Crystallization of wax esters - a prerequisite to understand wax-based oleogels

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From the range of oil structuring systems, waxes are a prime candidate to be taken into further consideration for product applications. In order to evaluate the structuring potential and tailor the properties of oleogels, it appears necessary to understand the mechanism of structuring and establish a relationship between composition, structure and functionality of the gels. Therefore, it is crucial to consider complex mixed gelators not as a ‘pure component’ but rather on a level of their molecular composition. Most natural waxes contain substantial amounts of wax esters being assigned to be decisive for the three-dimensional crystalline network waxes form when used as oleogelators. Diligent study of pre-existing XRD-data revealed that wax esters crystallize in two different crystal structures related to the position of their ester bond (symmetry). Wax esters with different total carbon numbers and symmetries were studied and characterized as neat component as well as in oleogels formed in medium-chained triglyceride oil at inclusion levels of 10 % (w/w). Regarding their thermal (DSC), viscoelastic (oscillatory rheology) and microstructural (BFM, cSEM) properties, single wax esters behave systematically, linked to their molecular make-up. Studying the behavior of oleogels structured by binary mixtures of wax esters revealed that chain length differences drive the solid phase mixing behavior. However, small chain length differences appear to induce crystallization in mixed structures, whereas large chain length differences induce separate crystallization of the wax esters. During storage, additional thermal events occur at specific mixing ratios, being related to compound formation or recrystallization of different crystal structures. To unravel the crystallization of wax esters and their contribution to the gelling behavior of natural waxes is necessary to control and to exploit their full potential as oleogelators in practical applications.