Egg White Proteins

June 9, 2008

Egg whites are made up primarily of water (90%) and protein (10%), with trace amounts of other molecules. Of the different proteins, there are three that are useful to know because of their effects on cooking.

Ovomucin - This protein thickens and solidifies the egg white when cooked. Although it makes up a very small percentage of the total protein in the white, ovomucin turns the liquid white into a compact solid. Over time the protein disintegrates in the egg so that the white can be digested more easily by the developing chick, but this also means that older raw eggs may not set as well as fresh ones.

Ovalbumin - This protein is the most abundant in the egg white, and because it has reactive sulfur groups, it contributes significantly to the color, flavor and texture of eggs. Very fresh eggs cook more quickly than older ones because ovalbumin’s heat resistance increases for a few days after laying.

Ovotransferrin - Ovotransferrin is the first protein to solidify during cooking, so it will determine the temperature needed to do so. The protein also binds to iron atoms so that bacteria can’t it. This is important for cooking because ovotransferrin will bind to the abundant iron in the yolk when the yolk is broken and mixed with the white. This binding makes the egg more resistant to solidification, which leads to a higher cooking temperature. This protein also causes the whites to change color when whipped in a copper bowl or mixed with iron supplement.

Recognizing how these proteins change the way eggs are cooked hopefully will lead to better breakfast results.

Source: On Food and Cooking, Harold McGee
photo credit: Greg M.

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