The role of water in food quality decay

The impact of water on food thermodynamics and physics, and therefore on its quality, is more important than any other food chemical component. When fundamentals of chemical kinetics apply, the rates of the reactions that are responsible of food quality decay can be described as a function of food composition and of other external elements interacting with foods. Among them, water activity and water content have been widely used to determine the role of water in the kinetic reactions of deterioration. Recently, researchers have found limitations in using the water activity parameter. According to them, the role of water in foods can be better described by evaluating the role in the stability of the quality attributes of the non-equilibrium states of amorphous food products. Following this approach, the dynamics of the changes are described in kinetics terms and can be efficiently better predicted by the glass transition temperature more than by the water activity. The glass transition, which is a second order transition in amorphous materials from the glassy to the rubbery state, is primarily dependent on water which is a plasticizer and is responsible for the physical state of multiphase systems (as foods are) together with the temperature. The subject of the role of water in the decay of food quality will be presented in this paper according to the principles of food material science.