Dispersions

Abstract

A central theme to this book has been the formation of multiple phases within foods. We have seen how mismatched intermolecular interactions can lead to phase separation (Chaps. 4 and 7), how the properties of phase separated systems depend on the interface (Chap. 5), and even considered crystallization as an example of phase separation (Chap. 6). In this chapter the focus is on the properties of dispersions.

Foods that are fine dispersions of one or more phases in another phase share some common properties regardless of what the phases are and can be helpfully considered as a group. Importantly, we are interested in small particles with at least one dimension larger than the molecular scale but not so large that the particle constitutes a distinct macroscopic object. Thus, while an ice cube in a drink falls outside our discussion, we can expect dispersions of fine ice crystals in a sorbet or bubbles in soda or oil droplets in mayonnaise to have some properties in common. Philosophically we are still trying to understand the properties of a whole system using knowledge of the interactions of its component parts, but to do so we are moving from the study of the molecular scale (~ 10⁻¹⁰–10⁻⁹ m) to the study of mesoscopic or colloidal scale assemblies of molecules (~ 10⁻⁸–10⁻⁵ m).