Kinds of Water

Foods contain different kinds of water. It’s important to note that there is a difference between free water and bound water:

1. Free water behaves physic – chemically as pure water. It is bulk water (about 96%).

2. Bound water can be further differentiated depending on the strength of its interaction with the food matrix

a. Constitutional water: it is part of the molecular structure of non water molecules in the food. It is very strongly bound to the food matrix, so strongly bound (to charged particles) that it is not available water. Typically we see these constitutional water in macromolecules like biopolimers, polisacharides and proteins. No solvent capacities. Very large evaporation enthalpy.

b. Vicinal water: mostly bound through hydrogen bonds and polar non charged molecules. It can be present (entraped) in the capillaries of the food matrix. It is able to hydrate complex food molecules forming monomolecular layer, hence de name Monolayer water. Monolayer water: it is formed by one water molecule layer around the food matrix (very strongly bound, strong interaction with food matrix).   These types of water have very reduced availability. No solvent capacities. Large evaporation enthalpy.

c. Multilayer:  It is an expanding hydration layer formed of several water layers  constituted through the attraction  between water molecules via hydrogen bonds. It is a transition zone towards free water and it can start behaving as a solvent, despite its lower availability.   Moderate to little evaporation enthalpy