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.

The gelation process of mixtures of γ-oryzanol and sitosterol structurants in sunflower oil was studied using light scattering, rheology, and micro-scanning calorimetry (Micro-DSC). The relation between temperature and the critical aggregation concentration (CAC) of tubule formation of γ-oryzanol and sitosterol was determined using these techniques. The temperature dependence of the CAC was used to estimate the binding energy and enthalpic and entropic contribution to the tubular formation process. The binding energy calculated at the corresponding temperatures and CACs were relatively low, in order of 2 RT (4.5 kJ mol−1), which is in accord with the reversibility of the tubular formation process. The formation of the tubules was associated with negative (exothermic) enthalpy change (ΔH0) compared with positive entropy term (−T ΔS0 >0), indicating that the aggregation into tubules is an enthalpy-driven process. The oryzanol–sitosterol ratio affected the aggregation process; solutions with ratio of (60 oryzanol–40 sitosterol) started aggregation at higher temperature compared with other ratios.

We report that the stability of an aqueous food grade fibril system upon pH change is affected by the presence of peptides that are formed during the process of fibril formation. We discuss several other relationships between food relevant properties and nano-scale characteristics, and compare these relationships for aqueous fibril systems to those of oil based fibril systems. In such fibril systems, dynamics, self-organisation, and sensitivity to external conditions, play an important role. These aspects are common to complex systems in general and define the future challenge in relating functional properties of food to molecular scale properties of their ingredients.

Small-angle neutron scattering (SANS) experiments have been performed on self-assembled tubules of sitosterol and oryzanol in triglyceride oils to investigate details of their structure. Alternative organic phases (deuterated and non-deuterated decane, limonene, castor oil and eugenol) were used to both vary the contrast with respect to the tubules and investigate the influence of solvent chemistry. The tubules were found to be composed of an inner and an outer shell containing the androsterol group of sitosterol or oryzanol and the ferulic acid moieties in the oryzanol molecule, respectively. While the inner shell has previously been detected in SAXS experiments, the outer shell was not discernible due to similar scattering length density with respect to the surrounding solvent for X-rays. By performing contrast variation SANS experiments, both for the solvent and structurant, a far more detailed description of the self-assembled system is obtainable. A model is introduced to fit the SANS data; we find that the dimensions of the inner shell agree quantitatively with the analysis performed in earlier SAXS data (radius of 39.4 +/- 5.6 angstroms for core and inner shell together, wall thickness of 15.1 +/- 5.5 angstroms). However, the newly revealed outer shell was found to be thinner than the inner shell (wall thickness 8.0 +/- 6.5 angstroms). The changes in the scattering patterns may be explained in terms of the contrast between the structurant and the organic phase and does not require any subtle indirect effects caused by the presence of water, other than water promoting the formation of sitosterol monohydrate in emulsions with aqueous phases with high water activity.

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Mixtures of g-oryzanol and b-sitosterol were used to structure different oils (decane, limonene, sunflower oil, castor oil, and eugenol). The g-oryzanol and b-sitosterol mixtures self-assemble into double-walled hollow tubules ($10 nm in diameter) in the oil phase, which aggregate to form a network resulting in firm organogels. The self-assembly of the sterol molecules into tubules was studied using light scattering and rheology. By using different oils, the influence of the polarity of the oil on the self-assembly was studied. The effects of temperature and structurant concentration on the tubuler formation process were determined and the thermodynamic theory of self-assembly was applied to calculate the change in Gibbs free energy (DG 0 ), enthalpy (DH 0 ), and entropy (DS 0 ) resulting from the aggregation of the structurants was determined. The self-assembly was found to be enthalpy-driven as characterized by a negative DH 0 and DS 0 . A decreasing polarity of the oil promotes the self-assembly leading to formation of tubules at higher temperatures and lower structurant concentrations.

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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.