FOOD MICROBIOLOGY

1. CONTAMINATION,
PRESERVATION AND
SPOILAGE OF EGGS
PRESENTED BY
• A. MARIAJOSEPHINE

2. CONTENT
• Introduction
• Composition of egg
• Contamination of egg
• Spoilages
• Bacterial spoilages
• Fungal spoilages
• Preservation

3. INTRODUCTION
• The spoilage of uneviscerated and eviscerated poultry is
somewhat different from the spoilage of canned meat.
• Various parts of world of evisverated, only this type of poultry is
considered in this section.
• Many of seceral hundered species of microoraganisms might be
found . However as the poultry is chilled and held in cold storage,
psychotropic microorganisms is predominate and cause
deterioration.

4. COMPOSITION OF AN EGG
• Hen’s egg consists of 3 main parts,
1. Shell
2. Egg white
3. Egg yolk
• SHELL
It consits of CALCITE CRYSTALS embedded in matrix of proteins and polysachharide
complex.
• EGG WHITE
It is composed of 20% to 25% of total white of fresh eggs is thin white. The chief
constituents of egg consits of ovalbumin, conalbumin, ovamucoid, ovamucin, lysosyme,
avidin, ovoglobulin, ovoinhibitor.
• EGG YOLK
It is the solid content of yolk is about 50% . The proteins in egg yolk are lipoproteins,
lipovitellins and lipovitellinin.

6. CONTAMINATION OF EGGS
• Freshly laid eggs are Sterile.
• Shells soon become contaminated by
1. Fecal matter from hen.
2. Cage or Nest.
3. Wash water if eggs are washed.
4. Handling.
5. Materials In which the eggs are Packed.
• Gram positive organisms
• Salmonella species

8. ROUTE OF ENTRY OF
MICROORGANISMS
• Fertile eggs get deteriorated more rapidly than infertile eggs.
• Deterioration takes place as physical and chemical changes.
• Eggs white becomes less viscous and spread rapidly.
• The size of the air cell and volume increases.
• Loss of water, carbondioxide, protein breakdown, egg flavour deteriorate.
• Bacterial decomposition takes place.
• Effect of heat.

10. CHANGES NOT CAUSED BY
MICROORGANISMS
• Untreated eggs lose moisture during storage and hence lost weight.
• Shrinkage shown by the size of the airspace or air cell of the cell.
• Changes in the physical state of the contents of egg seen by candling or
treating.
• As the egg ages, the egg white becomea thinner and more watery and yolk
membrane weakens.
• The poorer the egg, more movement of the yolk.
• Normal pH of egg is 7.6 to 9.5, storage increases the alkalinity of the egg
white.

11. CHANGES CAUSED BY
MICROORGANISMS
• Tasks to be accomplished by casual organisms to cause spoilage.
1. Contaminate the shell.
2. Penetrate the pores of the shell to membranes.
3. Grow through shell membranes to reach white.
4. Grow in egg white to reach egg yolk.
• Time taken to penetrate varies with organisms and temperature.
• In general, more spoilage is caused by bacteria than by molds.

12. BACTERIAL SPOILAGE OF EGGS
• Bacteria need to overcome the antibacterial properties of albumen to cause the
spoilage of eggs.
• Also they use the protien complexes as a source of nitrogen for growth .
• Bacterial spoilage is called as ROTS
1. GREEN ROTS
2. COLOURLESS ROTS
3. BLACK ROTS
4. PINK ROTS
5. RED ROTS

13. GREEN ROTS
• Pseudomonas fluroscenS
• Eggs are white in early stages, becomes bright green colour during later
stages. Yolk disintegrates and blend it with white.
• Odour is lacking or is fruity or sweetish.
• Contents of eggs fluorescence strongly under uv light.

15. COLOURLESS ROTS
• Caused by pseudomonas, Acinetobacter, Alcaligens.
• Detected by candling
• Yolk in later stage disintegrates or shows a white incrustation.
• Odour varies from a scarely detectable to fruity to highly offensive.

16. BLACK ROTS
• Most commonly caused by a species of Proteus, pseudomonas and
aeromonas.
• Proteus melanvogens causes black colouration. Yolk and dark colour in
white.
• Caused when egg is stored at temperature higher than the ordinary.
• Gas pressure develops in egg at high temperature.
• Putrid odour ( Hydrogen suLphide is evident ).

18. PINK ROTS
• Less often; caused by pseudomonas.
• They resemble like colourless rots. Except for the pinkish precipitate on the
yolk and a pink colour in the egg white.

19. RED ROTS
• Most infrequently occuring one .
• Caused by serratia species.
• Odour is mild and not offensive.

20. FUNGAL SPOILAGE OF EGGS
• Spoilage of eggs by fungi goes through stages of mold growth. The stages
give the defects their names. They are of two types.
1. Pin spot molding.
2. Fungal rotting.
• Pencillium, Clodosporium, Sporotrichum, Mucor, Alternaria and Botrytis.

22. PIN SPOT MOLDING
• Very early mold growth.
• Small compact colonies of mold appear on the shell and usually just inside it.
• Colour varies from the kind of mold;
1. Penicillium species Cause yellow, blue or green spots inside the shell.
2. Clodosporium species give dark green or black spots.
3. Sporotrichum species give pink spots.

23. FUNGAL ROTTING
• Final stage of spoilage.
• Mycellium of The mold has grown through the Pores or cracks in the egg.
• Jellying Of egg white is seen.
• The hyphae of the mold may weaken the yolk membrane enough to cause its
rupture. After this, the growth is stimulated by food released from the yolk.

24. DEVELOPMENT OF OFF
FLAVOURS
• Mustiness May be caused in the eggs By the bacteria sometimes.
• The growth of streptomyces near the egG may produce the earthy or musty flavors
that are absorbed by egg.
• A hay odor is caused by Enterobacter Cloacae.
• Fishy flavors are produced by Strains of Ecoli.

25. 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. They 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.
• Changes in the membranes occur with aging and favor more rapid bacterial
multiplication. The rates of physical and chemical changes in the egg depend on the
time and temperature of holding, the relative humidity, and the composition of the
atmosphere about the eggs.

26. • The character of albumen hinder microbial growth include a pH 9 to 10 that may be
reached during the storage. Lysozyme enzyme which degrades the cell walls of
gram postive bacterial.
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.
USE OF IRRADIATION:
• Some pathogens can be inactivated by ionizing radiation.

27. REMOVAL OF MICROORGANISMS:
• Washing with warm plain water.
• 1 to 3% acetic acid.
• Lye, acids, formalin hypochlorites, quarternary ammonium compounds.
• Temperature 32.2 to 60 c
USE OF HEAT:
• Coagulability of the egg white.
• Control rotting.
CHILLING:
• For commercial storage.
• Relative humidity of 70 to 80%

28. FREEZING:
• Washed by mechanically with final rinse in 200 to 500ppm chlorine.
• Broken and fall into inspection cups.
• Storing at -17.8 to -20.5 c.
• Spoiling of bacteria.
USE OF PRESERVATIVES:
• On the shell or on the wraps or containers.
• Chemical preservatives borates, permagnates, benzoates and salicylates.
• Hot solution of hypochlorite, lye, acids, formalin.

29. THANKYOU