How to determine if a watermelon is stuffed with nitrates. Nitrates and nitrites: method of determination in agricultural products

Watermelons are considered one of the healthiest foods for the body. They are low in calories, consist of a large number water and contain vitamins. But do not forget about the harm that fruits with a high content of nitrates can cause, which they are able to accumulate in themselves.

Nitrates are minerals used in agriculture... They are produced by the action of nitric acid on oxides, salts, and metals. Nitrates dissolve well in water. The main application of nitrates is plant fertilization. As you know, there are no products without nitrates. All plants contain nitrates. However, a large number of them can be toxic and dangerous to humans.

By themselves, nitrates are not particularly dangerous, but when ingested gastrointestinal tract they turn into nitrites (nitric acid salts), which are very toxic to the body and lead to oxygen starvation of tissues.

When nitrates enter the human body, they can reduce the amount of vitamins in food that enters the body, as well as lead to problems with thyroid... Excess daily allowance Consuming nitrates can lead to an upset stomach with blue skin, difficulty breathing and diarrhea, and other unpleasant signs of food poisoning.

Most often, the presence of nitrates in watermelons is checked in laboratory conditions, but there are special signs by which you can determine the presence of nitrates yourself at home. This article will tell you how to test a watermelon for nitrates using simple methods.

It is worth noting that the quality of the watermelon should be determined before purchasing it. In order to protect yourself when buying it, you should pay attention to some important signs... First, buy watermelons only in specialized places and markets that comply with all hygienic and sanitary standards for storing food. Sellers must have special sales permits.

Fruit should be neatly arranged and stored in clean containers on special trays. Watermelons should never be stored on the floor to avoid contact with dirt. You shouldn't risk buying a cracked, broken or crumpled fruit. Ripe watermelon that has grown in natural conditions, has a dry tip and will ring when tapped. It is not recommended to eat the fruit, if, when examining its cut, the surface has a slightly purple tint.

Pay attention to the season and do not buy watermelons too early. A smart buyer always knows when to refrain from buying. Nitrate fruits are most often sold until mid-July. If you buy a watermelon since mid-August and September, you can not worry about the presence of harmful substances in the fruits.

Many sellers are happy to provide their buyers with the opportunity to taste a bite before buying. In supermarkets, for demonstration, the fruit is cut in half and wrapped in a thin cling film through which you can easily see all the flaws. However, only visually it is impossible to determine that watermelons are free of nitrates.

Most accurately, a watermelon can be checked using special device- nitrate meter. However, this device is expensive. Popular signs by which you can determine the amount of nitrates are also quite effective.

Video "Testing watermelon for nitrates"

Validation rules

There are several methods for testing watermelons for nitrates at home. For example, if you put a watermelon in a container and it floats up, it means that the fruit is of good quality. If you dipped a watermelon into a bath, for example, and it went to the bottom, this will indicate a high content of nitrates in it.

If you find whitish and yellow streaks in the pulp of a watermelon, this also indicates nitrates. There is one more proven folk method, with which you can check the fruit at home. To do this, you only need a small amount of water.

It is worth cutting off a small piece of pulp, crumbling it and placing it in a small container of water for fifteen minutes. If the watermelon is safe, the water should just darken slightly and take on a pale pink hue. But if the water turns bright pink or red with an admixture of purple, this will indicate high content nitrate pollution. It is better to get rid of such a watermelon and in no case eat it.

Do not forget also about the rules for the use of watermelons. This fruit is a complete independent dish that should be consumed separately from the rest of the food. It is recommended to eat it 2 hours before the main meal or 2 hours after it. This is because you can not overload the stomach slightly by combining watermelon with other food.

Before consuming watermelon, take a few minutes to thoroughly wash it in running water... Nitrates in fruits and vegetables are unevenly distributed. Do not forget that the largest amount of nitrates accumulates in their skins. Do not eat the flesh all the way to the crust.

What to be sure of

It will also not hurt to make sure of the safety of the products sold by reading the documents that guarantee their quality and compliance with all standards. The surface of a quality fruit should not be grainy and not perfectly smooth. The granular structure of the pulp indicates the naturalness of the product. However, you should also not buy a watermelon that is too grainy, as it may be overripe. When cutting, pay attention to the fibers. In good quality fruits, they should be white. Yellowish fibers most often indicate a high nitrate content.

Ask where the watermelon was brought from. Most of the fruits are pink in color, and only a few northern varieties are bright red. Such specimens, as a rule, are not huge in size. Therefore, if you have a ten-kilogram fruit with red pulp in front of you, then most likely it is stuffed with nitrates.

