EGG STRUCTURE :

PHYSICAL AND CHEMICAL

COMPOSITION

Dr. Abhijeet Champati

Assistant Professor, Dept. of LPM
IVSAH, SOA (DU)
 FEMALE REPRODUCTIVE SYSTEM

• Birds are unique among animals as they reproduce

through an egg .
• Two parts
1)Ovary
2)Oviduct
• At the time of early embryonic development, two
ovaries and two oviducts are present.
• left pair develops and functional in all species of birds
• Kiwis - both the left and right ovaries develop and
only the left oviduct develops
 Photograph of the ovary of female
chicken, indicating the location of the
stigma on an ovum
stigma
Female Reproductive System in poultry
 REPRODUCTIVE TRACT : PARTS & FUNCTIONS
S.No Part Length Time spent Function
1 Infundibulum 9 cm 18 mins 1)Engulfs yolk
2)Reservoir for spermatozoa,
3)Fertilization
2 Magnum 33 cm (largest 2 hr 54 mins Thick white or albumen (40 %)
portion) added
3 Isthmus 10 cm 1 hr 15 mins Some albumen and inner and
outer shell membranes are
added
4 Uterus/shell 10 cm 20 hrs 40 mins Shell (CaCo3) over the egg
gland (47%calcium from her bones),
pigment deposition (Porphrin-
brown color)
5 Vagina 12 cm Cuticle is added,
(Muscular helps in turning and expelling the
portion) egg during oviposition
Total 74 cm 25-26 hours
 PROCESS OF EGG FORMATION
• The yolk is not the true reproductive cell
• Follicle stimulating hormone (FSH) regulates the growth and maturity of graffian
follicle as the bird attains sexual maturity
• The yolk weight also increases 7 days prior to ovulation due to the deposition of
yolk material over the ovum in (alternate layers of white and yellow)
• white layer -night time
• yellow layer - day time
• Due to the deposition of yolk, the nucleus migrates from the centre of the ovum
to the periphery and lies underneath the vitelline membrane
• The nucleus of the infertile egg is called 'germ spot' and that of fertile egg 'germ
disc'
• Luteinizing hormone (LH) that helps to release the ovum by rupture of graffian
follicle
• Ovulation
• Following ovulation, the ovum is picked up by the infundibulum for the deposition
of other constituents and formation and deposition of egg
• Albumin (4 layers) deposited - Magnum
• Inner and outer shell membranes – Isthmus
• Plumping out: where the water and salts from the yolk are absorbed into
the albumen, making it heavier and firm in shell gland
• Egg shell (CaCo3)and cuticle deposition – uterus/shell gland
• CaCo3, MgCo3 and other salts components of shell are deposited from
blood aided by carbonic anhydrase
• 5 hours before the oviposition shell pigments are added.(brown colour –
Porphyrin)
• Arginine vasotocin hormone from posterior pituitary responsible for
uterine contraction and Oviposition (laying of egg).
• During oviposition egg is turned by 180° with broad end coming out first.
• Egg laid is warmer (104-106 °F) than the environment, resulting in its
contents shrinking.
• This shrinking of content, results in formation of air sac between the two
shell membranes at the broad end.
Four Major structures from outside to inside are
Anatomy of an Egg
1. Eggshell
2. Outer membrane
3. Inner membrane
4. Chalaza
5. Exterior albumen
6. Middle albumen
7. Vitelline membrane
8. Nucleus of pander
9. Germinal disc
10. Yellow yolk
11. White yolk
12. Internal albumen
13. Chalaza
14. Air cell
15. Cuticle

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 EGG SHELL
• Hard outermost covering
• 8-11 % of egg weight
• Shell has two components : Matrix (spongy and mammillary) and Interstitial calcite crystals
• Mammillary matrix has protein fibres as mammillary cores close to outer shell membrane
• Spongy/palisade matrix has protein fibres running parallel to shell surface
• Interstitial calcite crystals: inorganic Ca, Mg salts deposited within the matrices
• Shell material composition: CaCO3 (94 %), MgCO3 (1 %), Mg3(PO4)2 (1%) and protein matrix
(4 %)
• The shell strength is directly determined by the Mg content
• Microscopic Pores- 8,000-10000 per egg, distributed unevenly over the shell surface (more at
broad end than narrow end).
• Exchange of volatile compounds between the shell membrane and cuticle.
• Shell provides a protective covering to the liquid contents of egg
• Shell thickness : 0.2-0.4 mm
• Cuticle- outermost acellular layer of egg
• Composed of organic matter and high % water
• Acts as a lubricant during laying process
• Prevents rapid exchange of air through the pores in shell
• 1st line of defense against microbial invasion
• Shell color is breed dependant :
• white, brown (ooporphyrin), bluish (oocyan),
emerald (methylester of biliverdin) in Emu
 SHELL MEMBRANE

