The Egg
BFST 2203
Food Proteins and Hydrocolloids
Gihan Wijelath
Taniya Nanayakkara
Shamara Perera
Sachini Bhagya

Content
• Introduction
• Structure of an egg
• Protein content
• Types of protein present in egg white & yellow
• Production of egg powder

Introduction
• Eggs are laid by female animals of many
species including birds, amphibians, reptiles
and fish
• Chicken eggs are the most popular choice of
egg consumption
• They an inexpensive source of protein
• Used as a reference standard against which all
other protein containing foods are assessed

Structure of an Egg
An egg basically consists of three parts:
• Shell
• Egg white
• Egg yolk

Structure of an Egg

Structure of an Egg
Eggshell
• The outer eggshell is made almost entirely of calcium
carbonate (CaCO3) and is covered with as many as 17,000 tiny
pores.
• It is a semipermeable membrane, which allows air and
moisture to pass through its pores.
• The shell also has a thin outermost coating called the bloom
or cuticle that helps keep out bacteria and dust .
Outer and inner shell membrane
• These two membranes are inside the shell surrounding the
albumen (white).

Structure of an Egg
• The two membranes are made partly of keratin and provide
an efficient defense against bacterial invasion.
• The outer membrane sticks to the egg shell while the inner
membrane sticks to the albumen.
Chalazae
• Strands that are twisted in opposite directions and anchor the
yolk in center of the egg. The more prominent the chalazae,
the fresher the egg.
Exterior albumen (outer thin albumen)
• The outer thin albumen; a narrow fluid layer next to the shell
membrane.

Structure of an Egg
Middle albumen (inner thick albumen)
• The inner thick white (chalaziferous layer) is a dense, matted,
fibrous capsule of albumen around the vitelline membrane of
the yolk.
• An excellent source of riboflavin and protein.
• In high-quality eggs, the inner thick albumen stands higher
and spreads less than thin white. In low-quality eggs, it
appears thin white.
Vitelline membrane
• Clear seal which holds the egg yolk

Structure of an Egg
Yellow yolk
• The yolk contains less water and protein than the white, some
fat, and most of the vitamins and minerals of the egg.
• It is also a source of lecithin; an effective emulsifier.
• Yolk color ranges from just a hint of yellow to a magnificent
deep orange, according to the feed and breed of the hen.
Air cell
• An air space forms when the contents of the egg cool and
contract after the egg is laid.

Structure of an Egg
• The air cell rests between the outer and inner membranes at
the eggs larger end.
• As the egg ages, moisture and carbon dioxide leave through
the pores of the shell, air enters to replace them and the air
cell becomes larger.
Germinal disk (blastoderm)
• A small, circular, white spot (2-3 mm across) on the surface of
the yolk; it is where the sperm enters the egg.
• The embryo develops from this disk, and gradually sends
blood vessels into the yolk to use it for nutrition as the
embryo develops.

Protein Content of an Egg
• Protein content of an egg accounts to about
12.6% by weight of the edible portion
Distribution of proteins in an egg
Egg white 57%
Egg yellow 43%

Table: Protein content of eggs
Description Protein Content (per
100g)
Protein Content (%)
Egg,whole,raw,fresh 12.56g 12.56%
Egg,white,raw,fresh 10.90g 10.90%
Egg,yolk,raw,fresh 15.86g 15.86%
Egg,whole,dried 48.37g 48.37%
Egg,whole,cooked,hardboiled 12.58g 12.58%
Egg,whole,cooked,fried 13.61g 13.61%
Egg,whole,cooked,omelet 10.57g 10.57%
Source: National Nutrient Database for Standard Reference Release 27 (2014), United
States Department of Agriculture

Protein Content of an Egg
• Contains all essential amino acids
• Rich in essential amino acid leucine
• Composition of amino acids in an egg matches
the requirement of amino acids by the human
body

Types of Protein Present in Egg White
and Egg Yellow
Egg White
• Egg white consists of about 90% water in
which about 10% of proteins is dissolved.
• Egg white is an alkaline solution which
contains approximately 40 different proteins.

