CHARACTERIZATION OF FOOD POLYMERS USING STATE DIAGRAMS

Food polymers often exist in an amorphous nonequilibrium state, which is formed in processes in which temperature is decreased below melting point or water is removed by evaporation or by ice formation. Amorphous materials have a glass transition temperature (T(g)) below which they are in a glassy state. Above T(g), they exist as liquid-like 'rubbers'. Most food polymers are thermoplastic and subject to water plasticization. Above T(g), various properties of the materials are changed. The most important changes are an exponential increase of molecular mobility and decrease of viscosity, which govern time-dependent structural transformations such as stickness and collapse in food processing and storage. Above T(g), molecular mobility improves diffusion, which affects crystallization, reaction rates, and food deterioration. At low temperatures the physical state is important to frozen food stability. T(g) values can be used to establish state diagrams, which describe the effect of composition on stability and show temperature and moisture effects on viscosity, structure, and crystallization. State diagrams may also show the formation of the amorphous state and describe various temperature-, moisture-, and time-dependent phenomena.