The effect of heat treatment of starch on its crystal structure and dynamic viscosity of starch pastes

Abstract

Analysis of literature data shows the uncertainty of a number of issues of the starch dextrinization process, namely the patterns of the change in the crystal structure of starch during heat treatment and the dependence of the viscosity of starch pastes of dextrins on the conditions of starch heat treatment. These questions were chosen as the topic of this study. A decrease in the average size of starch particles by 2.7 m and an increase in the intensity of reflexes of diffractograms in the range of 2=10–200 after its heat treatment at 1350C (the temperature at which the dextrinization process starts) are well explained by dehydration and a change in the degree of crystallization of biopolymer macromolecules due to their thermal transformations. The dependence of the dynamic viscosity of hot pastes on their shear rate was studied. The steady shear flow curves showed the presence of dilatant areas as a transition from the Newtonian flow regime to the pseudoplastic flow of starch pastes. It was found that the viscosities of heat-treated starch pastes depend on the processing conditions; the viscosities increase in the following order: starch heat-treated in the presence of an acid catalyst; native starch; starch heat-treated without a catalyst for 5 hours; and starch heat-treated without a catalyst for 2.5 hours. It was proposed to divide dextrins into two separate groups: with an increased and with a reduced degree of amylose polymerization.