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The relation between molecular structure of oilstructuring agents and their gel-forming capability was investigated for mixtures of the phytosterol ester γ-oryzanol with a series of phytosterols. Dihydrocholesterol, cholesterol, β-sitosterol, and stigmasterol were found to form firm transparent gels with γ-oryzanol in sunflower oil under the conditions used in this work. The mixture of β-sitosterol with γ-oryzanol in sunflower oil does not gel immediately on cooling, but mechanical agitation such as shear promotes gelling. Gels that are formed immediately after cooling show a higher modulus than gels for which there is a time delay between cooling and agitation (150 vs. 100 kPa). The effect of oscillatory shear parameters (amplitude, frequency) is small, as long as the yield stress of the gel is not exceeded. The gels withstand compression very well (up to deformations of 10%), but yield at very small deformations. The enthalpy of melting of the solid phase is estimated to be 26 ± 4 kJ/mol, putting it in the same range as for certain fibrillar steroidderived organogels.

Mixtures of c-oryzanol and b-sitosterol are able to form transparent organogels in edible oils. Small-angle X-ray scattering was used to elucidate the microstructure of the building blocks of these organogels in sunflower oil. It was found that the plant sterol(ester)s form hollow tubes with a diameter of 7.2 ± 0.1 nm. Tubes prepared with coryzanol-rich structurant show the least bundle aggregation, and can be supercooled during formation most easily. The tubes melt at elevated temperatures, in agreement with the loss of structuring capacity as observed in earlier experiments.Keywords Organogel Á Phytosterol Á Self assembly Á Fibril Á X-ray diffraction (XRD) Á Small-angle X-ray scattering (SAXS) Á Wide-angle X-ray scattering (WAXS) Á Differential scanning calorimetry (DSC)

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In this study, water-in-oil emulsions were prepared from water containing different salt concentrations dispersed in an oil phase containing a mixture of β-sitosterol and γ-oryzanol. In pure oil, the β-sitosterol and γ-oryzanol molecules self-assemble into tubular microstructures to produce a firm organogel. However, in the emulsion, the water molecules bind to the β-sitosterol molecules, forming monohydrate crystals that hinder the formation of the tubules and resulting in a weaker emulsion-gel. Addition of salt to the water phase decreases the water activity, thereby suppressing the formation of sitosterol monohydrate crystals even after prolonged storage times (∼1 year). When the emulsions were prepared with less polar oils, the tubular microstructure was promoted, which significantly increased the firmness of the emulsion-gel. The main conclusion of this study is that the formation of oryzanol and sitosterol tubular microstructure in the emulsion can be promoted by reducing the water activity and/or by using oils of low polarity.