Egg – Miracle within a Shell

For centuries, eggs have played a major role in feeding families around the globe. Early civilizations, across different religions and cultures, considered the egg to be sacred for the miracles of life it represented; as a symbol of new life, fertility and rebirth.

The history of eggs as an important food dates back to the times of early man, who used to raise chicken and other birds as an important source of food. Birds preceded man in the evolutionary chain and so have the eggs. The chicken was probably domesticated for its eggs from jungle fowl, native to tropical and subtropical Southeast Asia and India before 7500 BC. East Indian history of domestication of wild fowl is followed by Egyptian and Chinese one, followed by Europeans’, who has had domesticated hens since 600 B.C., and so on.

In short, eggs have been a staple in the human diet for thousands of years. From hunter-gatherers collecting eggs from the nests of wild birds, to the domestication of fowl for more reliable access to a supply of eggs, to today’s genetically selected birds and modern production facilities, eggs have long been recognized as a source of high-quality protein and other important nutrients.

Most people of the world relish egg of the chicken, Gallus domesticus. Nearly 200 breeds and varieties of chickens have been established worldwide. Only a few breeds are economically important as egg producers. India has the distinguished place in World Poultry History for its outstanding role in the evolution of modern Layer and Broiler breeds based on the Red Indian Jungle Fowl (C. Krishna Rao, IPSACON-2005).

When we mention of eggs, we think of eggs that come from a chicken. Although, the chicken egg is the most common, there are a wide variety of different types of eggs that are consumed, including eggs from duck, quail, goose, turkey, ostrich, pigeon, pheasant and emu, and even fish.

In modern times while all urban markets are flooded with white shelled eggs there is hardly any trace of the desi eggs. However, there is still a cross-section of the urban elite who yearn for the desi egg and are willing to pay a higher price because of the superior table qualities. Desi eggs from the Kashmir Valley are in more demand and are all set to hit the international market.

Again, there are Organic Eggs produced from hens that have been given all natural feed that do not contain any pesticides or herbicides and Free Range Eggs produced by hens that have been raised outdoors. And then there are Vegetarian Eggs, which come from hens that are raised on a vegetarian diet. In all, most commercially produced chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without roosters.

Composition:

The incredible egg is composed of yellow yolk and translucent white surrounded by a hard shell holding within a unique food chemistry.

Egg shell: Egg shell is an outermost covering of egg, made up of calcium carbonate. The colour that gets added in the uterus during shell formation may vary with the species and breed, from the more common white or brown to pink or speckled blue-green. However, egg shell colour has nothing to do with egg quality, flavour, or even nutritive value.

Air cell: The larger end of the egg contains the air cell (pocket of air) that forms when the contents of the egg cool down and contract after it is laid. A very fresh egg has a small air cell. With ageing, the size of the air cell goes on increasing, indicating deterioration in egg quality.

Shell membranes: Immediately after the shell there are two shell membranes; inner and outer that surrounds the albumen. Air cell forms between these two membranes. Shell membranes act as a barrier against bacterial penetration.

Egg white or albumen: Albumen present in the egg is again of two types; thin albumen, which is towards the shell and thick albumen, closer to the centre. Egg white is a major source of protein.

Chalazae:  These are the twisted and cord-like strands of egg white that anchor yolk in the center of egg. Its prominence is the proof of egg’s freshness.

Vitelline (yolk) membrane: Yolk membrane separates egg white from yolk and holds the yolk.Egg yolk: The yellow portion of an egg, colour shades of which vary with the diet fed to the hen. The yolk in a fresh egg is round and firm and is a major source of vitamins, minerals, and fat.

Nutrients: Eggs are very nutrient-dense and energy-dense with lots of vitamins, protein and fats. The necessary proteins, lipids, carbohydrates, vitamins, minerals, and functional nutrients are all present in sufficient quantities for the transition from fertilized cell to newborn chick, and the nutrient needs of an avian species are similar enough to human needs to make eggs an ideal source of nutrients for us, too. However, the eggs we eat are not fertilized, but all of the nutrients are present.

In reality, an egg is a package of three individual foods; the whole egg, the white, and the yolk, each of which has its own distinct nutritional composition. The albumen portion in an egg contains water (~ 88%), proteins and vitamins along with traces of fat, while yolk comprises of water (~ 50%), proteins, and fats and vitamins particularly fat-soluble vitamins A, D, E and K, along with minerals.