Video "Checking melons for nitrates"

Often the opinion that in melons can be found great amount nitrates. To check on the spot whether this is so, we offer to your attention this technique described in the video.

You can check watermelons for nitrates not only in laboratory conditions - there are signs by which it is easy to find out even at home whether they are good for food.

In addition, it is worth learning, because its quality can be determined even before buying. You need to pay attention both to the fruit itself and to the equipment of the trading place (often even good watermelon may be spoiled by inappropriate conditions). As an example, let's try to choose and test a watermelon for nitrates at home.

To protect yourself from buying a "harmful" watermelon, you need to pay attention to the following:

• You should buy watermelons in specialized markets, where appropriate storage conditions (hygienic and sanitary) are created, and there are also special permits;
• Watermelons should not come into contact with the ground - lie on the floor (to avoid dirt getting into microcracks). It is customary to store all fruits on special shelves in clean containers;
• It is better to avoid buying a cut, cracked, crushed or broken watermelon, since germs spread especially quickly in the sweet pulp of the berries (including under the halves covered with film). For the same reason, it is better to refuse to sample the sliced ​​watermelon on the market;
• Ripe and grown in natural conditions (without excessive feeding) watermelon rings when tapped, and its tip will be dry.

Testing for nitrates

There are several ways to test a watermelon for nitrate at home:

• A whole watermelon can be dipped in a container of water (for example, in a bathroom). If the watermelon floats, then it is of high quality, and if it goes to the bottom, then with nitrates;
• Slice pure watermelon will be uneven, with grains. A smooth, bright cut indicates a high content;
• Large yellowish or whitish veins in the pulp are also a sign that the watermelon has been overfed with fertilizers;
• You can see a cut of a watermelon in the light and if the surface is slightly shimmering purple, it is better not to eat such a fruit;
• A piece of watermelon pulp can be dipped into a clean one and left for 15 minutes. If the water simply becomes cloudy from the pulp - the watermelon is good, and if it turns bright pink or red, it means that the watermelon is with nitrates.

Drinking watermelon

It is also worth remembering the rules for using watermelon:

• Watermelon is a separate dish. You need to eat it two hours before or two hours after the main meal (the combination of watermelon with other food can overload the stomach);
• Before using the watermelon, wash it thoroughly with clean running water;
• Most of the nitrates are stored in the peel of the fruit, so you should not eat the watermelon to the very crust.

Based on materials: podskazchik.com

For reference:

Allowable nitrate content in watermelons: 60 mg per 1 kg.

Experts in the laboratory checked the samples for nitrate content and were pleasantly surprised: none of the watermelons, even those bought from the road, had them, at least in quantities that can be detected using the official test method.

Experts in the laboratory checked the samples for the content of nitrates: none of the watermelons, even the one bought off the road, had them.

Andrey Mosov, head of the Roskontrol expert area, doctor:“Such results of the study cannot but rejoice. However, I want to warn you about another danger that watermelons can conceal. According to sanitary rules, in bazaars and open markets It is strictly forbidden to sell cut watermelons and other melons. The pulp of a watermelon, especially in the sun, is an excellent breeding ground for microbes that have entered the berry from the outside. It is with an incision from the surface of a watermelon that microorganisms can penetrate into the pulp, causing damage to the watermelon or even dangerous to human health. It is not forbidden to sell melons in supermarkets in parts, however, how safe they are depends on the conditions and time of storage.

• Yellow fibers that run from the core to the crust. In a quality watermelon, they should be white.
• The cut surface is too smooth, glossy. In a "good" watermelon, it is uneven, sugary, sparkling with grains.
• Purple shade of pulp.

For whom are the rules written?

Alexander Borisov, Co-chairman of the Roskontrol Consumer Union: Unfortunately, this is already a common situation. Of course, for such actions, more precisely, inaction, administrative responsibility is provided, such as for "Violation of the consumer's right to obtain the necessary and reliable information about the goods (work, service) being sold, about the manufacturer, about the seller, about the performer and about the mode of their operation", however, the amount of fines is calculated from 500 rubles to 1 thousand rubles for officials, and from 5 to 10 thousand rubles for legal entities... Obviously, such fines do not work, do not motivate sellers to comply with the law.

You can check watermelons for nitrates not only in laboratory conditions - there are signs by which it is easy to find out even at home whether they are good for food.

