Albumin is a class of proteins found in egg whites, milk, blood, and various plant and animal tissues.
It is the most abundant type of proteins found in egg whites and in normal human blood plasma.
Albumins dissolve in water and form a semi-solid mass when heated, and this is what is responsible for egg whites turning solid and white when cooked.
The term albumin refers an abundant type of proteins found in egg whites but this can be confusing, since the egg white itself is called albumen.
While albumin refers to the predominant protein in the white, albumen but can easily be confused with the term albumen, which is a name for the egg white itself, and could be described as a solution of protein and water (egg whites are 88% water).
The two terms are often used interchangeably, however.
The word albumen comes from the Latin word albus, meaning white.
The albumen, and the albumin protein it contains, performs many complex functions in the eggs, including protection against microorganisms and providing water and cushioning to the growing chick.
In human nutrition, egg albumen is often described as a complete protein because it contains all the essential amino acids needed for human health and also has good digestibility, especially when cooked.
Types of Albumin in Egg White
The albumin in egg whites is specifically known as ovalbumin, which makes up 50 to 70% of the total protein (sources vary). Other proteins are ovotransferrin, ovomucoid, lysozyme, ovomucin, conalbumin, globulins, flavoprotein, ovoglycoprotein, ovomacroglobulin; and avidin.
Anti-nutrient in Egg Whites: Avidin
The protein avidin is an inhibitory substance with a large affinity for binding with biotin. When consumed, avidin’s binding with biotin can prevent its absorption by the gut, so eating large amounts of uncooked egg whites can interfere with biotin nutrient status, and perhaps even a deficiency of biotin. Cooking the egg whites denatures avidin and so prevents its binding with biotin, making cooked egg whites safe to eat.
Albumin in Milk and Blood
In milk, albumin is found as lactalbumin.
In humans, albumin is produced by the liver (up to 10 grams a day). In the blood, its main function is to help maintain colloidal osmotic pressure which prevents plasma from being lost through the capillaries, and so regulates the distribution of extracellular fluid. Albumin is also a carrier molecules, transporting many substances such as bilirubin, fatty acids, calcium, hormones, and some drugs.
Whipped egg white image © Carmen Rockett | Dreamstime.com