Glass Transition and Sticky Point Temperatures and Stability/Mobility Diagram of Fruit Powders

Principal components present in fruits are low molecular weight sugars and some organic acids. They have low glass transition temperature (T(g)) and are very hygroscopic in their amorphous state, so the dry product becomes sticky. Water acts as a plasticizer and decreases the glass transition temperature of the product with the increase in moisture content and water activity. To overcome this problem, ingredients having high T(g) value, such as maltodextrin, and food grade anti-caking agents were added to prepare vacuum dried fruit powders. The relationship between T(g) and a(w) provides a simple method for prediction of safe storage temperature at different relative humidities environment. Food powders namely, mango, pineapple, and tomato (3-4% w.b moisture content) were produced by mixing with maltodextrin and tri calcium phosphate at predetermined levels before drying. The relationship among glass transition temperature (T(g)), sticky point temperature (T(s)), moisture content and water activity of the three powders was represented in a stability/mobility diagram to find out safe storage conditions. Glass transition temperature of the fruit powders were interpreted in terms of the Gordon-Taylor model for verification. Glass transition and sticky point temperatures were compared by plotting them in a graph against moisture content.