Eggs: description, nutritional values, freshness



Eggs are foods rich in iron and high quality proteins, free of carbohydrates, calcium and vitamin C. We find out better the nutritional values ​​and how to recognize their freshness.

What are eggs

With the word "eggs", not followed by any other specification, we refer to those of hen (otherwise the name of the bird from which they come must be specified).

The egg is formed by three structures: an external one, the shell, a medium one, the egg white or egg white, an interior, the red or egg yolk .

The shell is formed for about 95% by calcium carbonate (necessary for the chick for calcification of the bones if the egg was fertilized). The shell is porous and of color ranging from white to brown depending on the pigments of blood origin, typical of some breeds of hens. When the egg is perfectly fresh, it has a characteristic opaque and greasy appearance due to a very thin layer of mucin which settles on its surface just before it is laid.

The albumen, of an essentially proteinic nature, suspends the yolk in its interior.

The yolk, whose more or less yellow color essentially depends on the feeding and the life in the open air of the laying hens (they are above all the carotenoids to confer a darker color) but also from the breed, since some hens are not able to absorb the carotenoids present in the diet and then lay pale eggs. Therefore the color of the yolk must not necessarily be related to the nutritional power of the egg, as well as the color of the shell.

In relation to freshness, the eggs are divided into three categories:

  • category A Extra . They are the freshest eggs, untreated and not refrigerated, marketable until the ninth day after laying (or on the seventh day from the packaging); after this period they lose the qualification of "extra" and can be marketed only with reference to category A;
  • category A. They are fresh, untreated and not refrigerated eggs; the minimum storage term shown on the label is calculated in 28 days from the date of laying ;
  • category B. They are the second quality eggs, or "downgraded", not transferable directly to the consumer but only to industrial companies in the food industry to be transformed into ovo-products, or to the non-food industry.

Based on weight, the eggs are classified into:

  • XL - Very large: 73 g and more
  • L - Large: of 63 g and more but less than 73 g
  • M - Averages: of 53 g and above but less than 63 g
  • S - Small: less than 52 g.

Nutritional value of eggs

Eggs do not represent, as many believe, a complete food from a nutritional point of view as they lack carbohydrates, calcium and vitamin C.

They are, however, an excellent food for the quality of the proteins, present both in the albumen and in the red, in a proportion of 13% of the total weight.

Egg white represents about 60% of the weight and contains, in addition to water (85%) also different proteins, among which the most abundant are ovalbumin (54%).

Red contains phosphorus proteins, lipoproteins and lecithin, a phospholipid component extracted for the first time precisely from the egg and containing, among other things, the choline which is indispensable particularly to nerve cells.

In addition, all the vitamins are present in the egg (in significant quantities vitamin A and D) with the exception of vitamin C.

As for the mineral constituents, the egg is rich in iron, present in assimilable form, calcium, phosphorus, potassium and magnesium.

The properties of the egg and how and when to use it

How to recognize fresh eggs?

Regarding the age of the egg, it is necessary to know that the bigger the air chamber, the older it is : you can see it with the light examination ( candling ), observing the egg in transparency once it is placed in front of a light source.

The shape of the egg also gives indications on the state of freshness as, with the passing of the days from the deposition, the testaceous membrane (double inner membrane) adheres less and less to the inner face of the shell, while the albumen begins to fluidify.

The membrane of the yolk thins out, so that this, which is spherical to the deposition, flattens and, in the most advanced cases, it also breaks due to the increase in volume determined by the water absorbed by osmosis from the albumen. For this freshness test the egg must be broken into a dish and its characteristics observed: the more the yolk is turgid and round and the egg white is firm and dense, the more fresh the egg is.

Another proof of freshness is the floatation test of the egg . The egg is immersed in an aqueous solution with 10% sodium chloride (cooking salt); having the fresh egg a higher specific weight, once immersed in the solution it goes to settle on the bottom, otherwise it will remain closer to the surface the less it will be fresh.

Curiosity about eggs

The albumen may be difficult to digest due to the difficulty of being attacked by gastric juices, with consequent irritation of the intestinal mucous membranes. For this reason it is preferable to cook the egg white, also eliminating an anti-vitamin factor (avidin and precisely an anti-vitamin H ) which is present in the clear but which is thermolabile.

In reality we have seen that the slightly boiled egg (like the soft-boiled one) leaves the stomach in less than 2 hours, the fresh one after 2 hours and the hard one or in omelette after 3 hours, the same average time required for the meat.

It is often believed that eggs hurt the liver or predispose to circulatory diseases, due to the presence of high amounts of cholesterol in the yolk (about 250 mg yolk).

It must be remembered that, since the amount of cholesterol produced by our body is much higher, it certainly cannot be the quantity present in the egg that significantly affects the level of cholesterol in the blood, unless it is abused (more than 2 eggs per week).

Eggs can only be contraindicated in biliary calculosis, as they can cause contractions of the gall bladder walls, resulting in colonic spasms.

How to replace eggs in recipes

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