Noncrystalline, freeze-concentrated structures are formed during food freezing. Such freeze-concentrated food materials often exhibit crystallization and recrystallization phenomena which can be related to the state of solutes and water. State diagrams are important tools in mapping the physical state and time-dependent properties of frozen materials at various storage temperatures. Transition of simple solutions, such as sucrose, can be used to describe vitrification and ice melting in freeze-concentrated materials. A maximally freeze-concentrated material often shows glass transition at Tg'. Ice melting occurs at temperatures above Tm' These transitions at temperatures above Tm' can be used to estimate crystallization and recrystallization phenomena and their rates in frozen foods. Furthermore, frozen food deterioration accelerates above Tm' and particularly as a result of temperature fluctuations during frozen food distribution and storage.
Keywords: crystallization; food quality; freezing; glass transition; state diagrams.