What Are Nitrites?

Nitrite, a general term for a class of inorganic compounds. Mainly refers to sodium nitrite, which is white to light yellow powder or granular, slightly salty, and easily soluble in water.

Nitrate and nitrite are widely present in the human environment and are the most common nitrogenous compounds in nature ^[1] . Nitrate in the human body can be reduced to nitrite, the precursor of N-nitroso compounds under the action of microorganisms.

The appearance and taste are similar to those of table salt, and are widely used in industry and construction. Meat products are also allowed to be used as limited colorants. The risk of food poisoning caused by nitrite is high.

Ingestion of 0.3 to 0.5 grams of nitrite can cause poisoning, and 3 grams lead to death ^[2] .

On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization initially compiled a reference, and nitrates or nitrites ingested under conditions that led to endogenous nitrosation were in the 2A carcinogens list. ^[3]

Chinese name: Nitrite
English name: Nitrite
nickname: Sodium nitrite

Chemical formula: NaNO2
Molecular weight: 69.00
Dangerous Goods Transport Number: Poisoning

Nitrite poisoning

Nitrite food poisoning is also called enterogenous cyanosis, cyanosis, and black mouth disease.

Nitrite poisoning is caused by eating marinated meat products, pickles and spoiled vegetables with high nitrate or nitrite content, which can cause poisoning, or caused by the accidental use of industrial sodium nitrite as table salt. It can also be seen in drinking. Containing nitrate or nitrite in bitter well water and steamer water, nitrite can oxidize methemoglobin, which normally carries oxygen in the blood, to methemoglobin, thus losing the ability to carry oxygen and causing tissue hypoxia. Nitrite is a highly toxic substance. Adults ingesting 0.2 to 0.5 grams can cause poisoning, and 3 grams can cause death. Nitrite is also a carcinogen. According to research, esophageal cancer has a positive correlation with the amount of nitrite ingested by patients. The carcinogenic mechanism of nitrite is: nitrite and secondary amines in food under conditions such as gastric acid , Tertiary amine and amide react to form strong carcinogen N-nitrosamine. Nitrosamines can also enter the fetus through the placenta and have teratogenic effects on the fetus.

Infants less than 6 months are particularly sensitive to nitrite. Infants with clinical "methemoglobinemia" are caused by eating foods with high nitrite or nitrate concentration. The symptoms are hypoxia, cyanosis, and even death. Therefore, the European Union stipulates that nitrite is strictly prohibited for use in baby food. The onset of nitrite poisoning is rapid, and the incubation period is usually 1 to 3 hours. The main characteristic of the poisoning is cyanosis caused by hypoxia in the tissues, such as bruising on the lips, tip of the tongue, and fingertips. Dizziness, headache, fatigue, rapid heartbeat, drowsiness or irritability, dyspnea, nausea, vomiting, abdominal pain, diarrhea, severe coma, convulsions, incontinence, and death from respiratory failure.

Nitrite used as a preservative in fleshy foods has been considered a carcinogen, but scientists at the National Institutes of Health have found that this carcinogen can be made into a drug to treat sickle cell disease and the heart The discovery of a variety of diseases such as disease is startling.

For over 100 years, scientists have believed that nitrite has no benefit, but today, scientists have found its value. According to the US Full Wave Broadcasting Corporation reported on September 5, while studying a nitrite-related compound, nitric oxide, Dr. Mark T. Gladwin and cardiologist Dr. Richard Cannon accidentally discovered The medicinal value of nitrite. Nitric oxide can expand blood vessels and increase blood flow, but it cannot be used as a medicine. However, nitrite, which is often used as a food preservative, has similar effects to nitric oxide and can be used as medicine, so the two scientists thought of nitrite.

Subsequently, the scientists conducted clinical trials. They injected a small amount of nitrite into healthy volunteers. As a result, the blood flow in the volunteers tripled, and when the volunteers exercised, the nitrite content in the body dropped immediately, indicating that the body was actively using nitrite. Therefore, scientists believe that nitrite can be used as a drug to treat diseases related to blood flow such as sickle cell disease, heart disease, and cerebral aneurysms.

