Microbial spoilage of egg and egg products

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  • Eggs are a highly nutritious food that contains proteins, minerals, fats, iron, phosphorus vitamins (A, B, D, E, and K).
  • The eggs most commonly consumed by humans are the eggs are of hens, ducks, and quails. 
  • The chicken’s egg, in particular, is very popular consists of the yolk (30-33%), albumen (60%), and the shell (9-12%).
  • Egg yolk is about 50% of proteins of which the main ones are lipoproteins, lipovitellins, and lipovitellinin.
  • Egg albumen is about 12% protein of which are ovalbumin (54%), Conalbumin (13%), Avidin (0.05%), ovotransferrin (10%), ovomucoid (11%), ovomucin (1.5-3%), and lysozyme (3.5%).
  • The shell of the egg is a rigid structure made largely of calcium carbonate on an organic matrix.
  • Internally, there are two shell membranes and the inner one that acts as a barrier when an organism penetrates the shell.
  • Eggs and other egg products such as poached egg, scrambled egg, fried egg or omelets, liquid, dried, or frozen egg products can undergo microbial spoilages.
Microbial spoilage of egg and egg products
Microbial spoilage of egg and egg products. Created with BioRender.com

Contamination source and causes

The eggs when laid are usually sterile therefore the contamination occurs after it is laid due to various reasons:

  • by  the fecal matters of the chicken
  • by specks of dirt or materials used for the cage or nest
  • water used during washing of eggs
  • equipment used during processing and handling
  • materials used to pack the eggs
  • the temperature used during storage
  • presence of eggshell cracks or micro-cracks

Spoilage of egg

  • The egg is very perishable and the quality can be severely reduced during the time of storage (i.e. both chemical changes or non-microbial spoilage and microbial spoilage).
  • The changes occurring in the egg are affected by the environmental conditions, temperature, moisture, the material used for packaging, and storage time.
  • Their high water content (74 %) and high nutrient content make them susceptible to microbial spoilage.
  • When an egg is broken it loses all its antimicrobial property which makes it prone to microbial spoilage.

Non-microbial spoilages

  • The water content and gases get evaporated through the pores of eggshells resulting in a decrease in weight.
  • Due to the evaporation of water content, the albumen becomes thinner.
  • The egg float, when placed on the water as carbon dioxide is lost through the pores of the shell and oxygen, gets into the egg that creates an air bubble inside.
  • The evaporation of carbon dioxide and water content through eggshell pore leads to increases in the pH of the albumen to an alkaline state (7.6-9.5).
  • The content of albumen and yolk gets mixed leading to the mottling of yolks.

Microbial spoilages

  • Eggshell the physical barrier, egg white, is an important line of defense against invading bacteria because it represents a not favorable environment for microbial development.
  • The egg contains such as antimicrobial activities, such as lysozyme, ovotransferrin, proteinase inhibitors (cystatin, ovomucoid, and ovoinhibitor), and vitamin-binding proteins (riboflavin binding protein, avidin- and thiamin-binding proteins).
  • The organism must contaminate the shell, penetrate the pores of the shell, grow through shell membrane to reach albumen and finally to yolk to cause of spoilage of egg.
  • The bacteria involved in the spoilage of eggs can resist the growth-inhibiting properties.
  • The microflora of the eggshell is dominated by Gram-positive bacteria such as Staphylococcus, Streptococcus, Aerococcus, Bacillus, and Micrococcus and Gram-negative bacteria, such as Salmonella, Escherichia, and Alcaligenes spp.
  • The bacteria such as Pseudomonas, Proteus, Alcaligenes, Enterobacter, Serratia, Stenotrophomonas, Cloaca, Acinetobacter, Moraxella, and Citrobacter spp. are responsible for making egg rotten with off-odors and color change.
  • Yellow pigmentation of the shell membrane occurs in eggs due to the action of Flavobacterium or Cytophaga species.
  • The mold that is responsible for causing egg spoilages is the species such as Penicillium, Cladosporium, Alternaria.
  • The early mold growth in egg surface is termed pin-spot molding and the final stage of spoilages is termed fungal rotting.

Some of the microorganisms causing egg spoilage and defects caused by them are:

 Kind of defects Spoilage causing microorganisms
Fluorescent green rot Pseudomonas putida
Musty or earthy odor Streptomyces
Hay odor Enterobacter cloacae
Fishy odor Escherichia coli
Black rot (H2S or putrid odor) Pseudomonas, Proteus, Aeromonas, Alcaligenes, Escherichia, Enterobacter spp.
Blue rot Pseudomonas aeruginosa Pseudomonas
Pink rot (after green rot) Pseudomonas fluorescen
Red rot (no odor) Serratia marcescens ,Pseudomonas spp
Green rot (almond-like odor) Stenotrophomonas maltophilia
The creamy color of the yolk, the tan color of the albumen Bacillus cereus
Colorless (fruit odor) Acinetobacter, Moraxella spp., Citrobacter
The yellow pigment in the shell membrane Flavobacterium spp., Cytophaga spp.
Pink or red color spots Sporotrichum
Black color spots Cladosporium
Yellow or blue or green spots Penicillium

Spoilage of egg products

  • The eggs are used in the food industry because of their various functional properties such as foaming, binding, gelling, etc.
  • Various egg products include poached egg, scrambled egg, fried egg or omelets, liquid, dried, or frozen egg products.
  • Eggs are also widely used to make food products such as sauces, pasta, biscuits, cakes, processed meats, fish products, milk products, etc.
  • Egg quality, hygiene practices, and the type of technologies used in the egg product industry should be considered to avoid microbial spoilage of egg products.


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About Author

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Sanjogta Thapa Magar

Sanjogta Thapa Magar has done Master’s degree (M.Sc.) in food microbiology from St. Xavier’s college. Currently, she is working as a Quality control microbiologist in the pharmaceutical industry. She is particularly interested in studying the antimicrobial property found in food.

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