Phase transitions of the starch–water system

Abstract When purified potato starch granules are heated in the presence of limited amounts of water (less than 1.5 H2O: starch, w/w), two endothermic transitions are observed by differential scanning calorimetry. The lower temperature endotherm is always observed at a fixed temperature, 66°C; it is the only endotherm observed when excess water is present. The higher temperature endotherm is observed at increasing temperatures as the water content is decreased. The size of this endotherm decreases with water content. The appearance of the higher temperature endotherm allows the determination of the stoichiometry for full hydration of starch, 14 H2O/hexose unit. The shift of the higher temperature endotherm is interpreted as the lowering of the melting point of starch crystallites by solvent water.