Functional Uses of Eggs
Functional Uses of Eggs—An Overview
Eggs are a multifunctional food. Egg components have the ability to coagulate when heated, to act as emulsifiers in oil and water formulations, and to form foams when whipped. Components of the egg make it an excellent source of high-quality protein, vitamins, and trace minerals. Eggs are used in some candies and icings to enhance color and flavor while minimizing crystal formation. A book published in 1977 lists 979 methods of preparing various egg dishes.
Some nonfood uses of eggs include their use as a source of avidin andnlysozyme, as well as for fining, softening, and polishing red wines. The eggncan also be used as a carrier of antibodies against some diseases of humansnand animals.
Eggs are composed of four distinct and separable parts: shell, shell membranes, albumen, and yolk. Each of these parts has value for different applications. Shell eggs are frequently converted into egg products such as liquid, frozen, or dehydrated whole eggs, albumen, yolk, as well as blends.
The nutritional value of the egg is extensively discussed in the following chapters. The egg is the perfect food for a chick; however, it is deficient in vitamin C for humans. The portion of the egg normally eaten is also deficient in calcium. Most of the calcium in an egg is found in the shell as calcium carbonate.
The exact quantity of various fatty acids, minerals, and vitamins is dependent on the level of each in the diet of the hen. Levels of most nutrients in the egg are influenced by age, breed or strain, season of the year, and diet of the hen.2 While most of the variations are relatively slight, the fatty acid composition can be markedly modified by changes in the fatty acid composition of the hen’s diet. The vitamin and trace mineral content are also variable depending on the amounts of the particular compound in the diet of the hen.
Although the shell of the egg is not generally considered edible, finely powdered eggshell can be utilized as a calcium source for humans.3 The absorption of eggshell calcium is greater than for conventional calcium sources. Finely ground eggshell is used as a calcium enrichment in some breads and confections.
Coagulation is the phenomenon of a liquid changing to a semisolid or solid. Heat coagulation can occur in both egg white and egg yolk. The proteins of the egg white coagulate at various temperatures. Conalbumin or ovotransferrin coagulates at 57.3°C; lysozyme at 81.5°C.4 The other proteins of the albumen coagulate at intermediate temperatures between these extremes. Egg yolk begins to coagulate at 65°C and ceases to flow at 70°C.
The action of coagulation is an unfolding of protein coils when heated and a bonding between the molecules that results in a change from a transparent watery liquid into an opaque, polycondensated solid in the irreversible reaction.5 The success of many cooked foods is dependent on the heat coagulation of egg proteins.
The effects of heat coagulation are most evident in the preparation of hard-cooked or fried eggs. The firmness of the coagulated albumen is directly related to the time and temperature of heat application. Eggs are frequently included as an ingredient in meatloaf to bind the other ingredients together, a result of coagulation of the egg proteins. Eggs are included in quiches, custards, flans, crepes, and many other foods for this binding action of the heated proteins. Eggs are included in batter mixtures to coat various foods prior to deep fat frying. The egg proteins bind the batter to the surface of the food product.
The coagulation property of egg proteins is used also in clarification of clear consommé. The albumen of one egg is added to each 5 quarts of cold white consommé, which is then heated to coagulate the egg proteins. The particulate materials are collected in the white consommé, and the broth is then strained through cheesecloth to remove the egg white and particulates.
A foam is a colloidal dispersion in which a gaseous phase is dispersed in a liquid or solid phase.4 The mechanism of foam formation during whipping of liquid egg products is described as an unfolding of the protein molecules so that the polypeptide chains exist with the long axes parallel to the surface.7 This change in molecular configuration results in a loss of solubility or precipitation of some of the albumen, which collects at the liquid-air interface. Many foods are capable of foaming; eggs are especially effective in this capacity. For a foam to be of value in cookery, it must be relatively stable.
Egg foaming is brought about by whipping of the liquid egg products. Whole eggs can be used to produce foam for yellow sponge cakes. However, egg whites are generally used for getting maximum foams. Egg whites with a large percentage of thick white take longer to whip to maximum foam volume, but the foam formed is more stable than foams formed from lower-quality eggs that contain a higher percentage of thin white.