In addition, it is worth learning how to choose the right watermelon, because its quality can be determined even before buying. You need to pay attention both to the fruit itself and to the equipment of the trading place (often even a good watermelon can be spoiled, being in improper conditions). As an example, let's try to choose and check a watermelon for nitrates at home.

Fast navigation through the article

Choosing a watermelon

To protect yourself from buying a "harmful" watermelon, you need to pay attention to the following:

• You should buy watermelons in specialized markets, where appropriate storage conditions (hygienic and sanitary) are created, and there are also special permits;
• Watermelons should not come into contact with the ground - lie on the floor (to avoid dirt getting into microcracks). It is customary to store all fruits on special shelves in clean containers;
• It is better to avoid buying a cut, cracked, crushed or broken watermelon, since germs spread especially quickly in the sweet pulp of the berries (including under the halves covered with film). For the same reason, it is better to refuse to sample the sliced ​​watermelon on the market;
• Ripe and grown in natural conditions (without excessive feeding) watermelon rings when tapped, and its tip will be dry.

Testing for nitrates

There are several ways to test a watermelon for nitrate at home:

• A whole watermelon can be dipped in a container of water (for example, in a bathroom). If the watermelon floats, then it is of high quality, and if it goes to the bottom, then with nitrates;
• The cut of a pure watermelon will be uneven, with grains. A smooth, bright cut indicates a high nitrate content;
• Large yellowish or whitish veins in the pulp are also a sign that the watermelon has been overfed with fertilizers;
• You can look at a cut of a watermelon in the light and if the surface is slightly purple, it is better not to eat such a fruit;
• A piece of watermelon pulp can be dipped in clean water and left for 15 minutes. If the water simply becomes cloudy from the pulp - the watermelon is good, and if it turns bright pink or red, it means that the watermelon is with nitrates.

Drinking watermelon

It is also worth remembering the rules for using watermelon:

• Watermelon is a separate dish. You need to eat it two hours before or two hours after the main meal (the combination of watermelon with other food can overload the stomach);
• Before using the watermelon, wash it thoroughly with clean running water;
• Most of the nitrates are stored in the peel of the fruit, so you should not eat the watermelon to the very crust.

Now, people are ready to stuff food with chemistry, just to give them marketable condition and put them up for sale immediately.

How to determine nitrates in watermelon, video

But who wants to go to the hospital after eating their favorite fruit or vegetable? For this, it is worth reading the articles to distinguish a good watermelon from a watermelon stuffed with chemical additives.

The more colorful and contrasting the watermelon, the better and juicier it will be.

An important indicator of the condition of a watermelon is the color of the veins inside the flesh of the watermelon. If their color is white, then the watermelon can be sent to your stomach with confidence. If streaks of yellow or purple, that is bad sign- such a watermelon, either not fully ripe, or the result of a pest invasion, but in most cases it is the effect of nitrates.

Immediately I remember the hippopotamus from "Well, wait a minute"

But oddly enough, this method almost always works, if you have the strength, of course, to squeeze the watermelon.

Gloss check

Also pay attention to the seeds - they must be ripe!

Fresh, snowy, soft crunchy

I will cut, I will cry in scarlet sweetness.
This is a miracle, moreover, a real one -
Our Baskunchak, Liman watermelon!

What a twist

It is usually said that there is little nitrate in the middle, and a lot closer to the peel. As it turned out, this is not always the case.

Water test

And you can also check this: throw a piece of watermelon pulp into the water, if it drowns - the watermelon is satiated with nitrates, and if it remains to swim - good!

By the way, read about how to choose the right melon and what to make from it here!

Torn from melon

When the watermelon ripens, it separates from the melon by means of the fact that its tail dries up on its own. If you do not see the tail or it is somehow tucked away, most likely the seller is hiding something from you.

The ripeness of a watermelon and the naturalness of its origin can be determined by the earthen spot.

On one of the barrels of the watermelon, there must be a brownish-yellow or orange-yellow spot - this is the side of the watermelon lying on the ground. But keep in mind that the stain must not be white!

Oh, this sound

The sound of a watermelon depends on whether the pulp has softened inside or not. It is the green fruit that will ring, and the ripe watermelon will make a dull sound.

Checking how the bees worked on the watermelon

These nets appear because bees touch the ovary during pollination, respectively, the more often pollination occurs, the sweeter the fruit will be.

Touch the peel for firmness

When the watermelon ripens and separates from the melon, it is no longer able to absorb water, so its rind hardens. If you can easily pierce the skin with your fingernail, this is an unripe fruit.

