Effect of bound water on thermal behaviors of native starch, amylose and amylopectin

Thermal behavior of dry native starch, amylose and amylopectin originating from different plants was investigated using Thermogravimetry (TG) and Diff erential Scanning Calorimetry (DSC). The decomposition temperature increase d as the molecular weight increased and a sudden increase was observed at a molecular weight of 50,000 that can be the critical value. DSC analyses ve rified that the amorphous phase in the specimens was swollen by bound water within a temperature range of 323-428 K. The change in swelling enthalpy d ivided by the peak temperature of swelling depended linearly on the Volume fraction of bound water, regardless of the origin and the composition or pu rity of the specimens. Furthermore, bound water depressed the melting point s of crystallites in the specimens, which agreed well with the prediction o f Flory's lattice theory.