Crystallization of Lipids in Oil-in-Water Emulsion States

The processes of lipid crystallization in bulk are well understood in terms of phase behavior and classical nucleation theory. Lipids in emulsion droplets crystalize and melt just like bulk lipids, but the kinetics of the processes can be different. The mechanism of physical instability is partial coalescence which arises when the crystals of fat penetrate the interfacial surfactant layer and, following a collision between droplets, penetrate the surfactant layer of a second droplet allowing lipid-to-lipid contact. This chapter considers first the effects of droplet structure on crystallization, lipid polymorphism, and the morphology of crystalline droplets and finally the stability of crystalline droplet dispersions. The focus is exclusively on oil-in-water dispersions and particularly on food and pharmaceutical applications. Although colloidal dispersions of oil in water are, by definition, emulsions, many food and pharmaceutical lipids are at least partially crystalline under conditions of storage or use and so should perhaps be more properly referred to as sols.