Water-in-oil Pickering emulsions stabilized by edible surfactant crystals formed in situ

Abstract

Water-in-oil (W/O) Pickering emulsions possessing long-term stability are important in the food industry and for other applications. However, the availability of food-grade particles is limited. In this work, the behavior of the nonionic surfactant sucrose stearate C-1801 as a food-grade W/O Pickering emulsion stabilizer is examined. C-1801 dissolved in hexadecane or edible oils like canola oil, soybean oil and olive oil at high temperature forms crystals upon cooling to room temperature. The spherical crystals exhibit Maltese-cross features and are of diameter 1–10 μm. At room temperature, stable W/O Pickering emulsions including high internal phase emulsions can be formed in which C-1801 crystals adsorb at the oil-water interface and excess crystals remain dispersed in the continuous phase preventing water droplets from coalescence and sedimentation respectively. Emulsions are however temperature-sensitive destabilizing upon reaching the melting point of the crystals. The emulsions prepared using edible oil remain stable after three cooling-heating cycles between 5 °C and 30 °C, and water-in-canola oil emulsions also survive three harsh freeze-thaw cycles between −20 °C and 30 °C. A network of aggregated droplets and crystals is formed in emulsions endowing them with high viscosity and long-term stability. This behaviour demonstrates that sucrose ester C-1801 is an excellent food-grade emulsifier for W/O food products.