Structure and rheology of oleogels made from rice bran wax and rice bran oil.

ABSTRACT

Structural and rheological properties of oleogels consisting of 0.5-25 wt% rice bran wax (RBX) in rice bran oil (RBO) were explored. RBX was an efficient, thermoreversible oleogelator capable of structuring RBO at concentrations as low as 0.5 wt% RBX. A qualitative temperature-composition phase diagram showed that oleogels containing higher concentrations of RBX were expectedly the most resistant to melting. In oleogels at higher RBX concentrations, polarized light microscopy revealed the presence of a network of interlinked, long aspect ratio wax crystal needles up to 50 µm long. Upon heating, RBX crystals did not undergo any structural transition, based on the constant short spacings at ~ 4.16 and ~ 3.73 Å, indicative of an orthorhombic subcell, and d001 long spacing at 74-76 Šthat persisted until RBX fusion. This long spacing was ascribed to the presence of wax esters consisting of long-chain saturated fatty acids (C24 and C22) esterified to C28 - C34 saturated fatty alcohols. During cooling from 90 to 20 °C, the increase in oleogel viscosity resulting from the RBX liquid-solid phase transition was corroborated by DSC-based crystallization onset and enthalpy data. Similarly, elastic moduli and hardness both rose with increasing RBX concentration. This study, which demonstrated that RBX can structure RBO with distinct concentration-dependent properties, serves as the foundation for the development of oleogel-based approaches to saturated and trans fats replacement in processed foods.