Investigating the crystallization behavior of mixtures of pure wax esters in oleogels

Abstract: In oleogelation, natural waxes appear as promising candidates for future food applications. However, their multicomponent nature causes strong variation in the gel properties. To exploit the full potential of wax-based oleogels, understanding the relationship between molecular composition, formed structure, and resulting functionality is crucial. Among the main components of waxes, long-chained wax esters (WE) are considered dominant for the crystalline network structure in wax-based oleogels.
In previous contributions, the properties of oleogels containing a single WE were found to evolve systematically. To extend the present knowledge base, mixtures of pure wax esters in oleogels must be investigated. So far, only preliminary data exist, suggesting that the carbon number difference between the respective WE determines the formation of either separate or mixed crystalline phases.
Building up on this, seven mixtures of two WE with a total carbon number ranging from 30 to 46 were characterized in oleogels - 10 % (m/m) of WE in medium chain triglycerides (MCT)-oil, three mixing ratios each - regarding their thermal properties (DSC), viscoelastic behavior (G*_max) and microstructure (light microscopy and cryo-SEM). According to the thermal properties, the mixtures behave systematically with respect to carbon number difference and mixing ratio. The formation of separate crystalline phases for large carbon number differences (≥ eight carbon atoms) is confirmed. In the case of separate crystallization, a synergistic effect on G*_max was observed. The micrographs revealed that the higher-melting phase serves as nucleation site for the lower-melting phase, resulting in an increased surface roughness. Furthermore, during storage, the WE molecules seemed to rearrange so that additional mixed crystalline phases appear at large carbon number differences and phase separation occurs for smaller carbon number differences of two or four carbon atoms.

The findings provide crucial insights to thoroughly understand the complex solid phase mixing behavior of natural waxes.