Thermal characterization and phase behavior of cornstarch studied by differential scanning calorimetry

A cornstarch-water system was characterized by differential scanning calorimetry (DSC). Glass transition and melting transitions of starch crystals and amylose-lipid complexes were observed in native cornstarch with moisture content (MC) between 11.9% and 24%. At medium to high MC levels, the glass transition was not detectable, but melting of ice and gelatinization of starch (G endotherm) were observed. The gelatinized cornstarch was completely amorphous and retrogradation was not observed under the experimental conditions. As expected, phase behavior and thermal properties of cornstarch-water system were significantly dependent on water content, composition, and gelatinization. The gelatinized cornstarch had higher glass transition temperature than the native cornstarch. Nonfreezing water of starch increased as MC increased and leveled off at 29.5% MC. The gelatinized cornstarch had less nonfreezing water at low MC and had more nonfreezing water at high MC compared to the native cornstarch. Water in the system was thought to exist in three forms: bound water, loosely bound water, and free water, all of which were MC dependent. State diagrams for the native and gelatinized cornstarch were configured out of the data obtained in this study.