What is N-Nitroso?

Because food is rich in protein, fat and essential amino acids, these nutrients will produce a certain amount of N-nitroso compounds after processing such as marinating, baking, frying, and frying; in addition, Some of the nutrients in food may be self-synthesized in the human gastric environment. Nitroso compounds, which cause harm to the human body. Therefore, the sources of N-nitroso compounds in food include processing and endogenous self-synthesis. ^[1]

Because food is rich in protein, fat and essential amino acids, these nutrients will produce a certain amount of N-nitroso compounds after processing such as marinating, baking, frying, and frying; in addition, Some of the nutrients in food may be self-synthesized in the human gastric environment. Nitroso compounds, which cause harm to the human body. Therefore, the sources of N-nitroso compounds in food include processing and endogenous self-synthesis. ^[1]

Chinese name

N-nitroso compounds

Molecular structure

R1 (R2) = NN = O

Classification

N-nitrosamine and N-nitrosamide

Species

200 kinds

N-nitroso compounds

The molecular structure of N-nitroso compounds is R1 (R2) = NN = O, which is divided into N-nitrosamines and N-nitrosamides. R1 and R2 of N-nitrosamines are alkyl or aryl; N -R1 of the nitrosamide is an alkyl group or an aryl group, and R2 is an amide group, including carbamoyl, ethoxyl, and nitryl; both types may have heterocyclic compounds. There are not many production and applications of N-nitroso compounds, but the precursors nitrous acid and secondary amines and amides are widely present in the environment and can form N-nitroso compounds in vitro or in vivo. A variety of N-nitroso compounds are found in the urban atmosphere, water bodies, soil, fish, meat, vegetables, cereals, and tobacco. Mostly liquid and solid, mainly enter the body through the digestive tract. It is highly toxic and has an oral LD50 of 150-500 mg / kg (body weight) for experimental animals. Acute toxicity: N-nitrosamine mainly causes central hemorrhage and necrosis of the hepatic lobules, can also cause pulmonary hemorrhage and bloody exudation of the chest and abdominal cavity, and has stimulating effects on the eyes, skin and respiratory tract; The damage to the liver is small, causing peripheral damage to the liver lobules. About 200 N-nitroso compounds have been found to be carcinogenic to experimental animals such as mice, rats, guinea pigs, rabbits, dogs, pigs, monkeys, and fish, and rodents are the most sensitive. Infection methods include inhalation, tracheal injection, oral, subcutaneous injection and intravenous injection, and nitrite and amine are mixed in feed and drinking water to feed animals. Oral daily doses of 1 mg / kg (body weight) or less can cause cancer. If a larger dose is given once, cancer can be induced after 9-12 months, and a placental carcinogenic effect is found. The target organs for carcinogenesis of some N-nitroso compounds are shown in the attached table. Nitrosamines are indirect carcinogens, nitrosamides are direct carcinogens, and the final carcinogens may be carbonium ions and azoalkanes. N-nitroso carcinogens have positive results in various mutagenic tests, as well as teratogenic and embryonic toxicity. An epidemiological investigation found that intake of N-nitroso compounds is related to the occurrence of human gastric and esophageal cancer, but the evidence is not sufficient.

N-nitroso compound source

Nitrate and nitrite are the most common types of nitrosating agents. Nitrite and nitrate are widely found in the natural environment. During the growth process of plants to synthesize the necessary plant protein, it is necessary to absorb nitrate as its nutritional component; the nitrate absorbed by vegetables is reduced to nitrogen in the plant due to the action of plant enzymes, and it generates amino acids and nucleic acids with organic acids synthesized by photosynthesis. And constitute the plant body. When photosynthesis is inadequate, excess nitrate is accumulated in plants. Nitrite and nitrate can also be added to foods by artificial additions, such as being used as preservatives and color protectants to preserve meat, fish, and cheese. As early as the beginning of the 20th century, it was found that the addition of nitrite was the reason for the color change and flavor of bacon, and it could inhibit the growth of certain spoilage and pathogenic bacteria to achieve the purpose of preservation and coloring. ^[1]

N-nitroso compounds toxicity and harm

Different types of nitroso compounds have large differences in toxicity. Most nitroso compounds are of low toxicity and

Moderately toxic, some are highly toxic or even highly toxic. Different compounds have different toxic mechanisms, among which liver injury is more common, but also kidney injury and vascular injury.

Carcinogenicity

Many animal tests have proven that N-nitroso compounds have carcinogenic effects. N-nitrosamines are relatively stable and need to be metabolized into active substances in the body to be carcinogenic. They are also known as pre-carcinogens. N-nitrosamides are unstable, can be directly degraded into diazo compounds at the site of action, and combine with DNA to exert direct carcinogenicity and mutagenicity. Therefore, N-nitrosamides are also called terminal carcinogens. To date, no animal has been found to be resistant to the carcinogenic effects of N-nitroso compounds. Not only that, multiple routes of administration can cause tumorigenesis in experimental animals, whether inhaled by the respiratory tract, ingested by the digestive tract, or subcutaneously. , Intramuscular injection, or skin contact can induce tumors. Repeated multiple exposures or a large dose can induce tumors, and both have a dose-response relationship. In animal tests, evidence for the carcinogenic effects of N-nitroso compounds is abundant. In human epidemiology. Epidemiological data in some countries and regions indicate that some human pain may be related to it. For example, the high incidence of gastric cancer in Chile may be caused by the heavy use of nitrate fertilizers, which may cause the nitrate and nitrite content in the soil to be too high; Japanese Love salty

