Crystallization of Water in the Xanthan-Water System

Isothermal crystallization of water in polysaccharide hydrogels was measured by dif ferential scanning calorimetry (DSC). The melting temperature ( Tm ₁ ) of ice depended on the crystal lization temperature (Tc) for freezing bound water, which was restrained by hydrogels. However, the Tm ₁ of free water and pure water were constant regardless of Tc. These facts suggested that freezing bound water formed metastable ice. The nucleation rates of pure water, free water and freezing bound water were almost the same in the temperature range examined. Pure water showed the high est rate of crystal growth. The crystal growth rate decreased in the following order: pure water > free water > freezing bound water. The average surface free energy of ice was estimated from the rate of crystal growth. The estimated values of surface free energy of ice from freezing bound water were lower than that of ice from pure water. The results suggested that not only water molecules, but also polysaccharide molecules and ions existed on the surface of ice formed in the hydrogels.