Glass Transition and Water Activity of Freeze-Dried Shark

Glass transition temperatures and water activity as a function of moisture content were determined for freeze-dried shark to further compare the two distinct criteria of food stability. The adsorption experiments were carried out at controlled water activity, at 21, 40, and 50°C using an isopiestic method and they were modeled using BET and GAB equations. Glass transition temperatures were measured by dynamic oscillation on shear. Results indicate that there is a difference in the temperature-related stability criteria predicted by the concepts of water activity (a w ) and the glass phenomenon (T g ). The glass transition concept tends to accommodate higher levels of moisture within the framework of a safe storage of a dried product.