Can eggs with darkened yolks still be eaten?

Generally, eggs with blackened yolks should not be consumed. The detailed explanation is as follows:

A blackened yolk usually indicates that the egg has spoiled. When eggs are stored for extended periods or under improper conditions, microorganisms can enter the egg and multiply. These microorganisms consume nutrients from the yolk to support their growth and reproduction, producing mycotoxins as a byproduct. These mycotoxins are harmful to humans and may cause symptoms of food poisoning such as abdominal pain and vomiting after consumption.

A blackened yolk can also result from improper cooking methods. When eggs are boiled for too long, cysteine from the egg white reacts with iron from the yolk to form black ferrous sulfide on the yolk's surface. Although this type of yolk discoloration generally does not pose a serious health risk, it may be accompanied by a decrease in taste and nutritional value. Therefore, to avoid this situation, it is important to use appropriate cooking times and methods.

When storing eggs, proper storage conditions and duration are important. Eggs should be kept in a cool, dry place, away from direct sunlight and high temperature or humid environments.