Table of Contents
- Introduction
- Contamination source and causes
- Spoilage of egg
- Non-microbial spoilages
- Microbial spoilages
- Spoilage of egg products
- References
Introduction
- Eggs are a highly nutritious food containing proteins, minerals, fats, iron, phosphorus, and vitamins A, B, D, E, and K.
- The eggs most commonly consumed by humans come from hens, ducks, and quails.
- Chicken eggs are particularly popular and consist of the yolk (30–33%), albumen (60%), and the shell (9–12%).
- The egg yolk contains about 50% proteins, with the main ones being lipoproteins, lipovitellins, and lipovitellinin.
- The egg albumen contains about 12% protein, primarily composed of ovalbumin (54%), conalbumin (13%), avidin (0.05%), ovotransferrin (10%), ovomucoid (11%), ovomucin (1.5–3%), and lysozyme (3.5%).
- The eggshell is a rigid structure mainly made of calcium carbonate, supported by an organic matrix.
- Inside the shell, there are two shell membranes, with the inner membrane acting as a barrier when an organism penetrates the shell.
- Eggs and other egg-based products—such as poached eggs, scrambled eggs, fried eggs, omelets, as well as liquid, dried, or frozen egg products—can be subject to microbial spoilage.
Contamination source and causes
Eggs are usually sterile when laid, but contamination can occur afterward due to various factors, including:
- Contact with the fecal matter of the chicken.
- Presence of specks of dirt or materials from the cage or nest.
- Water used during the washing of eggs.
- Equipment used during processing and handling.
- Materials used for packing the eggs.
- Storage temperatures that facilitate microbial growth.
- Presence of eggshell cracks or micro-cracks.
Spoilage of egg
- Eggs are highly perishable, and their quality can deteriorate during storage due to both chemical changes (non-microbial spoilage) and microbial spoilage.
- The spoilage process is influenced by environmental conditions, temperature, moisture, the type of packaging material, and the length of storage time.
- Eggs have a high water content (74%) and rich nutrient composition, making them highly susceptible to microbial spoilage.
- Once an egg is broken, it loses its natural antimicrobial properties, increasing its vulnerability to microbial contamination and spoilage.
Non-microbial spoilages
- Water content and gases evaporate through the pores of the eggshell, resulting in a decrease in the egg’s weight.
- Evaporation of water causes the albumen to become thinner.
- Eggs float when placed in water due to the loss of carbon dioxide through the shell pores and the entry of oxygen, which forms an air bubble inside.
- The loss of carbon dioxide and water through the shell pores increases the pH of the albumen, shifting it to an alkaline state (7.6–9.5).
- Mixing of the albumen and yolk contents can occur, leading to mottling of the yolk.
Microbial spoilages
- The eggshell serves as a physical barrier, while the egg white acts as an important defense against invading bacteria because it provides an environment that is generally unfavorable for microbial growth.
- Eggs possess antimicrobial components such as lysozyme, ovotransferrin, proteinase inhibitors (including cystatin, ovomucoid, and ovoinhibitor), and vitamin-binding proteins (such as riboflavin-binding protein, avidin, and thiamin-binding proteins).
- For spoilage to occur, microorganisms must first contaminate the eggshell, penetrate its pores, grow through the shell membranes to reach the albumen, and eventually reach the yolk.
- Some bacteria can resist the egg’s natural growth-inhibiting properties.
- The natural 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 species.
- Spoilage-causing bacteria include Pseudomonas, Proteus, Alcaligenes, Enterobacter, Serratia, Stenotrophomonas, Cloaca, Acinetobacter, Moraxella, and Citrobacter species, which can cause off-odors and color changes in eggs.
- Yellow pigmentation of the shell membrane can be caused by Flavobacterium or Cytophaga species.
- Molds responsible for egg spoilage include Penicillium, Cladosporium, and Alternaria species.
- Early mold growth on the egg surface is known as pin-spot molding, while the advanced stage is referred to as fungal rotting.
- Various microorganisms cause specific spoilage defects in eggs, leading to changes in appearance, texture, odor, and overall quality.
| Type of Defect | Microorganisms Responsible |
|---|---|
| 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 spp. |
| Pink rot (after green rot) | Pseudomonas fluorescens |
| Red rot (no odor) | Serratia marcescens, Pseudomonas spp. |
| Green rot (almond-like odor) | Stenotrophomonas maltophilia |
| Creamy yolk color or tan-colored albumen | Bacillus cereus |
| Colorless appearance with fruity odor | Acinetobacter, Moraxella spp., Citrobacter |
| Yellow pigmentation in shell membrane | Flavobacterium spp., Cytophaga spp. |
| Pink or red spots | Sporotrichum |
| Black spots | Cladosporium |
| Yellow, blue, or green spots | Penicillium |
Spoilage of egg products
- Eggs are used in the food industry for their functional properties, including foaming, binding, and gelling.
- Common egg products include poached eggs, scrambled eggs, fried eggs, omelets, as well as liquid, dried, or frozen egg products.
- Eggs are also key ingredients in the preparation of sauces, pasta, biscuits, cakes, processed meats, fish products, and milk-based products.
- To prevent microbial spoilage of egg products, factors such as egg quality, hygiene practices, and the technologies used in the egg product industry must be carefully considered.
References
- Al-Bahry, S. N., Mahmoud, I. Y., Al-Musharafi, S. K., & Al-Ali, M. A. (2012). Penetration of spoilage and foodborne pathogenic bacteria into fresh chicken eggs: A public health concern. Global Journal of Bio-Science & Biotechnology, 1(1), 33–39.
- Corry, J. E. L. (2006). Microbiological analysis of eggs and egg-based products. In Microbiological Analysis of Red Meat, Poultry and Eggs (Woodhead Publishing Series in Food Science, Technology and Nutrition). https://doi.org/10.1533/9781845692513.183
- Frazier, W. C. (1995). Food Microbiology (4th ed.).
- Gherardi, S. R. M., Santos, B. M., Silva, F. A., Stringhini, J. H., & Café, M. B. (2015). Physical and chemical alterations and functional properties of white eggs in relation to time and storage conditions. https://doi.org/10.13140/RG.2.2.21110.09282
- Kumari, A., Tripathi, U. K., Maurya, V., & Kumar, M. (2020). Internal quality variations in eggs during storage. Retrieved from www.ijset.net
- Mayes, F. J., & Takeballi, M. A. (1983). A review on microbial contamination of the hen’s egg. Journal of Food Protection, 46(12), 1092–1098. https://doi.org/10.4315/0362-028x-46.12.1092
- Mendes, F. R., Andrade, M. A., Café, M. B., Santos, J. S., Lacerda, M. J. R., Stringhini, J. H., & Leandro, M. (2012). Physical and chemical characteristics of sanitized commercial eggs experimentally contaminated with Pseudomonas aeruginosa and stored under refrigeration. Retrieved from www.sbz.org.br
- Robert, J. R. (2004). Factors influencing internal quality and shell quality of eggs in laying hens. Journal of Poultry Science, 41(3), 161–177. https://doi.org/10.2141/jpsa.41.161
- Techer, C., Baron, F., & Jan, S. (2014). Microbial spoilage of eggs and egg-derived products. In Encyclopedia of Food Microbiology (2nd ed., Vol. 3). https://doi.org/10.1016/B978-0-12-384730-0.00371-2
- Techer, C., Baron, F., & Jan, S. (2016). Spoilage of eggs and egg products. In Food Microbiology: Principles into Practice, 69(September), 296–300. https://doi.org/10.1002/9781119237860.ch17
