Developments in glass transition determination in foods using moisture sorption isotherms

The food polymer science (FPS) approach has been effectively used to investigate the physical stability of amorphous food materials. The glass transition, a key FPS parameter, has traditionally been determined using thermal techniques that scan temperature while holding the plasticizer (moisture) content constant. Moisture sorption isotherms provide information about the physical properties of food as the plasticizer level is adjusted and temperature is held constant. New automatic isotherm generators can be used to produce high resolution, dynamic isotherms much faster than traditional static methods. Dynamic isotherms for a small selection of amorphous materials have been investigated and shown to experience distinct inflection points in the water activity region where the glass transition temperature is close to the experimental temperature. Several studies on amorphous spray dried milk powder and amorphous polydextrose indicate very good agreement between glass transitions determined using thermal techniques and dynamic isotherm methods. This agreement suggests that dynamic isotherms are a viable alternative to traditional thermal methods for investigating glass transitions of amorphous foods.