Frozen state transitions in relation to freeze drying

摘要: Freeze-drying is used as a gentle dehydration method for heat sensitive materials especially in food and pharmaceutical industries. Most materials, including dissolved sugars water, do not crystallise during freezing prior to freeze-drying. Supersaturated, freeze-concentrated solutions are amorphous they solidify into glassy state when their temperature depressed below the glass transition temperature,T g. Differential scanning calorimetry has been show that maximally sugar solutions, properly frozen, heating transition,T g ′ , which followed by ice melting endotherm with onset atT m . Low molecular weight difficult freeze-dry have lowT andT slightly above T High such carbohydrate polymers, exhibit improved characteristics have and at about same close point of pure water. The amorphous, structure typical freeze-dried formed prefreezing retained after removal unfrozen water from material. Dehydration temperatures belowT allow within solid, solutes, but aboveT result collapse. frozen transitions properties can be shown diagrams derive proper freeze-drying conditions storage requirements various materials.