Although eggs of all birds may be eaten, the egg of chicken is used more often than any other. The natural function of an egg is to provide for the development of the chick. Its whole structure and composition is designed to fulfill this natural process.
Egg contains 12-14% proteins which are well balanced with respect to all the essential amino acids. Hence it is used as a standard against which the chemical score of other proteins is compared. The contents of two eggs provide nearly 25% of daily protein requirements of an adult man. Besides, egg proteins have an excellent supplementary value to all other plant protein foods. For example, cereal proteins are poor in amino acids, lysine. Pulses and oilseed proteins are poor in sulfur containing amino acid cysteine. Hence a combination of egg with any of the cereal or cereal pulse mixture will enhance the protein quality of food. The biological value of egg protein is the highest among the proteins from various foods.
Egg is one of the richest sources of lecithin - a phospholipid which forms a part of the structure of every cell wall in the body. Besides contributing to energy it is the source of essential fatty acids, linolenic acid and arachidonic fatty acids. Vitamins A, D and E are present in the yolk and egg fat also acts as the vehicle for these fat soluble vitamins. Egg fat is in highly emulsified form hence it is readily digested and absorbed.
On an average each egg contains 250 mg of cholesterol and the permitted intake is 300mg of cholesterol per day. Three to four eggs per week can be consumed by normal persons without any adverse effect.
There is a strong relationship between the mineral content of the hen’s diet and the concentration of minerals in the egg. Calcium is the most abundant mineral in the whole egg but it is concentrated in the shell. Important minerals such as phosphorus, iron, zinc and other trace elements are present in the egg. Egg is a rich source of biologically available zinc. Egg iron is bound to conalbumin and poorly absorbed in man.
Except for vitamin C, which is totally absent in the egg, other water soluble as well as fat soluble vitamins are present in the egg in appreciable amounts. The egg is particularly rich in vitamin A, riboflavin, folic acid and B12. The amount of these vitamins in the egg depends upon these nutrients present in the feed of the bird.
The nutritive value of the egg can be changed by manipulating the diet of the hen. Protein content cannot be changed much but addition of liquid oils to the hens diet, can increase the fat content of the egg. Exposure of the birds to sunshine or addition of vitamin D to the feed improves the vitamin D content of the egg. Vitamin D deficiency in the hen can reduce egg output. Even the cholesterol content of egg yolk can be reduced by feeding fish oil to the hen’s diet. No difference in nutritive value is noted between infertile and fertilized eggs.
By cooking eggs there is little or no change in the nutritive value of protein minerals or the fat soluble vitamins except there is some loss of thiamine and riboflavin. In hard cooked eggs, fried, poached and scrambled eggs the retention of riboflavin and thiamine is more than 85%. Heating egg white improves the availability of biotin as avidin gets denatured.
Egg is an excellent food and hence its quality is of very great importance. Fresh eggs are of the best quality. Quality of egg can be determined by many factors.like size, shell, air cell, egg white, egg yolk.
As the egg deteriorates they start to disintegrate and cannot hold the yolk in the center of the egg.
There are certain points which are to be remembered when one buys or handles the eggs.
Discard the broken ones, Refrigerate the eggs immediately at 4-7 Degree celsius, purchase the only amount of eggs needed for 1-2 weeks, cook eggs until at least the whites are completely coagulated and the yolk begins to thicken and are no longer liquidy. Cook slowly over moderate heat, it is best to cook and serve immediately and do not leave egg dishes at room temperature for more than 1 hour.
This article is written and submitted to The E Today by Shrushti Mehta.
We thank her for her research and analysis and hope to see the awareness about health and nutrition being spread ahead to larger mass of our citizens.