2020-11-28
From November 7th to 11th, Tianjin successively detected that cold chain practitioners were infected with new crown pneumonia, and the outer packaging of cold chain food was also detected with new crown virus. Previously, local sources of the epidemic in many parts of the country also pointed to the cold chain. Cold chain products such as imported salmon and Ecuadorian frozen vannamei shrimp were repeatedly detected to carry the new crown virus. As a result, more and more people have begun to choose domestic related products, and those who love to eat frozen fresh products have also chosen fresh products. But the aquatic products that were originally alive in supermarkets or markets are sometimes dying after being taken home, and they don’t feel fresh after they are cooked. Why is this happening? How can we choose the freshest aquatic products? Chen Shunsheng, a professor at the School of Food Science and Technology of Shanghai Ocean University, gave detailed guidance to everyone.
The fish swims flexibly. Most of the live fish on the market are grown or cultured in freshwater. Some of them are transported over long distances or kept in the pool for a long time after being caught to "oxygenize", causing serious consumption of nutrients and physical energy of the fish. Although this fish is alive, its vitality has been greatly reduced and the taste is not delicious enough. When selecting fish, the vitality can be judged by observing the fish's appearance, swimming state, and reaction speed to external stimuli. Fish with good physique can swim flexibly in the water. When touched with their hands, they react sharply and can quickly break free; fish with poor physique are not flexible, or their mouth is close to the water surface, or their tails are swimming down. Floating sideways on the water, which is what we often call "turning the belly", indicates that this fish is about to die and it is best not to buy it.
Shrimp selection will "jump". Live shrimp should also be selected for free movement, especially fresh shrimp will even jump up in the pot. In addition, the color of the fresh shrimp is clearer, the eyes are protruding, the flesh is firm, and the connection between the shell and the muscle is very strong. The body color of the dying or stale shrimp will change, the color will become darker, not so clear, and some will have loose head and chest. When picked up from the middle of the shrimp body, the two ends will droop slightly.
Crab selection is easy to "turn over". The river crab must be alive, because it likes to eat rotten fish and shrimp. This kind of rotting food itself contains toxins. When the river crab is alive, these toxins are excreted through metabolism. However, after death, the metabolism stops, harmful substances in the stomach may overflow, and the bacteria in the body will also multiply and decompose the meat of the river crab. Will be poisoned. Live river crabs are easy to "turn over": place the crab with the carapace down and the legs up to turn it over quickly. In addition, to judge whether a crab is fresh or not, you can also look at its "energy". Crabs that crawl quickly and have teeth and claws are relatively fresh. You can also hold it in your hand to see if the crab moves by itself or needs to shake. The former is fresher than the latter.
Shellfish must be selected to open and close quickly, and will spit bubbles. Shellfish generally move slowly and are not as easy to distinguish as fish and shrimp, but they can still be distinguished by careful observation. For example, if you touch an open shell with your hand, if it closes quickly, it means that the shellfish has strong vitality. If you can swallow sand, or even spray water, it means that shellfish are more fresh. Shellfish will close the shell after death, even if it is scalded with boiling water, it will not open. Therefore, if it is still closed after cooking, it means that the shellfish has died before. The shells of snails in shellfish cannot be opened and closed, but the reaction speed can also be seen by touching. For example, use a toothpick to touch the mouth of the snails. If the head is retracted quickly, the snails are fresh enough.
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