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, Tg, 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 Tg values for the thoroughly dried amorphous sugars increased, and water sorption reduced the differences in Tg for given amounts of sorbed water. The solvent type in vacuum-foam-drying slightly affected the water sorption and the dependence of Tg 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.