An-Najah Staff

Water-in-oil emulsions were prepared, structured only by a mixture of sitosterol and oryzanol and without further emulsifiers, containing 16 and 32% total sterol(esters)s on lipid phase and 10, 30 or 60% water. Previously, mixtures of β-sitosterol + γ-oryzanol were shown to form self-assembled tubules in triglyceride oil with diameter 7.2 ± 0.1 nm and a wall thickness 0.8 ± 0.2 nm. At 16% total sterol concentration, the SAXS diffraction patterns only demonstrate the presence of sitosterol and oryzanol crystals, but not of tubules. At 32% total sterol concentration, the diffraction patterns reveal the presence of tubules next to the crystals of the individual compounds. However, the tubule structure in these emulsions was more complicated than in pure oil and changed during storage, revealing the formation of bigger structures in the emulsion over time. In the cooling stage of a temperature cycle, water droplets nucleate at the tip of the fibres that reappear as a consequence of crystallisation.

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.