Eggs Compostion and Nutritional Content

Egg especially the hen's egg is a food product that is always present to every household refrigerator. Egg is one of the most versatile foods as they are used in so many different ways in food preparation. Eggs are a good source of high biological value protein and they are easily digested, therefore they are valuable food for people who are recovering from sickness.

Eggs are composed of three main parts:

Shell
Egg white
Egg yolk
88.5% of an egg is edible

Shell: The shell of an egg is porous (with tiny pores) to allow the developing chick to obtain oxygen, other than the oxygen, bacteria and odors can enter the egg. The pores also allow water and carbon dioxide to escape. The membranes that line the shell inside act as filters to bacteria to protect the inside. At one end of the egg, the membranes separate into an air space, to supply the chick with oxygen. The shell is generally strong, but the older birds tend to produce weaker shells. The shell's color varies according to the breed of the bird.

Two Layers of Egg white:

The thick white (nearest to the yolk)
The thin white (nearest to the shell)

Yolk: The color of the egg yolk is related to the diet of the hen and is due to the presence of carotenes and any colorings added to hen's feed. The nutritional value of the egg is not affected by the color of the yolk.

Nutritional content of egg white:

88.5% water
10.5% protein
Riboflavin and other B vitamins
A trace of fat

Nutritional Content of Egg yolk:

16.5% protein
33% fat
50% water
Fat-soluble vitamins A, D, E, and K
Mineral elements, including iron
Lecithin (an emulsifier)

Changes that takes place as the egg gets older:

Water moves from the white to the yolk.
Yolk linings weaken.
The thick white becomes thinner.
The size of the air space increases.
The shell looks dry because the moisture is lost through the shell.
Bacteria enter through the shell. Then the egg eventually decomposes as bacteria contaminate the contents.

How to check if the egg is fresh: You can check the eggs you buy if it is fresh by placing them in a bowl with a mixture of 2 tbsp salt dissolved in 575ml of water. If the egg sinks, it is fresh. If it floats on the surface, it is stale.

Storage:

- Eggs should be stored in a refrigerator, away from strong smelling foods, because it can easily acquire the smell of the food.
- Eggs should not be washed as this destroys the protective cuticle. They will normally stay in good condition if stored correctly for two to three weeks.
- Eggs are commercially stored in rooms of high humidity and low temperature to prevent moisture loss and deterioration.

Common uses of eggs in food preparation:

Thickening. Eggs are used to thicken custards, sauces, soups, etc., because of the coagulation of the egg proteins.
Emulsifying. Egg yolk contains lecithin which is an emulsifier and enables oil and water to be mixed to an emulsion without separating. This is use in making Mayonnaise and Cake.
Binding. Ingredients for rissoles, croquettes, and meat or fish cakes can be bound together with egg, which when heated will coagulate and hold the ingredients together.
Coating. Eggs are used as a coating for fried food, because they form a protective layer on the outside of the food which sets and holds it together and prevents it from overcooking.
Glazing. Egg yolk, egg white, or whole egg is use to brushed over pastries, bread, to produce a golden brown shiny glaze during baking.