Girl or boy?

Watermelon is a bisexual berry: the “male” individual is more elongated, has a convex bottom and a small circle, while the “female” berries have a wide circle. "Girls" are considered tastier: they have fewer seeds and more sugar.

If you do get caught on a nitrate watermelon, then you will be concerned about the following symptoms

2-6 hours after eating watermelon:

• nausea, less often vomiting;
• diarrhea (up to 10-15 times a day);
• abdominal pain, cramps;
• weakness;
• dizziness, headaches;
• temperature increase.

What to do in case of watermelon poisoning:

1. Flush the stomach large quantity warm, salted water or a slightly pink solution of potassium permanganate.
2. Take enterosorbents - medications, neutralizing poisons in the intestinal lumen. The most popular: activated carbon, Polysorb MP, Enterosgel, Smecta.
3. Drink as much fluid as possible to enhance the elimination of poisons from the body, as well as prevent dehydration.
4. Drink sweet lemon tea after nausea stops.
5. Do not take antidiarrheal drugs and painkillers, they mask the true state of the body.

If your condition does not improve within two hours, you should consult a doctor or call an ambulance!

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How to determine nitrates in watermelon?

NITRATES AND NITRITES:
determination method
in agricultural
products

Research work in chemistry and ecology

Recently, scientific societies have been created in many schools in which students are involved in research work. Our school is no exception. Last academic year, my student and I presented to the competent jury, consisting of researchers from the Khingan State Reserve, this work to the regional scientific and practical conference. Out of 24 competitive works, 6 (including ours) were recognized as winners.
The proposed material can be used as a lecture, accompanied by a demonstration experiment (or laboratory experiments, at the discretion of the teacher) when studying the topic "Nitrates" in the 9th grade.

Purpose of work. Study the literature on nitrates and nitrites, master the method of their determination, determine the content of nitrates and nitrites in agricultural products purchased in a store and grown in their own garden plot.
Promising goals. Determine the presence of nitrates and nitrites in greens, vegetables and fruits grown in the fields of the district. Check the compliance with the norms of the amount of applied nitrogen fertilizers.

Lesson plan

The problem of nitrates and nitrites.
Nitrosamines.
The quality of vegetables and the conditions for their cultivation.
Determination of nitrates in plants.
Determination of nitrites in plants.

The problem of nitrates and nitrites

The problem of nitrates is actively discussed by the public in our country. Let's try to understand this issue and we.
Nitrates - salts of nitric acid, for example NaNO3, KNO3, NH4 NO3,
Mg (NO3) 2. They are normal metabolic products of nitrogenous substances of any living organism - plant and animal, therefore there are no “nitrate-free” products in nature. Even in the human body, 100 mg or more nitrates are formed and used in metabolic processes per day. Of the nitrates that daily enter the body of an adult, 70% comes with vegetables, 20% - with water and 6% - with meat and canned foods.
But why are they talking about the danger of nitrates? When consumed in increased quantities, nitrates in the digestive tract are partially reduced to nitrites (more toxic compounds), and the latter, when entering the bloodstream, can cause methemoglobinemia. In addition, N-nitrosamines, which have carcinogenic activity (promote the formation of cancerous tumors), can be formed from nitrites in the presence of amines. When taking high doses of nitrates with drinking water or products after 4-6 hours appear nausea, shortness of breath, blue skin and mucous membranes, diarrhea. All this is accompanied by general weakness, dizziness, pain in the occipital region, palpitations. First aid - copious gastric lavage, intake activated carbon, saline laxatives, Fresh air... What is the safe proportion of nitrates?
The permissible daily intake of nitrates for an adult is 325 mg per day. As you know, in drinking water the presence of nitrates up to 45 mg / l is allowed. The recommended consumption of foodstuffs where drinking water is used (tea, first and third courses) is approximately 1.0–1.5 liters, maximum - 2.0 liters per day. Thus, an adult can consume about 68 mg of nitrates with water. Consequently, 257 mg of nitrates remain for food.
Studies have shown that the toxic effect of food nitrates is less pronounced than those contained in drinking water, approximately 1.25 times. In fact, it is safe to consume 320 mg of nitrate per day with food.
For vegetables and fruits, the following values ​​of maximum permissible concentrations of nitrates have been established (Table 1).

