The Egg and the Equivalent - Part Two
Click here to read The Egg and the Equivalent - Part One.
Egging'em on
Walking on shells
Eggs-cellent imitations
Eggs' functionality is one of the major reasons for its wide use as a food ingredient. When added to food products, eggs supply many different functions:
Foaming. Both egg whites and yolk can trap air to form foams, although the whites are much more effective. This is due to their high-protein, no-fat composition. "The surface-active film-forming proteins in eggs are responsible - primarily ovomucin, conalbumin and lysozyme," says Bauch. Globulins reduce the surface tension and increase viscosity to rapidly incorporate air at the beginning of the whipping process. They also coagulate during heating to form a stiff structure. "The ovomucin-lysozyme complex provides foam stability, and ovalbumin and conalbumin provide heat-setting properties," Froning says.
Stability of the foam increases with beating time up to a point. Excessive beating creates an unstable foam due to the breakage of the coagulated egg-protein films. An overbeaten egg-white foam curdles - liquid drains from the structure and the air pockets coalesce. The rate, time and configuration of the beater or mixer also influence foaming. Temperature also affects the result. Low temperature increases egg white viscosity, and increases the time required to incorporate air. Room temperature whipping increases volume and creates a finer air cell. Acids or acid salts, such as cream of tartar, increase foam stability. Sugar delays the surface coagulation of the proteins, and makes the resulting foam smoother and more stable, although it will delay the onset of foaming and can reduce the volume. Salt also can delay foam formation.
Yolks and whole eggs contain lipids that must be emulsified to create a stable foam, because free fat retards foaming. Lipovitellenin and lipovitellin adversely affect foam formation in egg whites. The proteins in the yolk do not surface-denature so they do not form a stiff structure without heat denaturization. Foams act as part of the leavening system in baked goods - heat expands the air pockets, then solidifies the protein-based structure.
Coagulation. In foods such as cakes, soufflés and custard, egg-protein coagulation forms a solid or semisolid structure as the proteins are exposed to heat. In other products, such as meat loaves or patties, this characteristic serves as a binder that holds the elements together. In breadings or when used as an egg wash, they help to adhere particles such as crumbs or seeds. According to Bauch, frozen batter-coated fried and baked fish using a batter with a higher egg content is crisper and retains moisture due to the film-forming properties of eggs. An egg-protein gel can thicken sauces and gravies.
The exact temperature at which this process occurs varies with pH, salt level, interaction of other ingredients and time of exposure. Egg whites coagulate at 62° to 65°C, yolk at 65° to 70°C, and whole eggs in a range between the two. Adding solutes, like salt or sugar, will raise the temperature required.
Emulsification. Because of the surface-active properties of phospholipids and lipoproteins contained in the yolk, it makes an excellent emulsifier. This quality keeps oil suspended in mayonnaise and egg-based dressings and provides emulsification in batters and doughs.
Texturization. Because of the fat supplied by egg yolks, they have a tenderizing effect on baked products, especially cakes. Eggs also affect crumb formation. However, when only whites are used in the same type of application, the result is a toughening due to their protein content. Eggs can act as humectants in breads and rolls, and increase shelf life. In confections, egg whites can control sugar crystallization and promote chocolate smoothness. "Large protein molecules in the white inhibit sugar crystallization in sugar/water mixtures," explains Bauch. "Where egg yolks are used, as in Irish cream chocolate centers, the lipids prevent sugar recrystallization."
Appearance. Eggs can contribute a yellow color to many products or provide a desirable brown color to baked foods. Egg washes produce gloss and shine on the surface of baked products.
Back to Top
It was commonly believed that the inside of a freshly laid egg is essentially sterile. Recently, it has been discovered that hens infected with Salmonella enteritis (S.e.) can lay infected eggs. More common than contamination prior to laying is external bacterial contamination. Because the shell is porous, external bacteria could potentially enter through the pores, especially if eggs are mishandled during the washing step. Cracks in the shell exacerbate the problem. What makes this particularly worrisome is that chickens, and therefore eggs, are prone to contamination by not only spoilage organisms, but also to food-poisoning microorganisms, particularly salmonella. Salmonellosis is especially dangerous to infants, pregnant women, the elderly, transplant patients and those with certain chronic diseases.
The problem is not as dire as a 1997 claim by the Center for Science in the Public Interest suggests, that the S.e. bacteria cause "hundreds and possibly thousands of deaths per year." At the time, Louis B. Raffel, president of the American Egg Board, rebutted this assertion by stating that "while only one death is too many, statistics from the Centers for Disease Control show only 10 salmonella-outbreak-associated deaths for the years 1995 and 1996." In addition, according to a May 1998 report from the Centers for Disease Control, "in 1997, a 10-year low of 44 confirmed outbreaks of S.e. were reported, suggesting progress toward the national objective of fewer than 25 outbreaks per year. Of the 1,096 ill persons, 124 (11%) were hospitalized and none died." Still, a June 1998 report, Salmonella Enteritidis Risk Assessment in Shell Eggs and Egg Products, issued by USDA, estimates that 2.3 million of 46.8 billion shell eggs produced yearly in this country "are infected with S.e., resulting in 661,633 human S.e. cases." This figure was an estimate taking into account available data and risk-assessment techniques from government, industry and academic sources, USDA reports.
