Mixed State Diagrams of Rice Starch/glycerol/water Ternary Systems

Amorphous rice starch/glycerol/water ternary systems are used in food, cosmetics, and functional materials. In the present study, we investigated the water adsorption ability of crystalline and amorphous rice starches and the mixed state of rice starch/glycerol/water ternary systems. The effect of amorphization on the mixed state was evaluated with thermogravimetric analysis (TGA) and wide-angle X-ray diffraction measurement (XRD). When amorphous rice starch was mixed with water and glycerol (40-80 wt%), the funicular and capillary states were observed: the funicular state is a dry state where solid and liquid form a continuous phase, and the capillary state is a sticky state where only the liquid is the continuous phase. This was attributed to the greater number of free hydroxyl groups in amorphous rice starch, which enhanced its affinity to hydroxyl groups. Amorphous rice starch systems exhibited a water evaporation temperature 14 °C higher than crystalline rice starch systems. Furthermore, when the mixed system contained amorphous rice starch and glycerol, the funicular region was expanded. A glycerol molecule has three hydroxyl groups, which enhance the adhesive force between starch particles and increase viscosity. These findings are useful for designing formulations for various products utilizing mixtures of rice starch and glycerol.