Implication of glass transition for the drying and stability of dried foods

Dry products obtained from most of the common drying processes are predominantly in a glassy amorphous form. The mobility of the solid matrix in this state is highly limited. For the product to be stable for long periods of storage, this physical state should not alter with time. When the temperature is above glass transition temperature (T-g) an amorphous solid exists in a rubbery state. In this state, the molecular mobility of the matrix and the reactants are accelerated, which results in an increased rate of physicochemical changes in dried products, such as sticking, collapse, caking, agglomeration, crystallisation, loss of volatiles, browning and oxidation. These changes play an important role in the ability to both process and store dried food products. This paper reviews the importance of T-g in relation to drying process and dried foods. (C) 1999 Elsevier Science Ltd. All rights reserved