Water and the Glass Transition — Dependence of the Glass Transition on Composition and Chemical Structure: Special Implications for Flour Functionality in Cookie Baking

Abstract

What is a glass? What is a glass transition? Why is the temperature at which a glass transition occurs (Tg) so important to the processing and storage stability of so many different types of foods? Why is the effect of water as a plasticizer on Tg of such widespread relevance to food products and processes? Why are considerations of non-equilibrium glassy solid and rubbery liquid states in foods, rather than equilibrium phases, more germane to issues of food quality and safety? Why are the kinetics of heat/moisture processes for foods and of deteriorative changes in food systems during storage more of ten appropriately interpreted in terms of the Williams-Landel-Ferry (WLF), rather than the Arrhenius, equation? What is the “food polymer science” approach, with its central concepts of ‘glass dynamics‚ and ‘water dynamics‚, and why has this research approach proved so useful to the study of glasses and glass transitions in foods? And why has there been, since the early 1980s, such interest in these questions, and such increasing research activity, especially in the last few years, in this area of food science and technology? These are the questions addressed in this paper.