Chefs have claimed for years that whipping of egg white in a copper bowl yields superior products. In a test at a cooking school,8 no difference was found in foam volume. However, when the foamed product was baked, the end product had a significant increase in volume. It was postulated that the conalbumin of the egg white complexed with the copper, forming a product with a lowered heat sensitivity. This allowed the air bubbles in the product to expand farther before being set due to coagulation of the proteins.
Eggs are used for their foaming ability in the preparation of meringues, angel food cakes, sponge cakes, and mousses.
The reduction of interfacial tension between water and oil is the first step in the formation of an emulsion.9 The surface active agents in egg yolk are essential to its function in emulsification. The surface active agents form a film around the oil globules and prevent their coalescence in emulsion food products. Egg yolk is itself an emulsion. The emulsifying capacity of egg yolk is not altered by modifying the fatty acid composition of the yolk.
In cookery, the emulsifying function of the egg yolk is utilized in the preparation of hollandaise and other sauces. In food manufacture, this function is used in the production of mayonnaise and salad dressings.
The naturally occurring pigments in chicken egg yolk include the alcohol-soluble xanthophylls, lutein, and zeaxanthin. The color of the yolk is influenced by the concentration of these pigments in the ration of the hen. It is possible to produce various yolk colors by feeding the hen fat-soluble dyes. Egg yolk color is of importance in the manufacture of noodles, sponge cakes, and scrambled eggs. In the hard cooking of eggs, a greenish color is formed on the surface of the yolk of an overcooked egg due to the formation of ferrous sulfide produced at the interface of the yolk and the albumen.
Fresh eggs have a very mild flavor. Eggs will absorb off-flavors if stored with apples, petroleum products, odoriferous vegetables, or other sources of odors. With long-term storage eggs will develop a stale flavor. Fresh egg flavor is desirable in scrambled eggs, fried eggs, poached eggs, soft-cooked eggs, and eggnog. As egg flavor is mild it blends well with the flavor of all foods.
INHIBITION OF CRYSTAL FORMATION
The ability of egg whites to minimize crystallization of sugars in icings and candies has been known for many years.12 In candy manufacture egg white is used to help ensure creamy smoothness as well as whiteness in such confections as divinity fudge and fondant. As the hot syrup is added to the beaten egg white, the albumen forms thin films around the tiny sugar crystals and prevents them from clustering together, which results in a grainy and crumbly candy.
The principal nonfood use of the egg is to reproduce the species. With the great increase in the consumption of poultry meat, the number of eggs required for chick production has expanded greatly. Several other nonfood uses of eggs were summarized by USDA personnel. Industrial egg albumen is used in finishing certain types of leather, particularly glazed, colored stock. Inedible eggs are utilized also in animal feedstuffs and plant fertilizers.
Eggs are often fed to show animals, such as dogs and horses, to improve the glossy sheen of the fur coat. Another important use of eggs is the production of vaccines in chick embryos. Vaccines for many infectious diseases are now produced in quantity using the chick embryo. These vaccines include several pox diseases, lymphogranuloma, and influenza of humans; for many diseases of the fowl; as well as vesicular stomatitis and infectious encephalomyelitis for horses.
The use of laying hens for the production of antibodies in the hen that are transferred to the egg is discussed in chapter 12. Currently research is underway to adapt the antibody therapy in the treatment of the HIV virus responsible for acquired immune deficiency syndrome (AIDS).14 Although the virus cannot be eradicated, daily consumption of IgY from eggs of hens properly infected with the HIV virus can control the negative effects of reduced immunity to opportunistic infections to some extent. A quite different use of eggs is in artistic and cultural applications.15 The decoration of eggs for Easter is an international activity. Eggshells were decorated for King Edward I of England, who presented the gold-leafed eggs to his court as gifts in the 13th century.
During the 16th century, in France, Louis XV presented Madame Du Barry the gift of a gilded egg containing the “surprise” of a cupid. Shell egg decoration reached its zenith in Russia when Peter Carl Fabergé (1846–1920) decorated eggs for the czars. Fragments of eggshell have been used in the preparation of mosaics dating back to the 15th century. Tempera painting uses an emulsion of egg yolk thinned with water. It dries quickly and is very stable. Eggs have been used in myths of creation, witchcraft and magic, fertility, purity, and resurrection.
