Food Emulsions and FoamsOpen image in new window
Many convenience foods, such as frozen desserts, meat products, margarine, and some natural foods, such as milk and butter, are emulsions. That is, they contain either water dispersed in oil or oil dispersed in water. These water and oil liquids do not no
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Introduction
Emulsions
Many convenience foods, such as frozen desserts, meat products, margarine, and some natural foods, such as milk and butter, are emulsions. That is, they contain either water dispersed in oil or oil dispersed in water. These water and oil liquids do not normally mix, and so when present together, they exist as two separate layers. However, when an emulsion is formed, the liquids are mixed in such a way that a single layer is formed with droplets of one liquid dispersed within another. Food emulsions need to be stable; if they are not, the oil and water will separate out. Stability is usually achieved by adding a suitable emulsifier. In some cases, a stabilizing agent is also required. Food foams, such as beaten egg white, are similar to emulsions except that instead of containing two liquids, they contain a gas (usually air or carbon dioxide) dispersed within a liquid. The factors affecting stability of emulsions also apply to foams. Some foods, such as ice cream and whipped cream, are highly complex being both an emulsion and a foam. Understanding of food emulsions and foams is complex, yet is important if progress is to be made in maintaining and improving the stability and hence the quality of these types of foods. This chapter will discuss the principles of formation and stability of emulsions and foams and the characteristics of the ingredients necessary to stabilize them.
Definition
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An emulsion is a colloidal system containing droplets of one liquid dispersed in another, the two liquids being immiscible. The droplets are termed the dispersed phase, and the liquid that contains them is termed the continuous phase. In food emulsions, the two liquids are oil and water. If water is the continuous phase, the emulsion is said to be an oil-in-water or o/w emulsion, whereas if oil is the continuous phase, the emulsion is termed a water-in-oil or w/o emulsion. Oil-in-water emulsions are more common and include salad dressings, mayonnaise, cake batter, and frozen desserts. Butter, margarine, and some icings are examples of water-in-oil emulsions. An emulsion must also contain an emulsifier, which coats the emulsion droplets and prevents them from coalescing or recombining with each other. Emulsions are colloidal systems because of the size and surface area of the droplets (in general, around 1 μm, although droplet size varies considerably, and some droplets may be a lot larger than this). Emulsions are similar to colloidal dispersions or sols, except that the dispersed phase is liquid and not solid. Colloidal dispersions are mentioned in Chap. 2.
V.A. Vaclavik and E.W. Christian, Essentials of Food Science, 4th Edition, Food Science Text Series, DOI 10.1007/978-1-4614-9138-5_13, # Springer Science+Business Media New York 2014
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Food Emulsions and Foams
Surface Tension To form an emulsion, two liquids that do not normally mix must be forced to do so. To understand how this is achieved, we must first consider the forces between the molecules of a liquid. Imagine a beaker of w
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