• Outer shell membrane - 0.04-0.07 mm thickness

• Inner shell membrane – 0.01-0.02 mm thickness
• Air cell/sac is situated in between the two membranes at the broad end
• Air cell - formed as a result of contraction of the egg contents, soon after
oviposition, due to differences in the temperatures exposed to by the egg
prior to and after oviposition
• The outer shell membrane is attached to the shell.
• The inner shell membrane closely surrounds the albumen
• The membrane is made of protein fibres
• Major line of defense against microbial invasion
 ALBUMEN
• Makes upto 56-60 % of egg weight
• Immediately below the inner shell membrane
• consists of 4 layers (outer to inner)
– Outer thin albumen (23%) of total albumen
– Outer thick firm or dense albumen (57%)
– Inner thin albumen (17%)
– Chalaziferous or inner thick white, which forms (3%)
• The cloudy appearance is due to CO2
• The firmness of the outer thick albumen is due to presence of ovomucin-lysozyme
complex
• As the egg ages, the CO2 is lost via pores, causing rise in pH resulting in weakening of this
layer
• The chalaziferous layer -very close to the yolk immediately surrounding the vitelline
membrane of the yolk –
• This layer twists into two chords on either sides of the yolk called chalazae, which are
formed due to rotational movement of the egg in the oviduct
• Chalazae serves as an anchor for the yolk (central position)
• Contains lysozyme which has antimicrobial properties
• Ageing/improper storage/microbial spoilage makes thick albumen watery
• Fresh egg white pH : 7.6 and with ageing it goes to 9.7 (alkaline)
 YOLK
• Central yellowish and round structure
• 27-32 % of egg weight
• Color varies from light yellow to reddish orange based on diet
• Yolk color can be assessed via Roche’s yolk color fan
• Yolk structure has a colorless vitelline membrane holding yolk contents together
• Under the membrane are 7-9 concentric rings of light and dark yellow material deposited
based on the diurnal eating behavior of bird (light white: night time; dark yellow: day time)
• The difference in color is due to the concentration of xanthophyll

Infertile egg Fertile egg

• The germ spot is present on the yolk mass surface and if fertile, embryo formation begins
here
• A passage connects the blastoderm to the yolk centre: Latebra
• Latebra anchors the germinal disc
• Proportion of yolk tends to be higher in smaller than larger eggs
• In an infertile egg it is unicellular (ovum) and contains haploid number of
chromosomes, called "Blastodisc". It is circular in shape, with a diameter of
about 3.5 mm and with vacuoles in it.
• Where as in a fertile egg, it is a multicellular structure having diploid number of
chromosomes, called "Blastoderm". It is oval in shape, with an average diameter
of about 4.5 mm and with no vacuoles in it.
• Double yolked eggs: This phenomenon can be related to hen age but genetic
factors are also involved. Young hens sometimes release two follicles from the
ovary in quick succession.
• Sometimes eggs may appear mottled due to continuous use of coccidiostat
• Greenish discoloration of yolk : cottonseed oilcake in feed
• pH of fresh egg yolk is 6.0 and with ageing rises to 6.9
 Clutch and Pause
• Birds lay eggs in clutches
• Eggs laid on successive days are called a clutch.
• Clutch size is an individual characteristic and may vary from 2 up to 100 eggs.
• However, the normal clutch size is from 4-6 eggs.
• The larger the clutch size – good layers while small clutch size indicates an
inferior layer.
• Ovulation usually occurs in the morning and almost never after 3:00 PM.
• Ovulation of a yolk for the next egg in a clutch occurs within 30-45 min of laying
the previous egg.
• and so that each day the hen gets later and later in its timing of laying
• the next ovulation is delayed until at least the next day and egg laying is thus
interrupted.
• This delay results in the break between successive clutches and the
cycle repeats itself a day or so later.
• Pause: the no. of days break between two consequtive clutches
 Chemical Composition of Egg
 A 56-60 g chicken egg contains 17-18 g yolk, 34-36 g albumen and 5-6 g shell and shell
membrane
Percentage (%) Water DM Protein Carbohydrate Fat Ash