Proteins: Our body structure like any other animal is built on proteins. And, irrespective of age, we need sufficient amount of proteins for building up of the tissues and taking care of their wear and tear. On an average, a single egg provides 6 – 7 gm of protein. The proteins in eggs are well distributed in both, white and yolk, with sufficient amounts of amino acids (including the essential ones); alanine, arginine, aspartic acid, cystine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine. More than 90 percent of proteins are digestible in cooked eggs, whereas in raw eggs only 50 percent are bio-available.

Egg white is made up of some forty-odd types of proteins including ovalbumin, ovotransferrin, ovomucoid, and flavoprotein. The major proteins found in egg yolk include both low-density and high- density lipoproteins, phosvitin, and livetin.

Lipids:  Egg white has virtually no fats or lipids, while egg yolk contains triacylglycerides, phospholipids, and cholesterol. Of the total phospholipids, phosphatidylcholine (lecithin) is the largest fraction followed by phosphatidylethanolamine. The lipids in the yolk are so finely emulsified that even infants can easily digest it. It is the fatty-acids present in the diet of the hen that influences the composition of egg yolk lipids. Since eggs are one of the richest sources of dietary cholesterol, its very presence deters many from going for it. Scientific data, on the basis of amount and type of cholesterol present, clear many doubts regarding the ill effects of the cholesterol from eggs and advocate its consumption on daily basis.

Vitamins: The wide spectrum of vitamins present makes eggs nutritionally rich. Eggs contain all the essential vitamins, except for vitamin C, since the developing chick does not require it. Eggs are one of the few natural sources of vitamins D, B12 and E. Riboflavin (B2) and niacin (B3) are concentrated in egg white or albumen. The yolk, on other hand, contains the majority of the water-soluble vitamins (including B-complex group) and cent percent of the fat-soluble vitamins (A, D, E and K).

Minerals: All essential minerals are found in eggs. Of particular importance is the iron found in egg yolk. In addition, eggs contain calcium, phosphorus, sodium, potassium, magnesium, zinc, copper, manganese and selenium.

Choline: Choline plays an essential role in maintaining healthy cell membranes and in brain development, especially in the development of the memory centers of the fetus and newborn. The requirement for choline increases during pregnancy and lactation owing to the high rate of its transfer from the mother to the fetus and into breast milk. Egg yolk lecithin (phosphatidylcholine) is an excellent source of dietary choline. An average size egg can provide about 100-125 mg of choline.

Carotenes: Egg yolk contains two important xanthophylls; lutein and zeaxanthin. Their level in the yolk decides the colour; more are the xanthophylls (alcohol containing carotenes), deeper is the shade of yellow. Carotenes are related to vitamin A and found in retina of eye.

Eggs are the cheapest food items considering their nutritive value and are available at every street corner in urban areas up to midnight. Every food item, for that matter, has its own nutritive values, however, fragility of this goodness always comes with a caution – handle with care. And eggs are no exceptions.


Handle with care: Here are some of the precautionary measures that we mustn’t overlook;

Virtually any food, including egg, can cause an allergic reaction, which is very individualistic in nature. Research studies on food allergy consistently report more problems with some foods than with others. Such foods should not be eaten in their pure, isolated form, in order to trigger an adverse reaction. Allergic reactions against egg white are more common than egg yolk.

Salmonella, causing food poisoning, can be present not only on the outside on egg shell but even inside a clean, un-cracked, whole egg.  Safe food techniques, like washing the eggs thoroughly before cracking them, may protect from infection to certain extent; however, in order to destroy the bacteria, eggs must be cooked at high enough temperatures for a sufficient length of time.

Even dishes and utensils used while preparing eggs should be washed in warm water separately from other kitchenware, and hand-washing with warm, soapy water is essential after handling eggs. This may minimize the possibility of transmission of infection.

Consuming raw eggs should be avoided unless otherwise prescribed for medical reasons. Raw egg white contains inhibitors of the digestive enzyme trypsin. It also contains an anti-nutrient called avidin, a glycoprotein that binds to the vitamin, biotin, thereby preventing its absorption. Biotin, formerly known as vitamin H, is necessary for fatty acid synthesis and the maintenance of blood sugar in our body, and is especially important during pregnancy when biotin status declines. Proper cooking of the eggs takes care of these inhibitors.

Create awareness: It is sad to recall that our country still has around 53% of children below five years of age suffering from protein malnutrition and infants born are worse of than those in strife-torn countries. Make an attempt to convey the message to masses to eat the nutritional, easily available and affordable wholesome food packaged in an egg.

India is the world’s fifth largest egg producer. By and large around 70% of eggs produced in the country are from the organized urban sector while the unorganized rural sector still contributes around 30%. In order to bring them under the wings of growth, celebrate World Egg Day with one-point agenda, to help creating awareness about the benefits of eggs.

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