Mathematical model for prediction of glass transition temperature of fruit powders

Glass transition temperature (Tg) has been identified as a critical factor to predict quality of foodstuffs during processing or storage. Differential Scanning Calorimetry (DSC) was used to determine the Tg of 4 types of berry powders as a function of water content, and equilibrium moisture content was measured over different saturated solutions using the gravimetric method. The Guggenheim-Anderson-deBoer model was used to predict water activity (a(w)). Four models were tested for their ability to predict Tg as a function of the solid fraction. The combined effects of Tg and a(w) were incorporated into a new mathematical expression. The expression requires the determination of Tg (dry solids) of the product and data on equilibrium moisture sorption. The mean percent error of the model predictions is less than 3.6% when compared to experimental data.