Albumen redirects here. This should not be confused with
albumin, a kind of
protein. In botany, the term albumen refers to the
endosperm inside a plant seed.
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 also come to 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 3.9 grams of protein, 0.3 grams of carbohydrate and 62 milligrams of
sodium. The U.S. large egg white 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.
- Function- Nourishment; blocks digestive enzymes
- Function- Binds iron
- Function- Blocks digestive enzymes
- Function- Plugs defects in membranes, shell
- Function- Enzyme that digests bacterial cell walls
- Function- Thickens albumen; inhibits viruses
- Function- Binds vitamin (biotin)
- Function- Bind vitamins, block digestive enzymes...
[4]
Uses
- It is often separated and used for cooking (for glairs, meringues, soufflés, and some omelets),
hence 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]
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 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
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 denaturization. The second stress
comes from the mixing of air into the whites which causes the proteins to come out of their natural state. These denaturized
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.[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 white to create this effect. 1/2 teaspoon/2ml of lemon juice can also be used to create the same
results.[9]
References
- ^ McGee, 77
- ^ McGee, 79
- ^ Exploratorium
- ^ McGee, 77
- ^ Gilbertus, 6
- ^ Elmhurst College
- ^ McGee, 102
- ^ McGee, 102-103
- ^ 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
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
