The darker the egg yolk, the more nutritious it is? The truth is...

"The darker the yolk, the higher the nutritional value."

It is often said that the darker the egg yolk, the higher the nutritional value. A typical example is free-range eggs. In people's perception, free-range chickens have a superior living environment and grow naturally, so their eggs are more nutritious and their yolks are indeed darker.

Rumor Analysis

That is not the case.

The color of the yolk is affected by many factors, such as the age, breed, health status, feed ingredients and pigment content of the hen. We cannot judge the nutritional value of eggs based solely on the depth of the yolk color.

The following four types of eggs include ordinary eggs (0.8 yuan), free-range eggs (1.5 yuan), organic eggs (2.3 yuan) and DHA eggs (3 yuan). Can you match the color of the yolk? Which one would you choose to buy? (Take a guess first, the answer will be revealed at the end of the article~)

Source: Taken by myself

The color of egg yolks is compared in the industry using the Roche color fan, which has 15 levels from light yellow to orange-red. A consumer survey found that 10 to 13 are more popular among consumers.

Image source: Digital Egg Tester

Some people believe that dark yolks mean that the chickens eat a natural, healthy diet and therefore produce more nutritious eggs. However, this is not true.

Egg yolk color is affected by many factors

The color of egg yolk is affected by many factors, such as the age, breed, health status of the hen, feed ingredients and pigment content.

1

The hen factor

Chicken age: Generally speaking, adult chickens have stronger ability to color the egg yolks than young chickens, but as they age, the hens' pigmentation ability decreases and the egg yolk color becomes lighter.

Breed: Different breeds of chicken have different abilities to pigment the egg yolk. For example, the ability of Leghorn chicken to deposit lutein is stronger than that of White Rock.

Health status: Disease or infection with certain viruses, bacteria or parasites can also affect the absorption of lutein, such as digestive tract or respiratory diseases, coccidiosis and other infections.

2

Feed factors

Pigment content: The richer the content of carotenoids (mainly lutein and zeaxanthin) in chicken feed, the darker the egg yolk color. Therefore, compared with farmed chickens that eat feed, free-range chickens that eat green vegetables, grass, and corn have a darker egg yolk color due to the high content of carotenoids. In addition, if colorants are added to the feed, the color of the egg yolk will also be darker.

Fat content: Carotenoids are fat-soluble, and fat can promote the absorption of carotenoids in feed. Therefore, adding an appropriate amount of fat to the feed can make the egg yolk darker. Usually, adding 3% to 5% animal fat to the feed can improve the coloring effect.

Vitamin A and calcium content: Vitamin A and calcium can both inhibit the absorption of carotenoids, so if the content of these two nutrients in the feed is too high, carotenoids will be absorbed less and the egg yolk color will not be too yellow.

Long-term storage of feed and antioxidants: If feed containing corn is stored for a long time, lutein and zeaxanthin will be oxidized and the content will decrease. If antioxidants such as vitamin E and ethoxyquin are added to the feed, it can prevent the pigment from oxidizing and losing its coloring ability.

Contamination with mycotoxins: When feed is contaminated with mold, it reduces the digestive tract's ability to absorb carotenoids, especially aflatoxins, and also reduces the gloss of eggs.

In addition to the above factors, anti-nutritional factors in feed, drugs, environmental control of the chicken house, etc. will also affect the color of the egg yolk.

High in carotenoids

It does not mean that the overall nutrition is high

Although there are many factors that determine the color of egg yolks, it must be admitted that in addition to the factors of the hen itself, the pigments in the feed play a key role . If the feed is natural and no colorants are added, the color of the egg yolk mainly comes from carotenoids, including lutein, zeaxanthin, etc.

For example, if the hens are fed mainly corn, the yolks of their eggs will be medium yellow (around 6 on the color scale). If the hens are fed mainly wheat or barley, the yolks will be relatively light (around 3 on the color scale). More extreme is that if the hens' diet contains almost no pigment, such as only white cornmeal, the yolks of their eggs will be very light, even close to white.

High carotenoid content ≠ high nutrition

Eggs with dark yolks tend to have higher carotenoid content. However, the lutein and zeaxanthin in the yolk are phytochemical pigments and cannot be converted into vitamin A, so they are not nutrients.

Source: Encyclopedia of Chinese Nutrition Science (2019 Edition/Volume 1)

The nutritional value of eggs mainly depends on the content of protein, fat, vitamins and minerals. The content of these ingredients has little effect on the color of the yolk.

In addition, it is worth noting that although carotenoids have certain health benefits to the human body, such as anti-oxidation and protection of vision, it is easier for us to obtain carotenoids through dark vegetables in our daily life.

