Egg white

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A raw egg yolk surrounded by the egg white Chicken egg01 monovular.jpg
A raw egg yolk surrounded by the egg white

Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. [1] It forms around fertilized or unfertilized egg yolks. The primary natural purpose of egg white is to protect the yolk and provide additional nutrition for the growth of the embryo (when fertilized). Egg white consists primarily of about 90% water into which about 10% proteins (including albumins, mucoproteins, and globulins) are dissolved. Unlike the yolk, which is high in lipids (fats), egg white contains almost no fat, and carbohydrate content is less than 1%. Egg whites contain about 56% of the protein in the egg. Egg white has many uses in food (e.g. meringue, mousse) and also many other uses (e.g. in the preparation of vaccines such as those for influenza [2] ).

Chicken domesticated bird, primarily a source of food or food

The chicken is a type of domesticated fowl, a subspecies of the red junglefowl. It is one of the most common and widespread domestic animals, with a total population of more than 19 billion as of 2011. There are more chickens in the world than any other bird or domesticated fowl. Humans keep chickens primarily as a source of food and, less commonly, as pets. Originally raised for cockfighting or for special ceremonies, chickens were not kept for food until the Hellenistic period.

In vertebrates, other than mammals, the passageway from the ovaries to the outside of the body is known as the oviduct. In female mammals this passageway is also known as the uterine tube or Fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body. Normally, these are paired structures, but in birds and some cartilaginous fishes, one or the other side fails to develop, and only one functional oviduct is found.

Embryo multicellular diploid eukaryote in its earliest stage of development

An embryo is an early stage of development of a multicellular diploid eukaryotic organism. In general, in organisms that reproduce sexually, an embryo develops from a zygote, the single cell resulting from the fertilization of the female egg cell by the male sperm cell. The zygote possesses half the DNA from each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The result of this process is an embryo.

Contents

Composition

Egg white makes up around two-thirds of a chicken egg by weight. Water constitutes about 90% of this, with protein, trace minerals, fatty material, vitamins, and glucose contributing the remainder. [3] A raw U.S. large egg contains around 33 grams of egg white with 3.6 grams of protein, 0.24 grams of carbohydrate and 55 milligrams of sodium. It contains no cholesterol and the energy content is about 17 Calories. [3] Egg white is an alkaline solution and contains around 148 proteins. [4] The table below lists the major proteins in egg whites by percentage and their natural functions. [3] [5]

Mineral Element or chemical compound that is normally crystalline and that has been formed as a result of geological processes

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often syntesize inorganic minerals that also occur in rocks.

Vitamin organic compound and a vital nutrient that an organism requires in limited amounts

A vitamin is an organic molecule (or related set of molecules) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrients cannot be synthesized in the organism, either at all or not in sufficient quantities, and therefore must be obtained through the diet. Vitamin C can be synthesized by some species but not by others; it is not a vitamin in the first instance but is in the second. The term vitamin does not include the three other groups of essential nutrients: minerals, essential fatty acids, and essential amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folic acid or folate), vitamin B12 (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones).

Glucose A simple form of sugar

Glucose (also called dextrose) is a simple sugar with the molecular formula C6H12O6. Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight. There it is used to make cellulose in cell walls, which is the most abundant carbohydrate. In energy metabolism, glucose is the most important source of energy in all organisms. Glucose for metabolism is partially stored as a polymer, in plants mainly as starch and amylopectin and in animals as glycogen. Glucose circulates in the blood of animals as blood sugar. The naturally occurring form of glucose is D-glucose, while L-glucose is produced synthetically in comparably small amounts and is of lesser importance.

ProteinAbundance
Ovalbumin 54%
Ovotransferrin 12%
Ovomucoid 11%
Ovoglobulin G2 4%
Ovoglobulin G34%
Ovomucin 3.5%
Lysozyme 3.4%
Ovoinhibitor1.5%
Ovoglycoprotein1%
Flavoprotein 0.8%
Ovomacroglobulin0.5%
Avidin 0.05%
Cystatin 0.05%

Ovalbumin is the most abundant protein in albumen. Classed as phosphoglycoprotein, during storage, it converts into s-ovalbumin (5% at the time of laying) and can reach up to 80% after six months of cold storage. Ovalbumin in solution is heat-resistant. Denaturation temperature is around 84°C, but it can be easily denatured by physical stresses. Conalbumin/ovotransferrin is a glycoprotein which has the capacity to bind the bi- and trivalent metal cations into a complex and is more heat sensitive than ovalbumin. At its isoelectric pH (6.5), it can bind two cations and assume a red or yellow color. These metal complexes are more heat stable than the native state. Ovomucoid is the major allergen from egg white and is a heat-resistant glycoprotein found to be a trypsin inhibitor. Lysozyme is a holoprotein which can lyse the wall of certain Gram-positive bacteria and is found at high levels in the chalaziferous layer and the chalazae which anchor the yolk towards the middle of the egg. Ovomucin is a glycoprotein which may contribute to the gel-like structure of thick albumen. The amount of ovomucin in the thick albumen is four times greater than in the thin albumen.

