Effects of Oil Type on Sterol-Based Organogels and Emulsions

Abstract

The present study investigates the effect of oil type on the formation, morphology and mechanical properties of phytosterol-based organogels. The formation of organogels can be satisfactorily predicted with a criterion based on Hansen Solubility Parameters (HSPs), provided that the sterol and sterol ester in these systems assemble as tubules. When structures other than tubules are formed, the predictability of the HSP-based criterion becomes void. In cases where organogelling occurred, the morphology and mechanical properties of the tubular network of the gels and water-in-oil emulsions were investigated. The findings revealed that the structure of the tubular network formed in oils with different compositions, could be grouped based on the dielectric constants of the oils. Curly and bundled tubules which formed networks, were observed in gels prepared with low dielectric constant oils (i.e. decane and limonene). For oils with a moderate dielectric constant (i.e. castor oil and sunflower oil), the tubules became less curly and straighter. Upon increasing the dielectric constant of the oil (eugenol), individual tubules were observed next to the bundled tubules. The results showed that straighter, bundled tubules are associated with firmer gels, whereas less straight (i.e. curly) tubules rendered weaker gels. The tubular network of the water-in-oil emulsions obtained for oils with a low dielectric constant appeared more open with straighter tubules. For oils with relatively high dielectric constant, the water-in-oil emulsions lost most of their tubular structure and only a few tubules could be observed. In the presence of emulsion droplets fewer tubules are formed, resulting in weaker networks.

The composition of edible oils modifies β‐sitosterol/γ‐oryzanol oleogels. Part II: Addition of selected minor oil components

“…However, gel hardness was about 50% less than for the sample with 1% w/w. The findings agree to some extent with a recent publication studying the influence of solvent polarity on sterol/sterol ester oleogels (Sawalha et al, 2020). Based on SEM images, the authors hypothesized that bundles with large segments of alignments promote the gels' hardness.…”

“…Moreover, there is no significance regarding the microscopic and macroscopic oleogel properties. However, the study also included SEM images of decane, limonene, sunflower and castor oil, and eugenol‐based oleogels (Sawalha et al, 2020). Castor oil and sunflower oil produced the hardest gels with a network based on reasonably straight but interconnected tubule bundles.…”

The composition of edible oils modifies β‐sitosterol/γ‐oryzanol oleogels. Part I: Stripped triglyceride oils

“…That appears to be in line with the Hansen solubility parameters presented by Sawalha et al (2020), showing the sterol/sterol ester combination cannot gel solvents with a higher polarity such as methanol and glycerol. However, some data appear contradictory, for example, when castor oil is used.…”

“…Nevertheless, the data presented by Sawalha et al (2013, 2020) indicates that the solvent type profoundly affects sterol‐ester/sterol oleogel properties and formation. Still, it seems that convincing correlations are not achievable if chemically diverse solvents are used that modify the structurants' solubility and tube formation.…”

“…However, some data appear contradictory, for example, when castor oil is used. While Sawalha et al (2020) report a firm oleogel similar to sunflower oil gels (32% w/w oleogelator), another study reported no gelation or weak gels (10% w/w oleogelator) (Calligaris et al, 2014). Moreover, the addition of 32% w/w oleogelator might enhance the gelling of more polar solvents might be practical to demonstrate whether a gel forms or not but exceeds the solubility of the sterol/ sterol ester in some solvents, which likely leads to the formation of other network building blocks such as sterol crystals.…”