Composition of White Egg
The white consists almost wholly of water and proteins, with a few minerals, which is very unusual for product of animal origin (90% of the dry matter consists of proteins).
It also contains free glucose (at double the concentration of blood plasma) which constitutes a primary source of energy available to the embryo. Each protein is known for its specific properties, both functional and nutritional.
Ovalbumin, the most abundant protein in albumen, is phosphoglycoprotein. It contains 3.5% carbohydrates with the number of moles of phosphates bonded to the serine residues varying from 2 to 0.
The molecule contains four free sulphydryl groups and two disulphide bridges, but the number of the latter increases during storage and an ‘S-albumin’ is formed which is more thermostable than the native protein. The proportion of S-ovalbumin, which is 5% at the time of laying, can reach 80% after six months’ cold storage.
Conalbumin (or ovotransferrin) is a glycoprotein consisting of two subunits. It has the capacity to bind bi- and trivalent metal cations into a complex. At its pHi one molecule can bind two cations and take on a red (Fe3+) and yellow (Cu2+) color. These metals complexes are more thermostable than protein in the native state.
Ovomucoid is a glycoprotein which is consists of three sub-units. It is heat resistant – except in an alkaline medium – and has an anti-trypsin activity.
Lysozyme is a holoprotein with a very high pH. It has a B-glucosaminidase enzymatic activity which allows it to lyse the wall of certain Gram-positive bacteria.
Ovomucin is a glycoprotein whose carbohydrate content is almost 30%. The stretched structure of the molecule and a result of the electrostatic repulsion due o the negative charges of the residues of sialic acid which are responsible to the viscosity of the gel layer of the albumen.
This protein is insoluble in water and soluble in salt solutions whose pH is higher than, or equal to 7.
Composition of White Egg
