Why do eggs turn green when cooked? The yellower the yolk, the better the egg quality?

Netizen question: I have the habit of eating boiled eggs every day. Recently I found that the shell of the boiled eggs turned green. What's going on?

Some people also say that the yellower the egg yolk, the better the quality of the egg. Is this true?

In fact, it is normal for egg yolks to turn green.

The reason why eggs turn green is that if they are boiled for a long time, methionine will release sulfide, which will react with the iron in the eggs to form dark-colored ferrous sulfide.

Green eggs do not have a big impact on the body, because the sulfide in the egg yolk is very small, which may turn into hydrogen sulfide and ferrous chloride under the action of stomach acid. If it does not react with stomach acid, it is also a water-insoluble compound and will not participate in the metabolic process.

Secondly, the digestive process of human intestines is microbial fermentation, and it is normal to produce metabolic wastes such as hydrogen sulfide and biogenic amines. The amount of hydrogen sulfide in the intestines far exceeds the water-insoluble ferrous sulfide on the egg yolk, so it is safe to eat.

As for the color of the egg yolk, we have learned about it before. It is mainly affected by the amount of carotenoids in it, which ultimately depends on the food the chicken eats.

If the egg yolk is yellow or red, it means that the chicken has eaten food with a high content of lutein. For example, it may have eaten more millet, corn residue and other foods.

However, adding pigments to feed, such as natural capsanthin, or permitted synthetic pigments such as capsanthin red, capsanthin yellow, and lucantin, can also achieve this effect.

It can be seen that the yellower the egg yolk, the better the nutrition. It is also possible that synthetic pigments have been added, which has no nutritional value. For daily consumption, there is no need to worry about the color of the egg yolk, whiter ones are still good.