The mechanism of amylose leaching from native and heat-treated starches in hot excess water

Abstract

In order to determine the optimizing parameters of the process of hydrothermal leaching of amylose, kinetic studies were carried out under isothermal conditions. Native (potato and corn) and heat-treated starches were used in the experiments. The obtained kinetic data are described by the Kruger-Ziegler equation. It is shown that in the temperature range of 60–700C, the apparent activation energy is 193 kJ mol–1 and 43–83 kJ mol–1 for native and heat-treated starches, respectively. With a further increase in the temperature, the activation energy decreases to 22 kJ mol–1 and 13–14 kJ mol–1 for native and modified starches, respectively. It is proposed to consider amylose leaching as a heterogeneous pseudochemical process, in which the process of breaking numerous hydrogen bonds between amylose macromolecules acts as a chemical reaction. From this point of view, the change in activation energy with increasing temperature is explained by the transition of the leaching process from the kinetic to the diffusion mode. Changes in the activation energies of modified starches are explained by a decrease in the number of hydrogen bonds between amylose macromolecules due to a decrease in their degree of linearity and size during thermal conversion. Changes in the structure of starch during their heating were investigated by the DTA method. The values of the apparent activation energy for two stages were determined as follows: 44 kJ mol–1 and ~26 kJ mol–1 for molecular dehydration and intermolecular dehydration of native starch, respectively, which indicates that both processes occur in the kinetic mode. Considering amylose leaching as a heterogeneous pseudochemical process shows that the main optimizing factors are temperature and starch pre-milling.