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In April of last year the Research Institute CIRM conducted
a survey on common nutritional stereotypes. From this survey
of doctors gastronomic experts foods industry managers
specialist journalists and junior school students, it emerged
that certain prejudices old and new regarding Italian dining
habits are still very much alive it seems that a large number
of Italian consumers have an exaggerated idea of the
nutritional value of eggs. And accordingly this article aims
to shed a little light on the subject.
COMPOSITION
An egg weight on average 60g and consists of three parts; the
shell (approx. 6g) is made of calcium and magnesium carbonates
calcium and magnesium phosphates and other organic substances
the albumen also called the white weight approx 20g is made of
water and protein and coagulates readily when heated the yolk
is positioned and held in the center by elastic band-like
structures (a thickening of the albumen) known as the chalaza,
and constitutes the most nutritionally valuable part of the
egg. It is rich in proteins of high biological value (linked
to iron and phosphorous) as well as fats vitamins and
minerals.
The white is surrounded by a shell, which in turn is made
up of two layers. In the wider portion of the shell these
layers tend to come unstuck generating a space full of air
called the air space which is important in determining the
freshness of the egg.
NUTRITIONAL VALUE
The egg is not a complete food as it lacks sugars and vitamin
C, but it is rich in other valuable nutrients 100g of whole
egg (2 eggs weighing 50g net each) contains 12.4% proteins
8.7% fats, a good amount of vitamin B1,B2,PP, A and D, and a
good quantity of iron phosphorous, sulphur and potassium up an
energy value of 128kcal (food composition tables National
Institute ed 1997).
Proteins have considerable nutritional
value; they contain amino acids that the human organism has
difficulty producing therefore they must be introduced through
diet to ensure growth and reconstruction of tissues proteins
contained in the white and the yolk of an egg are the best
source of protein for man albeit certain proteins in the white
can cause allergic reaction in individuals with particular
sensitivity.
Fats; Eggs contain a modest quantity of fats (compared to
16-47% found in cheese and 35% in salami and sausage products)
with various chemical structures; eggs contain triglycerides
rich in saturated fat phospholipids and cholesterol Note that
eggs now contain one forth less cholesterol than in the past
at 371mg/100g. for this reason Indications on weekly
consumption of egg given to hypercholesterolemia sufferers are
now less restrictive but there is still a ban on packaged
products with a high yolk content e.g. mayonnaise custards
certain desserts (typically tiramisu) or pasta dishes
containing which is also rich in cholesterol.
Phospholipids are highly unsaturated lipid
molecules of which lecithin is the most important; lecithin
abounds in the yolk and contains choline which is
indispensable to cell nuclei and particularly to nerve cells
These compounds are useful for contrasting
hypercholesterolemia and are necessary for the metabolism of
the liver.
DIGESTIBILITY
The digestibility of a food is calculated by measuring the
time between ingestion and passage from the stomach to the
intestine Research has shown that egg remains in the stomach
for a relatively brief period that varies according to how
the egg is cooked .
Two soft-boiled eggs remain in the stomach for less than two
hours while two fried eggs pass to the intestine after approximately
three hours.
Raw white of egg is difficult to digest as the gastric
juices find it difficult to break down and cooking the white
also has the effect of deactivating an antivitamin factor. As
for the yolk the fats are rendered more digestible by minimal
cooking albeit a greater heat would help digestion of the
proteins. Accordingly soft-boiled eggs are the most
beneficial.
The main effect of cooking an egg is that the proteins
coagulate turning from fluid become solid and thermolabile
vitamins are lost to a significant degree.
COMMERCIAL
ASPECTS
There are various commercial aspects connected with the
different characterizing features of an egg. The WEIGHT can
vary from more than 75g to less than 45g and must be
identified by law. The colour of the shell white or speckled
is strictly connected to the breed and has nothing to do with
the nutritional value of the egg itself. The colour of the
yolk can vary from light yellow to dark orange and depend
mainly on the presence of vegetal pigments (carotenoids) that
may be present in the feed but can also vary according to the
breed of anima. The taste generally fine delicate and pleasant
can also vary according to the type of feed given to the
laying hens. Odour in general is nit present although the
porosity of the shell can allows smells from adjacent products
to permeate into the egg.
LEGISLATION
Statutorily the single word egg defines a hen’s egg If the
egg is not produced by a hen then the word must be accompanied
by the species of fowl (pheasant duck goose etc.) Both Italian
law and EU regulations impose exact specification on eggs
destined for the commercial distribution. Among the numerous
aspects involved, producers must observe instructions on the
obligation to identify freshness and weight.
Freshness. Is evaluated by determining the
depth of the air space, which is inversely proportional to the
freshness of the product. Egg are classified in various
categories indicated by the letters A,B and C allowing the
customer to select the desired product; A EXTRA-egg with air
space less than 4mm; A-egg with air space less than 6mm; B-egg
with air space Between 6 and 9mm; C-egg with air space more
than 9mm Category C eggs are not retailed but used in the food
industry; category B egg are divided into three subgroups
according to the storage technique used. The weight is shown
using weight intervals/categories or by a number varying from
1 (heaviest) to 7 (lightest) After classification at the
packaging center the eggs are distributed for sale in
containers showing the quality and weight the week or date of
packaging and the name of the packaging company Retailers must
purchase eggs from the packaging centers where the product is
sealed with labels provided by the relative government
department. Egg can also be sold by the producer direct to the
consumer but in this case the eggs do not have to carry
indication relative to quality.
STORAGE
An egg gathered in accordance with recommended health and
hygiene conditions and put straight into refrigeration will
remain fresh for at least a month As cracks in the shell and
compression of the air space are to be avoided it is advisable
to place the egg with the narrow end downwards. Ageing
gradually denatures the membrane around the yolk, which will
appear less compact and when the shell is cracked open
Laceration of the air space leads to rapid decomposition with
hydrolysis of the proteins and an increasing level of ammonia
in the yolk.
DIETARY
ASPECTS
The yolk is introduced early into a child’s diet due to its
considerable nutritional properties Given the possibility of
an allergic reaction the white is usually introduced later
towards the end of the first year of life.
The inclusion of eggs in the diet of young people adults
and the elderly provides fundamental nutrients and the elderly
provides fundamental nutrients for growth and maintenance of
body structures.
The egg also improves the nutritional value of other food
sources as they can be used in a very versatile way in
numerous dishes; in egg pasta for example the lack of protein
and low mineral and vitamin content of wheat is compensated
for by the egg. The absence of uric acid precursors make the
egg an indispensable source of protein for gout sufferers
whose consumption of meat must be strictly limited.
The presence of choline stimulates liver function. Eggs are
not contraindicated in the prevention or cure of
arteriosclerosis.
From a dietary point of view accordingly the whole egg with
no added fat is tolerated well by everybody except individuals
with diseases of the gall bladder. In the case of gallstones
eggs can cause contraction of the gall bladder wall resulting
in colic pains.
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