Can eating sashimi with mustard kill insects? A must-read for seafood lovers!

Seafood is a favorite food for many people, and some people especially like to eat seafood sashimi, believing that seafood made into sashimi is more tender! So, are there parasites in raw seafood? Can eating seafood sashimi with mustard kill parasites? Today, let's talk about seafood sashimi and parasites.

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01

Myth: Seawater is full of salt, so parasites can’t survive

Analysis: No, marine fish can also have parasites.

Many people have such ideas: "Parasits cannot live in seawater", "There are no parasites in marine fish", "You don't have to worry about parasites when eating raw marine fish"...

But is this really the case?

In fact, although there are fewer parasites in seafood than in river fish, there are still quite a few, including not only common roundworms, but also Anisakis, a marine nematode.

Anisakis, also known as the sea nematode, can be found in almost all oceans around the world. It is truly the king of the seven seas. When humans swallow sashimi, the Anisakis larvae in the fish also enter the human digestive system.

The swallowed Anisakiasis larvae can drill into the walls of the digestive tract and other organs and tissues, causing a series of acute symptoms in humans such as vomiting, diarrhea, bleeding and inflammation.

As the Anisakids that burrow into organs die, their "corpses" will also form eosinophilic granulomas in our bodies.

02

Myth: Fresh seafood is safer than frozen seafood

Analysis: No, there are many parasites in newly caught seafood. Freezing can kill some of the parasites, but ordinary freezing cannot kill all of them.

Take the Anisakid nematode mentioned above as an example. It has poor adaptability to both low and high temperatures. It is afraid of both cold and heat. If the worm is exposed to 60 degrees, it will die in less than a minute.

Many studies have also shown that long-term low temperatures can also kill Anisakids. Some literature suggests that "to kill Anisakids, it is necessary to refrigerate at -30°C in a commercial air flow freezer for at least 15 hours. " Note that this refers to commercial deep freezing. Ordinary freezing at around -18°C cannot kill all parasites.

Therefore, it is best to eat fish after it is cooked. If you must eat it raw, it is recommended to eat fish that meets the frozen standards.

Many friends still like the fresh fish that have just been caught, and believe that not all fish have parasites.

It is true that not all fish have parasites. About 50% to 80% of fish are infected with parasites.

According to an article by Professor Sun Shizheng in the Chinese Journal of Parasitology and Parasitic Diseases, the detection rate of larvae in fish (88 species) in the South China Sea was 60.2%, and the detection rate of larvae in fish (20 species) in the Bohai Sea was 55%. According to Professor Ma Hongwei's research, the infection rate of Anisakis in fish and cephalopods in the Bohai Sea was as high as 81.8%.

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03

Myth: Since deep freezing kills some parasites, frozen seafood is safe

Analysis: Not necessarily, the bacteria problem on seafood is equally serious!

In fact, the dangers of eating raw seafood include not only parasites, but also bacteria. It is not easy to kill bacteria at -30℃. To preserve bacteria in the laboratory, the bacteria mixed with glycerol are frozen in a refrigerator at -80℃.

Therefore, the freshness of seafood is very important. Stale seafood is easily contaminated by bacteria.

Among the pathogenic bacteria pollution related to seafood, the most famous is the Vibrio family in the ocean, among which Vibrio parahaemolyticus and Vibrio vulnificus are the notorious duo.

Vibrio parahaemolyticus alone accounts for half of food poisoning, and in many places it has defeated the long-known Salmonella, and is the main cause of foodborne diarrhea worldwide. In China, there are millions of cases of foodborne diseases caused by Vibrio parahaemolyticus every year. The most classic symptom of Vibrio parahaemolyticus infection is gastroenteritis - diarrhea, vomiting, nausea, etc.; in severe cases, it can cause dehydration and other complications, and even cause death.

The stories about Vibrio vulnificus are even more frightening. The general story template is this: someone is scratched by a shellfish or pinched by a shrimp or crab when handling seafood. At the time, he thought it was nothing, but he started to have a fever and was sent to the hospital, only to find that he was infected with Vibrio vulnificus. The general ending of this kind of story is to induce sepsis, and then die or amputate.

