Egg white is the common name for the clear liquid -- also called the albumen -- 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 85 percent water and 15 percent proteins. The primary natural purpose of egg white is to protect the egg yolk and provide additional nutrition for the growth of the embryo, as it is rich in proteins and also of high nutritional value. Unlike the egg yolk, it contains a negligible amount of fat and cholesterol.
Protein
Egg proteins are classified as high-quality proteins and serve as a reference protein for defining the quality of other proteins. Its essential amino acid pattern is very close to the pattern of the tissue proteins. One large egg white -- approximately 33 gm -- will provide four gm of protein. Ovalbumin is the principal protein found in egg whites, constituting more than 50 percent of egg white protein; the other main proteins are ovotransferrin, 12 percent, and ovomucoid, 11 percent. Boiling egg whites improves the digestibility of the proteins with minimal or no loss in nutritive value.
Energy and Carbohydrates
One large egg white provides about 15 calories each. This is largely protein calories, since it contains trace amounts of carbohydrates.
Fats
Egg whites are a good substitute for whole eggs on a cholesterol-restricted diet. They contains zero saturated fats and zero cholesterol. Since egg whites are also low in calories, they can be used in energy-restricted and weight watcher's diets too.
Vitamins and Minerals
Egg whites are a good source of riboflavin -- B complex vitamin -- providing 0.15 mg per 33 gm per one large egg white. Other vitamins, like thiamine, are present in trace amounts. The mineral content of an egg white is not high, with two mg of calcium, four mg of phosphorus, 48 mg of potassium and 55 mg of sodium per 33 gm of white. An egg white lacks in iron and vitamin A, two principal components present in the egg yolk.
Non-nutrient Component
Trypsin inhibitors are found in animal foods like egg whites; they inhibit the activity of trypsin, an enzyme, in the gut and interfere with the digestibility of dietary proteins and reduce their usefulness. These inhibitors are heat liable and easily inactivated by cooking egg whites.
References
- ''Egg white''; Frederic P Miller, Agnes F Vandome, John McBrewster; 2010
- ''Nutritive Value of Foods''; Susan E. Gebhardt, Ruth H. Matthews; 1994
- ''Encyclopaedia of Health and Nutrition''; Arti Bhatia; 1999
- ''Nutritive value of indian foods''; C. Gopalan, B.V. Rama sastri, S.C. Balasubramanian; 2002
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