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Describe the structure and composition of an egg; Physical and chemical composition of eggs

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Eggs are made up 3 main parts: shell, white and yolk.
1. Shell; about 11% of the egg is shell. This is made up primarily of phosphate and calcium carbonate. The shell is porous, and odours and bacteria can enter through it to the egg white and yolk. The shell may be white or brown, depending on the breed of the hen, and to some extent, the type of feed. The colour does not relate to quality of the egg. Just inside of the egg are two membranes. These are made up of proteins called keratin and mucin. One of the membrane is closely associated with the shell; the other with the liquid content of the egg. As an egg gets older the content shrink and the other 2 membranes separate, forming an air space at one end of the egg.
2. Egg white; the egg white or albumin forms about 58% of the egg. It is found in three layers, 2 of which are thin and watery and the remaining 1 thick and viscous. The thin white is found immediately around the yolk and as an outer layer to the thick white near the inner shell membrane. The thick white lies between the layers of thin white. The ratio of thick and thin white are related to the storage conditions of the egg. The main components of egg white are water and protein. Most of the protein is ovalbumin, conalbumin and ovomucoid.
3. Egg yolk; the yolk forms about 31% of the egg. This is separated from the egg white by the vetelline membrane also known as the ‘yolk sac’. The yolk is held in position by the chalaza. These lope-like structures keep the yolk in centre of the egg. The yolk is made up of a small area of white yolk which is surrounded by yellow yolk. The germ (embryo) is positioned at the surface of the yolk and is attached to the white yolk. The higher the carotenoid intake, the more the yellow the yolk. The colour of the yolk is not an indication of the quality. The main components of egg yolk are water, fat and protein. Vitelline is the main protein.

Physical composition;
The physical appearance of an egg makes the first impression upon the consumer. If the product does not meet perceived expectations, consumer confidence diminishes. Therefore external and internal characteristic of eggs are prerequisite for safety, soundness and wholesomeness of the eggs.
- Most of the poultry egg are roundish or oval
- Most of the egg weigh about 35 to 73grams
- The chicken eggs is usually white or brown
- The main chemical component of egg shell is calcium which may have different levels in feed. Because of the differences in rearing system, the uptake of calcium may also be different.

Chemical composition;
• Calcium carbonate which is 97% of the egg shell
• Protein; it is 3% in shell, 10.5% in egg white and 16.5 in yolk
• Water; has 88.5% in egg white and 50% in yolk
• Fat; the egg yolk is 33% fat
• Fat soluble vitamins i.e. ADEK and also B vitamin
• Minerals i.e lecithin are mainly in eggs

Titany answered the question on April 25, 2022 at 08:40

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Describe the structure and composition of an egg; Physical and chemical composition of eggs

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