Intact starch granules for pickering emulsion: Exploring mechanism of cleaning with washing rice water and floury soup

Abstract

Since ancient times, Chinese households have known by life experience that washing rice water and wheat floury soup may be used to wash oil dishes, face and hair. However, till today, a detailed scientific explanation is still lacking. Herein, we demonstrated that the native starch granules may play the role of a Pickering emulsifier, enabling them to remove oil. We evaluated the properties of native starch granules from rice, wheat and potato stabilizing corn oil and anisole emulsion in water. It was found that rice starch, with the smallest granule size, had the best emulsifying performance. After pre-treating the starch granules in heating conditions in water, however, we found that wheat starch pre-treated at 70 °C demonstrated a much more extended ability to stabilize anisole droplets. Compared with starch from rice or wheat, intact potato starch granules were larger in average and displayed poor emulsion stabilization. In order to explore the role of size factor behind this difference, we fractionated potato starch granules into six fractions by size. It seems that a smaller granule size means better emulsifying ability. In addition, by optical microscopy, the native starch granules were observed to form a particular monolayer arrangement to stabilize the oil droplets, revealing the Pickering emulsion mechanism. Although the emulsion stability for native starch is short in general, it is still promising to apply them as complete environment-friendly detergents for daily usage.