Topics:
Animal Refresher, Poultry Science
Darkening of Egg Yolk in Hard-Boiled Egg
Darkening of egg yolk in a hard-boiled egg is due to the formation of:
- H₂S
- Iron sulfide — Correct Answer
- H₂ gas
- Riboflavin
Explanation:
Correct Answer: Iron sulfide (FeS)
The dark greenish-grey ring around the yolk of a hard-boiled egg is caused by Iron Sulfide (FeS), which forms when hydrogen sulfide (H₂S) — released from the albumin during overcooking — reacts with iron (Fe) present in the yolk.
Chemical Reaction
H₂S (from albumin) + Fe (from yolk) → FeS (Iron Sulfide) — dark compound
Prevention
- Do not overcook eggs.
- Place eggs in cold water immediately after boiling — this stops further H₂S diffusion into the yolk.
The H₂S is generated by the breakdown of sulfur-containing amino acids (cysteine, methionine) in albumin upon heating.
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This multiple choice question is from Animal Refresher, Poultry Science. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Refresher to strengthen your preparation.
