Water Sorption and Glass Transition Behavior of Polyalditol (PD30), a New Nonreactive Malto-Oligosaccharide Cryo- and Drying-Protectant

Abstract

Polyalditols are a new family of nonreactive polyols whose reducing power is reduced to <1% dextrose equivalent (DE) by catalytic hydrogenation of malto-oligosaccharides. This work investigated water sorption property and glass transition behavior of PD30, a polyalditol with an average molecular weight of ∼1000 Daltons and a DE value of <0.5. Properties of PD30 are compared with those of maltodextrin M180 (precursor of PD30), which has a DE of 16.5 to 19.5 and is used to make PD30. Water sorption properties were investigated by isothermal sorption and desorption methods. Sorption study showed that PD30 adsorbs less water than M180 at 22°C at relative humidity (RH) below 45%, but adsorbs more water at higher RH. The analysis with Guggenheim-Anderson-de Boer (GAB) model estimates the same monolayer hydration (∼0.05 g/g) for both M180 and PD30, but PD30 could adsorb more weakly bound water. Thermal desorption study showed that PD30 binds significantly less water than M180 at temperatures above 45°C. Glass transition temperature (Tg) of concentrated PD30 solutions was measured with differential scanning calorimetry. The Tg of PD30 is lower than that of M180 at the same solute concentration and upon equilibration to the same water activity, suggesting that water is a more effective plasticizer for PD30 than for M180. The onset Tg of the maximally freeze-concentrated PD30 aqueous solution (i.e., Tg′) is −24.5 ± 1.2°C, which is lower than that of M180 (−20.2 ± 0.7°C). Unfrozen water content in the freeze-concentrated PD30 solution is 0.33 g/g. The onset Tg′ is similarly depressed in the presence of NaCl for both M180 and PD30. We conclude that catalytic hydrogenation treatment of M180 alters water sorption property and glass transition behavior of PD30, which will have significant implications in drying process development and product stability.