Structure of egg , and composition Spoilage of egg

1. Contamination, preservation,
and spoilage of eggs
Anil Shrestha
Msc Medical Microbiology

2. Contamination
• Freshly laid eggs are sterile inside.
• The shells of eggs soon become contaminated
by fecal matter from the hen, by the cage or
nest, by wash water if the eggs are washed, by
handling, and perhaps by the material in
which the eggs are packed.
• The total number of microorganisms per shell
of a hen’s egg has been reported to range
from 10² to 10⁷ with a mean of about 10⁵.

3. • A comparison of the flora of the shell and the
flora isolated from spoiled eggs suggest a high
number of gram-positive bacteria in former
but a low number in the later. Therefore,
those organisms which frequently spoil or
“rot” the egg are in relatively low numbers
initially on the shell.

4. Preservation
• The egg has various ways of protecting itself
from microbial invasion. The shell and the thin
surface layer of proteinaceous material known
as cuticle or bloom are the first line of defense
and serve to retard entry.
• A rapid change in storage temperature may
permit bacteria to overcome the physical
barrier of the shell and its membrane.

5. • Changes in the membranes occur with aging
and favor more rapid bacterial multiplication.
The rates of physical and chemical changes in
the eggs depend on the time and temperature
of holding, the relative humidity, and the
composition of the atmosphere about the
eggs.
• The character of albumen hinder microbial
growth include a pH 9 to 10 that may be
reached during storage, lysozyme enzyme
which degrade the cell walls of gram-positive
bacteria,

6. • Asepsis- When eggs are broken for drying or
freezing, care is taken to discard those in which
microbial growth has taken place to reduce
contamination from equipment by cleaning and
sanitizing it.
• Removal of microorganism- washing with warm,
plain water removes dirt. 1-3% acetic acid was
effective in removing the flora but resulted in a
reduction of shell thickness and egg quality. Lye,
acids, formalin hypochlorites, quaternary
ammonium compounds, various detergent-
sanitizer combinations have been used at
temperature from 32.2 to 60 C.

7. • Use of Heat- The heat coagulability of the egg
white determine to a great extent the maximal
heat treatment that can be given shell eggs. 800
sec at 57.5 C; 320 sec at 60 C or above resulted in
some coagulation of the white when heat
treatments were employed that would control
rotting.
• Use of low temperature-
Chilling:- For commercial storage for 6 months or
longer, a temperature of -1.7 to -0.55 C and relative
humidity of 70 to 80 percent are recommended.

8. • Freezing:- The eggs first are selected by
candling and then are washed mechanically
with a final rinse in 200 to 500 ppm chlorine
and then broken on automatic breaking
machine. The eggs are broken, and the
contents fall into inspection cups.
• The frozen eggs are stored at -17.8 to -20.5 C.
• Bacteria that spoil eggs stored at low
temperatures, especially Pseudomonas
organisms as well as bacteria of the genera
Alcaligens, Proteus and Flavobacterium.

9. • Use of preservatives
Preservatives may be used on the shells of eggs,
in the atmosphere around them, or on wraps or
containers for eggs.
Chemical preservatives used are borates,
permaganates, benzoates, salicylates, formates.
Use of warm or hot solutions of hypochlorite,
lye, acids, formalin, quaternary ammonium
compounds and detergent-sanitizer
combinations.

10. • Use of irradiation
Experiments have indicated that pathogens in
liquid, frozen and dried eggs can be inactivated
by means of ionizing radiation

11. SPOILAGE
• Changes Caused by microorganism
1) Contaminate the shell
2) Penetrate the pores of the shell to the shell
membranes
3) Grow through the shell membranes to reach
the white
4) Grow in the egg white

12. Bacterial rots
• Green rots- Pseudomonas fluorescens
• Colorless rots- Pseudomonas, Acinetobacter,
Alcaligens and certain Coliform bacteria
• Black rots- Proteus melanovogens,
Pseudomonas, Aeromonas
• Pink rots- Pseudomonas
• Red rots- Serratia

13. Pin-spot molding
• Yellow/ blue/ green spots- Penicillium
• Dark-green or black spots- Cladosporium
• Pink spots- Sporotrichum
Fungal rotting
Penicillum, Cladosporium/ Sporotrichum/ Mucor/
Thamnidium/ Botrytis/ Alternaria