Various approaches show promise in eliminating the problem, says Froning, including irradiation of the eggs, competitive microorganisms (changing the microflora of the chicken's digestive tract), bactericidal feeds and hen vaccination. These techniques aren't yet being commercially used.
However, one method for pasteurization of in-shell eggs is currently used by Michael Foods' Papetti's Hygrade Egg Products, Elizabeth, NJ. This technique has been based in part on a paper titled "Immersion heat treatments for inactivation of Salmonella enteritidis within intact eggs," (Journal of Applied Microbiology, 1997), by James Schuman, Ph.D. "In terms of food safety, we've explored this technology in a very thorough manner," says Schuman, now a R&D food scientist for Michael Foods. "This process gives consumers a tremendous improvement in assuring that any lightly cooked egg product will be safe, without significantly changing the egg's flavor, appearance or consistency." FDA's Model Food Code currently recognizes pasteurized shell eggs as a new category that should be substituted in all uncooked or lightly cooked delicatessen and menu items that contain raw or undercooked eggs, such as Caesar salads, meringues, soft-poached eggs or custards.
One method to control bacterial spoilage in liquid-egg products is by adding nisin, the active ingredient found in Nisaplin, marketed by Cultor Food Science, Ardsley, NY. This peptide is a fermentation product of Lactococcus lactis and has been found to restrict growth against gram-positive bacteria, such as Bacillus cereus, and certain gram-negative species. The inhibition of the gram-negative bacteria is thought to result from heat damage to the organism's outer cell wall, combined with egg's naturally occurring ovotransferrin and lysozyme acting synergistically with nisin. Nisaplin contains a nisin concentrate with a standardized activity of 1 X 106 iu/gram. Trials in liquid egg have shown that shelf life of liquid eggs with 50 to 200 mg/liter Nisaplin approximately doubled. A petition to affirm nisin's Generally Recognized as Safe (GRAS) status in liquid whole eggs, yolks and whites has been accepted for filing by USDA.
Back to Top
When choosing an egg substitute, it's important to keep the end use in mind, and make certain that the product has been formulated to address any and all functions provided by the egg.
Many retail "egg substitutes" designed for the breakfast table or other types of home-cooking contain egg whites, but no yolk to eliminate that nutritional no-no: cholesterol. In addition, many contain added ingredients to enhance functionality and viscosity, and mimic the appearance of whole eggs.
"When changing from a whole egg recipe to an egg white only, the functions of the yolk have to be replaced," Bauch says. "Natural egg yolk contains fat and lecithin, which contribute to its emulsifying properties, fat-soluble vitamins and other nutrients. In general, products made with egg whites substituted for whole eggs suffer when tested organoleptically. Functionally, the products may perform, but best results are obtained when products are reformulated to reduce egg yolk, rather than eliminate it altogether. Retaining 25% to 33% yolk in the formula generally yields better overall quality."
Still, some product designers need to formulate without eggs. "Eggs are not the most cost-efficient source of protein for food formulations," according to a spokesperson from Parmalat Canada Ltd., Ontario, Canada. "Whole eggs are fragile and costly to use. Along with liquid eggs, they require refrigeration and can introduce serious microbial concerns. In addition, eggs are criticized for their high fat and cholesterol content. Food formulators are seeking more efficient ways of incorporating eggs' nutritional and functional properties into their products." They have a number of options depending on what end-result the product requires.
The functionality of egg protein can be supplied by either dairy or vegetable versions. For example, BiPro, a dairy protein manufactured by Davisco Foods International, Inc., Eden Prairie, MN, is comprised of beta-lactoglobulin and alpha-lactalbumen. These contribute gelling, water-binding, emulsification and aeration properties that can act as an egg-white replacer.
Most egg-replacement ingredients are optimized for specific applications. Parmalat's Ingredient Division has developed a line of whole-egg extenders based on dairy protein. "These products recognize the unique functionality of eggs in different end-use applications," says Janice Cox, technical development manager at Parmalat. "Some applications require the flavor and appearance from eggs, but mostly it's the attributes of texture, structure and body that the food product relies on eggs to contribute. This is where dairy preens can be modified and designed to provide comparable egg functionality at considerably less cost than egg." These products can be used to replace all or part of the egg, she notes - for example, 50% of the egg in cakes, quiche and pie fillings to 100% in muffins, frozen batters and pancakes. "Development continues with dairy proteins at Parmalat to take whole egg replacement to higher levels and for egg-white replacement."
Studies headed up by E. Allen Foegeding, professor, Department of Food Science, North Carolina State University, Raleigh, are looking at research on how whey proteins can be modified to become more cost-effective, viable alternatives to egg whites. Work at the Southeast Dairy Foods Research Center funded by Dairy Management Inc. focuses on the gelation properties of whey proteins.