As such, the egg has been used as a symbol for the cosmos, as a charm to encourage reproduction, as a medium for the exorcism of devils, and as a symbol of rebirth and has been called the devil’s food. The egg has often been revered as a symbol of life; some early societies even prohibited the use of eggs as food. Eggshell membranes are generally considered a waste. However, studies in Japan have shown that protein products prepared from hydrolyzed egg membrane are beneficial in stimulating skin regeneration after injury. Egg membrane protein tends to allow growth of human skin fibroblasts and facilitates the production of type III collagen. The egg membrane protein is currently being used for its emollient properties in many cosmetics and toiletries.
Egg white is used in the clarification of red table wines. In a process known as “fining,” egg white is mixed with 0.5 to 0.9 percent salt water (60 ml albumen to 40 ml water) to solubilize the globulins in the egg white. The diluted egg white is then beaten to a froth and mixed with about 10 volumes of wine before being added to the main volume of wine.17,18 The albumen from one to two eggs is used for a barrel of wine (225 l). The solution is added to the wine and mixed well. The egg albumen interacts with the higher polymeric phenols and tannins to soften and polish the red wines.
From this brief review, it is apparent that all parts of the egg have been found to have value either as food or for other purposes. More details on the major functions of the egg can be found in Yang and Baldwin.
1. Bickel, W. Hering’s Dictionary of Classical and Modern Cookery. 5th ed. London: Virtue and Company, 1997, p. 118.
2. Stadelman, W.J., and Pratt, D.E. Factors influencing composition of the hen’s egg. World’s Poult Sci J 1989;45:247.
3. Sugura, N., Horiike, S., Masida, Y., Kunou, M., and Kokubu, T. Bioavailability and commercial use of eggshell calcium, membrane proteins and yolk lecithin products. In Egg Nutrition and Biotechnology, Sim, J.S., Nakai, S., and Guenter, W., eds. New York: CABI Publishing, 1999, chap. 17.
4. Yang, Sheng-Chin, and Baldwin, R.E. Functional properties of eggs in foods. In Egg Science and Technology, 4th ed., Stadelman, W.J., and Cotterill, O.J., eds. Binghamton, NY: Haworth Press, 1995, chap. 16.
5. Coenders, A. The Chemistry of Cooking. Park Ridge, NJ: Parthenon Publishing Co., 1992, p. 119.
6. Escoffier, A. The Escoffier Cook Book. New York: Crown Publishers, 1969, p. 4.
7. Griswold, R.M. The Experimental Study of Foods. Boston, MA: Houghton Mifflin Co., 1962.
8. Corriher, S.O. Cookwise, the Hows and Whys of Successful Cooking. New York: William Morrow and Co., 1997, p. 234.
9. Vincent, R., Powrie, W.D., and Fennema, O. Surface activity of yolk, plasma and dispersions of yolk fractions. J Food Sci 1966;31:643.
10. Pankey, R.D., and Stadelman, W.J. Effect of dietary fats on some chemical and functional properties of eggs. J Food Sci 1969;34:312.
11. Baker, R.L., Darfler, J., and Lifshitz, A. Factors affecting the discoloration of hard cooked egg yolks. Poult Sci 1967;46:664.
12. Swanson, E.L. Egg whites and sugar crystals. US Egg Poult Mag 1933;39(9):32.
13. USDA. Eggs and egg products. U.S. Dep Agric Circ 583, 1941.
14. Coleman, M. Using egg antibodies to treat diseases. In Egg Nutrition and Biotechnology, Sim, J.S., Nakai, S., and Guenter, W., eds. New York: CABI Publishing, 2000, p. 351.
15. Galyean, R.D., and Cotterill, O.J. Nonfood uses of eggs. In Egg Science and Technology, 4th ed., Stadelman, W.J., and Cotterill, O.J., eds. Binghamton, NY: Haworth Press, 1995, chap. 20.
16. Newall, V. An Egg at Easter. Bloomington: Indiana Univ. Press, 1971.
17. Amerine, M.A., Berg, H.W., Kunkee, R.E. Ough, C.S., Singleton, V.L., and Webb, A.D. The Technology of Wine Making, 4th ed. Westport, CN: AVI Publishing Co., 1982, p. 317.
18. Margalit, Yair. Concepts in Wine Chemistry, South San Francisco, CA: Wine Appreciation Guild Ltd., 1997, p. 287.