Table 1

Maximum permissible concentration of nitrates
in crop products

What are the main sources of dietary nitrates? In practice, these are exclusively herbal products. In animal products (meat, milk), the content of nitrates is very low. The maximum accumulation of nitrates occurs during the period of the greatest activity of plants during fruit ripening. Most often, the maximum nitrate content in plants occurs before the start of harvesting. Therefore, unripe vegetables (zucchini, eggplant) and potatoes, as well as vegetables early maturation may contain more nitrates than those that have reached normal harvest maturity. In addition, the content of nitrates in vegetables can increase dramatically if nitrogenous fertilizers (not only mineral, but also organic) are used incorrectly. For example, when making them shortly before harvesting.

Vegetables are sources of nitrates

We talked about the general pattern of nitrate accumulation. However, the different plants there are also individual characteristics. Known "accumulators" of nitrates. These include green vegetables: lettuce, rhubarb, parsley, spinach, sorrel, which can accumulate up to 200-300 mg of nitrates per 100 g of greens. Beets can accumulate up to 140 mg of nitrates (this is the maximum permissible concentration), and some varieties even more. But in other vegetables, nitrates are much less. Fruits, berries and melons contain very little nitrates (less than 10 mg per 100 g of fruit).
In plants, nitrates are unevenly distributed. In cabbage, for example, nitrates accumulate most of all in the stalk, in cucumbers and radishes - in the surface layers, in carrots - on the contrary. On average, 10-15% of nitrates are lost when washing and peeling vegetables and potatoes. Even more - during thermal cooking, especially during cooking, when from 40% (beets) to 70% (cabbage, carrots) or 80% (potatoes) of nitrates are lost. Since nitrates are chemically quite active compounds, during storage of vegetables their content decreases by 30-50% in a few months.
Now that everything is known about dietary nitrates, let's try to imagine their real health risks. Let's consider the main sources of nitrates. Let's start with green vegetables (lettuce, parsley, dill, etc.). Their consumption almost rarely exceeds 100 g per day, and most often about 50 g, i.e. less than a third of the safe daily dose can be obtained with one serving. (It was noted above that, taking into account the bioequivalent, the safe proportion of nitrates in food products is about 320 mg.) Now let's move on to the beets. It is known to be consumed only boiled. Since during cooking (40%) and stripping (10%) half of the nitrates is lost, and catering recommends a portion of boiled beets of 125 g, then with beets we can get 100 mg of nitrates (less than a third of the daily dose). Boiled potatoes and cabbage are consumed in portions of 300 g. Taking into account the losses during stripping and cooking, with one serving of these products, we can consume about 60 mg of nitrates.
Similar calculations were made for the rest of the vegetables and other culinary treatments. It turns out that with the usual rational consumption of fresh or cooked vegetables, we can almost never exceed the safe daily dose of nitrates with food. Moreover, in accordance with the recommendations for a balanced diet, you should not constantly eat the same foods, such as potatoes or cabbage.
Indeed, if we turn to the recommended rational average daily food intake, then potatoes should be consumed 265 g (calculated on the purchased product), vegetables and melons - 450 g (including 100 g of cabbage). Such a diet can give us a maximum of 200 mg of nitrates. In practice, as calculations have shown, the average daily intake of nitrates with the main root crops, vegetables, melons and fruits, taking into account the data of actual nutrition and the actual content of nitrates in food, does not exceed 100 mg. At the same time, about a third of nitrates comes from beets, a little less from cabbage and potatoes. For other vegetables and fruits - less than 10%. If you violate the principles of rational nutrition, for example, eat some vegetables, and even raw (as some fans of vegetarianism and raw food recommend, eat up to 1.5 kg of raw vegetables per day), then you can really exceed the safe dose of nitrates by almost two times (more than 650 mg per day), which we pay attention to.
For added safety, it is useful to recall the second principle of good nutrition, which involves the need for a variety of food.

Important information: how to identify nitrate watermelon

Therefore, we do not recommend constantly consuming, and even three times a day, the same vegetable for a snack. To limit the use of vegetables and fruits in the diet due to the danger of nitrate poisoning should not be, this will deprive us of the necessary vitamins. The nitrate content is now under strict control in the places where vegetables are produced and in trade centers.

