ABSTRACT
The presence of charged particles can have large implications for the systems in which these particles are present, and this is certainly also true for foods. Foods contain dissociated salts, acids, and bases; biopolymers such as proteins and polysaccharides carry charge as well, depending on pH. Reactions between charged particles depend on a particular way on the charge but also on the properties of the medium in which they are present. Many fundamental investigations have been carried out in the first half of the twentieth century by famous scientists. It is essential to understand the behavior of ions to understand properties of foods, and this includes
kinetics where ions can exert a major effect. The activity concept is indispensable to understand the behavior of ions, so that is what we start with. Thus, the present chapter builds further upon the activity concept introduced in Chapter 3. After discussing the sometimes peculiar aspects of ion activities, we will take a look at the consequences for kinetics between charged particles.
