Nitrates and nitrites can be found in many foods. In a moderate diet they are not a threat, but when there are a lot of them, they can harm your health. Nitrates and nitrites penetrate the plants from the fertilized soil, are also added in the production process as preservatives, nitrogen compounds can also be supplied with drinking water.
Nitrates are a group of chemical compounds, salts and esters of nitric acid – HNO3, and nitrites are chemical compounds, salts or esters of nitrous acid – HNO2. Most nitrates and nitrites are found in vegetables. The content of these chemical compounds depends on the soil and climatic conditions, the level of fertilization with nitrogen compounds, as well as on the vegetable species and variety. Individual plants differ in their ability to accumulate nitrates. However, not only vegetables are the source of these chemicals in the daily diet.
Vegetables rich in nitrates
Most nitrates are found in stems and petioles. Very large amounts of nitrates accumulate in lettuce, beetroots, spinach, radishes and potatoes. Few nitrates are found in seeds and fruits. The cultivation method has a significant influence on the content of the discussed chemical compounds in vegetables. Vegetables from organic farming contain less nitrates and nitrites than those from conventional crops. The level of nitrogen compounds also changes under the influence of heat treatment and storage. When parsley is dried, the level of nitrate content is reduced by more than 50%. At the same time, however, nitrite levels increase, even by over 100%.
Lowering the level of nitrates can also be caused by storing vegetables. The influence of ensiling on the content of both compounds is particularly interesting – it causes a reduction in their level. Some herbs and plants from which infusions are made have a high nitrate content, especially nettle and sage. Fresh vegetables provide nitrates, but not nitrites – these compounds are made of nitrates, as a result of improper storage and transport of vegetables and subjecting them to technological processes. Among the factors affecting the rate of change one should mention humidity, temperature, oxygen availability and acidity. Nitrates easily accumulate in greenhouse plants, and therefore also in most novelties.
Cold meats and cheese also supply nitrates and nitrites
While in the case of vegetables, nitrates were derived from the fertilized soil, in the case of cured meats and other meat products they are added as a preservative – most often they are potassium nitrite (E249), sodium nitrite (E250), sodium nitrate (E251) and nitrate potassium (E252). For safety reasons, they can only be added in combination with cooking salt. Polish standards allow the use of nitrates in the production of salami sausages, in which the nitrate content is below 60 mg / kg, and the sum of nitrates and nitrates content can not exceed 600 mg / kg. In other meats, ready-made products and pasteurized meat preserves, the total content of nitrates and nitrates can not be greater than 125 mg / kg of the product. In the dairy industry, nitrates are used in an amount of 20 g / 100 l milk in the production of ripened cheeses in order to prevent undesirable butter fermentation and secondary cheese bloating. During the ripening process, nitrates are reduced to nitrates, which inhibit inappropriate butter fermentation. Nitrates and nitrites prolong the shelf life of meat and, additionally, limit the risk of developing botulism botulinum, besides, they give the meat products the right taste, color and smell.
Drinking water as a source of nitrates
Nitrates are also found in drinking water. However, they are not stable, so they are easily transformed – to nitrites or ammonia. In addition, nitrites can be formed in water treatment processes and water supply lines, as a result of the activity of nitrifying microorganisms, including bacteria.
Nitrites 10 times more toxic than nitrates
The harmful effect of nitrates and nitrites on the body has already been well understood. Toxicity of nitrite represents an extremely high level – they are even 10 times more harmful to health than nitrates. Both groups of chemical compounds work in a similar way – they have oxidizing properties, thus causing oxidation of hemoglobin to methemoglobin. In addition, they can cause the oxidation of vitamin A. Oxidative effects of increased doses of nitrite can also have a negative effect on the liver.
Excessive consumption of nitrites can lead to methemoglobinemia, a condition where the iron from the ferrous mold is oxidized to the iron form. Iron ion is at the center of hemoglobin. Nitrites oxidizing hemoglobin cause that it can not be combined with oxygen. As a result, it ceases to fulfill its basic function. Changes in hemoglobin to methemoglobin are extremely dangerous for infants up to 3 months old. Their blood contains fetal hemoglobin, which is particularly susceptible to oxidation.
Methemoglobin impairs oxygen transport and thus causes hypoxia of the central nervous system. Nitrites may pass through the placenta, so methemoglobinemia may already be present in the fetus. The toxic effects of nitrates and nitrites on the blood are also manifested in damage to erythrocytes and erythroblasts in the bone marrow.
Besides, when heating products containing nitrogen compounds, nitrosamines are formed (therefore, you should not grill and heat cured meats), which have a strong carcinogenic effect. Nitrosamines are also formed spontaneously during food storage as well as in the digestive tract.
Safe dose of nitrites and nitrates
The permitted dose of nitrite in the diet is 0.2 mg per day per kilogram of body weight. Nitrates can be consumed in higher doses – 5 mg per day per kilogram of body weight. For this reason, it is worth choosing vegetables from organic crops and limit the consumption of cold meats for cold meats without E (eco) and rennet cheeses.
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