Shaken, not stirred: On the effect of mechanical stress on oleogel properties

Predictability and stability of the desired functional properties are critical to the successful industrial application of oleogels. During production, storage and transportation, oleogels are inevitably subjected to mechanical stresses such as those caused by conveyor belts, vibrating surfaces and stock transfers.

This work focuses on the effect of mechanical stress on oleogel properties using two standardized treatment methods: Rotational forces on a shaking plate and low-frequency periodic shocks. Oleogels with two different structuring mechanisms were investigated. Crystalline networks are represented by wax-based oleogels, sunflower wax (SFX), rice bran wax (RBX) and candelilla wax (CLX), whereas fibrillar networks are represented by β-sitosterol and γ-oryzanol (S+O). Key properties such as oil binding capacity (OBC), hardness (F_max) and elasticity were evaluated.

The results show significant effects of mechanical treatments on the oleogel properties, with the response depending on the structuring agents. In rheology and storage tests, slower gelation kinetics were observed for S+O-based oleogels compared to wax-based oleogels. Mechanical treatment during cooling, especially rotation, was found to accelerate the S+O gelation process, resulting in higher F_max values than the reference (statically crystallized) after 48 h of storage. 

Among the wax-based systems, CLX showed the highest OBC, but reduced F_max under both treatment methods. In contrast, SFX and RBX exhibited divergent behavior, with reduced F_max under rotational treatment, but a remarkable increase in gel strength after periodic shocks - up to 250 % (F_max for SFX). Interestingly, even with large changes in gel strength, the OBC did not appear to be significantly altered by mechanical stress. Not only the microstructure (microscopy) but also the molecular composition of the waxes (HPLC-ELSD) is considered to explain the observed changes.

The results highlight the critical role of post-processing mechanical treatments on oleogel properties. They therefore represent an important building block for exploiting the industrial potential of oleogels.