Nitrosamines

It was already mentioned above that under certain conditions nitrates can be reduced to nitrites. In an acidic environment, nitrites give nitrous acid, and it, interacting with secondary and tertiary amines, forms carcinogenic nitrosamines:

Depending on the nature of the radical, a wide variety of nitrosamines can be formed, of which more than 100 compounds have a carcinogenic effect. Nitrosodimethylamine and nitrosodiethylamine are most commonly found in food. Most nitrosamines are found in smoked meat products, sausages prepared with the addition of nitrites - up to 80 μg / kg, in salted and smoked fish- up to 110 μg / kg. (IN fresh meat and fish, nitrosamines are not detected or are found in trace amounts - less than 1 μg / kg.) Among dairy products, nitrosamines are found mainly in cheeses that have passed the fermentation phase (up to 10 μg / kg).

From plant products, nitrosamines are found mainly in pickled products, and from drinks - in beer, where their total content can reach 12 μg / l.

Nitrosamines meet in smoked fish and beer

The quality of vegetables and the conditions for their cultivation

The quality of vegetables depends on many reasons, including the fertilization applied and the plant protection products used.
Nitrates are used as fertilizers and are known as nitrates: sodium (Chilean), potassium (real), ammonia (ammonium) and calcium (Norwegian). Nitrates - essential component plant nutrition, since the nitrogen entering them is the main construction material cells.
The ability to accumulate nitrates in different cultures is not the same. The greatest accumulation is observed in green crops: dill, parsley, green onions (from 400 to 2500 mg / kg). Tomatoes (10–190 mg / kg), sweet peppers (40–330 mg / kg), and eggplants (80–270 mg / kg) are significantly less capable of accumulating nitrates.
To obtain vegetables with a low content of nitrates, it is necessary to correctly use the alternation of crops in the crop rotation, watering and the optimal density of sowing or planting, it is necessary to rationally use fertilizers. It is known that tomatoes, peppers and eggplants are characterized by a low accumulation of nitrate nitrogen in fruits, however, there are significant varietal differences and a particular effect is exerted by conditions, primarily illumination. Therefore, thickening of crops increases the risk of nitrate accumulation. For the same reason, the content of nitrates in greenhouse vegetables.
An important role is played by the form of applied nitrogen fertilizers and the timing of their application. Maximum amount nitrates in vegetable products accumulates when ammonium and sodium nitrate is used, and the minimum is when urea, ammonium sulfate and urea-formaldehyde fertilizer are added. For vegetables, the dose of applied nitrogen should not exceed 20 g / m2. Liming acidic soils helps to reduce the content of nitrates in the soil over the next four years. It is better to apply mineral fertilizers together with organic fertilizers in optimal proportions, not forgetting about microelements.
Nitrogen fertilizing is stopped 1.5 months before harvesting (after July 10-15, it is better not to apply them).
The accumulation of nitrates in vegetable products is influenced by soil moisture. A more moderate nitrogen nutrition of plants is observed with an irrigation regime at the level of 80–90% of the highest moisture content.
Pesticides must be used with caution as they together with nitrates, they can create an additional unfavorable background. It is necessary to select plant varieties that accumulate the least nitrates, regularly destroy weeds, loosen the soil, widely use biological agents plant protection.
Compliance with the listed conditions will increase the yield of vegetables and improve their quality.

Determination of nitrates in plants

Put several slices of this or that part of the plant on a glass slide. Then apply one drop of 1% diphenylamine solution to each section and watch for the appearance of a blue color. Compare the intensity of this color with table. 2 and with a colored scale showing the degree of need of plants in nitrogen fertilizers. The content of nitrates decreases with the age of the plants, and by the time of flowering they almost disappear.

table 2

Plant needs scale
in nitrogen fertilizers

The pale blue color of the cut from diphenylamine indicates the acute need of the plant for nitrate ions. Blue coloration indicates a lack of nitrogen in the plant, and dark purple indicates that the plant is provided with nitrogen.

Determination of nitrite in plants

Equipment and reagents. Blade, pipette, diphenylamine (crystalline), sulfuric acid(conc.), streptocide solution (dissolve 0.5 g tablet in 50 ml of pharmacy hydrochloric acid), antipyrine solution (dissolve one tablet in 50 ml of pharmacy hydrochloric acid).
As a result of the participation of enzymes and carbohydrates in plants, nitrates are reduced to ammonia through nitrites:

The resulting ammonia interacts with organic acids, resulting in amino acids:

NH3 + organic acid amino acid.

However, the excess amount of nitrates is not restored and, getting into the human body, has an adverse effect on it. When it enters the human gastrointestinal tract, nitrates turn into nitrites, which cause poisoning of the body: dizziness appears, performance decreases, the content of lactic acid, cholesterol, proteins in the blood increases, hemoglobin is blocked, because nitrites can interact with it, forming methemoglobin. As a result, tissue respiration is impaired. At high doses, "cyanosis" develops and death occurs.

