Thermal Analysis Toward Freeze-Drying Cycle Optimization

In an ideal freeze-drying cycle, it is important that the temperature of the product be less than the glass transition temperature since the latter temperature determines the point at which structural collapse occurs. Given the well-known function of water as a plasticizer, the effects of the water content in a product on its glass transition temperature can be exploited to optimize the freeze-drying cycle time. This work reviews the development of freeze-drying cycles for model systems containing sucrose and sodium chloride with varying water contents. The glass transition temperatures of the model systems were determined by differential scanning calorimetry and used to determine parameters for decreasing the time of the primary drying stage of the freeze-drying cycle. The application of this approach to non-thermal drying of food systems will be discussed.