Hydration and the phase diagram of acid hydrolyzed potato starch.

We investigated hydration of acid hydrolyzed potato starch (maltodextrin) employing a multi-method approach. In particular, synchrotron radiation X-ray scattering and differential scanning calorimetry were used, and, for the first time, the material was investigated with sorption calorimetry and a newly developed quartz crystal microbalance with humidity scanning. The dry starch was found to be in an amorphous state. During hydration it exhibits a glass transition in both bulk and thin film samples, followed by an exothermic event where the starch crystallized. Recrystallized bulk samples displayed neither a pronounced glass transition nor crystallization upon hydration whereas both events occurred in thin film samples. The hydration-driven crystallization resulted in an X-ray pattern consistent with the coexistence of A and B type crystallites; however, at higher water concentrations only the B form occurred. The results were used to construct the first ever acid hydrolyzed starch-water phase diagram.