抄録
Water-soluble carbohydrates commonly exist in an amorphous state in foods and undergo glass-rubber transition (glass transition) at the glass transition temperature (Tg). The critical water content (Wc) and critical water activity (awc) are the water content and water activity (aw) at which the glass transition occurs at 298 K (typical ambient temperature), respectively. For amorphous water-soluble carbohydrates, Wc can be predicted from the Tg of anhydrous solid (Tgs) using previously reported equations. However, an approach for predicting awc is still lacking. This study aimed to establish an awc-predictive approach for amorphous water-soluble carbohydrates based on Tgs. 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 Tgs on the GAB parameters (C, K, and Wm) was evaluated using the Tgs values reported in previous literatures. C and Wm decreased and increased logarithmically, respectively, with increasing 1/Tgs. K was fixed to 1 (constant), as it showed little variation. These results enabled the prediction of the GAB parameters from Tgs. The GAB model could then predict awc from Wc, which was determined using the previously established equations. The predicted awc values were in good agreement with the experimentally determined awc. Additionally, we demonstrated that this awc-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.
