Water sorption, glass transition, and protein-stabilizing behavior of an amorphous sucrose matrix combined with various materials

The effects of various additives on the physical properties of an amorphous sugar matrix were compared. Amorphous, sugar-additive mixtures were prepared by freeze-drying and then rehumidified at given RHs. Sucrose and eighteen types of substances were used as the sugar and the additive, respectively, and water sorption, glass-to-rubber transition, and protein stabilization during freeze-drying for the various sucrose-additive mixtures were examined. The additives were categorized into two groups according to their effects on T_g and water sorption. Presence of polysaccharides, cyclodextrins, and polymers (large-sized additives) resulted in a decrease in equilibrium water content from the ideal value calculated from individual water contents for sucrose and additive, and in contrast, low MW substances containing ionizable groups (small-ionized additives) resulted in an increase. The increase in T_g by the addition of large-sized additives was significant at the additive contents >50 wt.% whereas the T_g was markedly increased in the lower additive content by the addition of small-ionized additives. The addition of small-ionized additives enhanced the decrease in T_g with increasing water content. The protein stabilizing effect was decreased with increasing additive content in the cases of the both groups of the additives.