WHOLE EGG 100 65.6 34 12-13 1.0 10-11 11.7

WHITE 58 88 12 10-11 0.9 0.2 0.8

YOLK 31 48 52 17.5 1.0 32.5 1-2

SHELL & SHELL 11 2 98 4-6 0 0 92
MEMBRANE
Bird Wt. (g) Water % Protein % Lipid % CHO % Ash %

Chicken 58-60 73.7 12.9 11.5 0.9 1.0

Duck 75-80 70.4 13.3 14.5 0.7 1.1

Goose 200 70.4 13.9 13.3 1.5 1.0

Pigeon 17-18 72.8 13.8 12.0 0.8 0.9

Quail 10-12 73.7 13.1 11.1 1.0 1.1

Ostrich 1.2-1.3 kg 72.6 13.1 11.8 1.7 0.8

 MAJOR PROTEINS IN ALBUMEN OF TOTAL
PROTEINS
Egg white contains approximately 40 different proteins:
Ovalbumin 54%
Conalbumin 13%
Ovomucoid 11%
Lysozyme 3.5%
Globulins (G2, G3) 8.0 %
Ovomucin 1.5%
Other protein components include, flavoprotein (0.8%), ovoglycoprotein (0.5%),
ovomacroglobulin (0.5%), ovoinhibitor (0.l%) and avidin (0.05%).

Protein quality (Biological value)

• Egg – 100
• Milk – 80
• Beef – 79
• Fish – 66-88
 Lipids in Yolk
• Readily digestible lipids
• Egg lipids are found mostly in yolk, only 0.05% is contained in albumen.
• Fatty acid content:
monounsaturated (46.5%) > saturated (37.5%) > polyunsaturated (16.5%)
• Highest fatty acid content:
monounsaturated: oleic acid (18:1) approximately 40% from lipid total.
• The composition of lipid is 65.5 % triglyceride, 28.3 % phospholipid, and 5.2 %
cholesterol
• Lecithin is the major phospholipid in egg yolk.
• It is also responsible for the emulsifying property of egg
• Yolk is high in cholesterol
• A 50 g edible portion of egg contains 226 mg cholesterol

• Energy content in 1 egg (55-58 g) : 78 kilocalories (324 kilojoules)

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Vitamins & Minerals in Egg
Vitamins and minerals in 50 g edible portion of egg
Constituent Whole egg White Yolk

Biotin, mg 0.04
 Functional Properties of Egg
Properties Application
Thickening Eggs thicken foods like custards puddings, sauces,
and creamy fillings
Leavening Souffles, sponge & butter cakes, quick breads, and
puffy omelets are leavened by eggs
Coating Meat dishes, breads, and cookies are some foods
with egg components as the base ingredients for
coatings
Binding Eggs bind other ingredients for making meat loaves,
casseroles, and croquettes
Emulsifying Eggs prevent mixture separation in mayonnaise,
salad dressing, and cream puff filling
Clarifying Tiny particles are coagulated in soups and coffee to
create a clear solution
Retarding Crystallization of sugar is slowed in cake icings and
Crystallization candies
 Benefit of Egg Components
• Sialic acid could prevent infection
• Immunoglobulin in yolk can play a role as
antibody.
• PHOSVITIN has a function as food antioxidant.
• Choline: aids brain function and enhances
thinking capacity and memory. It is an important
part of a neurotransmitter that helps preserve the
integrity of the electrical transmission across the
gaps between nerves.
• Lutein and zeaxanthin: contribute to improving
eye health and protecting eyes from ultraviolet
rays
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 Allergen in Egg
• There are 4 proteins in egg white may provoque an allergy:
- ovomucoid (11%)
- ovalbumin (54%)
- ovotransferrin (12%)
- lysozyme (3.5%)

Egg Allergy Symptoms

 Egg allergy is like most food allergy reactions: It usually happens within minutes
to hours after eating eggs.
• the skin - in the form of red, bumpy rashes (hives), eczema, or redness and
swelling around the mouth
• the gastrointestinal tract - in the form of belly cramps, diarrhea, nausea, or
vomiting
• the respiratory tract - symptoms can range from a runny nose, itchy, watery
eyes, and sneezing to the triggering of asthma with coughing and wheezing
 Misconceptions About Nutritive
Value of Eggs
• 1. Pay more with the desired shell color for
nutrient.
• 2. Deep yellow yolk are higher in nutritive
value.
• 3. Fertile eggs are more nutritive than non-
fertile eggs.
• 4. Organic eggs are more nutritious.
• 5. Raw eggs are more digestible than cooked.
THANK YOU