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 also come to have many culinary and non-culinary uses for humans.

Contents

Composition

Uses

Denaturation

Egg white foam

Creating an egg foam

Stabilizing egg white foam for culinary purposes

Copper Bowl

Adding an acid

References

Works cited

See also

External links

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 3.9 grams of protein, 0.3 grams of carbohydrate and 62 milligrams of sodium. The U.S. large egg contains about 20 calories.^[2]
Albumen, the scientific name for 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%
:Function- Nourishment; blocks digestive enzymes

★ Ovotransferrin 12%
:Function- Binds iron

★ Ovomucoid 11%
:Function- Blocks digestive enzymes

★ Globulins 8%
:Function- Plugs defects in membranes, shell

★ Lysozyme 3.5%
:Function- Enzyme that digests bacterial cell walls

★ Ovomucin 1.5%
:Function- Thickens albumen; inhibits viruses

★ Avidin .06%
:Function- Binds vitamin (biotin)

★ Others 10%
:Function- Bind vitamins, block digestive enzymes...
^[1]

Uses

★ It is often separated and used for cooking (for glairs, meringues, soufflés, and some omelets), whence it derives its name: when albumen is beaten or cooked it turns white.

★ 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.^[5]

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 strings are raveled up in a tangled 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.^[6] As these proteins strings unfold and entangle with other proteins, new bonds form between these amino acids and the amino acids of neighboring proteins, causing the texture change in a cooked egg.
Copper (II) sulphate can also cause the same reaction, when egg albumen is placed with a strong concentration of copper sulphate, the egg white will rapidly denaturalize and turn opaque, and form entangled white threads of protein seen when cooking egg whites.

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. The second stress comes from the mixing of air into the whites which causes the proteins to come out of their natural "folded" state. These proteins "unfolded" 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.^[7]

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.^[8]

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 yolk to create this effect. 1/2 teaspoon/2ml of lemon juice can also be used to create the same results.^[9]

References

1. McGee, 77
2. McGee, 79
3. Exploratorium
4. McGee, 77
5. Gilbertus, 6
6. Elmhurst College
7. McGee, 102
8. McGee, 102-103
9. 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

★ Egg (food)

★ Egg yolk

★ Eggshell

★ Cooking

External links

★ Contemporary Wet Plate Collodion Negatives & Photographs at collodion.com

★ The Contemporary Wet Plate Collodion Experience Manual at collodion.com

★ How to make albumen photographic paper

★ Nutritional Info

★ Albumen images