"I saw a post on the Internet saying that tofu milk contains nitrite, which will cause cancer when eaten. My family often eats tofu milk, and I am a little worried. I hope that The Chinese Business Daily 'Curiosity' can verify the authenticity of this post. A few days ago, Ms. Yang, a citizen of Xi'an, contacted a reporter from Huashang Daily and told her concerns. In this issue of "Curiosity", the reporter of Huashang Daily and the Xi'an Nutrition Society jointly reveal whether there is nitrite in tofu milk.
Net-taught tofu milk contains nitrites
Tofu milk is China's traditional cuisine, usually everyone in the stewed fish, stew ribs when adding a piece, can play a role in fishy, but also to give meat a special flavor, or directly as a pickle to eat is very suitable for taste.
Recently, there was an online post that said: "Tofu milk, a fermented pickled product, the key word is stinky brine, unhealthy, because it contains a lot of nitrite, so it will cause cancer." It contains a lot of mold, which is harmful to health. ”
Tofu milk is also salted, will it be like the net post said, nitrite exceeds the standard? Many people who love to eat curd milk, for many years to add a little curd milk when cooking, or eat with a little curd milk to eat, will it be harmful to the body?
There are many types of tofu milk
Some citizens feel "unhealthy"
The reporter of Huashang Daily visited the market and found that whether it is a large supermarket or a small supermarket, or a seasoning area of the free market, the figure of tofu milk can be easily seen. Tofu milk has red tofu milk, green tofu milk, white tofu milk and other types.
Mr. Zhou, who buys tofu milk in the supermarket, told the China Business Daily reporter that tofu milk is a "must-have dish" on his dinner table, and when he usually eats, take a piece out, whether it is steamed buns or white porridge, all have a unique flavor.
Mr. Zhou said that he had also heard that tofu milk may contain nitrites, and was worried that tofu milk was not a healthy food and that eating it regularly would affect his health.
The reporter of Huashang Daily randomly purchased three kinds of curd milk in the market, and at the same time brought the tofu milk that had been opened in the homes of two citizens to the laboratory of the Xi'an Nutrition Society for testing.
Nitrite detection test in tofu milk
Experimental location: Xi'an Nutrition Society Life Laboratory
Experimenters: Zhang Ting, Zhang Xu, Zhao Zeng, directors of Xi'an Nutrition Society
Experimental consultant: Wang Yongjian, president of Xi'an Nutrition Society
Experimental objective: To detect whether tofu milk contains nitrite
Experimental principle: Nitrite in food is easily soluble in water, can react with color developers to form colored compounds, if the experimental results show purple red, indicating that the sample contains nitrite, and the color scale card comparison for semi-quantitative detection, the darker the color, the higher the nitrite content in the sample.
Experimental samples:
Sample 1: Red curd milk, purchased in a large supermarket
Sample 2: Stinky tofu milk, purchased in a small supermarket
Sample 3: White curd milk, purchased on the free market
Sample 4: The public provides curd milk, refrigerated storage, and opens for one month
Sample 5: Members of the public provide curd milk at home, store it refrigerated in the refrigerator, and open it for one week
Experimental procedure:
1. Take 1 g each of the 5 samples and put them into a 10 ml tube
2. Add pure water to 10ml in each test tube, shake well and let stand;
3. Take the supernatant of 1ml of sample solution separately in a cuvette;
4. Add 2 drops of rapid test agent (1) to 1ml of sample supernatant, shake well and let stand for 5 min;
5. Add 2 drops of rapid test agent (2), shake well and let stand for 10 minutes;
6. Observe the color of the liquid in the colorimetric tube and compare it with the standard colorimetric card.
Note: Samples with color interference are centrifuged and tested
Experimental results
None of the five samples detected nitrites
The experimental results showed that the 5 samples of this test were negative and no nitrite was detected. That is to say, whether it is newly purchased unopened tofu milk or tofu milk that has been opened in the homes of citizens, no nitrite has been detected inside.
(Note: The results of this experiment are only responsible for this sample)
What are the hazards of nitrite?
