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.