A Holoprotein or conjugated protein is an apoprotein combined with its prosthetic group.

Foam

Visual representation of protein denaturation. A globular protein becomes unfolded when exposed to heat. Diagram -2 denaturation.svg
Visual representation of protein denaturation. A globular protein becomes unfolded when exposed to heat.
Aerated egg whites are frequently employed in shaken cocktail recipes, such as this Ramos gin fizz, for textural and aesthetic purposes. Ramos Gin Fizz.jpg
Aerated egg whites are frequently employed in shaken cocktail recipes, such as this Ramos gin fizz, for textural and aesthetic purposes.

The physical stress of beating egg whites can create a foam. Two types of physical stress are caused by beating them with a whisk, the first of which occurs as the whisk drags the liquid through itself, creating a force that unfolds the protein molecules. This process is called denaturation. The second stress comes from the mixing of air into the whites, which causes the proteins to come out of their natural state. These denatured proteins gather together where the air and water meet and create multiple bonds with the other unraveled proteins, and thus become a foam, holding the incorporated air in place, because the proteins consist of amino acids; some are hydrophilic (attracted to water) and some are hydrophobic (repelled by water). This process is called coagulation. [6] [3]

Denaturation (biochemistry)

Denaturation is a process in which proteins or nucleic acids lose the quaternary structure, tertiary structure, and secondary structure which is present in their native state, by application of some external stress or compound such as a strong acid or base, a concentrated inorganic salt, an organic solvent, radiation or heat. If proteins in a living cell are denatured, this results in disruption of cell activity and possibly cell death. Protein denaturation is also a consequence of cell death. Denatured proteins can exhibit a wide range of characteristics, from conformational change and loss of solubility to aggregation due to the exposure of hydrophobic groups. Denatured proteins lose their 3D structure and therefore cannot function.

Flocculation, in the field of chemistry, is a process in which colloids come out of suspension in the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.

When beating egg whites, they are classified in three stages according to the peaks they form when the beater is lifted: soft, firm, and stiff peaks. Overbeaten eggs take on a dry appearance, and eventually collapse. Egg whites do not beat up correctly if they are exposed to any form of fat, such as cooking oils or the fats contained in egg yolk.

Cooking oil oil consumed by humans, from vegetable or animal origin

Cooking oil is plant, animal, or synthetic fat used in frying, baking, and other types of cooking. It is also used in food preparation and flavouring not involving heat, such as salad dressings and bread dips, and in this sense might be more accurately termed edible oil.

Stabilizing foam for culinary purposes

Copper bowl

Copper bowls have been used in France since the 18th century to stabilize egg foams. The copper in the bowl assists in creating a tighter bond in reactive sulfur items such as egg whites. The bond created is so tight that the sulfurs are prevented from reacting with any other material. A silver-plated bowl has the same result as the copper bowl, as will a pinch of powdered copper supplement from a health store used in a glass bowl. Drawbacks of the copper bowl include the expense of the bowl itself, and that the bowls are difficult to keep clean. Copper contamination from the bowl is minimal, as a cup of foam contains a tenth of a human's normal daily intake level. [3] [7]

Copper Chemical element with atomic number 29

Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

France Republic with mainland in Europe and numerous oversea territories

France, officially the French Republic, is a country whose territory consists of metropolitan France in Western Europe and several overseas regions and territories. The metropolitan area of France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean. It is bordered by Belgium, Luxembourg and Germany to the northeast, Switzerland and Italy to the east, and Andorra and Spain to the south. The overseas territories include French Guiana in South America and several islands in the Atlantic, Pacific and Indian oceans. The country's 18 integral regions span a combined area of 643,801 square kilometres (248,573 sq mi) and a total population of 67.3 million. France, a sovereign state, is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre. Other major urban areas include Lyon, Marseille, Toulouse, Bordeaux, Lille and Nice.

Sulfur Chemical element with atomic number 16

Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula S8. Elemental sulfur is a bright yellow, crystalline solid at room temperature.

