Lecture
Pathways of nitrate intake and their effect on the human body. According to
data from the World Health Organization, the daily norm of nitrates is
5 mg of NaNO3 per 1 kg of human body weight, or 300-325 mg.
When calculating the daily nitrate norm, the consumption of food products and drinking water is taken into account. According to the standard, 1 L of drinking water may
contain up to 45 mg of nitrates [2, 5, 10, 11].
Water, like food products, is contaminated with nitrates. The problem of exceeding the permissible amount of nitrates in water is very acute in the south
of Ukraine and other areas of intensive farming.
Drinking water does not meet standards in the Kherson, Chernivtsi,
Crimean, Donetsk, Luhansk and other regions of Ukraine. Besides
nitrates, water sources contain many different harmful mineral salts, which
come from chemical plants. It has been established that oversaturation
of drinking water with mineral salts contributes to the development of hypertensive diseases, ulcers of the stomach and duodenum, and diseases of the kidneys and
liver.
From 58.7 to 86% of the daily intake of nitrates into the human body
comes from vegetables. According to data from the Research Institute of Nutrition Hygiene and the Research
Center of the Ministry of Health of Ukraine, the content of nitrates in vegetables and
fruits on the territory of Ukraine is given in Table 1.1 [2, 5].
Nitrates themselves are non-toxic, but in excessive amounts in the human body they are converted into nitrites, which affect health. The conversion of nitrates into nitrites occurs under the action of enzymes of microorganisms, the salivary gland, the stomach and intestines, from where they enter the blood and
tissues. One part of them reacts with other substances, while the other part
(50-80%) is excreted from the body through the kidneys within 10-12 hours.
Under the action of nitrites, the divalent iron (Fe2+) of blood hemoglobin is converted into trivalent iron (Fe3+). Hemoglobin is converted into methemoglobin, which binds oxygen much worse and has a dark brown color. With a normal content of nitrites in food products, about 2% methemoglobin
is formed in the body, which, thanks to the enzymes of the red blood cells of an adult, is converted back into hemoglobin.
In children from 2 months to 1 year of age, hemoglobin has a different composition, and the enzyme
system does not have these protective properties, which is why they suffer from methemoglobinemia. The clinical manifestations of this disease are associated with a decrease in the oxygen saturation of arterial blood and insufficient oxygen supply to the tissues of the body (hypoxia). Methemoglobinemia is characterized by a dark blue or violet coloration of the mucous membranes and skin, general weakness, weakness, breathlessness on exertion, decreased blood pressure, and cardiac and pulmonary insufficiency. The first
signs appear when the blood contains 6-7% methemoglobin, a mild form –
10-20%, a moderate form – 20-40%, and a severe form – when its content exceeds 40%. This disease is observed not only in infants, but also in older children and
adults. Methemoglobinemia of up to 20% in adults has no clinical signs.
5, 10, 11].
Nitrates in high concentrations also interfere with the absorption
of vitamin A, and disrupt the function of the thyroid gland, the heart, and the central
nervous system.
Even more threatening to the human body are nitrosamines. These are
compounds of nitrates and nitrites with amino acids formed in the stomach
of the human. They have also been found in air and food products.
Amines are part of vegetables, fruits, meat and dairy products, and eggs consumed by humans, so whenever nitrates and nitrites are present in food products, there are always favorable conditions for the formation of nitrosamines.
It has been experimentally proven that nitroso compounds cause the formation of tumors in all organs except bones. The danger is increased by the fact that
cancerous tumors form from the constant entry into the body
of even very small amounts of nitrates and nitrites. In addition to direct carcinogenesis, some of them (N-nitroso-methylurea, N-nitrosoethylurea)
cause anomalies and developmental defects in the body.
Nitrosamines act on the developing fetus in the body approximately
10 times more strongly than on adults. Some researchers note that the cause of seemingly random cancer,
especially at a young age, should be sought in abnormalities that occurred
during pregnancy and in infants.
Human milk may contain from 0.22 to 42.4 mg of nitrates, and according to
some authors – from 50 to 90 mg per 1 L. Even at low doses of nitrates
children become poisoned. The toxic dose of nitrates for adults is 600 mg,
for young children – 100 mg, for infants – 10 mg [2, 5, 10, 11].
Elderly people are also sensitive to nitrates, as are those suffering from anemia and cardiovascular, respiratory or excretory system diseases. Human sensitivity to nitrates increases under conditions of elevated nitrogen oxides, carbon (II) and (IV) oxide (carbon monoxide and carbon dioxide) content in ambient air. The environment
is increasingly being polluted with these chemical compounds through
emissions from various industrial enterprises, transport, wastewater, etc.
It has been proven that with sufficient content of vitamin C (ascorbic acid) and E (tocopherol), pectin substances, and polyphenols in human food, which
act as inhibitors of methemoglobin formation, the development of
malignant tumors can be prevented. Fiber contained in vegetables and fruits delays
the absorption of nitrosamines into the blood [3, 4, 9, 13, 14].
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Consequently, the means of preventing nitrosamine formation in the human
body may include reducing the content of nitrates and nitrites in food
products, especially in fruits and vegetables, consumption of vitamin preparations,
a special diet containing food components such as pectin, fiber,
and vitamin E in certain ratios.
Reducing the content of nitrates in food products and food
raw materials. The content of nitrates in vegetables, according to data from Ponamarev P.Kh. and Sirokhman I.V., can be reduced primarily by selecting varieties that accumulate little nitrate, following fertilizer application recommendations, and also using scientific advances in the application of micronutrient feeding and slow-release nitrogen fertilizers. These fertilizers are granules coated with special substances that reduce their solubility in soils and release into plants gradually. The use of
nitrification inhibitors, which restrain nitrate formation in the soil, makes it
possible to reduce the content of harmful salts in vegetables by 2-5 times. Band application of fertilizers also lowers the amount of nitrates in vegetables and increases yields.
