Protein Gels

Gels are largely differentiated from other systems in which small proportions of solid are dispersed in relatively large proportions of liquid by the property of mechanical rigidity or the ability to support shearing stress at rest. Rigidity is considered the characteristic property common to all gels. It can be accompanied by viscous retardation, which delays the response to stress. Attempts to explain the fact that a gel, which consists mostly of fluid, behaves as a rigid solid, and yet retains many properties characteristic of the fluid component, have resulted in many contributions to the colloid chemical literature and numerous hypotheses concerning the nature of gel structure. This chapter describes gels in which the solid component is protein, and the liquid component is usually water or an aqueous solution. It also describes gels with long-range forces, network gels and their properties, gelatin gels and their properties, and gels of denatured proteins. Some theories applicable to certain gel systems, such as immobilization of solvent by adsorption, are also presented.