Glass Transition and Sticky Point Temperatures of Food Powders and its Relationship with Moisture Content and Water Activity

Abstract

Food powders are convenience foods and they have long storage life at ordinary temperature. The principle components of food powders are carbohydrate and its derivatives, protein, organic acids etc. Among that carbohydrate and its derivatives and organic acids have the largest effect in influencing sticky nature of the dried powders. These components have low glass transition temperature, Tg, and are very hygroscopic at their amorphous state. As they depress the Tg, the dry product becomes sticky. Due to less residence time during spray and vacuum drying, the solutes like sugars and acids present in the food become amorphous. 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, drying aids having high Tg value, such as isolated protein, maltodextrin, food grade anti caking agents can be added. The relationship between Tg and aw provides a simple method for prediction of safe storage temperature at different relative humidity environment. Food powders namely, mango, pineapple and tomato powders were produced by mixing with maltodextrin, glycerol monostearate and tri calcium phosphate at predetermined levels and dried using vacuum drying method. Completely dried mango, pineapple and tomato powders at 3-4% (wb) moisture were produced. The relationship among Tg, moisture content and water activity of the three powders was developed to find out the safe storage conditions. Also the comparison between glass transition and sticky point temperatures was made for the above stated powders.