CONTAMINATIO

N AND

SPOILAGE OF EGG

Ramya.H

1st year M.Sc. Food & Nutrition

CONTAMINATION OF EGGS

Freshly laid eggs are sterile.

Shells soon become contaminated by

1. fecal matter of hen

2. Cage or nest

3. Wash water if eggs are washed

4. Handling

5. Material in which the eggs are packed.

CHANGES NOT CAUSED BY

MICROORGANISMSUntreated eggs lose moisture during storage and

hence lose weight.

Shrinkage shown by the size of the airspace or air cell of the egg.

Changes in the physical state of the contents of the egg seen by candling or breaking.

As the egg ages, Egg white becomes thinner and more watery and yolk membrane weakens.

The poorer the egg, more movement of the yolk.

Normal pH of egg-7.6 to 9.5,storage increases the alkalinity of the egg white.

CHANGES CAUSED BY

MICROORGANISMS

• Tasks to be accomplished by causal organisms to cause spoilage :

(1) contaminate the shell

(2) penetrate the pores of the shell to membranes (shell must be moist)

(3) grow through shell membranes to reach white

(4) grow in egg white to reach egg yolk.

• Time taken to penetrate varies with organism &temperature.

• In general, more spoilage is caused by bacteriathan by molds.

BACTERIAL SPOILAGE OF EGGS

• Bacteria need to overcome the anti – bacterialproperties of albumen to cause spoilage of eggs.

• Also, they use the protein complexes as a sourceof nitrogen for growth.

• Bacterial spoilage is called as rots. Three chiefones are green rots, colorless rots & black rots.

• The other two are pink rots & red rots.

GREEN ROTS

• Caused by Pseudomonas fluorescens (grows at 0΄C).

• Egg white in early stages, becomes bright green in color during Later stages, yolk disintegrates & blends with white.

• Odour is lacking or is fruity or sweetish.

• Contents of egg fluoresce strongly under UV light.

COLOURLESS ROTS

• Caused by Pseudomonas, Acinetobacter, Alcaligens.

• Detected by candling.

• Yolk in later stages, disintegrates or shows a white incrustation.

• Odour varies from a scarcely detectable to fruity to highly offensive.

BLACK ROTS

• Most commonly caused by a species of Proteus. Pseudomonas & Aeromonas can also cause this.

• Proteus melanovogenes causes black coloration yolk & dark color in white.

• Caused when egg is stored at temp. higher than the ordinary.

• Gas pressure develops in the egg.

• Putrid odour (hydrogen sulfide is evident).

BLACK ROT

PINK ROTS

• Less often; caused by strains of Pseudomonas.

• They resemble colorless rots ; except for thepinkish precipitate on the yolk & a pink colour inthe egg white.

RED ROTS

• Most infrequently occurring one.

• Caused by a species of Serratia.

• Odour is mild & not offensive.

FUNGAL SPOILAGE OF EGGS

• Spoilage of eggs by fungi goes through stages ofmold growth. The stages give the defects theirnames.

• There are two stages :

(1) Pin Spot Molding

(2) Fungal Rotting

• Molds that cause spoilage of eggs include species of Penicillium, Clodosporium, Sporotrichum,Mucor, Alternaria & Botrytis.

PIN – SPOT MOLDING

• Very early mold growth.

• Small, compact colonies of molds appear on the shell & usually just inside it.

• Colour varies with the kind of mold :

(1) Penicillium species cause yellow or blue or green spots inside the shell.

(2) Clodosporium species give dark – green or black spots.

(3) Sporotrichum species give pink spots.

FUNGAL ROTTING

• Final stage of spoilage.

• Mycelium 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 yolkmembrane enough to cause its rupture. Afterthis, growth is stimulated by food released fromthe yolk.

DEVELOPMENT OF OFF -FLAVOURS

• Mustiness may be caused in eggs by the bacteria sometimes.

• The growth of Streptomyces near the egg may produce earthy or musty flavors that are absorbed by the egg.

• A hay odour is caused by Enterobacter cloacae.

• Fishy flavors are produced by strains of E.coli.

METHODS OF PRESERVATION

There are various methods that help preventspoilage of eggs :

• Use of heat

• Chilling

• Freezing

• Use of preservatives

• Use of irradiation

THANK YOU