Why is seafood not tasty when it’s dead? For tips on choosing seafood, just read this article!

Friends who have bought seafood know that after fresh seafood is slaughtered, even if it is only taken home and put in the refrigerator for a short while, when it is cooked, the taste will not be as fresh and sweet as when it was alive, and the meat will not be as "Q" as when it was fresh.

This is quite different from pork, beef and mutton, which need to be left for a while after being slaughtered to become more tender. Why is this? Let's talk about this today.

Such fresh seafood

Why is it not delicious when it's dead?

If you want to know why seafood becomes "unpalatable" after it dies, you must first understand the general changes that occur in seafood after it dies.

Seafood is rich in protein and unsaturated fatty acids, and because they live in water, their body parts often carry a lot of bacteria and other microorganisms. It is conceivable that after seafood dies, bacteria and other microorganisms will lose the restraint of the seafood immune system and will rapidly multiply in this "paradise" full of protein and fatty acids, causing the seafood to rot and deteriorate .

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Soon, the enzymes in the seafood will begin to break down the protein , destroying the originally chewy and firm muscle tissue, making it loose and soft, and the taste becomes worse;

The rich unsaturated fatty acids are oxidized to produce various substances with odors , such as aldehydes, ketones, and other volatile substances such as cumene, styrene, and ethyl acetate;

Myoglobin is oxidized to metmyoglobin , which makes the originally pink red seafood turn gray and brown; and the rapid reproduction of bacteria will also cause black and gray spots to appear on the surface of seafood;

Therefore, once the seafood dies, the texture, smell and color will change quickly, and the color, aroma and taste will all decline, and naturally it will not taste good.

It's actually not bad at this point, it just doesn't taste good. Some seafood will release toxins that are harmful to the human body after death, which is even more dangerous. For example, tuna, mackerel, and sardines are rich in histidine. If they are not properly stored after death, bacteria can easily convert histidine into histamine in a high temperature environment.

Histamine can cause food poisoning , leading to rashes, headaches, vomiting, diarrhea, and even serious conditions such as difficulty breathing and coma. Therefore, if you want to eat seafood safely, you must be careful when choosing seafood varieties and avoid those that are prone to carry or produce toxins .

Is the freshness of seafood a double-edged sword?

Fresh seafood does not even need any seasoning, just boiled in plain water to be incredibly sweet and fresh. The fresher the seafood, the more pronounced the sweetness and freshness.

The strong umami taste of seafood mainly comes from the rich " umami amino acids " in the body. "Umami amino acids" refer to a class of amino acids with special umami taste, such as glutamic acid, aspartic acid, phenylalanine, glycine, tyrosine, etc. Among them, sodium glutamate, the sodium salt of glutamic acid, is the main ingredient of MSG. The content of glutamic acid and aspartic acid in seafood is generally very high.

At the same time, seafood also contains a large number of nucleotides, such as adenosine monophosphate, inosinic acid, and guanylic acid, which can multiply the taste of glutamic acid, aspartic acid and other umami amino acids, making seafood more fresh. In addition, fresh seafood also has a slight sweetness, which mainly comes from the glycogen in the meat and some slightly sweet amino acids, such as glycine and alanine.

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Studies have shown that the content of glutamate, disodium inosine monophosphate, and adenine nucleotide in saltwater shrimps and crabs is higher than that in freshwater shrimps and crabs. This is probably one of the reasons why people think seafood tastes better than river fish.

But these umami substances seem to be a double-edged sword . When seafood is alive, the above umami substances are constantly produced and accumulated, making the seafood "fragrant to the point of being confusing"; but once the seafood dies, they begin to decompose rapidly, greatly reducing the edibility of the seafood:

Umami amino acids release a pungent ammonia smell after decomposition, which is unpleasant. Some sulfur-containing amino acids also produce hydrogen sulfide after decomposition, which emits a rotten egg smell ;

The glycogen that once gave the meat its sweet taste also breaks down faster, releasing lactic acid, giving the seafood a rancid, sour taste .

There is also a substance called trimethylamine oxide that exists in seafood. It can bring a sweet and fresh taste to seafood, but after the seafood dies, it will quickly decompose and produce trimethylamine and dimethylamine. These two substances will give seafood a strong fishy smell .

The mixture of the above-mentioned stench, sourness and fishy smell will make people shudder at the smell of dead seafood and stay away from it.

Want to eat fresh seafood

How to choose and how to store?

If you want to eat fresh seafood, the most convenient way is to go directly to the fishing boat and eat while catching; the second best way is to wait on the shore and buy the seafood that has just been hauled ashore by the fishing boat. But if you don’t live in a coastal area, these methods are not convenient for modern people, and we can only go to the market or supermarket to buy. Then you will definitely use the following tips:

1. Live seafood is preferred . It should be noted that you need to pay attention to the movements and reaction speed of live seafood. You can use a fishing scoop to gently touch them. Whether it is fish, shrimp, crab or shellfish, those that move faster and react quickly to external stimuli are often fresher.

2. Look at the meat quality . If the meat is firm and elastic and not sticky to the touch, it means that the protein has not been broken down and the seafood is fresher.

3. Weigh the seafood . After the seafood dies, nutrients such as protein are decomposed, which will reduce the weight of the seafood. Therefore, it is better to choose seafood of the same size that is heavier, as it is often fresher.

4. Try not to buy too much. It is best to eat it now . If you cannot finish the seafood you bought at home, you can divide it into small portions and store it in the freezer. This way, you can take a portion to defrost each time to avoid the impact of repeated defrosting and freezing on the meat quality.

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By the way, here is a way to save money: Compared with fresh seafood, quick-frozen seafood has almost no nutritional loss and is more fresh . The disadvantage is that seafood has a high water content, which makes it easier to produce ice crystals during the freezing process, affecting the elasticity of the meat. However, considering that quick-frozen seafood is easy to store and much cheaper than fresh seafood, it is still worth recommending. For some seafood that does not have a big impact on the taste after freezing, such as prawns, you can choose frozen ones.

During the Mid-Autumn Festival, take this selection guide with you to the supermarket to choose seafood for your family, just in case.

References

[1] Wang Xiao, Zhang Jiguang, Xu Kunhua. Nutritional composition analysis and quality evaluation of three kinds of marine shrimp muscle[J] 2014.08.039

[2] Liu Tiantian, Liang Zhongyong, Fan Sihua. Analysis of characteristic flavor components of North Sea sand crab [J]. Food Science, 2018, 39 (14): 236-241.

[3] Pan Ying, Wang Fucai, Luo Chengju. Comparative analysis of the nutritional components of the muscle of Penaeus vannamei cultured in marine and freshwater [J]. Journal of Qingdao Ocean University, 2001, 11, 3(6): 828-834.

Planning and production

Author: Wang Lu, registered dietitian

Review | Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center

Planning丨He Tong

Editor: He Tong

Proofread by Xu Lailinlin

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