In response, Dr. Gladwin joked, "We are equivalent to treating human organs as hot dogs ^[4] . Adding nitrite is equivalent to adding protective measures to protect the heart, lungs and brain from hypoxia. Oxygen. "

Related reports on nitrite

On August 15, 2012, the website of the Zhejiang Provincial Administration for Industry and Commerce announced that

Blood swallow nitrite severely exceeds the standard ^[5] In the food quality random inspection in the field of circulation, it was found that there was a serious problem of excessive nitrite content in blood swallow products. The problem was mainly from Malaysia. Blood swallows with a price of tens of thousands or more were burst and made by dyeing, and some of the blood swallow harmful substances were 350 times higher than the standard nitrite, and even the weight was supported by fish gelatine, pectin, and agar powder.

Since 2012, the bird's nest market has been vigorously rectified nationwide. On August 15, 2012, the Zhejiang Provincial Administration for Industry and Commerce announced the results of spot checks on blood swallows. Among the more than 30,000 spot blood swallows in question, the average nitrite content was 4400 mg / kg, up to 11,000 mg / kilogram. According to the national compulsory standard "National Food Safety Standard for Food Additives", nitrite only allows trace residues of cured bacon and other products. The limit is 30 mg / kg, and the maximum residue of smoked ham must not exceed 70 mg / kg. . For the non-intentionally added, naturally occurring nitrite, the National Standard for Limits of Contaminants in Foods stipulates that the limit is generally 3 mg-5 mg / kg, and the limit for pickled vegetables is only 20 mg / kg.

"Many processing plants use chemical agents to remove hair, which saves most of the labor costs; then by adding glue, water, sticky and other methods, 500 grams of raw materials can be produced into about 750 grams of finished products." The industry insider said. Through special colloids (super77, etc.), the bird's nest is applied to achieve multiple purposes such as assisting in setting, improving appearance, increasing weight, and covering up defects. This has been an open secret in the bird's nest industry.

On June 12, 2012, the Ministry of Health and the State Food and Drug Administration jointly issued an announcement that in the future, catering service units such as hotels, food stalls, and snack bars will prohibit the use of nitrite as a food additive. For this reason, people and experts who have been concerned about food safety applaud.

Nitrite production method

1. Nitrite salts of alkali metals and alkaline earth metals can be obtained by passing equivalent amounts of nitric oxide and nitrogen dioxide into the hydroxide solution of the metal.

2. Decomposing nitrate can produce nitrite and oxygen.

Basic use of nitrite

As a color protection agent for meat products, nitrite can react with myoglobin in meat products to produce rosy nitroso myoglobin, which can improve the color of meat; it can also enhance the flavor of meat and the role of preservatives to prevent meat poisoning Clostridium spp. And extend the shelf life of meat products ^[6] .

Nitrite toxicity

Introduction to Nitrite Toxicity

It is worth noting that high doses of nitrite can still be very toxic. Ingestion of nitrite can cause nitrite food poisoning,

Sodium nitrite Long-term use can even cause cancer of the esophagus and stomach. Moreover, scientists lack clinical trials to prove that nitrite can treat diseases such as heart disease. So, scientists are actively recruiting volunteers for clinical trials, and are starting to find suitable drug manufacturers to develop nitrite drugs.

Nitrite has antiseptic properties and can be combined with myoglobin in meat to be more stable. Therefore, it is often added to sausages and bacon as a color retention agent in the food processing industry to maintain a good appearance; secondly, it can prevent meat The production of Clostridium toxicans improves the safety of edible meat products. ^[7] However, the human body absorbs excessive amounts of nitrite, which will affect the operation of red blood cells, making the blood unable to carry oxygen, and the lips and fingertips will turn blue, commonly known as "blue blood disease", which will seriously cause brain deficiency. Oxygen and even death. Nitrite itself is not carcinogenic, but under cooking or other conditions, the nitrite in meat can react with amino acid degradation to generate highly carcinogenic nitrosamines.

