The composition of edible oils modifies β-sitosterol/γ-oryzanol oleogels part II: Addition of selected minor oil components

Abstract

The first part of this study showed that the triglyceride composition of purified oils has little impact on sterol/sterol ester oleogels. Hence, changes in the gels’ properties observed in previous studies must arise from minor polar components, particularly by changing the interactions within the fibrillar network. Selected molecules (oleic acid, tocopheryl acetate, monoglycerides, and water) were added to three purified oils to unravel the individual contributions introduced by different functional groups. While all additives retarded the molecular self-assembly of sitosterol with oryzanol, distinct effects were found for gel hardness, transition temperatures and enthalpies, strain sweep responses, and microstructure. It was discovered that the maximum storage modulus in the linear viscoelastic region does not necessarily relate to the gels’ compression firmness. In samples comprising oleic acid and tocopheryl acetate, discrete interaction mechanisms with the scaffolding elements were suggested since results between the two additives developed differently and were dose-dependent. A network supporting effect was suggested at low concentrations, in line with previous results for oils comprising low levels of thermal deterioration products. The microstructure of oleogels was considerably modified with additives. Unfortunately, effects are difficult to quantify due to the packed surface observed in AFM micrographs.

Effect of type of emulsifier and co‐solvent on the morphology, thermal, and mechanical properties of γ‐oryzanol and β‐sitosterol organogels

“…SEM micrographs of organogel samples prepared with various types of emulsifiers and co‐solvents (see Figure 1) are shown in Figure 2. Typical tubular microstructures similar to those observed in previous studies (Sawalha et al, 2021; Scharfe et al, 2022a, 2022b) were observed in all samples. The variation of the oil phase resulted in obvious variation in the alignment between the tubules and the persistence length of the tubules.…”

“…The samples were heated from 0 to 120°C at a constant heating rate of 10°C/min. The gel–solution (gel–sol) transition temperatures were identified as the peak melting temperature at which the dissolution of the tubules occurs (i.e., break‐up of hydrogen bonding between sitosterol and oryzanol) (Scharfe et al, 2022a, 2022b). The gel–solution (gel–sol) transition temperatures are presented as relative values (°C/°C) with respect to that of the neat gel sample prepared with decane only, thus without additives or co‐solvents.…”

“…Recently, results on gel formation in water saturated oils were reported. It was found that the gels were stable for at least 7 days yielding a hardness of approximately 75% compared to the dry reference gel (Scharfe et al, 2022a, 2022b). Likewise, adjusting the polarity of the oil phase through the use of non‐polar oils (i.e., non‐edible long chain hydrocarbons such as decane) decreases the solubility of water in the oil phase, thus, inhibiting the formation sitosterol hydrate crystals and consequently promoting the formation of the tubules (Sawalha et al, 2012).…”

“…This area has been investigated considering the effects of the fatty acid composition and the presence of minor components in seed oils on oleogels (Scharfe, 2021). A way of doing this is through the use of “pure or purified oils.” This could be done on the one hand by studying systems based on seed oils depleted from polar minor components (Scharfe et al, 2022a, 2022b). However, following this approach still interactions based on the double bonds of the fatty acids constituting the TAGs are present.…”