The main chemical component of protein is a kind of protein. When eggs are kept for a long time, some protein in protein will break down into amino acids. Do you know amino acids? Its chemical structure has a basic amino group -NH2 and an acidic carboxyl group -COOH, so it can react with acidic and alkaline substances. Therefore, people will deliberately put some alkaline substances in the mud when making preserved eggs, such as lime, potassium carbonate and sodium carbonate. They will pass through the holes in the eggshell and combine with amino acids to form amino acid salts. These amino acid salts are insoluble in protein, so they crystallize in a certain geometric shape to form beautiful pine flowers.

The main chemical composition of preserved eggs is another kind of protein, which contains sulfur. After a long time, the egg yolk will also decompose into amino acids, and release what we usually call rotten egg-flavored gas-hydrogen sulfide. Egg yolk itself contains many minerals, such as iron, copper, zinc and manganese. Hydrogen sulfide can react with these minerals to form sulfide. Therefore, the blue-black yolk is the source of these sulfides. Most of these sulfides are extremely insoluble in water, so they are not absorbed by the human body.

In addition, because a large amount of protein in preserved egg yolk is decomposed into amino acids, the yolk of preserved egg tastes much fresher than ordinary eggs. Preserved eggs are nutritious and delicious, but they are too alkaline to eat. Suggestion: Add some old vinegar when eating preserved eggs, which can sterilize, neutralize some alkalinity of preserved eggs and taste more delicious.