Revisiting pure component wax esters as basis of wax‐based oleogels

Abstract

Current research on wax‐based oleogels indicates wax esters to be the key component in many natural waxes. This necessitates understanding the properties of pure wax esters to unravel the gelling mechanism in wax‐based oleogels. Therefore, available literature data on pure wax esters is summarized and critically reviewed. The detailed analysis of the pre‐existing data on crystallographic (SAXS) and thermal properties, facilitates the interpretation of subsequently performed experiments: Specific wax esters with different carbon numbers and symmetries were studied as such and in oleogels formed in combination with medium chained triglyceride oil at inclusion levels of 10% (w/w). They were characterized regarding their thermal (differential scanning calorimetry [DSC]) and viscoelastic (oscillatory rheology) behavior. It is found that all observations concerning pure wax esters behave systematically, linking molecular makeup, crystal structure, and behavior. The experimental study of oleogels structured by four different binary mixtures of wax esters revealed that substantial chain length differences induce separate crystallization (CN30 + 36 and CN30 + 42). Mixtures of wax esters with only limited chain length difference (≤ 2 carbon atoms) reconfirmed earlier speculations on mixing behavior and crystal structure. Applying mixtures of wax esters only differing in their position of the ester bond (CN36 [14_22] + CN36 [22_14]) indicated ideal mixing behavior in the solid phase of the gels. Surprisingly, the data revealed that additional thermal events occur at specific mixing ratios, predominantly at 1:1 (w/w). Their supposed relation to compound formation certainly needs further confirmation. Rheological analysis confirmed that sequential crystallization results in highest firmness values for the systems studied.

An Attempt to Relate Oleogel Properties to Wax Ester Chemical Structures

“…The platelet-based cardhouse networks are often interpreted to be needle-based. This misinterpretation of light–microscopic images was previously pointed out by Hwang et al in 2015 [ 23 ] and repeatedly confirmed, e.g., [ 9 , 18 , 24 ].…”

“…The axes for these properties were normalized such that the single FA occurring between a CN of 14 and 24 and a single FaOH with a CN between 16 and 32 could be depicted. The mean CN of the WE fraction was calculated assuming a statistical recombination of the respective FA and FaOH moieties, as previously described [ 9 ]. In line with the other parameters, the axis for the mean CN of the WE fraction was from the shortest CN present (CN = 30) to the longest CN present (CN = 56).…”

“…Nonetheless, until now, no relationship between the molecular composition, the process parameters and the resulting structure and functionality for wax-based oleogels has been identified. Many recent publications indicate WE to be decisive for the network formation of natural waxes [ 9 , 23 , 26 ]. In a previous contribution of ours [ 9 ], the relevance of WE crystallization for wax-based oleogels was illustrated by comparing the microstructures of either WE-based or SFX-based oleogels.…”

“…Many recent publications indicate WE to be decisive for the network formation of natural waxes [ 9 , 23 , 26 ]. In a previous contribution of ours [ 9 ], the relevance of WE crystallization for wax-based oleogels was illustrated by comparing the microstructures of either WE-based or SFX-based oleogels. Similar crystal habits could be generated by the adaption of the cooling rate.…”

Hardness, plasticity, and oil binding capacity of binary mixtures of natural waxes in olive oil

“…Wax esters are the main components in SFW (96–100%) and RBX (92–97%), while this amount for BW and CDW were significantly lower (58–71%) and (16–35%), respectively, that shows the diversity of different components in these waxes ( Blake et al (2014) . In a recently published paper, Brykczynski et al (2022) showed a significant increase in G* in binary wax esters (1:1 w/w ratio) containing similar total carbon number wax esters, suggesting some sort of “compound” formation, or synergistic interaction at the molecular level. Previous studies showed the total carbon number for RBW and SFW were (44–64) and (36–54), respectively ( Blake et al (2014) ).…”