The plasticizing effect of water on proteins, polysaccharides and their mixtures. Glassy state of biopolymers, food and seeds

The additive group-contribution technique can be used to predict the glass transition temperature of biopolymers, and of their mixtures with each other and with water. This method, together with the plasticization mechanism of biopolymers by water (based on shielding intra- and inter-macromolecular hydrogen bonds and dipole-dipole interactions), was applied to obtain an equation for the glass transition temperature vs. food system composition. The analytical expression obtained was used for the calculation of plasticization functions, i.e. the glass transition temperature water concentration dependence. for 13 proteins, polysaccharides and their mixtures. The data calculated are in agreement with the experimental data published by a number of laboratories. The proposed plasticization function increases the accuracy of the predicted T-g values compared to other equations such as those of Gordon-Taylor and Couchman-Karasz. The glassy state is of importance for mechanical and other physical properties, and physical stability of dry, instant food and drinks and for the long-term storage viability of seeds. Some potential applications of the glass transition phenomenon to food and grain processing are considered. (C) 2000 Elsevier Science Ltd. All rights reserved.