As a foodie, I love eating crabs very much. Both sea crabs and freshwater crabs are on my food list, especially their crab paste and crab roe, which are simply delicious.
However, once I bought a few hairy crabs and raised them home for a few days, only to find that one of them was dead. Just as I was about to cook the dead hairy crab, my cousin, who was a guest at home, immediately stopped me and told me that the dead crab was poisonous and could not be eaten.
This confuses me because it is common to see frozen, thawed or even decomposed sea crabs for sale in the market, and I have been eating sea crabs for years without problems, so why can't I eat dead crabs?
Later, after checking the information, I realized that this was really the case. Of course, whether you can eat dead crabs depends on the species of crabs. The main ones that cannot be eaten are crabs that live in freshwater and unsafe saltwater environments, such as hairy crabs, blue crabs, and so on.
Hairy crabs, for example, have hairy hairs, carapace grooves, and gills that are ideal for bacterial growth. In addition, the crab's diet is also very messy, including fish, plants, snails, shrimp and worms.
Once the crab dies, the crab's stomach may rupture, and the bacteria will spread to the muscles and the outside world, and the bacteria on the surface of the body will also enter the crab's body. Crabs themselves are rich in protein and are a breeding ground for bacteria to multiply, which multiply quickly to break down proteins into toxic substances, the most dangerous of which is histamine.
At 20 degrees Celsius, histamine levels reached 6.3 mg per 100 g and 7.4 mg per 100 g at the 3rd and 12th hour after death, respectively.
Of course, low temperatures can reduce the rate at which bacteria multiply. In a refrigerated environment at 4 degrees, histamine levels reach 4.5 mg/100 g and 9.1 mg/100 g at 24 and 72 hours, respectively.
And this histamine is not easily destroyed even if the crab is cooked. Ingestion of 8 to 40 mg of histamine can cause mild poisoning symptoms, and more than 100 mg can cause severe poisoning.
Common symptoms of poisoning include headache, nausea, vomiting, diarrhea, abdominal pain, and in severe cases, dehydration, convulsions, and shock. Therefore, freshwater crabs that are kept at low temperatures and cannot judge the time of death should never be eaten.
This is because compared to freshwater crabs, the environment is closer to the natural state and the quality of the food is higher, and frozen crabs are often frozen while they are still alive.
In addition, the higher salt content in the body of sea crabs makes the bacteria multiply more slowly, thus delaying the process of food spoilage. This explains why we see frozen seafood that is still safe to eat when sold.
Of course, thawed sea crabs should still be eaten as soon as possible, because the taste will deteriorate over time, and there is also a risk of food spoilage. Similarly, the same goes for other seafood, which should be eaten as soon as possible after thawing.