The egg, a great design of nature.
Tips on the structure, composition and properties of eggs
Eggs are a high nutritional and culinary food. In addition, it comes in the best possible packaging, resistant, natural and optimal for storage.
The formation process is a complex one, ranging from ovulation to egg laying. For the egg to fulfill the quality requirements, the numerous components that make up the egg must be synthesized correctly and must be arranged in the right sequence, quantity and orientation.
The structure of the egg is designed by nature to protect and maintain the embryo from which the chick would emerge after hatching and therefore its contents have an enormous nutritional value.
The egg is protected from external contamination by the physical barrier provided by its shell and membranes and by the chemical barrier provided by the antibacterial components present in its contents.
A cross section of an egg allows a clear differentiation:
the egg white or albumen and
separated from each other by membranes that maintain their integrity.
It represents 9% of the egg weight and is composed of calcium carbonate (94%), magnesium carbonate (1%), calcium phosphate (1%) and organic matter (4% protein).
Its color depends of the presence of a pigment composed of ovoporphyrins, linked to the breed of the hen.
On its surface there are numerous pores (between 7,000 and 15,000) that facilitate gas exchange between the inside and outside of the egg.
Keratin protein layer that closes the pores, but allows gas exchange (outflow of CO2 and water vapor and inflow of O2).
This space is formed by the albumen contraction after laying and forces the separation of the membranes.
It increases with egg age, CO2 and water vapor losses.
It is the central and orange part of the egg.
It represents 30 to 33% of the egg weight and is made up of multiple layers of white and yellow yolk, a germinal disc, a vitelline membrane and latebra.
Contains the germ cells, where fertilization and later embryonic development takes place. This is possible thanks to the great wealth of nutrients in the yolk.
It represents approximately 60% of the total weight of the egg. It is composed of 4 layers that form the so-called “albuminoid sac”, whose function is to protect the yolk:
Thin fluid inner layer
Thick fluid layer
Thin dense outer layer
They are on the inner side of the shell, and represent approximately 3% of the egg’s weight.
They are part of the egg’s defensive barriers against contamination.
The inner membrane is thinner than the outer membrane.
Its chemical composition depends on the hen’s diet, with lipids or fat fraction being the most variable component.
Table 1 shows the average chemical composition of eggs, including vitamins, minerals and other important ingredients.
Table 1. Chemical composition of eggs
Source: USDA National Nutrient Reference Database for Standar Reference. Release 27
In terms of nutritional value, eggs are one of nature’s most nutritious and economical foods. It is considered one of the most complete foods because of the balanced proportion of proteins, fats, carbohydrates, minerals and vitamins it contains.
Eggs are one of the most complete foods and a basic ingredient in food and cooking.
It has a high amount of nutrients and very few calories, in addition to a healthy fat composition.
Eggs are considered a protein food.
It has the best quality proteins, which means, the ones that most closely resemble the ones our body needs.
Its high proportion of essential amino acids, which we cannot manufacture and therefore must obtain from food, are very important.
It also contains almost all vitamins (except C) and minerals of great interest (iron, phosphorus, selenium).
Two medium eggs (about 100 grams of edible part) are considered a ration for an adult, and one egg for a child up to 9 years of age.
One portion (two eggs) provides 7% of the necessary daily calories and proteins of high biological value, which are necessary and easily assimilated by the body.
Eggs do not contain carbohydrates; the energy they provide comes from lipids.
There is no nutritional difference between white and brown eggs.
The color of the shell depends on the breed of the hen laying the eggs.
Hens of brown commercial breeds lay colored eggs, and white hens lay white eggs.
The egg flotability in water to evaluate the freshness it is not reliable. One way to evaluate the freshness is checking the consistency of the egg white
A fresh egg has two zones in the white; a more consistent one and a liquid one, which are well distinguishable.
When the egg is fresher, the dense white is tighter and more jelly-like and loses that firmness as it loses freshness.
When it is difficult to distinguish the two zones, the egg is less fresh.
The height of the yolk is another indicator of freshness.
A fresh egg has a hemispherical yolk above the dense white, and both have a height that stands out above the liquid white
When the egg loses freshness, the yolk membrane also becomes less firm and the yolk f lattens, until it is completely flattened, with its profile barely standing out from the white.
At the end, the membrane is so weak that it is easy to break when the egg is broken.
Another way to evaluate freshness is the height of the air space (the bubble that forms inside the wide part of the egg between the membrane and the shell). The smaller the air space, the fresher the egg.
The success of this egg formation process is based on the hens being fed with high quality nutrients and kept in a situation of environmental comfort and optimal health
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