Glass Transitions: Opportunities and Challenges

摘要

Glass transition is a well-known transformation of the solid-fluid states of noncrystalline solids and liquids. In food systems the glass transition is often a property of carbohydrates and proteins, as observed in numerous food materials (White and Cakebread 1966; Slade and Levine 1995). Glass transition results in various physicochemical and thermal phenomena associated with the solid-liquid transformation of a supercooled liquid. A number of noncrystalline polymers, as well as sugar melts, exhibit glass transition at approximately 100-150°C below their equilibrium melting temperature (Roos 1993). The glass transition of low water and frozen foods has been recognized as one of the most important factors affecting food properties, processing characteristics, and shelf life (Roos 1995a). Glass transition contributes to numerous engineering properties of foods, their structure and texture, and reaction kinetics. It is also useful in understanding sensory properties, including hardness, crispiness, softness, and flavor release (Slade and Levine 1995; Roos 1995a; Roudaut et al. 2004). Knowledge of molecular mobility and changes in mechanical and physical properties over the glass transition can be used to control the characteristics of food solids, for example, in drying, freeze-drying, freezing, and extrusion. An overview of the importance of the glass transition in food engineering, including selected food systems and processes, as well as challenges in using glass transition data in the control of food properties, food processing, and storage stability, will be highlighted in this review.