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, wax esters with different carbon numbers and symmetries were studied and characterized regarding their thermal (DSC) and viscoelastic (oscillatory rheology) behavior. Pure wax esters and binary mixtures of wax esters were studied as such and in oleogels formed in combination with medium chained triglyceride oil at WE-inclusion levels of 10 % (w/w). Interpretation of the observations was based on detailed analysis of pre-existing data on crystallographic (SAXS) and thermal properties. It is found that all observations concerning single pure WE’s obey a systematic framework linking molecular make up, crystal structure and behavior. The study on the gelling of four different binary mixtures of wax esters revealed that substantial chain length differences do have the expected consequence of separate crystallization. Mixtures of wax esters with only limited chain length difference reconfirmed earlier speculations on mixing and crystal structure. Applying mixtures of wax esters only differing in their position of the ester bond indicated ideal mixing behavior in the solid phase of the gels. Actually, the data revealed that despite these expected observations in both systems, additional thermal events occur at specific mixing ratios. 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.

Influence of Minor Oil Components on Sunflower, Rice Bran, Candelilla, and Beeswax Oleogels

“…[ 22 ] Indeed, network formation was found to be promoted in WE compositions with narrow chain length distribution. [ 23 ] However, there seems to be a small effect of the oil type on the solubility of SFX and RBX since the dissolution, and the gel formation temperatures are slightly higher in stripped sunflower oil. However, this observation could not be reconfirmed in 4% w/w oleogels and is possibly related to minor deviations caused during sample preparation.…”

“…That leads to relatively large deviations between the repetitions since the networks are very dense. [ 3,23 ] Repeating the experiments at, e.g., 4% w/w wax concentration would hence be beneficial. However, the break‐up behavior shows a much better response at high wax concentrations.…”

“…Various studies reported the absolute values of G ′′ for different waxes, which increase in the following order RBX < CLX < BWX < SFX. [ 22,23,50 ] In SFX samples, there is no considerable effect considering the type of oil and PC concentration. However, the results indicate a higher G ′′ max for gels from oils containing PCs, which relates to more interaction points within the network.…”

“…[ 22 ] The proportion of the two alkyl chains in WE's influences the phase transition, with symmetric WE showing higher melting temperatures. [ 23,24 ] The self‐assembly of WE is due to the interlocking of alkyl chains which is more favored if adjacent chains have the same number of carbon atoms. [ 25 ] These structural units form large plates of stacked crystals (symmetrical), while asymmetric chains result in smaller, more needle‐like shapes.…”

“…[ 25 ] These structural units form large plates of stacked crystals (symmetrical), while asymmetric chains result in smaller, more needle‐like shapes. [ 23 ]…”