If you eat marinated meat products, pickles and spoiled vegetables with high nitrate or nitrite content, you can cause poisoning and die from respiratory failure. ^[8]

Nitrite Toxicity Hazard

Infant methemoglobinemia (also known as methemoglobinemia): Excessive nitrate intake can induce methemoglobinemia in infants. As a large amount of nitrite in the human body is combined with hemoglobin in the blood, the methemoglobin content rises. Hemoglobin cannot be combined with oxygen. At this time, the person is hypoxic, and clinical manifestations include cyanosis of lips, nails, and purple spots on the skin, which can lead to death. It often occurs in areas with high levels of nitrate in drinking water and is more common in infants.

Congenital malformations of infants: Nitrite can enter the fetus through the placenta. Infants within 6 months are particularly sensitive to nitrates and have teratogenic effects on the fetus.

Goiter: Some studies suggest that high nitrate intake can reduce the body's digestion and absorption of iodine, which leads to goiter, but whether nitrate is the direct cause of human goiter needs further investigation.

Cancer: When using nitrous acid to develop color, nitrite reacts with amines in meat to form nitroso compounds, or is converted to nitrosamines in the acidic environment of the intestine. These nitroso compounds are carcinogens ^{[ 6]} .

Causes of acute nitrite poisoning

1. Nitrite is mistakenly eaten as table salt, alkali.

2. Doping and making false.

3. Poisoning.

4. Eat vegetables containing a lot of nitrite, especially stale leafy vegetables.

Causes of chronic nitrite poisoning

1. Drink bitter well water and steamer water with high nitrate or nitrite content.

2. Eating cured meat products, pickles and spoiled vegetables with high nitrate or nitrite content.

Mechanism of poisoning:

Nitrite is a strong oxidant under acidic conditions. After entering the body, nitrite can oxidize methemoglobin in the blood to methemoglobin, lose its oxygen transport function, cause tissue hypoxia, and bruises and poisoning.

Symptoms of nitrite poisoning

1. Headache, dizziness, weakness, chest tightness, shortness of breath, palpitations, nausea, vomiting, abdominal pain, diarrhea and lips, nails, whole body skin, mucosal cyanosis, etc.

2. The skin and mucosa of the whole body show different degrees of bluish-purple (purpura caused by methemoglobinemia).

3. Severe poisoning can cause coma, convulsions, respiratory paralysis, etc. ^[1] .

Nitrite detection method

1. Take 3 ~ 5 ml of venous blood from the patient, and the blood color is blue-purple.

2. Centrifugal precipitation, the plasma was pale yellow, indicating that the blue-violet was caused by the abnormality of the cell itself.

3. After shaking, shake in oxygen or air for 15 minutes. If it returns to bright red, it indicates that the original blue-purple is caused by oxidation of methemoglobin.

4. Basic judgment can be made basically through the above simple test.

Nitrite rescue measures

1. Oral doctor's order: For acute poisoning incidents, oral doctor's order should be routinely handled, such as oxygen inhalation, intravenous access, inspection, etc., and then

Sodium nitrite Explain medical history, examine patients, and establish medical records to win rescue time. Do not ask the patient's history and write down the medical records slowly in the usual order. Treatment will usually be delayed after the diagnosis is made.

2. Oxygen absorption: Nitrite is easily produced by eating pickled vegetables and cooked leftovers. Bulk salt extracted from industrial salt by illegal elements is a major source of nitrite. Nitrite is an oxidant. It can make normal methemoglobin oxidize to methemoglobin, lose the ability to supply oxygen and make the tissue hypoxia. Observed patients with blue complexion, cyanosis of the lips, blue-purple venous blood were all signs of hypoxia, so they were given oxygen treatment immediately.

3. Application of methylene blue (methylene blue): it is a special antidote for nitrite poisoning, which can restore methemoglobin and restore normal oxygen delivery function. Dosage is calculated at 1 ~ 2mg per kilogram of body weight. At the same time, hypertonic glucose can increase blood osmotic pressure, increase detoxification function and have a short-term diuretic effect.

4. Symptomatic treatment: For patients with affected cardiopulmonary function, treat symptomatically, such as using respiratory stimulants, arrhythmia correction drugs, and so on.

5. Nutritional support: After the condition is stable, supportive therapy such as energy mixture and vitamin C are given.

