ABSTRACT
Water activity depressing power of solutes need to be considered when selecting ingredients or additives for food product formulation. Water activity can be lowered or controlled by several methods, such as separating water, and/or adding solutes. The moisture sorption isotherm is the relationship of moisture content with the water activity of a food at a specified temperature. The water activity shift by temperature is mainly due to the change in water binding, dissociation of water, physical state of water, or an increase in the solubility of solute in water. Water sorption can be influenced by the surface area and porosity of the food material. Protein and starches adsorb much more water at low water activity than do fatty materials or crystalline substances like sugar. Gabriel developed the water activity of glucose syrup as a function of pH and degrees Brix using a second-order polynomial equation.
