Protein/Emulsifier interactions

Abstract

Many food emulsions are more complex than a simple colloidal dispersion of liquid droplets in another liquid phase. This is mainly because the dispersed phase is partially solidified or the continuous phase may contain crystalline material, as in ice cream. However, one characteristic that all emulsions have in common is that they are (thermodynamically) unstable. The four main mechanisms that can be identified in the process of breaking down an emulsion are creaming, flocculation, coalescence, and Ostwald ripening. There are two ways in which the process of breakdown of an emulsion can be influenced. First, use of mechanical devices to control the size of the dispersion droplets and second, the addition of stabilizing chemical additives like low molecular weight emulsifiers or polymers to keep it dispersed. The main purpose of the latter is to prevent the emulsion droplets flocculating and from fusing together (coalescence), often achieved by repulsive droplet/droplet interactions. These interparticle interactions are determined mainly by the droplet surface, which is coated with emulsifiers, often surface-active components of biological origin like proteins, mono-and diglycerides, fatty acids, or phospholipids. The forces most commonly observed are electrostatic double layer, van der Waals, hydration, hydrophobic, and steric forces. They are responsible for many emulsion properties including their stability. The complex mechanisms involved in formation, stabilization, and destabilization of emulsions make fundamental studies on applied systems difficult. One approach has therefore been to clarify the basic physical and chemical properties of emulsions by the study of simpler model systems. The adsorption behavior of single-emulsion components like proteins, fatty acids, surfactants, or phospholipids at liquid/air or liquid/liquid interfaces have given information about surface activity, adsorbed amounts, kinetics, conformation, and surface rheology. The development of experimental techniques has made it possible to extend these studies to multicomponent systems. This has provided further information concerning competitive adsorption, displacement, and complex formation, which can be related to emulsion and foam stability. © 2008 Springer New York.