Determination progress

To conduct a qualitative test for the presence of nitrites in plants, several crystals of diphenylamine are applied to the surface of a fresh cut and moistened with two drops of concentrated sulfuric acid. Intense blue coloration of the cut indicates the presence of a large amount of nitrites, pink - for their low content and the absence of coloration - for the absence of nitrites or their very insignificant content.
To determine nitrites and nitrates, you can use the available pharmaceutical preparations: antipyrine (pyramidon) and streptocide, which perform the function of a reducing agent, while a characteristic staining appears.
For the study, we took vegetables grown on our own land plot and bought in the store. Tomatoes, bananas, pears, and cucumbers have been found to be free of nitrates and nitrites. Peaches, cabbage, radishes, peppers, apples contained small amounts of nitrites. Eggplants, carrots and oranges were very high in nitrite. This means that it is undesirable to eat them. What to do if there is an excess of nitrites in the product?
Greens - parsley, dill, lettuce and more - must be put, like a bouquet, in water on a straight line sunlight... Under such conditions, nitrates in the leaves are completely processed within 2–3 hours and then practically are not detected. After that, the greens can be safely eaten. Before cooking, beets, zucchini, cabbage, pumpkin and other vegetables must be cut into small cubes and covered with warm water 2-3 times, keeping for 5-10 minutes. Nitrates are highly soluble in water, especially warm water, and are washed out from vegetables. Boiling vegetables reduces the nitrate content by 50 and even 80%. Pickling, salting, pickling also reduce the nitrate content of vegetables. But drying, juicing and mashed potatoes, on the contrary, increase the concentration of nitrates.
Knowing about the accumulation of nitrates in plants and the conversion of nitrates to nitrites and N-nitrosamines will help you eat right and stay healthy.

REFERENCES

Bandman A.L., Volkova N.V. and others. Harmful chemical substances... Inorganic compounds of elements of V – VIII groups. Reference edition. Ed. V.A.Filova et al. L .: Chemistry, 1989, 592 p .; Dorofeeva T.I. These are two-faced nitrates. Chemistry at school, 2002, no. 5, p. 45;
Melnichenko G.F., Kirsanova V.F., Bitkova N.P. Growing of ecologically clean vegetable products: tomatoes, peppers, eggplants. Blagoveshchensk, 1993, 62 p .;
Skurikhin I.M., Nechaev A.P. Everything about food from the point of view of a chemist. M .: Higher school, 1991, 288 p .;
Shchitova E.P. Experiments in chemistry with an ecological focus. Blagoveshchensk, 1993, 27 p.

Property melons and gourds it is known to take nitrogen fertilizing with gratitude and put aside nitrates in reserve. But for a person, such a berry can be dangerous. You need to know how to choose a nitrate-free watermelon. These harmful substances present in any vegetables in small quantities. Watermelons hold the record for the accumulation of nitric acid salts.

Why are nitrates dangerous to humans?

In the human body, in the large intestine, nitrates pass into nitrites and are absorbed into the blood. In this case, nitrites form the methemoglobin compound. The hemoglobin in the blood is needed to carry oxygen to the cells. Methemoglobin does not perform this function and oxygen starvation begins in the body. At 30% substitution, nitrate poisoning occurs, at 50% death can occur.

Mild poisoning is expressed by depression, nausea, vomiting, diarrhea. The doctor diagnoses poisoning by an enlarged and dense liver. The danger is higher in children, since they have a low body weight, and there is no enzyme capable of converting methemoglobin to hemoglobin. Therefore, a child cannot be given a watermelon to a baby.

In the human gastrointestinal tract, protein products are broken down, amines and other nitrogenous compounds are present. Combining with nitric acid salts, carcinogens, nitrosamines are obtained.

WHO has defined as the permissible daily intake of nitrates 3.7 mg, nitrites 0.2 mg per kilogram of human weight. In terms of a weight of 70 kg, this is 350 mg of sodium nitrate.

During heat treatment, in the presence of vitamin C, during storage, nitrates are destroyed. The danger of nitrates in watermelon is great precisely because it is eaten without pretreatment and in large quantities.

How to determine nitrates in watermelon?

If before the advice out of season was the most correct, then modernity is making adjustments. New ultra-early ripening varieties and hybrids appear that ripen early, without accelerators. Such watermelons are small, only 1.5-2 kg, and we were taught not to choose small fruits. This means that if the variety is ultra-early, then the watermelon cannot be large.

