Model-based prediction of the moisture sorption kinetics and humidity-induced collapse for freeze–dried cakes

Abstract

Freeze–drying produces highly hygroscopic porous materials derived from ice microstructures. Because of this feature, moisture sorption over time during storage in contact with moist air, in the worst case, induces collapse. In this study, a mathematical model of the moisture sorption kinetics applicable to glassy freeze–dried matrices is developed. The model is based on the glass transition properties and sorption equilibrium data with a sorption rate constant, which includes the specific surface area of the freeze–dried cake. The glass transition lines and moisture sorption isotherms of dextrins are experimentally obtained and applied to predict the durations before the humidity-induced collapse in the range of 0–24 h. The impacts of the combinations of the temperature and relative humidity (20–40 °C, 40–100%) are successfully visualized in stability maps. The proposed mathematical model can be a robust tool for guiding favorable formulations to produce stable freeze–dried products against storage.