The Physical State of Water in Foods

Abstract

Foods are characterised by their heterogeneous nature, typically they contain many components, more than one phase and spatial heterogeneity on a variety of scales. A further complication is that almost all foods are unstable chemically and physically and are thus highly time dependent in their properties. A good example is a loaf of bread (Fig. 1.1); the major components are wheat flour and water; minor components are sodium chloride, air, sugar, and possibly alcohol from fermentation; there will also be yeast cells in various states of decomposition and damage. The yeast is a highly complex and organised system, it is not however a major component. The chemically most complex major component is flour. This contains gluten and other proteins, starch, lipids and other polysaccharides, each one of these components is itself chemically heterogeneous. The air, although a small component by weight, plays a major role in determining the size and shape of the loaf and is responsible for the foam structure of the crumb.