ABSTRACT
The basic theme of this chapter, and indeed of the book, is how we can apply basic knowledge about chemical kinetics and chemical thermodynamics to foods. However, foods are very complex in terms of composition as well as structure. It may happen that the presence of, for instance, a sugar has an effect on the kinetics of the reaction of a totally different compound, say hydrolysis of an ester, without the sugar taking part in that reaction. Another example is that the denaturation temperature of proteins may be significantly raised by the mere presence of other macromolecular compounds. Yet another example is that kinetics of reactions of charged molecules depend on the presence and valencies of other ions. All this may seem surprising and unexpected at first sight and the question arises how this is possible. As we have seen in Chapter 3, whether or not a component will react depends on its chemical potential. Chemical kinetics equations, as shown in Chapter 4, have been derived based upon the law of mass action, which describes rates of reactions as particular functions of the concentration of reactants. Obviously, reactants will have to come together before they can react, as is also briefly discussed in Chapter 4. If a reaction is thermodynamically favorable and reactants can meet, there may be an activation barrier that prevents the reaction from happening, as discussed in Chapter 5. Thus, previous chapters have shown the basic concepts needed to describe the tendency of chemical and physical systems, including foods, to approach thermodynamic equilibrium in terms of thermodynamics and reaction kinetics. Figure 14.1 shows this sequence in a highly schematic way.
