Effect of Glass Transition Temperature Range on the Caking Behavior of Freeze-dried Carbohydrate Blend Powders.

Glass transition temperature (T_g) and degree of caking for maltodextrin with added plasticizers (glucose, maltose, and sorbitol) were investigated. Onset and offset T_gs were evaluated by differential scanning calorimetry. From the onset and offset T_g-curves and water sorption isotherm, each critical water activity (a_wc) value was determined (water activity at each T_g = 25 °C). The a_wc range between onset T_g and offset T_g was extended by the addition of plasticizers. The degree of caking increased at a water activity just above a_wc of onset T_g, and completely caked at a water activity just below a_wc of offset T_g. Effect of a_w on the degree of caking became more gradual with the addition of plasticizers because of the extended a_wc range. According to the dependence of viscosity on temperature and water activity, a predictive model for the caking of amorphous powders was proposed based on the onset and offset T_g curves. [ABSTRACT FROM AUTHOR]