Black fungus is taking lives again. How should it be soaked safely?

There are many cases of poisoning and even death caused by eating improperly soaked fungus. How does fungus become poisonous? How can we soak fungus safely and eat it scientifically?

Fungus, rich in nutrients, is a common guest on our dining table. But in recent years, this delicacy has unknowingly become a "deadly weapon".

In recent years, black fungus has caused a lot of trouble, and news about black fungus poisoning has appeared on the Internet from time to time. There have been many cases of poisoning in many parts of the country due to eating black fungus that has been soaked for a long time, resulting in multiple organ damage.

(Picture from the Internet)

And in May of this year, the tragedy of fungus poisoning occurred again!

On May 20, a 34-year-old woman in Dongguan, Guangdong, experienced nausea, vomiting, and black stools after eating black fungus that had been soaked for more than 24 hours. After a series of tests, she was found to have black fungus poisoning, with toxins accumulating in the liver, causing acute liver failure, and was subsequently sent to the ICU of Dongguan Traditional Chinese Medicine Hospital for treatment.

▲A woman who was poisoned by eating black fungus was sent to the hospital (Photo from Xin Wanbao)

According to the woman's husband, Mr. Zhang, his wife spent about 20,000 yuan a day in the ICU, and more than 40,000 yuan in just three days. Due to the extremely unstable income during the epidemic, the family now has no savings. Considering the high medical expenses, the woman was subsequently transferred to her hometown for treatment by her family, but due to the toxins causing organ failure, the rescue was ineffective and she died.

How could a person die from eating black fungus? Could it be that black fungus that has been soaked for a long time can become "poisonous" out of thin air?

my country has a long history of eating and using black fungus

Fungus grows on withered trees and absorbs the essence of the trees to provide the nutrients it needs for its growth. It is not good-looking and wrinkled like an ear, hence the name. Because it is mostly dark brown in color, it is also called black fungus. Some people also call it wood moth, tree chicken, wood machine, mulberry ear, cloud ear, etc.

(Picture from the Internet)

Fungus is widely planted in my country and is known as "the meat of vegetarians". my country has a long history of eating fungus. As early as the Zhou Dynasty, ancient people knew how to pick fungus as a food ingredient. There are records of cooking fungus in a large number of historical documents. An ancient book once recorded that at the banquet of the royal family and nobles at that time, there were generally more than 30 kinds of delicacies, among which "爾" was the ancient name for fungus. In addition, "Qimin Yaoshu" contains various cooking methods for fungus. The first medical book in my country that records the medicinal value of fungus, "Shennong Bencao Jing", records the medical value of fungus as a food ingredient.

Experts have investigated that black fungus is rich in nutrition and tastes good, and is one of the most popular home-cooked ingredients among consumers. According to the Chinese Food Composition Table, every 100g of edible water-soaked black fungus contains 1.5g of protein, 6g of carbohydrates, 34mg of calcium, 52mg of potassium, and 0.53mg of zinc. Among them, iron content is the richest. Scientific investigations show that the iron content in fungus is nearly seven times higher than that in pig liver, so among all foods, fungus is also known as the "king of iron".

In addition to being rich in iron, fungus also contains vitamin B2, gelatin and crude fiber, which are beneficial to the human body, such as clearing the stomach and intestines and facilitating bowel movements.

▲ Fungus (Picture from Sohu.com)

In modern medicine, fungus is also the favorite of domestic and foreign researchers. Researchers have extracted a component from fungus, called fungus polysaccharide, which has multiple biological activities and has the effects of improving immunity, anti-ulcer and anti-aging.

In addition, fungus polysaccharides can also help prevent blood coagulation. In 1980, Professor Hammersmith of the University of Minnesota Medical School found that fungus can inhibit platelet aggregation, prevent blood coagulation, and reduce the risk of coronary artery disease.

Although Westerners don't eat fungus very often, they have used it in medicine, and some medicinal uses continued until the mid-19th century. In 1597, herbalist John Gerard mentioned the medicinal use of fungus in his book: soaking fungus in beer or boiling it in milk and drinking it in small sips can help prevent and treat sore throats. Some herbalists also soak fungus in vinegar to gargle.

How does the fungus that has been soaked for a long time become poisonous?

There are two main types of fungus on the market, one is fresh fungus and the other is dried fungus. At present, the fungus sold on the market is basically dried fungus, which needs to be soaked before it can be eaten.

Xu Weisheng, an associate researcher at the Institute of Nutrition and Health at the Chinese Center for Disease Control and Prevention, told reporters that dried black fungus itself is actually non-toxic. It is mainly because of problems in the storage and soaking process that the black fungus produces bacterial or mold toxins.

Investigations and studies have shown that fungus that has been soaked for too long is prone to infection with "Pseudomonas cerebrovenans", and the "bacitracin (BA)" toxin secreted by it is the "culprit" of poisoning.

