Oleogelation with Mixtures of Pure Wax Esters: Considering Chain Length Disparity and Lamellar Orientation

Abstract Among the main components of natural waxes, long-chained wax esters (WEs) (WE) are considered dominant for the crystalline network structure in wax-based oleogels. So far, only preliminary data on their mixing behavior exists, suggesting that the carbon number difference between the respective WEs (ΔWE) determines the formation of either separate or mixed crystalline phases. However, to thoroughly understand the complex solid-phase mixing behavior of the WEs in natural waxes, a more systematic understanding of WE mixing is required. Oleogels structured by a binary mixture of WEs in a medium-chain triglyceride oil were investigated regarding crystallization behavior and physical properties using X-ray scattering, differential scanning calorimetry, oscillatory rheology, and microscopy. According to ΔWE, the systems were categorized into large, medium, small, or no chain length mismatch. Differences in the lamellar orientation of the respective WEsorthogonal or tiltedwere another parameter studied. It was found that ΔWE plays a dominant role, deciding whether separate or simultaneous crystallization occurs. Mixtures with a high ΔWE (≥8) exhibit separate crystallization, characterized by multiple thermal events, distinct lamellar spacings, and stepwise gelation. As ΔWE decreases, endothermic melting events were found to be increasingly overlapping. At small ΔWE, this results in peak fronting or multiple co-existing solid phases. With the exception of mixtures with ΔWE = 0, mixed oleogels consistently exhibited higher maximum complex shear moduli, Gmax*. Micrographs revealed that the higher-melting phase serves as a nucleation site for the lower-melting phase. Hence, structure reinforcement by reduced homogeneity and increased platelet−platelet interactions may arise from an increased surface roughness.