Zhang Ting explained that nitrite, a general term for a class of inorganic compounds. Mainly refers to sodium nitrite, sodium nitrite is white to light yellow powder or granules, slightly salty taste, easily soluble in water. Nitrates and nitrites are widely present in the human environment and are the most common nitrogen-containing compounds in nature.
Acute nitrite poisoning can oxidize hemoglobin into methemoglobin, so that tissue hypoxia, headache, chest tightness and shortness of breath, palpitations, nausea, vomiting, abdominal pain, diarrhea and lip cyanosis and other symptoms, severe poisoning can be coma, convulsions, respiratory paralysis and so on.
According to the book "Food Safety Evaluation", nitrites will hinder the production of vitamin A in the body, reduce the amount of vitamin A stored in the liver, and cause vitamin A deficiency. Nitrite inhibits the absorption of iodine by the thyroid gland, reduces the synthesis of thyroxine, stimulates the compensatory function of the thyroid gland, and causes thyroid disease; long-term excessive intake of nitrite is also easy to synthesize N-nitrosamine carcinogens in the stomach.
For these reasons, the state has set strict limit standards for nitrite residues in food. The causes of acute poisoning are mostly due to accidental eating, adulteration, and a large amount of unfree vegetables at one time. The cause of chronic poisoning is often the consumption of cured meat products with excessive nitrite or nitrite content, poor quality kimchi and spoiled vegetables over a period of time.
Why are pickled foods prone to nitrites?
It is said in the online post that because tofu milk is a pickled food, nitrite will appear. In this regard, Zhang Ting said that pickled foods are indeed prone to nitrite.
"The nitrite produced in food is mainly the role of microbial reducing bacteria, which converts the nitrate in food into nitrite. Once such microbial reducing bacteria encounter conditions conducive to their breeding and reproduction, they convert the nitrate in food into nitrite. Some foods such as kimchi, its raw material cabbage is rich in nitrates, under the action of microorganisms will produce nitrite, in the production of kimchi, a good fermentation process so that nitrites showed a first rise and then fall, and finally nitrites tended to zero state. ”
In fact, it is not easy to produce nitrite in tofu milk
So, why does tofu milk not contain nitrites? Zhang Said that the main reason is that the raw material of tofu milk is soy products, "the raw materials of soy products belong to legumes crops, which are lower than the nitrate content of vegetables, fruits and grass crops, because the intracellular protein synthesis of legume crops is more vigorous, and it has the performance of converting nitrate into amino acids." Therefore, compared with pickled vegetables and fruits, fermented soy products, including curd milk, are not easy to produce nitrites. ”
It is most appropriate to eat half a piece of tofu milk at each meal
Tofu milk has a history of more than 1,000 years and is one of the unique fermented products in China. The fermentation of mold is carried out in the production process of curd milk, which makes the digestion and absorption rate of protein higher and the vitamin content more abundant. Because microorganisms break down the phytic acid in beans, it makes it easier for minerals in soybeans, which are less absorbed by the body.
It is worth noting that the amount of sodium and purine in curd milk is generally high, and patients with hypertension, cardiovascular disease, gout, kidney disease and gastrointestinal ulcer patients should eat less or not eat to avoid aggravating the disease.
The general population can use curd as a condiment for meals, through the sample packaging on the nutrition facts sheet shows that for every 10g (about half the weight of medium-sized curd), sodium content accounts for 18%-20% of adults' daily sodium intake, it is recommended that the amount of a meal should not exceed half a piece, while reducing the sodium-rich condiments such as salt, monosodium glutamate, soy sauce, and oil consumption in a meal.
Nitrites are most afraid of these foods
Zhang Ting suggested that if the public is worried about ingesting nitrite in certain foods, they can often eat the following foods, which are the "fierce enemies" of nitrite.
"In the daily diet, you can consume more foods rich in vitamin C, such as fresh dates, bell peppers, cauliflower, bitter melon, kiwifruit, strawberries and other foods, as well as vegetables and fruits containing a variety of plant antioxidants, fresh green leafy vegetables, purple, orange-red and other colorful fruits and vegetables, as well as garlic, onions, curries, basil leaves and other foods with unique odors, regular consumption can enhance the body's antioxidant capacity and reduce the impact of nitrite on health." Huashang Daily reporter Mao Mina