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

Abstract

The role of selected minor oil components on sterol/sterol ester oleogels was studied. Therefore, oleic acid, tocopheryl acetate and monoglycerides were admixed with three vegetable oils, having different fatty acid compositions. Before that, minor natural components were removed from untreated oils (purification). Moreover, purified oils were subjected to a humidity treatment to increase their water content. All additives retarded the molecular self‐assembly of sitosterol with oryzanol, and the effect was dose‐dependent. Gel hardness only increased at low concentrations of tocopheryl acetate and decreased in all gels at higher concentrations. In contrast, Gmax′ was invariable in samples with oleic acid and monoglycerides and increased in gels containing tocopheryl acetate and water. Therefore, Gmax′ does not necessarily relate to the gels' compression firmness. Atomic force microscopy showed that the microstructure of oleogels was considerably modified by the additives. In general, a packed surface of twisted, thick bundles of tubules may be associated with a stiffer gel. Moreover, a composite structure in gels with monoglycerides was visible and confirmed by differential scanning calorimetry (DSC). DSC was used to determine gel–sol transition temperature and was associated with the number of tubules in the gel. The gel–sol temperature increased in samples 1.0% w/w oleic acid and tocopheryl acetate and decreased in gels with monoglycerides and water. The results show that oleogel properties can be significantly modified by minor components with functional groups. That was associated with interactions with the sterol and sterol ester in solution and with the surface of the tubules (ferulic acid moieties of oryzanol) in oleogels.

Gelation Behavior and Stability of Multicomponent Sterol-Based Oleogels

“…The time performance seen for I1271/I1303 exposed the intensity inversion under r2, demonstrating a steeper and faster inversion compared with r1 ( Figure 4 c). As recent reports showed, the bundling effect on oleogel structure would be influential on the hardening and stabilization of the oleogels [ 35 , 36 ]. As mentioned earlier, the interfibrillar aggregation is decisive, and the way that the bundle formation (size and number of bundles) occurs and evolves over time is part of the multi-step oleogelation process.…”

“…As mentioned earlier, the interfibrillar aggregation is decisive, and the way that the bundle formation (size and number of bundles) occurs and evolves over time is part of the multi-step oleogelation process. Reports showed changes in bundle arrangement where fibrils aggregate differently depending on structuring agent concentrations as well as in the presence of polar components [ 20 , 35 ]. This could be largely influenced not only by the oil medium and gelator concentration and ratio but also by cooling rates.…”

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

“…Subsequently, the addition of relevant minor components could provide information about the gels' modifications regarding their functional groups. [21] To this end, XRD, the determination of FTIR spectra, and molecular modelling have proven to be powerful tools. [48,59,60]…”

“…A similar effect has been reported in the presence of PCs for sterol/sterol ester oleogels. [21,36] Finally, Figure 9C depicts the strain at which the sample starts to be irreversibly damaged, which relates to the systems' ability to store deformation energy during amplitude sweeps. The value was determined in agreement with the official methods defining the end of the LVR as the strain at which G′ deviates by 5% from its maximum value.…”

“…The standardization of oils is recommended to avoid the superimposition of several effects contributing to the modifications of oleogels. [21,[35][36][37] To the best of our knowledge, only one study included an oil purification procedure to remove minor oil components before preparing SFX oleogels. [38] Different soybean oils with varying iodine values (112, 136, and 159) and PC levels (7.5%, 6.2%, 2.8%, and stripped) were used, exemplifying different oil polarities.…”