6. Gastric lavage: if the poisoning time is short, gastric lavage should be treated in time.

Common nitrites include sodium nitrite and potassium nitrite. There have been many reports of accidental use of sodium nitrite as table salt in China. In addition to removing poison and oxygen in time, the detoxifying agent is methylene blue (methylene blue). In critically ill patients, 200 to 400 ml of fresh blood can be transfused. If necessary, transfusion therapy can be considered.

Determination of nitrite content

Preparation for Nitrite Determination

Therefore, measuring the content of nitrite is a very important item in food safety testing.

Limits of nitrite in some foods (calculated as NaNO ₂ )

Product name	Limit standard mg / kg	Product name	Limit standard mg / kg
Common salt (fine salt), milk powder	2	Sausage (sausage) fragrant belly, pickled vegetables, Cantonese-style bacon	20
Fresh meat, fresh fish, food	3	Meat products, ham sausages, enemas	30
vegetables	4	Other meat cans, other preserved cans	50
Infant formula, fresh eggs	5	Western-style cooking, smoked ham and canned food, canned western-style ham	70

Explanation:

Trace amounts of nitrite often exist in drinking water and cannot be used as a diluent for measurement.

If the color is very dark after the color development, or there is precipitation or it fades to light yellow, it means that the content of nitrite in the sample is very high, it is necessary to increase the dilution factor to re-measure.

Repeated experiments should be carried out for samples exceeding the standard, and sent to the laboratory for accurate quantification when conditions permit.

The storage period is 18 months at room temperature and protected from light. See the packaging for the production date.

Attached:

Instructions for using nitrite rapid detection tube:

Principle of the method: The speed test tube made according to the national standard GB / T 5009.33 is compared with the standard color card for quantitative measurement.

Nitrite operation method

1. Rapid detection of nitrite in common salt and rapid identification of common salt and nitrite

: Take a flat spoon of table salt with a small spoon in the bag, add it to the test tube, add distilled or purified water to the 1ml mark, cover it, shake the solid part, and compare it with the standard color plate after 10 minutes. The value on the board multiplied by 10 is the content of nitrite in mg / kg of salt (the national standard stipulates that the limit of the nitrite in table salt (fine salt) should be 2 mg / kg). When the sample appears blood red and precipitates or fades quickly to yellow, it can be determined that the nitrite content is quite high, or the sample itself is nitrite. 2. Liquid sample detection: Take 1ml of clear liquid sample directly into the test tube, cover with a lid, shake the reagent, compare with the standard color plate after 10 minutes, find out the same color level as the solution in the test tube, the The value on the color scale is the nitrite content mg / L in NaNO2.

(Cow milk and soy milk can also be tested directly, and the result should not exceed 0.25mg / L. Colored liquid samples can be decolorized and filtered after adding some activated carbon for determination).

3. Detection of solid or semi-solid samples: Take 1.0g or 1.0ml to 10ml colorimetric tubes, and add distilled water or deionized water (purified water) to the mark. Shake well and place the supernatant ( (Supernatant obtained by filtration or centrifugation) 1.0ml was added to the detection tube, covered with a lid, and the reagent was shaken. After 10 minutes, it was compared with the standard color plate. The value on this color plate was multiplied by 10 to obtain the sample. Nitrate content mg / kg, L (calculated as NaNO2). If the test result exceeds the highest value on the color plate, it can be determined after quantitative dilution and multiply the dilution factor when calculating the result (such as taking 1.0mL from a 10ml colorimetric tube and transferring it to another 10ml colorimetric tube, adding water to Scale, take 1.0mL from it and add it to the test tube for measurement. Multiply the test result by 100 (fold dilution) to obtain the nitrite content in the sample.

Nitrite urine test

Some bacteria in the urinary system can reduce the nitrate of protein metabolites in the urine to nitrite. Therefore, the determination of the presence of nitrite in the urine can quickly and indirectly know the urinary bacterial infection as a screening for urinary tract infections. test.

Clinically, the incidence of urinary tract infections is high and sometimes asymptomatic. This is especially true in female patients. Diagnosis of urinary tract infections requires a long time and certain conditions for urinary bacterial cultures. Qualitative tests for urinary nitrites can be obtained quickly The results help the diagnosis of the disease.

