Water Sorption Glass Transition 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 Tg 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 Tg by the addition of large-sized additives was significant at the additive contents > 50 wt.% whereas the Tg 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 Tg with increasing water content. The protein stabilizing effect was decreased with increasing additive content in the cases of the both groups of the additives.