Researchers are "picking a few key functional applications and determining if we can make whey proteins function like egg white," says Foegeding. "The first application is 'cooked egg white,' where our goal is to create the same texture with a whey protein gel. We have modified whey protein isolate so that it forms gels that have the same sensory texture as egg white. This was relatively easy, because we have been working in whey protein gelation for over 10 years and pretty much understand what regulates texture of egg and whey gels."
Another focus is determining why egg-white foams work better than whey foams in angel food cakes. "Our research to date suggests that the critical difference is that during baking, egg white foams can expand, then form a stable structure, while whey-protein foams expand like egg foams, but collapse in the latter stages of baking," Foegeding explains. "We are using various microscopic (confocal laser microscopy) and rheological techniques to investigate this problem. We hope to have an answer within the next year or so."
The gelation mechanism is the same for egg whites and whey protein. Proteins are denatured by heat, exposing hydrophobic and sulfhydryl groups. "This does not change the viscosity significantly, and the 'denaturation' phase is fast, seldom observed in practical applications," says Foegeding. "The denatured proteins aggregate, becoming linked together by hydrophobic interactions and disulfide bonds. There is a rapid increase in viscosity, occurring in a second or less, then the fluid turns into a solid gel."
Foegeding has lowered the gelation temperature of whey via the addition of divalent cation salts, such as calcium chloride. "We have shown that the gel temperature decreases from 80°C to 73°C. However, the bad news is that it has a lower gelation temperature because it is forming a particulate type of gel network. This type of gel has much lower water-holding properties."
An alternative way to decrease the gelation temperature, says Foegeding, is to form "soluble polymers" by heating at over 75°C under low-salt conditions. Other terms, such as "pre-denatured," have been used to describe this process but it is the formation of polymers/aggregates, not denaturation per se, that alters the functionality.
Soy protein also has been formulated into vegetarian egg replacers for baking applications, mayonnaise and salad dressings. Mono- and diglycerides and lecithin from soy can be incorporated into egg replacers to substitute for the phospholipids occurring naturally in egg yolk. Eggs and soy lecithin both contain phosphatidylcholine and phosphatidylethanolamine, and soy also contains phosphatdylinositol. Liquid lecithin can be used for "wet" applications, but powdered lecithin is available for dry mixes. Dry versions have the benefit of easier handling.
Hydrocolloids can supplement the protein gels, and supply viscosity and water-binding characteristics to egg replacers. These include xanthan and guar gums and, occasionally, starch. They help to provide mouthfeel and rheology that more closely approximate that of fat, or at least a fat replacer, than that of the protein, since they don't necessarily form a rigid structure upon heating.
Egg replacers designed merely for functionality often lack the rich, rounded background notes that eggs supply. Egg flavor results from the combination of at least 141 components, 87 present in whole egg, 75 from egg yolk, and 57 in egg white. Most of these are highly volatile. "Egg is a very complex material. The most important descriptors used for egg and egg flavor are 'sulphury' and 'aldehydic,' followed by ammoniacal, metallic and rubbery," notes Laurence Rouquet, flavorist, Quest International, Inc., Hoffman Estates, IL.
Lipid oxidation and the Maillard reaction contribute to cooked-egg flavors. Aldehydes and heterocyclic nitrogen-containing compounds (pyrazines, pyradines and thiazoles) also play a major role. Says Rouquet, "Sulphuric compounds have also been found in cooked egg, particularly dimethyl disulfide, which contributes the oniony or 'bad egg' smell.
"Egg flavor can work in synergy with other flavors," Rouquet continues. "For example, flavors associated with vanilla yield the well-known french vanilla flavor." She notes that, unlike another alkaline food flavor, chocolate, "the pH may affect the functionality of a real egg, but it doesn't have much effect on the egg flavor."
Typical egg yolk contains fat-soluble carotenoids that create a golden yellow color. Often, substitutes contain beta-carotene, which not only imparts an "eggy" color, but also a little extra nutritional punch. Another good choice in the "exempt from certification" category is the carotenoid-based color, annatto. This comes in oil-soluble, water-soluble or water/oil-dispersible versions made with emulsifiers. FD&C colors also can be used to simulate the yolk color, but they tend to result in a less golden hue. The final choice depends on the color required, the matrix and additional factors such as light stability.
So whether a product designer chooses eggs in one of their many guises or some form of egg substitute designed to fill in for the egg, close attention needs to be paid to the exact functionality required. Combining functionality, flavor, health and safety is a complex proposition, and that's no yolk.
• Photo: American Egg Board
• Photo: Dairy Management Inc.
• Photo: California Egg Commission
© 1998 by Weeks Publishing Company
Weeks Publishing Company
3400 Dundee Rd. Suite #100
Northbrook, IL 60062
Phone: 847-559-0385
Fax: 847-559-0389