The black spots on frozen shrimp are due to the reaction of polyphenol oxidase in the body with tyrosine, thereby producing melanin.

Generally, there is more polyphenol oxidase on the shrimp heads, so the shrimp heads will turn black. When the frozen shrimp are taken out of the freezer and thawed, the polyphenol oxidase is oxidized. So dark spots appear on the body.

If there are only black spots on the shrimp heads, the shrimps are clean and do not have any odor. The shrimps can be eaten after boiling. If there are small black spots on the shrimps, If you have black spots, it is best not to eat them to avoid accidental poisoning.