The nature of nonfreezing water in carbohydrate polymers

•A thermodynamic analysis of nonfreezing water in carbohydrate polymers is presented.•The amount of nonfreezing water is not related to the amount of “bound” water.•The glass transition interferes with the cooling process and prevents crystallization.

In an aqueous environment, carbohydrate polymers are surrounded by hydration shells consisting of water molecules that are sometimes called “bound”. When polymer solutions are subjected to low temperatures, a part of water turns into ice, another part remains in the biopolymer phase and is called “nonfreezing water”. Thermodynamic analysis of water freezing shows that the amount of non-freezing water does not reflect the amount of bound water, neither can it be used as a measure of strength of polymer-water interactions. Upon deep cooling, crystallization of water should desiccate polymers more than is observed in experiment. The reason for existence of non-freezing water is an interplay between the crystallization of water and the glass transition in biopolymers that prevents dehydration.