The story about Vibrio vulnificus is not exaggerated. Instead, it makes people ignore the possibility of food-borne infection of Vibrio vulnificus. In fact, eating raw oysters or other shellfish is also a major factor in Vibrio vulnificus infection.

04

Myth: You can kill parasites by dipping in mustard

Analysis: It’s totally useless.

Whether it is wasabi, horseradish, or mustard seeds, these plants that are crowned as the source of mustard all contain a pungent chemical - isothiocyanate , which is what we usually call mustard flavor.

Experiments have proven that isothiocyanates have bactericidal effects, and soaking them in mustard sauce can indeed kill some parasites. The same is true for soy sauce with high salt concentrations, which can also kill some bacteria and parasites by using high osmotic pressure.

However, there are two points to note: First, time. Whether it is killing bacteria or parasites, it takes a certain amount of time to react. It takes about an hour to kill parasites with mustard, but it takes half a day to soak with soy sauce.

Second, if you want to kill parasites with mustard, you need to find the parasites from the fish fillet before you soak them in mustard. Otherwise, the parasites hiding deep in the fish meat cannot be exposed to the mustard. Now that they have been found, why not just throw them away? Do you have to eat a bite of mustard-flavored Anisakis?

To sum up, eating raw fish with mustard does not kill bacteria and parasites, it just makes it taste better.

The same goes for raw pickles. The soup made of soy sauce, MSG and chili peppers is unlikely to threaten the bacteria and parasites deep inside.

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in conclusion

There are also many parasites in marine fish. In addition to the common roundworms, there may also be Anisakida, which is unique to the ocean. Deep freezing can kill some parasites. Compared with fresh sashimi, frozen sashimi has relatively fewer parasites. There are many bacteria in frozen seafood, including Vibrio parahaemolyticus and Vibrio vulnificus. Only by putting the parasites directly into mustard for an hour can the parasites be killed by mustard. Eating seafood with a little mustard at ordinary times will not kill the parasites at all.

For safety reasons, it is best to cook seafood thoroughly before eating it. If you want to eat seafood sashimi, it is recommended to go to a regular restaurant, or purchase it through regular channels, and eat it as soon as possible.

References:

[1] Zhang Wang, Chen Xiukai, Li Zhenggao, et al. Research progress on Anisakiasis[J]. Advances in Veterinary Medicine, 2014, 35(07): 93-97. DOI: 10.16437/j.cnki.1007-5038.2014.07.021.

[2] Cao Zhan, Liu Jinsong, He Fang, et al. Overview of Anisakiasis[J]. Journal of Tropical Medicine, 2004(04):494-497.

[3] Xia Fan, Yang Lijun, Wang Jing, et al. Research progress on pathogenicity mechanism and rapid detection methods of pathogenic marine Vibrio[J]. Food Industry Science and Technology, 2011, 32(01): 366-370+376. DOI: 10.13386/j.issn1002-0306.2011.01.086.

[4] Sun Yixiang, Chang Hongjun, Yang Xingxin, et al. Research progress on Vibrio parahaemolyticus infection and its phage control in aquatic animals [J/OL]. Bulletin of Microbiology: 1-17 [2023-04-19]. https://doi.org/10.13344/j.microbiol.china.221017.

[5] Guo Yukun, Zhu Yuan, Fan Xiaoming, et al. Research progress on the pathogenic mechanism of Vibrio vulnificus[J]. Chinese Journal of Injury and Repair (Electronic Edition), 2022, 17(01): 81-84.

[6] Zhang Na, Guan Wenqiang, Li Chunyuan. Study on the inhibitory effect of mustard essential oil on postharvest pathogens of fruits and vegetables [J]. Freshness and Processing, 2008, No.49(06):39-41.

[7] Huang Qihong, Wu Lingyan, Huang Xuanying, et al. Observation on the bactericidal effect of mustard sauce on several pathogenic bacteria[J]. Food Safety Guide, 2022, No.353(24):110-112.DOI:10.16043/j.cnki.cfs.2022.24.030.

Author: Liu Aiqi

Review | Zhang Na, Associate Researcher, Doctoral Supervisor, Peking University School of Public Health

Han Hongwei, Researcher at the National Food Safety Risk Assessment Center

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