Effect of Cooling Rate on the Oleogel Properties of Wax–Wax-Hydrolyzate Mixtures

Abstract

In this contribution, the effect of cooling rates on a wide compositional range of waxes as oleogel structurants was systematically investigated. The different waxes exhibited varying levels of wax esters (WE), fatty acids (FA), fatty alcohols (FaOH) and hydrocarbons (HC) and were systematically altered by combinations of sunflower wax (SFW), bees wax (BW) and their hydrolyzed variants (SFWh, BWh). By applying slow, medium and high cooling rates, the resulting gel properties were investigated in terms of firmness, calorimetry and microstructure. It was found that the calorimetrical signal is mainly affected by the waxes’ composition. However, due to enlarged dynamic induction times upon crystallization, a shift in dissolution temperature could be observed in heating scans. In our latest work we were able to formulate the degree of homogeneity (DoH), with which it was possible to predict the undercooling in SFW mixtures. The introduction of a novel method emerged for firmness measurements of oleogels treated with the different rates. Thus, it was possible to detect with high sensitivity for all waxes for applied cooling rates, caused by modification of microstructure. Combination of different methods further elucidated that higher rates need to be applied to further scale firmness of oleogels in industrial processes.

An Attempt to Relate Oleogel Properties to Wax Ester Chemical Structures

“…For stored products, this could mean low cooling rates. In conclusion, the responses of the WE-based oleogels studied at different cooling rates are in line with published data on wax-based oleogels [ 24 , 25 , 44 ].…”

“…The maximum crystal face length in the respective oleogels also systematically changes, as illustrated by Figure 11 b. These data are in line with expectations based on generally acknowledged crystallization kinetics, e.g., for wax-based oleogels [ 24 , 25 ]. They confirm that smaller crystals in compositionally equal systems typically yield more rigid gels.…”

“…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 ].…”

“…These micrographs prove that for WE also, the microstructure does not only change as a function of the molecular make-up but can also be manipulated by variation of the crystallization process. As generally established, increasing cooling rates result in higher nucleation rates and reduced induction times [ 24 ]. Furthermore, the results confirm that low cooling rates appear to induce more regular crystal habits as shown elsewhere [ 9 ].…”

Wax based oleogels and their application in sponge cakes

“…To avoid these factors introducing ambiguity, we extrapolated the minimal amount of material necessary to form crystals in previous contribution. 36 Regarding the ability to form oleofoams, the CGC might be a characteristic value since it incorporates the effectiveness of scaffolding and also the solubility. Stabilization of the incorporated bubbles may hence be a function of the microstructure and solid quantity present.…”