Egg white

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File:Raw egg.jpg
An egg yolk surrounded by the egg white.

Egg white is the common name for the clear liquid (also called the albumen or the glair/glaire) contained within an egg. It is the cytoplasm of the egg, which until fertilization is a single cell (including the yolk). It consists mainly of about 15% proteins dissolved in water. Its primary natural purpose is to protect the egg yolk and provide additional nutrition for the growth of the embryo, as it is rich in proteins and is of high nutritional value. Unlike the egg yolk, it contains a negligible amount of fat. Egg whites have many culinary and non-culinary uses for humans.

Composition

The egg white is approximately two-thirds of the total egg's weight out of its shell with 90% of that weight coming from water. The remaining weight of the egg white comes from protein, trace minerals, fatty material, vitamins, and glucose.[1] The U.S. large egg's white weighs 38 grams with 9.6 grams of protein, 0.3 grams of carbohydrate and 62 milligrams of sodium. The U.S. large egg white contains about 20 calories.[2] Egg white contains approximately 40 different proteins.[3] Below is a list of the proteins found in egg whites by percentage along with their natural functions.

  • Ovalbumin 54% Nourishment; blocks digestive enzymes
  • Ovotransferrin 12% Binds iron
  • Ovomucoid 11% Blocks digestive enzymes
  • Globulins 8% Plugs defects in membranes, shell
  • Lysozyme 3.5% Enzyme that digests bacterial cell walls
  • Ovomucin 1.5% Thickens egg white; inhibits viruses
  • Avidin .06% Binds vitamin (biotin)
  • Others 10% Bind vitamins, block digestive enzymes...

[4]

Egg white is also conspicuously lacking in dietary cholesterol, which is a target component for reduction in the American diet.[5]

Uses

  • It is often separated and used for cooking (for glairs, meringues, soufflés, and some omelets), hence it derives its name: when egg white is beaten or cooked it turns white.
  • In recipes calling for egg yolk, two egg whites can often be used to replace one egg yolk.[5]
  • In schools it is often used to teach pupils how to test for protein using Biuret reagent.
  • It is used to remove sediments from champagne and beer and to clarify broths.
  • It was used in the emulsion of traditional photographic paper.
  • It was used in medieval medicine to treat wounds and broken bones.[6]
  • They are recommended for consumption by chemotherapy and renal patients as a source of 90.0g of lean protein.[7][8]
  • It is used by athletes and bodybuilders as a health food supplement.[9]
  • It can be used as a base for waterproof glues. [10]

Nutrition

Biotin deficiency can be caused by excessive consumption of raw egg whites over a long period (months to years). Egg whites contain high levels of avidin, a protein that binds the vitamin biotin strongly.

Denaturation

All proteins, including those in egg white, are made of long chains of amino acids which are similar to beads on a string. In a raw egg, these chains are raveled up in a specifically arranged compact mass. Chemical bonds and interactions between the amino acids within each protein hold this mass in a specific shape and stop it from unraveling. As an egg cooks, the heat causes the bonds within the proteins to break, a process called denaturation.[11] As these proteins chains unfold and entangle with other proteins, new bonds form between these amino acids and the amino acids of neighboring proteins, causing the texture to change.

Egg white foam

Creating an egg foam

The physical stress of beating the egg white can create a foam. There are two types of physical stress caused by the beating of the egg whites with a whisk, the first being that 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 becomes a foam holding the incorporated air into place.[12]

Stabilizing egg white 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 will have the same result as the copper bowl or a pinch of powdered copper supplement from a health store used in a glass bowl will yield the same result as well. Drawbacks of the copper bowl include the expense of the bowl itself, as well as the fact that the bowls are difficult to keep clean. Copper contamination from the bowl is minimal as a cup of foam will contain a tenth of one's daily normal intake level.[13]

Adding an acid

Cream of tartar (potassium bitartrate) is an acidic salt that can be used to change the pH of the egg white to an acidic range by boosting the number of free-floating hydrogen ions in the egg white. This has the effect of stabilizing the foam, and is therefore an alternative to using a copper bowl. 1/8 teaspoon/0.5g cream of tartar should be used per one egg white to create this effect. 1/2 teaspoon/2ml of lemon juice can also be used to create the same results.[14]

References

  1. McGee, 77
  2. McGee, 79
  3. Exploratorium
  4. McGee, 77
  5. 5.0 5.1 Cook for lower cholesterol. American Heart Association. Retrieved on 2008-01-18.
  6. Gilbertus, 6
  7. Fresh Egg Whites, Kosher Egg whites, Pure Protein Food - Eggology, Inc
  8. Transplant Chronicles (pdf) 11. National Kidney Foundation (Summer/Fall 2007).
  9. Eggology Official Website [1]
  10. Glue of the Month, 2002 March [2]
  11. Elmhurst College
  12. McGee, 102
  13. McGee, 102-103
  14. McGee, 103

Works cited

  • Elmhurst College, Denaturation Protein
  • Exploratorium, Anatomy of an Egg
  • Gilbertus. Compendium Medicine Gilberti Anglici Tam Morborum Universalium Quam Particularium Nondum Medicis Sed & Cyrurgicis Utilissimum. Lugduni: Impressum per Jacobum Sacconum, expensis Vincentii de Portonariis, 1510.
  • Good Eats, Let Them Eat Foam. DVD. Television Food Network, June, 13 2001.
  • McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004.

See also

External links

Wikibooks
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