-oleogel however did not significantly differ after 4 weeks at 5 °C, despite of the appearance of spherulitic crystalline clusters. The changes in the physical properties of wax-based oleogels during storage time were further explored using differential scanning calorimetry, polarized light microscope, powder X-ray diffraction and rheology.