Recently, a health program said that if an egg is boiled for more than 10 minutes, the yolk may turn blue, and the blue yolk is poisonous and will increase the risk of cancer after eating. Is this really true?
Why does the yolk of a long-boiled egg turn blue?
The protein in eggs is rich in cysteine, an amino acid containing sulfur that produces hydrogen sulfide when heated. At the same time, egg yolk also contains the mineral iron. Once hydrogen sulfide is formed, it will react with iron to form iron sulfide, and the color of iron sulfide is green. This reaction will continue at high temperatures and iron sulfide will continue to accumulate on the surface of the egg yolk. Therefore, the longer the egg is boiled, the greater the gray-green component on the surface of the yolk.
As for the claim of carcinogenicity, it is not really reliable. Although hydrogen sulfide has some association with the incidence of colorectal cancer and may promote the proliferation and migration of SW480 colon cancer cells, hydrogen sulfide produced during egg cooking will be rapidly converted to ferrous sulfide, so hydrogen sulfide does not to be found in eggs. Accumulation while iron sulfide is a safe, non-toxic compound that does not cause cancer.
Therefore, if the yolk turns green, it will have the greatest impact on its "appearance" and will not affect human health.
In addition, many people like to eat "soft-hearted eggs", which means cooking the eggs only until they ripen three times, and the yolks are practically still liquid. Such hard-boiled eggs can be tempting in terms of taste and visual effects, but from a safety and nutrition point of view, eating fully boiled eggs is recommended. This is because eggs are a food more susceptible to bacterial contamination, especially salmonella.
So how exactly can you cook an egg with a "full result"? It's not that hard, just follow the 3 steps below.
The first step, wash the eggs and put them in a saucepan of cold water; the second step, cover the pot, turn on the heat and start the timer for 3 minutes after the water boils; third step, turn off the stove after 3 minutes, do not open the lid and simmer for 5 minutes. I can. Such hard-boiled eggs are not only fully cooked, but the yolks generally do not turn green.