ABSTRACT
Chemical kinetics is generally discussed with respect to reactions between molecules (or ions or radicals) in a gas phase or in a very dilute solution. In foods, we often have other situations. The system never is gaseous, it is rarely very dilute, and it may have more than one phase containing reactants. Changes may occur within molecules, especially macromolecules. Reactions may be between particles, causing, for instance, their aggregation. Numerous other changes may occur, such as phase transitions, leading to a change in rheological properties, color, or other perceptible property. In nearly all such cases we are greatly interested in the rate at which these processes occur. This we cannot derive from the bond energies involved or from other thermodynamic considerations: these may tell us what the driving force is, but in general the rate results from a driving force divided by a resistance, and the resistance may be very large or highly variable.
