The Dirtiest Thing on Eggs: You Might Be Eating Them! (Not What You Think)

Eggs are rich in nutrients. As an essential ingredient in the kitchen, they are inexpensive, good quality and nutritious.

When buying eggs, we will find that some eggs are clean on the surface, while others are covered with chicken droppings. Everyone will naturally avoid the eggs with chicken droppings and choose the eggs with clean surfaces.

But are eggs without chicken poop really clean? Not necessarily!

Invisible pathogens on eggs

Hens lay eggs and defecate through the "cloaca", so eggs and chicken feces always meet. Although eggs without chicken feces look clean, they may still carry some dirt that we cannot see with the naked eye, that is, pathogens.

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A survey shows that the total number of bacteria on the surface of eggshells is about 1.5 million. Although this number sounds scary, you don't have to be too scared. In fact, bacteria exist in the environment, and there may be 10,000 to 1 million colonies per square centimeter on our human body, forming different numbers of bacteria.

What we need to be wary of are the “dirtiest” pathogens in eggs - including Staphylococcus aureus, Escherichia coli and Salmonella.

A study once tested commercial eggs in Fangshan District, Haidian District and Shunyi District of Beijing. The results showed that the detection rate of E. coli on eggshells in the three regions was high, with an average rate of 80%; the average rate of Salmonella was 15%; and the average rate of Staphylococcus aureus was 5%.

When there is obvious feces and dirt on the eggshell surface, Salmonella and E. coli can be detected, and the number of colonies is larger. When the eggshell surface is relatively clean, mostly E. coli is detected, and the number of colonies is smaller.

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Eggs are contaminated after they are laid. For eggs with light surface contamination (eggs that look clean), it takes a certain amount of time for microorganisms to infect the contents. Generally, if they are stored at 25°C for 3 days, Salmonella can pass through the eggshell and shell membrane to infect the contents of the eggs. For eggs with heavy surface contamination, microorganisms will multiply in large numbers in a shorter period of time and invade the interior of the eggs.

Salmonella that needs attention

Salmonella is a major foodborne pathogen commonly found in eggs, meat and raw milk.

Salmonella can contaminate eggs from infected hen reproductive tissue before the shell is formed and can then contaminate the interior of the egg.

What's more frightening is that Salmonella is very easy to survive: it is salt-tolerant and cold-tolerant, can survive for weeks in a dry environment, 3 weeks in water, and 2 months in feces. Infection with Salmonella can cause abdominal pain, diarrhea, nausea, vomiting, fever, and even death.

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Survey data in our country show that among the many diseases caused by eating eggs, the proportion of diseases caused by eating eggs contaminated with Salmonella can be as high as 70% to 80%. This shows that we must be vigilant about Salmonella and not take it lightly.

Tips for eating eggs safely

Although the salmonella in eggs is very dangerous, it is not difficult to deal with. You can avoid its harm to the greatest extent by following the following 6 points when eating eggs.

1. Buy eggs

When buying eggs in the supermarket, choose clean eggs with intact eggshells. Eggs with more contaminants on the eggshells and cracked eggs are more likely to be contaminated by pathogenic bacteria, so it is best not to buy them.

2. Store eggs properly

After buying it home, you can store it in a cool and dry place, preferably in the refrigerator, and make sure to store it separately from fruits, vegetables, meat, etc. to avoid cross contamination.

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Generally, you don’t need to wash the eggs you buy, because there is a protective film on the surface of the egg shell that can reduce the entry of microorganisms into the egg. If you wash it too much, the protective film will be damaged, and the eggs will easily go bad even if they are put in the refrigerator. However, if there is a lot of chicken manure and dirt on the surface of the egg shell, you can wash it. The washed eggs should be eaten as soon as possible.

Also, please note that eggs that have been refrigerated should continue to be kept at refrigerated temperature, and do not transfer previously refrigerated eggs to room temperature for storage. Because of the temperature difference, water droplets will form on the eggshell, which may facilitate the entry of microorganisms into the egg, making the egg easy to deteriorate.

3. Don’t store it for too long

Don't buy too many eggs at one time. It's better to buy less and more frequently to avoid storing them for too long. Although there is a protective film on the surface of eggs, as the eggs are stored for a longer time, the protective ability of this protective film will become weaker and weaker. In addition, the longer the eggs are stored, the more likely they are to be contaminated by salmonella.

4. Try not to eat soft-boiled eggs

Soft-boiled eggs usually have a soft, solidified egg white, while the yolk is still in a liquid, flowing state. In this state, the temperature of the yolk center may not reach above 60°C, which makes it difficult to kill Salmonella. It may carry Salmonella and other bacteria, increasing the risk of food poisoning. In comparison, fully cooked eggs are safer to eat.

If you really like soft-boiled eggs, choose "edible raw eggs" produced by regular manufacturers, and store and eat them according to the instructions.

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5. Don’t boil eggs in water

Even if you use boiling water to rinse eggs taken out of the refrigerator, it may not reach the temperature that kills salmonella, and most people just stir and drink it, so the time required for sterilization is almost not enough. Such operations cannot guarantee the killing of all salmonella and other bacteria, which increases the risk of food poisoning.

6. It is not recommended to eat raw eggs

Raw eggs are eggs that have "crackled" during the incubation process, that is, dead eggs. They may contain parasites and pathogenic bacteria such as Salmonella, Escherichia coli, and Salmonella typhi, which will increase the risk of food poisoning.

In short, although eggs are delicious, you must pay attention to the safety of eating them. The "dirtiest" pathogens on eggs, although we cannot see them with the naked eye, are dangerous and should not be taken lightly.

References

[1]https://www.cfs.gov.hk/sc_chi/multimedia/multimedia_pub/multimedia_pub_fsf_29_01.html

[2] Zhao Lei, Luo Hongxia, Huang Yanfang, Wang Jian, Ju Ronghui. Detection and analysis of three main pathogenic microorganisms in commercially available eggs [J]. Modern Food Science and Technology, 2010, 26(2): 200-202

[3] Wang Jie. Investigation and analysis of salmonella contamination in eggs and research on coating preservation technology in Baoding area[D]. Hebei University of Engineering, 2021. DOI: 10.27104/d.cnki.ghbjy.2021.000449.

This article is a work of Science Popularization China-Starry Sky Project

Produced by: Science Popularization Department of China Association for Science and Technology

Produced by China Association for Science and Technology Technology Publishing House Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Author: Xue Qingxin, registered nutritionist

Review丨Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center