Relationship between enthalpy relaxation and water sorption of ball-milled potato starch

This study reports on the enthalpy relaxation and water sorption behaviors of ball-milled potato starch. Ball milling converts the semi-crystalline state of starch to an amorphous state, and a prolonged procedure promotes enthalpy relaxation. It has been reported that prolonged treatment leads to a decrease in starch water sorption. In the present study, ball milling of potato starch was carried out for up to 90 h. The relaxed enthalpies and water sorption isotherms were measured by differential scanning calorimetry and equilibrium sorption of water vapor. Enthalpy was found to increase and water sorption to decrease with milling time. The time-dependant increase in enthalpy was found to follow the Kohlrausch-Williams-Watts (KWW) equation. The sorption isotherms were analyzed with a dual-mode sorption model and the concentration, C'(H), of Langmuir type sorption sites was found to decrease with time. This decrease was also found to follow the KWW equation. Moreover, a linear relationship was found between the decrease in C'(H) and the increase in enthalpy. (C) 2010 Elsevier Ltd. All rights reserved.