Beaten egg whites Blancs d'oeufs battus.jpg
Beaten egg whites

Health issues

Although egg whites are prized as a source of low-fat, high-protein nutrition, a small number of people cannot eat them. Egg allergy is more common among infants than adults, and most children will outgrow it by the age of five. [8] Allergic reactions against egg white are more common than reactions against egg yolks. [9] In addition to true allergic reactions, some people experience a food intolerance to egg whites. [9]

Eggs are susceptible to Salmonella contamination. Thorough cooking eliminates the direct threat (i.e. cooked egg whites that are solid and not runny), the threat of cross-contamination remains if people handle contaminated eggs and then touch other foods or items in the kitchen, thus spreading the bacteria. In August 2010, the FDA ordered the recall of 380 million eggs because of possible Salmonella contamination. [10]

Uses

Egg white is a fining agent that can be used in the clarification and stabilization of wine. Egg white can also be added to shaken cocktails to create a delicate froth. Some protein powders also use egg whites as a primary source of protein.

In the 1750s, egg whites were believed to prevent swelling, and were used for that purpose. To help soothe areas of skin that were afflicted, egg white mixed with Armenic bole could help restore the fibers. Egg whites are also used in bookbinding during the gilding process, where it is referred to as 'glaire', and to give a book cover shine. [11]

The albumen from egg white was used as a binding agent in early photography; such prints were called albumen prints.

See also

Related Research Articles

Mayonnaise thick, creamy sauce often used as a condiment

Mayonnaise, informally mayo, is a thick cold sauce or dressing usually used in sandwiches and composed salads. It is a stable emulsion of oil, egg yolk, and acid, either vinegar or lemon juice. There are many variants using additional flavorings. The proteins and lecithin in the egg yolk serve as emulsifiers in mayonnaise. The color of mayonnaise varies from near-white to pale yellow, and its texture from a light cream to a thick gel.

Marshmallow sugar-based confection

A marshmallow is a sugar confectionery that in its modern form typically consists of sugar, water and gelatin whipped to a squishy consistency, molded into small cylindrical pieces, and coated with corn starch. Some marshmallow recipes call for eggs. This is the modern version of a medicinal confection made from Althaea officinalis, the marshmallow plant.

Meringue dessert, made from whipped egg whites and sugar

Meringue is a type of dessert or candy, often associated with French, Spanish, Swiss, and Italian cuisine, traditionally made from whipped egg whites and sugar, and occasionally an acidic ingredient such as lemon, vinegar, or cream of tartar. A binding agent such as salt, corn starch, or gelatin may also be added to the eggs. The key to the formation of a good meringue is the formation of stiff peaks by denaturing the protein ovalbumin via mechanical shear. Meringues are often flavoured with vanilla, a small amount of almond, or coconut, although if extracts of these are used and are based on an oil infusion, an excess of fat from the oil may inhibit the egg whites from forming a foam.

Angel food cake type of sponge cake

Angel food cake, or angel cake, is a type of sponge cake made with egg whites, flour, and sugar. A whipping agent, such as cream of tartar, is commonly added. It differs from other cakes because it uses no butter. Its structure comes from whipped egg whites known as a protein foam. Angel food cake originated in the United States and first became popular in the late 19th century. It gained its unique reputation along with its name due to its light and fluffy texture, said to resemble the "food of the angels".

<i>Salmonella enterica</i> species of bacterium

Salmonella enterica is a rod-shaped, flagellate, facultative aerobic, Gram-negative bacterium and a species of the genus Salmonella. A number of its serovars are serious human pathogens.

Yolk part of an egg which feeds the developing chicken embryo

Among animals which produce one, the yolk is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some kinds of egg contain no yolk, for example because they are laid in situations where the food supply is sufficient or because the embryo develops in the parent's body, which supplies the food, usually through a placenta. Reproductive systems in which the mother's body supplies the embryo directly are said to be matrotrophic; those in which the embryo is supplied by yolk are said to be lecithotrophic. In many species, such as all birds, and most reptiles and insects, the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother. In many other animals, especially very small species such as some fishes and invertebrates, the yolk material is not in a special organ, but inside the ovum.

Eggnog sweetened dairy-based beverage

Eggnog, egg nog or egg-nog, historically also known as milk punch or egg milk punch, is a rich, chilled, sweetened, dairy-based beverage. It is traditionally made with milk, cream, sugar, whipped egg whites, and egg yolks. In some contexts, distilled spirits such as brandy, rum, whisky or bourbon are added to the drink.

Balut (food) A developing bird embryo boiled and eaten from the shell

Balut is a developing bird embryo that is boiled and eaten from the shell. It originated from and is commonly sold as street food in the Philippines. Often served with beer, balut is popular in Southeast Asian countries, such as Laos, Cambodia, Thailand and Vietnam.

Salmonellosis infection caused by Salmonella bacteria

Salmonellosis is a symptomatic infection caused by bacteria of the Salmonella type. The most common symptoms are diarrhea, fever, abdominal cramps, and vomiting. Symptoms typically occur between 12 hours and 36 hours after exposure, and last from two to seven days. Occasionally more significant disease can result in dehydration. The old, young, and others with a weakened immune system are more likely to develop severe disease. Specific types of Salmonella can result in typhoid fever or paratyphoid fever.

