Overnight Tremella has excessive nitrite content and should not be eaten. Will it cause poisoning?

gossip:

Tremella, also known as snow fungus, is a common ingredient on the table, especially Tremella soup, which is considered a beauty and skincare helper by many female friends. However, it is always troublesome to soak Tremella immediately before eating it, so many people soak a lot of Tremella at a time, enough for two or three meals, and store it in the refrigerator after soaking. This method saves a lot of time.

However, there is a rumor among the people that: "The nitrite content in overnight Tremella exceeds the standard and cannot be eaten!" This makes it difficult for Tremella lovers. Although they like to eat Tremella very much, it is too troublesome to soak it on the spot every day. The thought of doing so makes them lose interest.

Hmm...is it true that overnight white fungus cannot be eaten?

the truth:

As long as it is handled properly, eating overnight Tremella fuciformis will not cause poisoning and you can still eat it with confidence.

Why does Tremella contain nitrite?

Many people are curious about why Tremella contains nitrite. In fact, most vegetables contain nitrite, but the content is different. This is because vegetables are often treated with nitrate fertilizers during the planting process, and vegetables are prone to excessive nitrate accumulation. After picking, they have to be stored, transported, cooked, and stored. During this process, nitrates will be converted into nitrites.

Of course, the fungal plant Tremella fuciformis is no exception. When growing Tremella fuciformis, the culture medium contains a rich nitrogen source, which belongs to the nitrate type. This makes Tremella fuciformis enriched with nitrates during the growth process, which are further metabolized into nitrites.

Nitrates and nitrites, which one is more toxic?

Nitrate is the primary nitrogen source necessary for plant growth and is relatively non-toxic in itself, but its metabolite nitrite requires caution.

A small amount of nitrite is not harmful to the human body, but excessive nitrite is toxic and closely related to human methemoglobinemia. Nitrite poisoning can oxidize Fe2+ in hemoglobin to Fe3+, converting normal hemoglobin into methemoglobin, which loses its oxygen-carrying capacity and causes tissue hypoxia. It can also paralyze peripheral blood vessels. [1]

Ingestion of 0.3-0.5 grams of nitrite can cause poisoning, and 1-3 grams can cause death. [1]

In addition, nitrites and protein decomposition products will produce nitrosamines under the conditions of gastric acid. Nitrosamines are carcinogens. Eating foods with high nitrite content frequently will increase the risk of gastric cancer.

Is it safe to leave Tremella overnight?

Rumor has it that overnight white fungus will produce a large amount of nitrite, which can cause harm to health or poisoning. Regarding this matter, we can look at a related data study.

Some people have tested the nitrite content of Tremella fuciformis treated under different conditions and found that measures such as boiling water treatment, soaking and changing water, and refrigerated storage can reduce and inhibit the nitrite content. [2]

- Boiling water treatment: After soaking, the dried Tremella was boiled for 10 minutes. The nitrite content of Tremella after soaking was 25.43 μg/g before boiling and 16.25 μg/g after boiling. After that, it was placed at room temperature and stored at 4°C for 48 hours, and the nitrite content was 74.94 μg/g and 58.31 μg/g respectively. This shows that boiling can reduce the nitrite content of Tremella, and refrigeration can inhibit the increase of nitrite content.

- Change water and boil treatment: The dried fungus was soaked in water every 30 minutes for 4 times, then boiled for 10 minutes, and then soaked in clean water. The water was changed every 30 minutes for 4 times. After this treatment, the nitrite content was reduced from 25.43 μg/g to 9.75 μg/g. After that, it was stored at room temperature and refrigerated at 4°C for 48 hours, and the nitrite content increased to 16.25 μg/g and 16.06 μg/g, respectively. This shows that soaking and changing water after boiling can further reduce the nitrite content.

-Increase boiling time: As the boiling time increases, the nitrite content will gradually decrease. After boiling for 30 minutes, the nitrite content of the soaked Tremella fuciformis decreased from 24.53 micrograms/gram to 6.5 micrograms/gram.

According to this data, even if the Tremella is simply boiled in water and refrigerated for 48 hours, eating 100 grams of Tremella will only ingest about 0.006 grams of nitrite, which is far from the toxic dose and is not harmful to the body. Moreover, this is the amount after 48 hours of storage. If the Tremella is stored overnight for 24 hours, the nitrite content will be even lower.

Therefore, the claim that eating overnight Tremella fuciformis can cause poisoning is not reliable.

Not only Tremella, but other vegetables we eat will also remove most of the nitrite through blanching, such as cabbage, spinach, celery, etc.

Therefore, even if it is overnight white fungus, as long as the unused part after boiling water treatment can be refrigerated in time, there is no problem eating it overnight. During the soaking period of white fungus, the water can be changed every half an hour to further reduce the content of nitrite.

Note: Do not eat Tremella that has been soaked for a long time. It is best to soak it in the refrigerator. It is recommended that the soaking time should not exceed 3 hours, and the water should be changed frequently.

References:

[1] Sun Changhao. Nutrition and Food Hygiene 7th Edition[M]. People's Medical Publishing House. 2017:45

[2] Wu Benpei, Lei Bo. Effects of food processing on nitrate and nitrite content in Tremella fuciformis[J]. China Brewing, 2016, 35(05): 111-114.

The article is produced by Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting.

Author: Xue Qingxin, member of Chinese Nutrition Society, registered dietitian, health manager, public nutritionist

Reviewer: Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center