Kinetically Stable Aqueous Lipid Dispersions Prepared by Crystallization Processes

Abstract

Lipids provide a wide range of functional properties utilized in technical applications, and the mechanisms usually are based on the physical properties of the liquid‐crystalline phases. Even the solid state of lipids can sometimes provide similar functions, which are described in this article. Crystallization from an aqueous dispersion of the lamellar liquid‐crystalline phase of monoglycerides can form hydrophilic lipid crystals, which are able to attach large proportions of water to the dominating surfaces of the leave‐shaped crystals formed by the polar head group planes. Such lipid crystal dispersions have been utilized as a general ointment base and as stabilizers in food applications. Many lipid‐based emulsions are prepared by cooling during a mixing process. A general mechanism for stabilization of such emulsions is the formation of crystals of polar lipids at the oil/water interface. These lipid crystals form an interfacial film, which expose hydrophilic surfaces toward the water phase and hydrophobic surfaces toward the inner oil core. The interfacial tension versus temperature at the corresponding oil/water interface starts to decrease abruptly at the same temperature as crystals of the polar lipid start to form in the oil phase, as identified by x‐ray diffraction. The crystal formation in the corresponding binary system triglyceride oil/polar lipid followed in the polarizing microscope shows a simple eutectic behavior. The polar lipid crystal formation at the oil/water interface requires that the triglyceride oil/polar lipid composition of the binary system corresponds to the polar lipid side of the eutecticum. Examples of both oil‐in‐water and water‐in‐oil emulsions formed in this way are described. Other aspects of lipid crystals in emulsions, which involve the oil core, are also discussed. An interesting phenomenon is the formation of a beta‐crystal gel state, which recently has been characterized.