Crystal Transformation from Anhydrous α-Maltose to Hydrous β-Maltose and from Anhydrous Trehalose to Hydrous Trehalose

Abstract

  Anhydrous sugars such as maltose and trehalose are useful for making dry powder of foods and liquids. The crystal-transformation rate of maltose and trehalose were investigated under humid conditions and by kneading. The enthalpy for solubilization was 7.0 kJ/mol for the anhydrous maltose. The crystal-transformation rate of anhydrous α-maltose to hydrous β-maltose depended on the temperature at 75% humidity. However, that of anhydrous trehalose did not depend on the temperature, and transformation was very rapid. An anomeric change to maltose and no such change to trehalose might have caused this. The activation energy of crystal transformation was 79 kJ/mol for maltose and zero for trehalose. The rate of crystal transformation of anhydrous maltose while kneading depended on the purity of the anhydrous α-maltose and the amount of water present. This crystal transformation rate fitted the Avrami equation.