This toxin was first discovered in the 1930s, when residents of Java Island in Indonesia were poisoned after eating fermented coconut food. Dutch scholars Mertens and Vanveen discovered a Gram-negative bacterium in the process of studying this poisoning incident, which was named Pseudomonas cocovenenans, and isolated the fumonisin toxin from this pathogen.

In addition, in 1997, my country also discovered a similar toxin called Flavobacterium fumonisin toxin A. It was reported that this toxin was isolated from a sample of fermented rice flour poisoning. It is an exotoxin produced by Flavobacterium fumonisin. Research has shown that its chemical structure is exactly the same as that of fumonisin.

▲Chemical formula of fumonisin

Yang Meifang, deputy chief physician of the infectious department of the First Affiliated Hospital of Zhejiang University School of Medicine, said in an interview with the media that fumonisin is a toxin produced by Pseudomonas cerebroventris that can cause food poisoning. It is mostly found in summer and autumn and can easily survive in warm and humid environments. Whether it is humans or animals, eating food contaminated by this toxin may cause poisoning, and severe cases may cause death. There has been little research on this toxin in China before, and clinical cases are rare.

Xu Weisheng further explained that fumonisin is similar to most infectious diseases caused by bacteria, and is also caused by unsanitary environments or spoiled food. The probability of normal black fungus producing fumonisin in a short period of foaming is very low. The main factors for the production of fumonisin in dry black fungus that has been soaked for many days are as follows:

(1) Long-term soaking;

(2) Suitable temperature: The optimal growth temperature of Pseudomonas cocovenenans is 37°C, and the optimal toxin production temperature is 26°C;

(3) The external environment is not clean: for example, the soaking container is not clean, leaving food residues, or there is expired or spoiled food around it during soaking. If the fungus that produces fumonisin happens to be consumed by people in a toxic dose, it will inevitably cause a poisoning reaction.

▲ Spoiled black fungus that has been soaked for 3 days (Photo from @严健)

Will other foods become toxic if soaked for a long time?

Xu Weisheng said that in addition to black fungus, white fungus can also be infected with bacteria if it is not stored and soaked properly. In addition, fermented rice and flour products and other spoiled starch foods may also contain rice fermenting bacteria.

If other foods such as rice cakes, vegetables, and jellyfish are soaked for a long time in an unsanitary environment, will they also breed Pseudomonas cereus and produce fumonisin? In this regard, the Zhejiang Provincial Center for Disease Control and Prevention conducted relevant experiments. Dr. Xu Xiaomin from the Institute of Psychochemical Toxicology of the Center for Disease Control and Prevention said that different bacteria prefer different growth environments and require different carriers. For example, aflatoxin mainly uses moldy peanuts as carriers, while the growth of Pseudomonas cereus mainly uses spoiled fermented cornmeal products and fungus as carriers. Therefore, if it is other foods such as vegetables, even if they are soaked in water for a long time, fumonisin will not be produced.

Bacillus acid poisoning first manifests itself as gastrointestinal symptoms, which can later cause multi-organ damage. After the appearance of gastrointestinal symptoms, the disease usually enters a remission period on the second or third day. At this time, organ damage has not yet appeared, giving the illusion that the disease has healed. However, the condition often suddenly worsens on the third or fourth day, leading to worsening of the disease and death.

Therefore, once such poisoning occurs, all people who ate the same batch of food will be admitted to the hospital regardless of whether they are sick or not. Experts point out that after the patient is admitted to the hospital, he or she needs to undergo a thorough gastric lavage first, and then take 10-30g of activated carbon orally to absorb the toxins remaining in the gastrointestinal tract. If the molecular weight of the toxin is low, the doctor will accelerate the intravenous infusion of the patient to excrete the toxin through diuresis.

There are also reports of poisoning from fresh fungus.

Nutrition expert Xu Weisheng told reporters that there have been reports of poisoning from fresh fungus, mainly because eating fresh fungus induces solar dermatitis or photosensitive dermatitis.

Fresh fungus contains a special ingredient called porphyrin, which is a photosensitive substance. When people eat fresh fungus, the photosensitive substance enters the body. If it is exposed to strong sunlight or ultraviolet light, the photosensitive substance will combine with the carrier protein to form a complete antigen, stimulating the body to produce antibodies, resulting in antigen-antibody reactions, such as itchy skin and red bumps.

Of course, it is also safe to wash fresh fungus and blanch it in boiling water to completely remove the photosensitive substances contained in it before eating it. According to reports, most patients who develop solar dermatitis after eating fresh fungus have the experience of picking it, which may also be related to the high content of porphyrin in the picking environment. After all, the vegetables we often eat, such as celery, toon, coriander, and amaranth, also contain another photosensitive substance, furanocoumarin.

In addition, experts pointed out that there are many fresh vegetables in life that are not suitable to be eaten raw, such as beans, potatoes, vegetables rich in nitrates, day lilies, water chestnuts, etc. Blindly eating them raw may cause food poisoning.

