Structure and Composition of Egg - FOODZAQ

Hello friends, Welcome to my blog FOODZAQ. Today we are discuss about structure and composition of egg. Eggs are very good source of high quality protein, which is comparatively inexpensive. Egg contain shell, shell membrane, egg white and egg yolk. Egg white contain more than half of the protein of an egg. Egg white also contain significant amount of protein and lower amount of fat than the yolk. Eggs are rich source of selenium, vitamin D, B6, B12 and minerals such as zinc, iron and copper.

STRUCTURE OF EGG

Egg contain 4 major parts and they are :

1. Egg shell
2. Shell membrane
3. Egg white (Albumin)
4. Egg yolk

1. Egg shell

shell contain approximately 11.2% weight of egg. Egg shell is made up of calcium carbonate and with lesser amounts of calcium phosphate. Egg shell consist of 3 parts and they are : 

(1) Mammillary layer

In hens, the thickness of mammillary layer is about 0.11mm.

(2) Spongy layer

This layer is super imposed of mammillary layer, It give rigidity and strength to the shell.

(3) Pores

Pores are found the surface of shell, which permit gaseous exchange. In fresh egg pores are small. but under influence of high temperature of high temperature, number of visible pores are increased.

2. Shell membrane

A shell membrane contain both outer and inner membranes. Both membranes helps to protect quality of egg. both membranes are porous and composed of fibers. The outer membrane which is thicker (48micro meter) than the inner membrane (22micro meter).

Air cell

Egg contain Little or No air cell when they are laid. After being laid  because of the lower temperature of the outer surroundings of egg than it was in the hens body, there is a contraction of inner content of egg. This results air being drawn in to the shell and air cell is formed. usually the air cell is formed at large end of the egg.

3. Egg white

It contain 4 layers and they are

1. Outer thin layer.
2. Firm layer or jell like layer
3. Inner thin layer
4. Chalaziferous layer

Chalaziferous layer

It is the membrane surrounded the egg yolk and extended to the firm layer of the albumin. The extreme end of albumin is called chalaza, which prevents yolk from raising rapidly towards the shell when egg is at rest.

4. Egg yolk

Egg yolk contain vitelline membrane, germinal disk, latebra and yolk material.

1. Vitelline membrane

The yolk of the egg is enclosed in a sac called vitelline membrane. It is thin, strong and almost calories and responsible for maintaining a spherical shape.

2. Germinal disk

The yolk carries germinal disk or germ spot, which under suitable condition develop into chick. The germinal disk appears a small light colored spot on the surface of yolk.

3. Latebra

It connect germinal disk to the yolk material.   

COMPOSITION OF EGG

Egg shell

Egg shell contain 8-11% of total weight of egg. The composition of egg shell is

• Calcium Carbonate = 93%
• Magnesium carbonate = 1.3%
• Phosphorous pentoxide = 0.7%
• Other organic matters = 4-5%

Egg white

Contain 56-61% of total weight of egg. The composition of egg white is

• Water =  88%
• Protein = 11%
• Fat = 0.2%
• Minerals = 0.8%

Egg white contain different type of proteins and they are

• Ovalbumin = 55% of the egg white protein.
• Conalbumin =  13% of the egg white protein.
• Ovamucoid = 10% of the egg white protein.
• Lysozyme = 3.5% of the egg white protein.

Egg yolk 

Egg yolk contain 27-32% of total weight of egg. Composition of egg yolk is

• Water = 48%
• Protein = 17.5%
• Fat = 32.5%
• Minerals = 2%

MINERALS FOUND IN EGG

Egg contain calcium, phosphorous, iron, sodium, potassium and sulphur.

1. Calcium

Calcium is the most abundant mineral in egg. It is most concentrate in the shell. It is also present in significant amount in egg yolk and small amount in egg white.

2. Phosphorous

 P is the most abundant mineral in yolk. 

FAT FOUND IN EGG

Fat in the egg is concentrated to the yolk portion. Egg is one of the richest of lecithin. A average egg contain 250ml of cholesterol and the permitted intake is 300ml of cholesterol per day.

VITAMINS FOUND IN EGG

Except vitamin c, which is totally absent in egg. Egg is rich in vitamin A, riboflavin, folic acid and vitamin B12.

PIGMENTS FOUND IN EGG

Shell

• Oopophyrine (Brown color)
• Oocyanine (greenish color)

Egg white

Contain small amount of ovaflavin (greenish color)

Egg yolk

Contain carotenoids (yellow) and xanthophyll (yellow)

Guys, Thank you for reading my blog FOODZAQ. I hopes you should understands about structure and composition of egg. If you have any suggestion or doubts please feel free to comment below. If you like this blog, you can check my previous blogs as well. Thank you again. Have a great day.