Fish and pickled vegetables have a high incidence of gastric cancer. The former contains higher levels of amines, especially secondary and tertiary amines, while the latter contains more nitrites and nitrates. ^[2]

2. Teratogenicity and Mutagenicity

It has been found in genetic toxicity studies that many N-nitroso compounds can induce genetic mutations, chromosomal abnormalities and DNA repair disorders through body metabolism or direct action. N-nitrosamide can cause brain, eye, rib and spine deformities in rats, while N-nitrosamines have very weak teratogenic effects. Dimethylnitrosamine is mutagenic and is often used as a positive control for mutagenicity tests. ^[1]

N-nitroso compounds prevention and control measures

There are many ways to prevent N_nitroso compounds from harming human health. According to the source of the N-nitroso compounds in the aforementioned food, the nitrite and nitrate in the food can be controlled from the source, and the N_ Nitro compounds. In addition, the establishment of limit standards for N-nitroso compounds in food, strict control of industrial emissions, scientific fertilization and other measures are also effective in controlling N. A reasonable way to produce nitroso compounds.

(1) Scientific and rational fertilization. In the process of vegetable cultivation, no or less ammonium nitrate and other nitrate nitrogen fertilizers should be applied.

Using molybdenum fertilizer, organic fertilizer, microbial fertilizer, humic acid fertilizer, etc., screening low nitrite nitrogen fertilizer suitable for vegetable application can also effectively reduce nitrate content in vegetables [1183; In addition, nitrogen fertilizer is combined with phosphorus and potassium Application can promote the synthesis of protein and important nitrogen compounds, reduce the accumulation of nitrate, control and reduce the content of nitrite in vegetables.

(2) Block the synthesis of N-nitrosamines in food. Use and find some blocking agents to stop natural foods

Middle amines react with nitrite to reduce nitrosamine synthesis. For example, the addition of vitamin C, vitamin E, phenols, gallic acid, and certain reducing substances in food processing has the effect of inhibiting and reducing nitrosamine synthesis, and has no effect on the color development and antibacterial effect of nitrite. At present, many countries in the world are advocating the addition of vitamin C in the processing of meat products. In the United States, at the same time as adding 120 mg / kg of sodium nitrite, 50 mg / kg of vitamin C is added to reduce nitrite to NO and promote the production of nitroso myoglobin. Can reduce the amount of nitrosamines in meat products.

(3) Improve food processing methods. The use of sawdust cold smoke produced by liquid smoke or smoke generators to replace smoked products with burning wood smoke can eliminate or reduce the synthesis of nitrosamines. When marinating meat and fish products, the salt, pepper, paprika and other ingredients used should be packaged separately. Do not mix them to produce nitrosamines. At the same time, nitrate and nitrite should be minimized during the processing of meat products.

(4) Improve and improve diet. It seems that nitrate and nitrite in food cannot be completely eliminated at present.

It is necessary to reduce the harm of nitrite to the human body and cultivate scientific food consumption and eating habits. Do not eat mildew and overnight cabbage. Try to buy fresh vegetables. From a nutritional point of view, fresh vegetables have less loss of nutrients; from a safety point of view, fresh vegetables have a lower nitrite content. In addition, vegetables must be cleaned, washed, cut, fried, and eaten when cooking. Do not eat unfermented sauerkraut. The pickled sauerkraut s nitrite content rose to the highest level after 6 days, and then gradually decreased. After 20 days, it was basically completely decomposed. Therefore, it is best to sauerkraut for 1 month before eating. In pickling, 400 mg of vitamin C can be added per kilo of pickles to block the formation of nitrosamines by nitrite. Artificial fermentation is used instead of natural fermentation when processing kimchi. The ratio of artificial inoculation to fermented kimchi and natural fermentation can speed up the fermentation rate. Reduce fermentation time. The large amount of lactic acid can inhibit the infection of mixed bacteria, improve the yield of kimchi, and improve the flavor of kimchi and the quality of kimchi strains [119]. Soak vegetables before cooking. Nitrite is soluble in water. Vegetables, especially sauerkraut, should be washed and soaked before cooking. As the number of water changes increased and the soaking time prolonged, the nitrite content in sauerkraut decreased significantly [12 0 |. Do not drink 6 kinds of water containing a large amount of nitrite: burn on the stove overnight or leave it warm for 1 to 2 days without swallowing warm water, boiled water re-boiled overnight in the automatic water heater or the residue after repeated boiling Boiling water, which is not the same day as the water in the thermos, steamed through the steamer, rice, meat and other foods, bitter well water. The above 6 kinds of water contain relatively high amounts of nitrite and are not suitable for drinking.

(5) Formulate corresponding standards and regulations. The food hygiene supervision department should start from the source and strictly monitor the use of nitrate and nitrite by enterprises. The GB 2760-2011 "National Food Safety Standard Food Hygiene Standards for Food Additives" promulgated by China has made clear regulations on the use of nitrate and nitrite for different types of food, and stipulates its maximum use limit. ^[1]