Reduction of nitrates is facilitated by multiple applications of nitrogen fertilizers during
the growing season and discontinuation of feeding 1-2 months before harvest.
Vegetable nutrition should be balanced in macro- and micronutrients,
taking into account the biological characteristics of individual vegetables and other factors affecting nitrate accumulation [2, 5, 10, 11].
Reduction of nitrate content in lettuce and spinach is achieved by using micronutrients and potassium chloride for feeding during their cultivation. The use of micronutrient feeding and application of potassium
chloride helps increase the nutritional value of lettuce and spinach.
During storage of vegetables, their nitrate content decreases, but in some it increases.
The nitrate content in green vegetable crops is influenced by the method and
temperature of storage, as well as varietal characteristics.
Green onions are stored in sealed polyethylene film
bags at a temperature of 0-1 °C. Over 60 days of storage under such conditions, depending
on the variety, the nitrate content decreases by 30-67%. When green onions are stored in an open container, the amount of nitrates even increases by 3-
10%. The nitrate content during storage of bulb onions does not decrease,
of white cabbage – decreases, of carrots – increases.
When radish is stored in polyethylene bags at a temperature of
1-2 °C, the amount of nitrates changes almost not at all. A decrease in the amount
of nitrates is observed during radish germination.
During storage of carrot juice, it has been established that the higher
the nitrate concentration in it and the higher the storage temperature, the
more nitrites are formed.
During storage of spinach and parsley at room temperature,
the nitrate content increases sharply within 24 hours.
Storing vegetables in open ground or in contaminated containers or packaging materials leads to an increase in nitrate content. This is all
explained by more intensive development of microorganisms.
The increase in nitrate content in produce stored at room
temperature is also caused by increased intramolecular
respiration, during which nitrates are converted into nitrites. The process of converting nitrates into nitrites also occurs at sub-zero storage
temperatures, but it proceeds very slowly.
The nitrate content can be reduced during the preparation of vegetables. Vegetables
should preferably, where possible, be consumed boiled, since the content
of nitrates in them is lower than in fresh ones.
Since in chopped and damaged vegetables the process of conversion
of nitrates into nitrites is accelerated, they should not be kept for a long time in such a
state, nor used for making juices. Juices should
be consumed immediately, without leaving them for any time even in the refrigerator.
Frozen vegetables should be subjected to heat treatment (boiling, frying) without thawing.
When feeding children, the following recommendations should be observed [2, 5, 10, 11]:
1. It is undesirable to use juices from carrots, table beets, cabbage, etc. that are contaminated with nitrates. Carrots may contain nitrates at 10.0-
334 mg/kg, beets - 40.0-3200, white cabbage - 10.0-1900 mg/kg of raw product. Up to 40% of the nitrates pass into juice extracted from carrots,
from beets – up to 70%, from cabbage – up to 60%. Juices containing permissible amounts of nitrates should be stored only in the refrigerator. At room
temperature the conversion of nitrates into more toxic nitrites is accelerated.
2. Do not include in the diet lettuce, spinach, or parsley contaminated with nitrates. Lettuce and spinach may contain nitrates from 240 to
3600 mg/kg, parsley – up to 2508 mg/kg.
3. Limit consumption of greenhouse-grown vegetables: radish, dill,
cauliflower, cucumbers, tomatoes, lettuce, parsley, which contain 1.5-
2 times more nitrates than those grown in open ground.
4. Avoid consuming early vegetable greens grown on citizens' private plots and sold at markets, especially unregulated ones. In order to obtain a high yield in a short time and sell the produce at a high price early in spring, growers do not spare fertilizer, and this
leads to the accumulation of a large amount of nitrates in such vegetable
produce. It is practically impossible to
monitor this produce for nitrate content.
5. Do not feed children thawed and slightly frozen fruits
and vegetables that have been stored thawed for a long time before consumption. When
thawed, they are easily affected by microorganisms causing
nitrate accumulation, and under such conditions are converted into more toxic
nitrites. For this same reason, juices, purees, and other fruit and vegetable
preserves that have been kept for a long time without refrigeration in open containers should not be consumed.
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6. It is not advisable to keep peeled, chopped, or mashed fruits
and vegetables for a long time before consuming them. Do not use mechanically damaged
fruit. In such products nitrates rapidly convert into nitrites.
7. Do not consume or use for cooking various dishes
water from sources that have not been checked or are not monitored for nitrate content.
During pickling of cabbage or salting of cucumbers and tomatoes, the nitrate content in the finished product decreases. In doing so, consumption of
parsley, dill, and celery, which are rich in nitrates, should be limited. A significant amount of nitrates
concentrates in the brine (marinade), so it should not be consumed.
The nitrate content in prepared vegetable dishes is shown in Table 2.1.
Table 2.1 – Nitrate content in finished products depending on
the use of different vegetables in their preparation
Dish, product Nitrite content per serving,
mg/kg
Soup with meat 18
Pea soup 20
Sorrel, sauerkraut, potatoes 42
Segedin goulash, potatoes 44
Cutlet, vegetable mixture, potatoes 65
Egg, baked potato, red cabbage salad.
Pork ribs, spinach, potatoes 90
Boiled pork, horseradish sauce, sauerkraut, potatoes 100
Vegetable soup with beef 120
Vegetable soup with dill 340
Taking into account the recommendations on storage, processing, and preparation
of fruits and vegetables for consumption makes it possible to reduce nitrate intake from food. Systematic monitoring of food products for nitrate content will certainly contribute to resolving these issues.
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