When people with obvious urinary tract infection use bacteria to reduce nitrate to nitrite, the characteristic phenol coupling produces red as a positive reaction.

The positive rate of urine nitrite depends on the retention time of urine in the bladder for more than 4 hours. The positive rate can reach 80%. If the urinary tract infection bacteria can not reduce nitrate to nitrite or the urine stays in the bladder for a short time or lacks in urine Nitrite also produces a negative result. Positive results indicate the presence of more than 100,000 / ml bacteria in the urine.

Normal value: negative (-)

Clinical significance of nitrite

Nitrite-positive results are common: pyelonephritis caused by E. coli (Escherichia coli) has a positive rate of more than two-thirds of the total; symptoms caused by bacteria such as Enterobacteriaceae such as Escherichia coli Or asymptomatic urinary tract infections such as cystitis bacteriuria.

A negative urine nitrite test does not mean that there is no bacterial infection. It is only due to some bacterial infections that do not have the ability to reduce nitrates. The urinary system infection cannot show positive. Such bacteria include non-fermentative bacteria such as Acinetobacter or urine in the bladder. Failure to retain for more than 4 hours.

Note that urinary tract infections cannot produce negative results if the nitrate cannot be reduced to nitrite or if urine remains short in the bladder or lacks nitrate in the urine.

Nitrite precautions

1. Vegetables should be properly stored to prevent rot, and do not eat rotten vegetables.

2, leftover cooked vegetables should not be stored at high temperature for a long time before consumption.

3. Don't eat a lot of freshly pickled vegetables. Put more salt in the pickled vegetables, pickle them for at least 15 days before eating; .

4. Do not eat a lot of leafy vegetables in a short period of time, or simmer for 5 minutes with boiling water, and discard the soup before cooking.

5. The amount of nitrate and nitrite in meat products should be strictly in accordance with national health standards and should not be added.

6, bitter well water should not be used for porridge, especially not stored overnight.

7, to prevent the wrong use of nitrite as table salt or alkaline surface.

8. Eat more vitamin C and vitamin E, as well as fresh fruits.

9. Soak the vegetables in boiling water for 3 minutes before eating, and soak the potatoes in 1% saline or vitamin C solution for a whole day and night ^[6] .

Nitrite source

1. Nitrite as a coloring agent and preservative in food.

2. It is converted from the added nitrate in food.

3. Vegetables, especially from stale vegetables.

Common knowledge about nitrite

Treatment method for excessive nitrite consumption

1. Replenish liquids, especially boiling water or other transparent liquids;

2. Supplement electrolytes lost by vomiting and diarrhea, such as potassium, sodium and glucose;

3. Avoid antacids;

4. Don't stop the diarrhea first, and let the toxins go out before consulting the doctor;

5. No need to induce vomiting

;

6, the diet should be light, first eat food that is easy to digest, avoid food that is easy to stimulate the stomach.

In view of the above reasons, the state has established strict limit standards for nitrite residues in food. However, as high concentrations of nitrite can not only improve the perception and color of meat products, but also greatly shorten the processing time of meat products, so meat The phenomenon of nitrite exceeding the standard is more common. Even a few unscrupulous operators use soaked and bleached pork with hydrogen peroxide, then add a large amount of nitrite, and finally process it to achieve the color effect of normal meat products; there is also a large amount of nitrite-containing bacon as long as it is smoked overnight It can reach the color and hardness of normal fumigation for more than ten days, and it is "extra bright".

How to reduce nitrite and nitroso compounds

· Eat more fresh vegetables and meat.

Store foods at low temperatures to reduce protein breakdown and nitrite formation.

· Do not eat pickled products, sausages, sauerkraut, etc.

· Do not eat pickles that have been pickled for about 7 days, and eat less pickles that have been pickled for 15 days.

Condiments such as pepper and chilli are packaged separately from salt.

· Regular exposure to food to decompose nitroso compounds.

· Do not drink water left in the steamer for a long time.

Foods that can block the synthesis of nitroso compounds:

Contains vitamin C and vitamin E-rich vegetables and fruits.

· Garlic and tea.

· Vinegar.