Types of Proteins Present in Egg
White
• 54% Ovalbumin
• 12% Ovotransferrin
• 11% Ovomucoid
• 4% Ovoglobulin G2
• 4% Ovoglobulin G3
• 3.5% Ovomucin
• 3.4% Lysozyme
• 1.5% Ovoinhibitor
• 1% Ovoglycoprotein
• 0.8% Flavoprotein
• 0.5% Ovomacroglobulin
• 0.05% Avidin
• 0.05% Cystatin

Ovalbumin
• Ovalbumin is an almost spherical glycophosphoprotein
which is the most common protein in egg white.
Figure 1. Crystal structure of ovalbumin
Source: Roth, K; Available from:http://www.chemistryviews.org/details/ezine/1492619/.html
• Storage protein

Ovotransferrin
• Composed of 686 amino acids
• Consists of 2 forms which contains neither phosphorus
nor sulfur
• Disulfide crosslinks are present
• Has antimicrobial and iron-binding ability
Figure: Crystal structure of ovotransferrin
Source : Dong,A , Egg Components

Ovomucoid
• Ovomucoid is a glycoprotein
• Consists of 9 disulphide bonds
• Has a stable spatial structure that it is not denatured even upon
boiling
Figure: Crystal structure of ovomucoid
Source: Roth, K; Available from:http://www.chemistryviews.org/details/ezine/1492619/.html

Types of Proteins Present in the Egg
Yolk
• The major proteins in egg yolk are lipoproteins
 Livetin
 Lipovitellin
 Phosvitin

Phosvitin
• A type of phosphoprotein
• About 16% egg yolk proteins
• Consists of about 10% phosphorus
• Has iron and calcium binding capacity
Figure: Crystal structure of phosvitin
Source: http://www.uscnk.com/directory/Phosvitin(PV)-1679.html

Production of egg white powder

Powdered egg whites are simply egg whites
that have been dehydrated and ground into a
powder.
Powdered egg whites or egg white powder are
also sold as spray-dried egg whites and spray-
dried albumin.
Since egg white is often taken as a
supplement, it is also sold as "egg white
protein" or "egg white protein powder,".

Egg breaking and Egg white separating Filtering
Separating Tank storage and pH fit
Reverse osmosis Fermentation
Spray drying Chilling
Dry heating

The first step in the process is the breaking of the eggs.
There are 3 main fractions
egg white
egg yolk
whole egg
The white fraction is the one used for the production of
albumen powder. The fractionation is achieved by breaking
the egg over a small cup which only holds the egg yolk
allowing for a vessel under this cup to collect the egg white.

The egg white is then filtered to get rid of any
residual pieces of egg shell or other large
contaminants.
Afterwards it is pumped to storage tanks where the
pH is adjusted, using citric acid, and stored until the
egg white is to be used in the production.
Next the egg white is transferred to a separator
which further separates any remnants of egg shell or
other physical residues.
The egg white is subjected to a reverse osmosis
treatment which increases the dry weight.

After the concentration the next goal of the process is to break down
the glucose and fat present in the egg white.
• Glucose - add either enzymes or bacteria
• Fat - add lipase
This procedure is performed in fermentation tanks.
Time required- 24 hrs
Glucose content should be monitored.

After fermentation pH is corrected using lactic
acid.
The egg white is then pumped to a cooling tank
where the temperature is lowered to 4
degrees Celsius.- chilling

Finally the liquid egg white is transformed into
albumen powder using a box spray dryer.
-spray drying
Last step in the process is dry heating in large
conical dry blenders (87 degrees Celsius for 12
hours )
[Elimination of microbial threat- salmonella]

Advantages of egg white powder
• Can be stored and transport in room
temperature.
• Good shelf life
• Time saving
• Can store in smaller space
• Requires no refrigeration

References
The Anatomy of a Chicken Egg [online] available at
http://imaginationstationtoledo.org/content/2011/04/the-
anatomy-of-a-chicken-egg/ (accessed on 12th August 2015)
Structure of the egg [online] available at
http://www.en.eggs.dk/the-egg/structure-of-the-egg.aspx
(accessed on 12th August 2015)
National Nutrient Database for Standard Reference Release 27
[online](2014), available at
http://ndb.nal.usda.gov/ndb/foods

American egg board[online]available at
http://www.aeb.org/food-manufacturers/eggs-product-
overview/egg-products-specifications/45-egg-white-types/139-
driedrd;accessed 11th august 2015
discoloration of albumen powder; [online]available at
http://www.livsmedelsakademin.se/sites/default/files/media/dis
coloration_of_egg_white_powder_final.pdf; accessed on 11th
august 2015

Thank you