Organogel-emulsions with mixtures of ß-sitosterol + [gamma]-oryzanol: Influence of water activity and type of oil phase on gelling capability

In this study, w/o-emulsions were prepared from water containing different salt concentrations dispersed in an oil phase containing mixture of ß-sitosterol and ¿-oryzanol. In pure oil the ß-sitosterol and ¿-oryzanol molecules self-assemble into tubular microstructures to produce a firm organogel. However, in the emulsion the water molecules bind to the ß-sitosterol molecules forming monohydrate crystals, which hinder the formation of the tubules, 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). The formation of tubular microstructure in the emulsion was further investigated by using several oils with differing polarity. With low polarity oils such as decane and limonene, the formation of hydrated sitosterol crystals was suppressed and the tubular microstructure was promoted which significantly increased the firmness of the emulsion-gel. The main conclusion of this study is that the formation oryzanol and sitosterol tubular microstructure in the emulsion can be promoted by reducing the water activity and/or by using oils with low polarity.