Therefore, the study of sweet berries must be carried out in aggregate according to a number of signs:

• appearance;
• the structure of the pulp when examined at home;
• use of control methods and devices.

Watermelon research begins at the counter. You can not buy goods from the collapse of the roadside. For a day of standing in a gas-polluted environment, the product will gain a lot of exhaust gases, no less harmful than nitrates. On the ground, the crust will become dirty, the grains of sand will injure the shell, and it will not be possible to completely wash such a watermelon. Usually, roadside trade is illegal, there is no sanitary certificate for the product on the content of harmful substances.

Buying agricultural products, including watermelons and melons, is safe in special places and with a quality certificate.

The watermelon should have a dry tail. It should be carefully examined, a sign that the watermelon was removed green will be a soaked tip or cut with a sharp knife. In addition, this will be a sign that the watermelon has been stale for a long time. And without a tail, you should not take the fruit. This means the seller has something to hide. The tail can naturally dry out in the garden of an unripe watermelon, which is specially turned over several times, twisting the tail.

Stripes of dark and light color should be contrasting, not blurry, the drawing is clear. In a ripe watermelon, you can slightly scratch the skin, and then a white dense layer and a clearly audible watermelon smell will be found below. All this is a sign that the watermelon was recently sitting in the garden.

On examination, you need to check well if there is a puncture in the peel of the watermelon, through which they fed what the watermelon is pumped with for quick redness. And not only watermelon, other melons and tomatoes also receive injections from unscrupulous sellers. An injection of nitrate accelerates redness.

You cannot buy a watermelon with black spots on the surface, a small spot of rot, with a crack or dent. You cannot ask to cut a triangle to inspect the middle. A cut fruit with an unwashed crust and a dirty knife can lead to bad consequences.

To find signs of nitrate watermelon at home, research needs to be continued. First, put it in a bowl of water. If the fruit is ripe, it will float. A drowned watermelon can be left unchecked and returned to the owner. After that, wash the watermelon with soap and a brush, dry.

The cut fruit should have a grainy surface, not a smooth, glossy cut. The seeds should be developed and black. There should be no thick yellow strands or nitrogen supply overpasses on the cut. The veins are thin white, this is the normal structure of the fruit. The pulp should not be in the middle of an intense color, but gradually turn yellow towards the periphery. These are indications of the presence of a large amount of nitrogen. A watermelon with nitrates, the photo of which is posted below, shows its inside view.

Finally, put a 20 gram piece of watermelon into a transparent glass and knead in water. If the water becomes cloudy, everything is fine. If colored, it indicates the presence of nitrates. Moreover, the more intense the color, the more impurities in the watermelon.

The instrumental research method is the most reliable. He suggests:

• laboratory analysis;
• examination using test strips;
• use of a special device, nitrate meter, or ecotester.

Only a specialist will decide to keep a tripod for titration of a sample and potassium alum at home. But this is how the amount of nitrates in agricultural products is checked in laboratory conditions. There are indicator strips that are inexpensive, do not determine very accurately, approximately. And you can purchase an ecotester device that gives a result, and a warning about the dangerous content of nitrates.

If a dangerous dose is found, you should not eat a watermelon, it is better to part with it. In order for the risk to be minimal, you should wait until mid-August and only then feast on watermelon. But even at this time, vigilance should be observed. Manufacturers are trying to get big harvest and feeding is always carried out, only during a certain period of cultivation.

How to choose a sweet watermelon?

When buying a watermelon, experts advise choosing "girls". From a scientific point of view, this does not apply to berries. There are no boys and girls among the fruits. but folk signs show that a watermelon with a flat or slightly recessed top is sweeter and has fewer seeds. "Boys" are considered if there is a small tubercle on the top. Perhaps these are some peculiarities in pollination, but this rule of choice is valid.

Another sign of a ripe berry may be a small orange spot where the fruit was lying on the ground. If the filling went quickly, the ground was warm, the spot was small, the berry was tasty. If the spot is large, white, then the taste of the watermelon will be different. This means that the berry lay on the ground for a long time, the ground was cold, so you should not expect sweets from such a berry.

When cutting a watermelon, you need to leave 3 cm of pulp about the crust, fertilizers accumulate there. And give the children a piece from the very middle. You don't have to eat a lot of treats in one sitting. Better to stretch the pleasure, eat the fruit in small portions, while listening to the state of the body.

Bon appetit and health!

How to choose a ripe watermelon without nitrates - video