7
Proteins
Proteins are polymers, more specifically polyelectrolytes, which are
discussed in Chapter 6. However, proteins were hardly considered in that
chapter because they are highly specific and intricate molecules. They are
built of 20 different monomers, with side groups of different reactivity.
Proteins evolved to fulfil a wide range of highly specific physiological
functions, and each protein has a specific composition and conformation.
Every protein species is unique; the number of species occurring in nature is
presumably far over 10^10. Chemical reactivity is at least as important as
physical chemistry for protein properties in general and for many problems
related to proteins in foods. Despite these qualifications, some important
physicochemical rules can be derived, and this is the subject of this chapter.
Proteins play many roles in foods, the most important one being
nutritional. Another one is flavor binding, and so is flavor formation during
processing and storage. The activities of the proteins called enzymes are of
obvious importance. Two main groups of physicochemical functional
properties of proteins can be distinguished:
- Their role in formation and stabilizing of emulsions and foams,
and in stabilizing suspensions. These functions depend on the propensity of
proteins to adsorb at most interfaces. These aspects are discussed in
Chapters 10–13.