Can eating overnight vegetables cause nitrite poisoning? Chengdu Disease Control Experiment: More than half of the samples were detected with nitrite

Feng Min Chuanguan news reporter Wei Feng

Cooking at home, it is inevitable that there will be leftovers, many people will continue to eat overnight dishes after heating up out of frugality, and many people think that overnight dishes, especially overnight vegetables, contain nitrites, which can lead to poisoning and even cause cancer. Many netizens must have a lot of questions: What is nitrite? Do overnight vegetables really contain nitrites? This starts with the source of nitrite in vegetables.

First of all, plant foods naturally contain nitrates and nitrites, which are widely present in the environment where humans live. Nitrogen in soil and fertilizer can be converted to nitrate under the action of nitrogen fixing bacteria and hydrochloride-producing bacteria in the soil, while plants such as vegetables absorb nitrate from the soil during growth, reduce it to nitrogen under the action of enzymes in plants, and further react with organic acids synthesized by photosynthesis to generate amino acids, proteins and nucleic acids.

When photosynthesis is insufficient, plants can accumulate more nitrates in their bodies. The content of nitrate in fresh vegetables is mainly related to crop types, cultivation conditions (such as soil and fertilizer types) and environmental factors (such as drought, sunlight, temperature, etc.), and the nitrate content in different types of fresh vegetables may vary by dozens of times. The nitrite content in vegetables is usually much lower than the nitrate content, but if the vegetable is improperly stored or treated with special treatment (such as pickling), the nitrate in the vegetable will form nitrite under the action of nitrate reducing bacteria. In other words, the nitrite content in not-fresh vegetables can also be significantly increased.

So, how high is the nitrite content in the overnight vegetables, and will eating it lead to poisoning or even cancer?

Recently, Chengdu CDC conducted an experiment and purchased four common green leafy vegetables in the market: cabbage, mustard greens, oil wheat vegetables and scoop white.

Then, the Chengdu CDC staff cooked four vegetables for 20 minutes. After cooking, each cooked vegetable is divided into 4 samples, two for vegetable water only and the other two for vegetable water. This results in 16 samples. When the vegetable samples are cool enough to be eaten, the nitrite content in 16 samples is measured immediately.

The results showed that none of the 16 samples were detected with nitrite. That is to say, the four freshly cooked vegetables, whether it is the vegetables themselves or the nitrite content in the vegetable water, is minimal, it can be said that there is almost none.

Next, the Chengdu CDC staff put two of the four samples of each vegetable in the refrigerator (one is vegetable water only, the other is vegetable water containing vegetables), and the other two are placed at room temperature. A day later, the nitrite content in 16 samples was tested, and the results were surprisingly found: 5 of the 8 samples stored at room temperature were detected with nitrite, and some samples had high detection values, up to 60.50 mg/kg. None of the 8 servings of vegetables or vegetable water stored in the refrigerator detected nitrites.

You may ask again, what do these detection values of nitrite mean? How high is the test value, is it harmful to people? Originally, nitrite can make the ferrous hemoglobin in the hemoglobin into methemoglobin and make the human blood lose the effect of carrying oxygen, resulting in the body due to tissue hypoxia and poisoning, once 20% of the ferrous hemoglobin in the blood is converted into methemoglobin, the human body will appear poisoning.

The characteristic manifestations of poisoning are cyanosis, symptoms and signs include headache, dizziness, fatigue, chest tightness, shortness of breath, palpitations, nausea, vomiting, abdominal pain, diarrhea, lips, nails and skin throughout the body, mucous membrane cyanosis, etc., in severe cases, hazy consciousness, irritability, coma, respiratory failure and even death.

Some time ago, there was a hot search news on the Internet, saying that a hospital had treated 2 newborns suspected of nitrite poisoning in a month. The cause of infant poisoning is due to the fact that in order to "de-fire" the baby, the family gave the baby a formula mixed with overnight vegetable water. The doctor explained that the excessive nitrite of the overnight vegetable water can cause poisoning in the baby. The news is also accompanied by a picture of the baby at the doctor, the baby is full of bruises, which is the typical symptom of nitrite poisoning.

In fact, nitrite is a class of nitrogen-containing inorganic compounds that are common in nature, it is not only harmful, in addition to industrial use, it is used as a limited amount as a food additive in food production. China's national food safety standards stipulate that the residual amount of nitrite in meat products shall not exceed 30mg/kg, and the limit in pickled vegetables shall not exceed 20mg/kg.

Excess nitrite can lead to poisoning, and in severe cases, even death. Usually ingestion of 0.3 to 0.5 g of nitrite can cause poisoning. Earlier, our test found that the nitrite content of overnight cabbage, mustard greens and whites placed at room temperature exceeded the limit values of meat products and pickled vegetables in China's national food safety standards, and some even exceeded 60mg/kg. However, the ordinary amount of food (such as eating 1 kg) is not enough to cause poisoning in adults. Nitrite poisoning that we usually occur is more caused by accidental ingestion (nitrite looks similar to table salt) or additive abuse.

However, for children, especially infants under 6 months of age, they are particularly sensitive to nitrites and have slow metabolism due to reasons such as the fact that their intestinal barrier has not yet been established. Even doses that do not constitute acute poisoning in adults can lead to poisoning, and develop methemoglobinism (also called intestinal cyanosis).

How can nitrite poisoning be prevented?

1. Fresh vegetables have very low nitrite content, and everyone does not have to worry at all. The increase in nitrite in freshly pickled kimchi, stored for too long or rotten vegetables requires attention.

2. Eating leftover vegetables under the action of bacteria may lead to an increase in nitrite content, it is best to refrigerate at low temperatures, but also do not store for too long, vegetables are eaten fresh, nutritional value and safety are much better.

3. Infants and young children must be scientifically fed, especially for infants within 6 months of age, breast milk is the most ideal food, even if breast milk is insufficient, it is also necessary to follow the scientific use of formula milk supplement feeding. Don't listen to some so-called health concepts to feed vegetables, herbs and other things, because their gastrointestinal tract is particularly fragile, and many foods that are common to adults may be very dangerous for them.

4. Nitrite is similar to table salt in appearance and taste, and households and catering enterprises should avoid misuse of nitrite.

5. Well water in individual areas contains more nitrate (called "bitter well water"), if the rice cooked with this water is stored for too long, the nitrate can be reduced to nitrite under the action of bacteria and lead to poisoning.

Experimental test: Wen Jun, Peng Xiyu

Source: Chengdu Disease Control