Eggs


1. Raw materials

Eggs

Because of eggs' versatility, nearly all baked goods contain them. Eggs have six distinct parts: thin white, thick white, yolk, shell, air cell and chalazae. About two-thirds of the weight of the edible part of an egg is egg white; about one-third is the yolk. Overall most of the whole egg is moisture, with smaller amounts of protein fat and emulsifiers.

The egg white or albumen consists - apart from a small amount of minerals and glucose - entirely of water and protein. The proteins in the egg white are extremely important for its functionality, egg white is 90 % water and 10 % protein.

Compared to the yolk, egg white has little flavour or colour. It has both thick and thin portions, with the tick portion thinning as the egg ages. As it thins, egg white loses its ability to form stable foams.

Egg yolks are about half moisture and half yolk solids. As eggs age, yolks pick up additional moisture form the white. When this happens the yolk thins out. It has a protective membrane that weakens as it ages, making it more difficult to separate the yolk from the white. The solids in egg yolks consists of proteins fats and emulsifiers with small quantities of minerals and yellow-orange carotenoids. The proteins in the yolk are not the same as in the egg white. Most of the egg yolk proteins are "lipoproteins" i.e. proteins that are bound to fats and emulsifiers.

component
whole egg
egg white
yolk
moisture
76 %
88 %
50 %
proteins
12 %
10 %
17 %
Fats and emulsifiers
10 %
0 %
30 %
others
2 %
2 %
3 %

The most well-known emulsifier in egg yolk is lecithin. Lecithin is not a single substance. It is a complex mixture of emulsifying lipids. Lecithin is also found in cereal grains and soy beans. The emulsifying lipids in lecithin are called phospholipids. They consists of two fatty acids attached to glycerol. Instead of the 3rd fatty acid phospholipids contain a phosphate group. The fatty acids are attracted to fats and oils while the phosphate group is attracted to water. Because of this characteristic phospholipids can act as emulsifiers. The phospholipids become even more effective when there is phospholipase (enzyme) present.

By bonding to lipids as well as to water emulsifying phospholipids hold together, or bind, complex mixtures of ingredients present in cake batters.

It is also interesting to remember that shell colour has no effect on flavour, nutrition or functionality of the eggs. Eggs contain two protective membranes between the shell and the white. Soon after an egg is laid, an air cell forms between the membranes at the egg's larger end. As the egg ages, loses moisture (the shell is porous and sometimes eggs are coated with a tiny film of oil to prevent moisture loss) and shrinks, the air pocket increases in size. This is why older eggs float in water while fresh ones sink.

Eggs have the following functionalities:

Coagulated egg proteins in both egg whites and egg yolks are important structure builders in baked goods. Eggs are as important as flour (and sometimes even more so) in building structure in cakes and muffins. In fact, without eggs, most cakes collapse.

Coagulated egg proteins also provide thickening and gelling in custards etc. Eggs are considered thoughners because of their ability to provide structure. Eggs are probably the only common bakery ingredient containing significant amounts of both thoughners (proteins) and tenderisers (fats and emulsifiers). The tenderisers are concentrated in the yolk.

Because of the tenderising fats and emulsifiers in the yolk, egg yolk contributes less toughening than an equal amount of egg whites. The proteins in the yolk bound as lipoproteins, do not coagulate as quickly as egg white proteins and hence produce a shorter, more tender structure. But remember that egg yolk, despite the fact that they contain tenderisers, are classified as thoughners or structure builders.



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NoŽl Haegens

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