Egg white

Egg whiteis the clear liquid (also called thealbumenor theglair/glaire) contained within anegg. Inchickens, it is formed from the layers of secretions of the anterior section of the hen'soviductduring the passage of the egg.It forms aroundfertilizedor unfertilizedegg yolks. The primary natural purpose of egg white is to protect the yolk and provide additional nutrition for the growth of theembryo(when fertilized).
Egg white consists primarily of about 90% water into which about 10%proteins(includingalbumins,mucoproteins, andglobulins) are dissolved. Unlike the yolk, which is high inlipids(fats), egg white contains almost no fat, andcarbohydratecontent is less than 1%. Egg whites contain about 56% of the protein in the egg. Egg white has manyuses in food(e.g.meringue,mousse) as well as many other uses (e.g. in the preparation ofvaccinessuch asthose for influenza).
Egg white makes up around two-thirds of a chicken egg by weight. Water constitutes about 90% of this, with protein, traceminerals, fatty material,vitamins, andglucosecontributing the remainder.A raw U.S. large egg contains around 33 grams of egg white with 3.6 grams of protein, 0.24 grams ofcarbohydrateand 55 milligrams ofsodium. It contains nocholesteroland the energy content is about 17calories.Egg white is an alkaline solution and contains around 149 proteins.The table below lists the major proteins in egg whites by percentage and their natural functions.
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 aholoproteinwhich 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 as great as in the thin albumen.
Thephysical stressof beating egg whites can create afoam.  Two types of physical stress are caused by beating them with a whisk:denaturationandcoagulation.
Denaturation occurs as the whisk drags the liquid through itself, creating a force that unfolds theproteinmolecules.
Coagulation 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 wherethe air and water meetand create multiple bonds with the other unraveled proteins, and thus become a foam, holding the incorporated air in place; because the proteins consist ofamino acids, some arehydrophilic(attracted to water) and some arehydrophobic(repelled by water).
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 ascooking oilsor the fats contained inegg yolk.
Copperbowls have been used inFrancesince the 18th century to stabilize egg foams. The copper in the bowl assists in creating a tighter bond in reactivesulfuritems such as egg whites.  The bond created is so tight that the sulfurs are prevented from reacting with any other material.  Asilver-platedbowl has the same result as the copper bowl, as will a pinch of powdered copper supplement from ahealth storeused 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 normaldaily intake level.
Although egg whites are prized as a source of low-fat, high-protein nutrition, a small number of people cannot eat them.Egg allergyis more common among infants than adults, and most children will outgrow it by the age of five.Allergic reactionsagainst egg white are more common than reactions against egg yolks.In addition to true allergic reactions, some people experience afood intoleranceto egg whites.
Eggs are susceptible toSalmonellacontamination. Thorough cooking eliminates the direct threat (i.e. cooked egg whites that are solid and not runny), but 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, theFDAordered the recall of 380 million eggs because of possibleSalmonellacontamination.
Cooked eggs are a good source of biotin. However, daily consumption of raw egg whites for several months may result inbiotin deficiency, due to theiravidincontent, as the avidin tightly binds biotin and prevents its absorption.
Egg white is afining agentthat can be used in theclarification 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.
The albumen from egg white was used as a binding agent in early photography during an 1855-90 period; such prints were calledalbumen prints.
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 withArmenian bolecould help restore the fibers. Egg whites are also used in bookbinding during thegildingprocess, where it is referred to as 'glaire', and to give a book cover shine.