Multiple Emulsions Stabilized by Biopolymers
Rachel Lutz and Abraham Aserin¹; Chapter 6 in Multiple Emulsions - Technology and Applications, 2008, John Wiley & Sons
Abstract: Multiple (or double) emulsions are complex liquid dispersion systems known also as emulsions of emulsions, in which the droplets of one dispersed liquid (water in oil or oil in water) are further dispersed in another liquid (water or oil, respectively), producing W/O/W or O/W/O. The inner dispersed droplets (hereafter called inner droplets or just droplets, while the droplets of the multiple emulsion will be termed, for simplicity, the globules) in the multiple emulsion are separated from the outer liquid phase by a layer of another phase. A schematic representation and microscopic image of a W/O/W multiple emulsion globule is shown in Figure 5.1 . W/O/W multiple emulsions are the most studied system because they have the potential to become commercial products — mainly in food systems but also in cosmetics and pharmaceuticals (Garti and Benichou, 2001 ; Garti and Lutz, 2004 ). For close to 60 years, multiple emulsions were considered an emerging technology and a major scientifi c challenge (see Seifriz, 1925 , for the fi rst report), but in practice, only a few industrial products based on multiple emulsions exist in the marketplace. The main use of multiple emulsion systems is as confi nement and protection systems for controlled release of active compounds. In the food industry (Matsumoto, 1986 ; Yoshida et al., 1999 ) W/O/W multiple emulsions can improve the solubility of certain active matter, solubilize oil - insoluble materials, serve as protective liquid reservoirs for molecules sensitive to external environmental reactivity such as oxidation, light, and enzymes, and serve as entrapment reservoirs for masking undesired fl avors and odorants. Applications in the cosmetics industry (Kim and Lee, 1999 ; Gallarate et al., 1999 ) include aqueous preparations that provide a good “ feel ” and slow release of active materials or fl avors, deposition of water - soluble agents onto the skin from wash - off systems. Most applications are related to the pharmaceutical industry (Okochi and Nakano, 2000 ; Shima et al., 2006 ; Vasiljevic et al., 2006 ), such as enhancing the chemotherapeutic effect of anticancer drugs, drug immobilization, treatment of drug overdoses, and protecting insulin from enzymatic degradation. In the agriculture industry the potential applications (Versteeg, 1978 ) are sustained release systems for fertilizers and pesticides, and in the fuel industry (Lin and Wang, 2003 ) as alternative fuel for diesel engines. This chapter deals mainly with the food industry. The formation of a multiple emulsion requires only two simple consecutive emulsifi cation steps, yet close examination of the results of such simple preparations reveals that the unsolved technical problems are not easy to overcome. In recent decades researchers have contributed information on the selection of different ingredients such as various blends of emulsifi ers (mostly nonionic), oils, and viscosity agents. These reviews provided new ideas on novel analytical tools and advanced preparation techniques to better understand the nature of the instability of multiple emulsions and to control release pathways (Garti and Benichou, 2001 ; Grossiord and Seiller, 2001 ; Bibette et al., 2002 ; Garti and Lutz, 2004 ).
Key words: Emulsion stability • Biopolymers • Nonionic surfactants • Polymeric surfactants • Steric stabilization • Electrostatic stabilization • Depletion flocculation • Bridging flocculation • Creaming phenomena • Multiple emulsions • Hydrocolloids • LUMiFuge
¹ Casali Institute of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.Contact us
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