Water sorption and glass-to-rubber transition of amorphous sugar matrices, vacuum foam- and spray-dried from alcohols

The objective of this study is to understand the impact of preparation conditions on the physicochemical characteristics of amorphous sugar. Amorphous sugar (α-maltose, isomaltulose, trehalose) matrices were prepared from alcohol (methanol, ethanol) solutions, and their water sorption behavior and glass transition temperatures, T_g, were compared with those of aqueous freeze-dried amorphous sugar. Vacuum-foam- and spray-drying procedures were employed as drying methods. Water sorption for amorphous sugars, dried by different methods, was generally significant in the following order: vacuum-foam-drying < spray-drying ≤ freeze-drying. In the same order, the T_g values for the thoroughly dried amorphous sugars increased, and water sorption reduced the differences in T_g for given amounts of sorbed water. The solvent type in vacuum-foam-drying slightly affected the water sorption and the dependence of T_g on the sorbed water amount. The obtained findings suggested that physicochemical characteristics of amorphous sugar may relate to the sugar molecule conformations in solvent and dried state.