Water content, water activity, water structure and the stability of foodstuffs

Determination of water content, whatever the accuracy of the analytical method, is not sufficiently informative in relation to the stability of the investigated food product. Water activity (aw) brings a supplement of information as it accounts for the availability of water for degradation reactions. The understanding of why certain products are more stable than others at the same aw needs an elucidation of water structure. Of particular importance are the interactions (hydrophilic, hydrophobic) between water and the components of the foodstuff and the effect of the soluble molecules of the food on the hydrogen bonding in solvent water. Studying water in foods should start with an anlytical determination of water content for commercial and legal reasons which are evident. This has to be completed with the measurement of the thermodynamic activity of water in the food. Such a parameter (aw) should hold an important place in the identification of the food product, especially as regards its shelf life. A further step in unveiling the behaviour of water in foods consists in determining water molecules in the molecules in the studied food matrix. The tripartite (analytical, thermodynamical and structural) approach to water in foods will be examined based on examples of sugars and sugar rich products.