Data source: Chinese Food Composition Table (6th Edition/Volume 1)

Therefore, we cannot judge the nutritional value of eggs solely based on the depth of the yolk color.

Egg yolks that are too red or too yellow may pose a safety risk

Although the color of the egg yolk is not equivalent to nutritional value, the public's preference for dark yolks has led some companies to find new ways to do it. Light yolk? No problem, by adding colorants, you can achieve a darker effect.

1

Legal additives

At the 315 Gala in 2019, the China Consumers Association exposed the inside story of "beautification eggs". Some manufacturers in the industry add cantharidin (a carotenoid) to the feed to deepen the color of the egg yolk, making the egg yolk look better.

Image source: 2019 315 Gala

You may sigh and think this is too heartless. In fact, it is legal to add cantharidin to chicken feed (to turn egg yolk orange-red). As early as 2006, the "Catalogue of Feed Additives" stated that cantharidin can be added to poultry feed as a colorant.

In addition to canthaxanthin, apocyanate (which turns egg yolk yellow) is also a commonly used colorant. These two are widely used around the world.

Source: Ministry of Agriculture official website

However, if colorants are added and the eggs are advertised as "pure natural, free-range", it is misleading. At present, there is no national standard for free-range eggs in China. Therefore, when buying eggs, there is no need to pursue darker colored eggs such as "free-range eggs" or "stupid eggs". Freshness and safety are the primary principles for buying eggs.

Image source: The eggs involved in the 2019 315 Gala

Speaking of safety, there are also some feeds on the market that change the color of egg yolks by adding industrial pigments, which increases health risks⬇️

2

Illegal additives

I don’t know if you still remember the name Sudan Red. In 2006, “red-heart duck eggs” in the Beijing market were found to have illegally used “Sudan Red”. Later, “red-heart” eggs suspected of containing Sudan Red were found in Fujian, Zhejiang, Liaoning and other places one after another, and Sudan Red became famous for a while.

Sudan Red is an industrial dye. Animal experiments have found it to be carcinogenic, so it is prohibited for use in food production in my country, the European Union and other places. The International Agency for Research on Cancer (IARC) has identified Sudan Red as a Class III carcinogen, but it is not certain whether it will cause cancer in people. In 2005, the Ministry of Health issued a notice to the public (No. 5 of 2005), prohibiting the production, operation and use of Sudan Red as a food additive.

Sudan Red is not an additive, but an illegal additive. Therefore, if you buy eggs in bulk on the roadside or at a market, and the yolk is particularly red, there may be "safety risks".

In summary, a dark yolk does not necessarily mean high nutrition. As a nutritious food, eggs have a relatively stable nutritional value if they are not fortified. When choosing eggs, you do not have to overly pursue the depth of the yolk color, but should focus on whether the eggs are fresh, the source is reliable, and the overall quality and safety.

Finally, it’s time to reveal the results of the guessing game. Did you guess correctly?

Source: Taken by myself

Looking in the mirror of rumors

There is no need to overly pursue the nutritional value of a particular food. No single food can meet all the nutritional needs of the human body. Balanced, diverse and sufficient intake is the key.

References

[1] Ministry of Agriculture and Rural Affairs of the People’s Republic of China. Announcement No. 658 of the Ministry of Agriculture of the People’s Republic of China. http://www.moa.gov.cn/nybgb/2006/dliuq/201806/t20180616_6152306.htm

[2] Ministry of Health of the People’s Republic of China. Announcement on the prohibition of using Sudan Red as a food additive (No. 5 of 2005). http://www.nhc.gov.cn/sps/s7891/200804/d91ff96a780b4f198203fdfe1070457e.shtml

[3] CCTV2. 2019 315 Gala.

[4] Wang Huaiyu. Factors affecting egg yolk color and control measures [J]. Animal Husbandry, 2008(10):56-56.DOI:10.3969/j.issn.1008-0414.2008.10.020.

[5] Shen Manman, Wang Ying. Analysis of factors affecting egg yolk color deposition[J]. Guangdong Feed, 2014(6):3.DOI:CNKI:SUN:GDSL.0.2014-06-020.

[6] Chinese Government Website. “Red-heart” eggs suspected of containing Sudan red have been found in Fujian, Zhejiang, Liaoning and other places. https://www.gov.cn/jrzg/2006-11/22/content_449674.htm

[7] Yang Yuexin. Chinese Food Composition Table 6th Edition Volume 1 and 2[M]. Peking University Medical Press, 2018

[8] Chinese Nutrition Society. Encyclopedia of Chinese Nutrition Science (2019). Beijing: People's Medical Publishing House, 2019

Author: Li Chun, National Registered Nutritionist

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