(Picture self-made)

For example, edamame, broad beans, kidney beans, lentils and other beans and potato tubers contain hemagglutinin and antitrypsin. Hemagglutinin is a toxin that can cause red blood cells in the blood to agglutinate, and antitrypsin is a toxic protein that inhibits the activity of proteases. Some people may develop hemolytic anemia (favism) by eating uncooked broad beans. In addition, sprouted and green potatoes cannot be eaten because they contain high amounts of solanine (solanine), which is not easily destroyed even after being cooked. Eating them will cause food poisoning.

How to eat wood ear mushrooms scientifically and avoid "highly toxicity"?

Fumonisic acid is highly heat-resistant and will not be destroyed even after being boiled at 100°C or even subjected to high pressure and high heat (121°C). Therefore, if fumonisic acid has been produced in food, no matter what kind of food it is made into or what kind of daily cooking method is used, it cannot be completely killed, and eating it may cause severe food poisoning.

So can we still eat black fungus? How can we avoid poisoning?

Xu Weisheng said that first of all, the soaking environment must be kept clean. Wash the fungus before soaking, change the clean water every half an hour, and wash it thoroughly. In this way, the soaked fungus is safe and edible. According to experts from the Institute of Psychochemical Toxicology of Zhejiang Provincial Center for Disease Control and Prevention, a five-day simulated soaking test of fungus has proved that it is difficult to produce fumonisin during the soaking process of fungus if a good sanitary environment is maintained.

"But many ordinary families may not follow such strict procedures." said expert Xu Weisheng. "Most people usually simply wash them, or do not wash them at all, and soak them directly in tap water. For various reasons, they forget to do it, or expose them to high temperatures overnight. Due to improper soaking, bacteria are introduced, causing infection. At this time, the fungus is no longer the original black fungus. It must have a different touch and taste from the ordinary fungus after soaking, and the color of the water used to soak the fungus must have changed significantly."

If the fungus shows abnormal changes in sensory characteristics such as stickiness, softness, and lack of toughness, don't be reluctant to throw it away. Of course, not only fungus, but also white fungus, various other dried goods and dried vegetables should pay attention to such problems when soaking.

Xu Weisheng also gave everyone some small suggestions:

1. Although fungus is good, it is best to eat it in moderation

The first element of health is to achieve balanced nutrition and diverse food. As a kind of diversified diet, black fungus should also be eaten in moderation. After all, we should consume no less than 12 kinds of food every day and no less than 25 kinds of food per week to be healthier. Therefore, before eating black fungus each time, just choose the amount of soaking for the meal.

2. Soak in cold water for 1-2 hours

Before soaking, wash it first, choose a clean container, and soak it in cold water for 1-2 hours, and the fungus will generally be soaked. During this process, you can change the water every half an hour and wash it again to ensure a healthy diet.

3. Cook thoroughly and stir-fry until done, nutritious and delicious

The soaked black fungus can be blanched in boiling water. After that, whether you eat it cold or stir-fried, the black fungus will be safe and nutritious.

Written by Lai Tianying, Song Meng, and Liu Daheng (Medical and Health Group)

Editor/Feng Xiaohong New Media Editor/Chen Xuanzhi

Interview experts:

Xu Weisheng (Associate Researcher, Institute of Nutrition and Health, Chinese Center for Disease Control and Prevention)

References:

1. Wang Xia, Meng Zhaohe, Hu Wenjuan, et al. Research progress on fumonisin poisoning abroad [J]. Foreign Medicine: Hygiene, 1987(01):3-6.

2. Liu Kun, Meng Lingzhi, Wang Shengbo, et al. New progress in the research of fumonisin in food detection[J]. Jilin Agriculture, 2018, (17): 81.

3. Today’s headlines: “What made the wood ear mushroom, the meat among vegetarians, so popular among ancient scholars?”

https://www.toutiao.com/i6790641659165016587/?tt_from

4. Sina.com: "A 34-year-old woman ate overnight black fungus and died despite rescue efforts! Don't eat such things..."

https://www.sohu.com/a/397911030_374888

5. Sohu News: "Why did black fungus become a "poison"? Disease control experts conducted an experiment and the truth came out..."

https://www.sohu.com/a/246504226_467371

6. Tencent: "Black fungus turns into deadly "poisonous fungus" and the culprit is actually this"

https://new.qq.com/omn/20180811/20180811A0E6GI.html

7. Zhejiang News: "Black Fungus Poisoning Follow-up: Disease Control Department's Experiment on Soaking Dry Fungus in Patient's Home Results Unexpected"

http://zjnews.zjol.com.cn/zjnews/zjxw/201808/t20180810_7987907.shtml

Produced by: Science Central Kitchen

Produced by: Beijing Science and Technology News | Science Plus Client

Reproduction without authorization is prohibited