Water Sorption Isotherm and Critical Water Activity of Amorphous Water-Soluble Carbohydrates Characterized by the Glass Transition Temperature.

Water-soluble carbohydrates commonly exist in an amorphous state in foods and undergo glass-rubber transition (glass transition) at the glass transition temperature (). The critical water content () and critical water activity () are the water content and water activity () at which the glass transition occurs at 298 K (typical ambient temperature), respectively. For amorphous water-soluble carbohydrates, can be predicted from the of anhydrous solid () using previously reported equations. However, an approach for predicting is still lacking. This study aimed to establish an -predictive approach for amorphous water-soluble carbohydrates based on . First, the water sorption isotherms of four hydrogenated starch hydrolysates were investigated, and the results were analyzed using the Guggenheim-Anderson-de Boer (GAB) model. Second, the effect of on the GAB parameters (, , and ) was evaluated using the values reported in previous literatures. and decreased and increased logarithmically, respectively, with increasing 1/. was fixed to 1 (constant), as it showed little variation. These results enabled the prediction of the GAB parameters from . The GAB model could then predict from , which was determined using the previously established equations. The predicted values were in good agreement with the experimentally determined . Additionally, we demonstrated that this -prediction approach is also applicable to amorphous water-soluble electrolytes and partially water-insoluble carbohydrates. Thus, this approach can be used for the quality control of amorphous water-soluble carbohydrates and carbohydrate-based foods.