Crustaceans, including foods such as shrimp, prawns and lobsters, are among the favorites to liven up a good meal during these holidays. And, in many homes, these days seafood, a food rich in high-quality proteins, with numerous essential amino acids, low in carbohydrates and fats, becomes one of the great protagonists of many Christmas gatherings.
However, there is something that can spoil a good gastronomic moment, even if there are no compelling reasons for us to throw it away. We are referring to the presence of black spots in products such as prawns and shrimp. The first reaction to the presence of these stains will be displeasure, with the feeling that they are spoiled and that if we eat them, they will harm us.
However, this process is completely natural and does not entail risks (unless other indicators of deterioration do appear, which tell us that it is better not to consume that product). Will we have to discard crayfish, shrimp or prawns with dark spots, especially on the head and tail?
Why do black spots appear on crustaceans?
To understand this natural process, we must begin by explaining that crustaceans have an exoskeleton, an external structure that gives them their body shape and protects them from external threats. When they grow, this exoskeleton changes and, during this process, an enzyme intervenes, with the strange name polyphenol oxidase, which is responsible for the hardening of the shell and also for a process called melanosis. This is the development of black pigments in crustaceans, which normally occurs 10-12 hours after the death of the animal and is related, as the name indicates, to melanin, the pigment responsible for the color of areas such as the skin.
These black spots are caused by a system of enzymes naturally present in the shell that, in the presence of air, can chemically transform colorless compounds into brown pigments near the surface and shell. It is more or less the same thing that would happen to an apple when it turns brown due to oxidation when we cut it in half and light hits it.
When the enzymes appear, what we could say is the oxidation of the phenolic compounds in the animal’s body to form quinones, which in turn give rise to melanins, the pigments that we said are responsible for the black color. Normally these spots appear on the head or tail, which are the areas of the shellfish where all the enzymes that cause the reaction are found. As time goes by, these spots spread to other areas of the body.
Can you eat seafood with black spots?
These black spots that are formed by the oxidation process of enzymes usually cause a certain rejection when consuming, reluctance and fear that the product is not completely fresh and, therefore, that it is harmful to health. However, the presence of these black spots is not indicative of deterioration and, therefore, its consumption is safe because melanin does not provide smell or flavor nor is it harmful.
A product with black spots is not harmful nor is it synonymous with deterioration, although it is also true that it is not attractive to the eye. But we must know that if stains appear, it means they have been stored for a few days, which we must take into account, especially in the case of products such as seafood, which are so perishable. That is why it is so important to pay attention to other signs that indicate that the seafood is not in good condition.
Four ways to prevent black spots on seafood
The industry has several measures to prevent melanosis. The key is to slow down this process. The common denominator factor for all of them is to complicate the life of this enzyme and, to this end, the most widespread action of the industry is the use of sulfites, a preservative substance that must be declared compulsorily and that, although it has clear advantages, also It is true that it poses a problem because it can cause allergic reactions in sensitive people.
Refrigeration, freezing, cooking or packaging in a protective atmosphere without oxygen (we must bear in mind that one of the elements necessary for the development of melanosis is oxygen) are other effective measures to prevent the appearance of black spots.
But what can we do at home to eliminate them? The answer is no consolation when they have already appeared because there is no measure that can eliminate them completely. But if we are careful when preserving these foods, we can prevent them from appearing and ensure that the crustaceans remain intact. It can help us to follow the following guidelines:
- Avoid shocks: if we are not careful when handling this type of food, the risk of an enzymatic reaction occurring increases, which is what results in the formation of melanin.
- Do not break the cold chain: whether we have bought frozen or refrigerated crustaceans, it is key to maintain a constant cold temperature, which will help us delay melanosis (but not prevent it).
- Cooking: heat helps us to inactivate enzymes, therefore, if we buy fresh product it is advisable to cook it to prevent the appearance of melanosis. If there are already stains, we can eliminate some, not all, because melanin is sensitive to heat.
- Add some acid: another good way to prevent prawns and prawns from darkening too soon is to add a little acid, such as lemon or vinegar, which will lower the pH and this will stop the enzymatic activity, preventing blackening.
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