The Haugh unit is a measure of egg protein quality based on the height of its egg white (albumen). The test was introduced by Raymond Haugh in 1937 and is an important industry measure of egg quality next to other measures such as shell thickness and strength.

Separating eggs process, generally used in cooking, in which the egg yolk is removed from the egg white

Separating eggs is a process, generally used in cooking, in which the egg yolk is removed from the egg white. This allows one part of the egg to be used without the other part, or each part to be treated in different ways. Recipes for custard call for egg yolks, for example. The most common reason for separating eggs is so the whites can be whipped.

Genoise

A genoise is an Italian sponge cake named after the city of Genoa and associated with Italian and French cuisine. Instead of using chemical leavening, air is suspended in the batter during mixing to provide volume.

Boiled egg

Boiled eggs are eggs, typically from a chicken, cooked with their shells unbroken, usually by immersion in boiling water. Hard-boiled eggs are cooked so that the egg white and egg yolk both solidify, while soft-boiled eggs may leave the yolk, and sometimes the white, at least partially liquid and raw. Boiled eggs are a popular breakfast food around the world.

Poached egg egg that has been cooked by poaching

A poached egg is an egg that has been cooked, outside the shell, by poaching, as opposed to simmering or boiling liquid.

Egg allergy food allergy that is an allergy or hypersensitivity to dietary substances from the yolk or whites of eggs, causing an overreaction of the immune system which may lead to severe physical symptoms

Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus.

Conalbumin glycoprotein

Ovotransferrin (conalbumin) is a glycoprotein of egg white albumen. Egg white albumen is composed of multiple proteins, of which ovotransferrin is the most heat reliable. It has a molecular weight of 76,000 daltons and contains about 700 amino acids. Ovotransferrin makes up approximately 13% of egg albumen. As a member of the transferrin and metalloproteinase family, ovotransferrin has been found to produce heat shock proteins. When these heat shock proteins are induced in the skin, they provide protection against cold stress and other environmental stresses.

Egg as food animal product

Some eggs are laid by female animals of many different species, including birds, reptiles, amphibians, mammals, and fish, and have been eaten by humans for thousands of years. Bird and reptile eggs consist of a protective eggshell, albumen, and vitellus, contained within various thin membranes. The most commonly consumed eggs are chicken eggs. Other poultry eggs including those of duck and quail also are eaten. Fish eggs are called roe and caviar.

Aquafaba residual water from cooking legumes, used in recipes to substitute egg whites

Aquafaba is the viscous water in which legume seeds such as chickpeas have been cooked.

Salmonellosis annually causes, per CDC estimation, about 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths in the United States every year.

References

  1. Ornithology, Volume 1994 By Frank B. Gill p. 361
  2. James, John M.; Zeiger, Robert S.; Lester, Mitchell R.; Fasano, Mary Beth; Gern, James E.; Mansfield, Lyndon E.; Schwartz, Howard J.; Sampson, Hugh A.; Windom, Hugh H.; Machtinger, Steven B.; Lensing, Shelly (1998). "Safe administration of influenza vaccine to patients with egg allergy". The Journal of Pediatrics. 133 (5): 624–8. doi:10.1016/S0022-3476(98)70101-5. PMID   9821418.
  3. 1 2 3 4 5 McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004, edited by Vinay.
  4. Exploratorium
  5. Takehiko Yamamoto, Mujo Kim (1996-12-13), Hen eggs, ISBN   9780849340055
  6. "Science of Cooking: Ask the Inquisitive Cooks!". exploratorium.edu.
  7. McGee, Harold J.; Long, Sharon R.; Briggs, Winslow R. (1984). "Why whip egg whites in copper bowls?". Nature. 308 (5960): 667–8. Bibcode:1984Natur.308..667M. doi:10.1038/308667a0.
  8. “Egg Allergy Facts” Asthma and Allergy Foundation of America
  9. 1 2 Arnaldo Cantani (2008). Pediatric Allergy, Asthma and Immunology. Berlin: Springer. pp. 710–713. ISBN   978-3-540-20768-9.
  10. Roan, Shari (August 20, 2010). "Eggs and salmonella: What you need to know". Los Angeles Times. Retrieved September 14, 2011.
  11. Vandenesse, Urbain de, "Egg White." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Abigail Wendler Bainbridge. Ann Arbor: Michigan Publishing, University of Michigan Library, 2011. Web. Accessed 31 March 2015. <http://hdl.handle.net/2027/spo.did2222.0002.627>. Trans. of "Blanc d'oeuf," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 2. Paris, 1752.

Further reading