Glass Transitions: Opportunities and Challenges

Abstract

Glass transition is a time-dependent change in the state of a noncrystalline material. It often explains solid–liquid transformations in foods and it may control changes in food structure and texture as well as chemical reactions. At temperatures around the glass transition, an amorphous solid transforms to a supercooled liquid (rubber) which contributes to changes in molecular mobility and flow properties of food materials. These glass-transition-related changes can also be observed from changes in dielectric and mechanical properties of food solids around the glass transition. Changes at the glass transition affect food quality by contributing, for example, to stickiness and caking of powders, collapse of freeze-dried structures, crispness of extruded snack foods, crystallization of sugars, and ice recrystallization in frozen foods. Glass transition measurements have been useful for applications in the control of process and storage conditions of foods and they have contributed to product development and improvements of food quality. Understanding of the glass transition behavior of food components and materials provides numerous opportunities and challenges to the food industry and research.