Lesson "qualitative determination of proteins in foods." Protein tests: from the variety of studies to the specifics of analyzing total protein in blood serum Description of the test for total protein in blood

Topic: Squirrels. Qualitative determination of proteins in products .

Educational: organize the activities of students to study and initially consolidate knowledge about the chemical properties of protein.

Educational: Create meaningful and organizational conditions for students to develop:- skills to carry out analysis, synthesis and, based on them, generalization and conclusions;- skills of safe work with laboratory equipment and reagents;
- the ability to set goals and plan one’s activities;

Educational:

To promote students' awareness of the value of the subjects they study in their professional activities.
- Ensure developmentability to work independently and together, listen to the opinions of classmates, prove your opinion;

Equipment and reagents: boxes for reagents, solutions of sodium hydroxide, copper sulfate (II), concentrated nitric acid, chicken protein solution, a stand with test tubes, alcohol lamps, matches, test tube holders, minced meat, bread, potato tuber, milk (homemade and store-bought), cottage cheese, sour cream, boiled peas, buckwheat, distilled water.

I. Organizational moment.

Vocational cycle teacher : Hello guys! We also welcome our guests!

II. State the topic and purpose of the lesson. (slide No. 1)

Updating knowledge:

Chemistry teacher: OnIn previous chemistry classes, we began to get acquainted with proteins and learned about their structure and functions in the body

Vocational cycle teacher: And while studying professional modules, we learned how to prepare dishes from products that contain proteins.

Chemistry teacher: Tell me guys, what else would you like to know about proteins as chemicals?

(Suggested answer: Find out the chemical properties of protein)

What reactions can be used to determine the presence of protein in foods?)

Vocational cycle teacher: Okay, what about cooking technology?

(Suggested answer: What changes occur to proteins during cooking?-)

I II . Learning new material:

Chemistry teacher: We have set goals for ourselves, and now we will begin to implement them. So. Chemical properties of protein. I want to ask you, as experts in this field. What happens to the protein (for example, a chicken egg) if it is heated and fried?(slide No. 2)

(Suggested answer: color, density, smell, taste will change) Chemistry teacher: Moreover, the same changes occur with protein if it is exposed to salts of heavy metals, acids, and alcohols.

And this process is called protein denaturation. (slide number 3)

Vocational cycle teacher : And where does this property manifest itself in food preparation technology:

(Suggested answer: - Souring of milk is used in making yogurt.
- Clarification of broths is based on the coagulation of proteins during heat treatment
- cooking meat, fish, cooking cereals, vegetables, etc.)(slide No. 4;)

Chemistry teacher: Now let's get acquainted with qualitative reactions to protein. What does a quality response mean?

(Suggested answer: this is something that can be used to recognize a substance)

Demonstration: slides

1. Xanthoprotein reaction (to benzene rings contained in some amino acids). Under the influence of concentrated HNO3, proteins turn yellow.Slide No. 5

2. Biuret reaction (to detect the –CONH– group). If you add a little NaOH to a small amount of protein solution and add CuSO4 solution drop by drop, a red-violet color appears.(slide No. 6)

Vocational cycle teacher : If we didn’t conduct an experiment, where do we get information about the presence of protein in the product?

(Suggested answer: from the information on the ingredients label, it says...)

Chemistry teacher: But now you yourself will try to determine the presence of protein and its relative amount in products; a group of laboratory technicians will do this. And a group of other experts will study the presence of protein according to the information provided by the manufacturer.

(work in pairs on options according to instruction cards)

Group of laboratory experts :

Instruction card: Add a little to a small amount of the dispensed product.NaOH and add CuSO4 solution drop by drop.

Key: The appearance of a red-violet color indicates the presence of protein. The color intensity indicates the quantitative composition.

Option No. 1: homemade and store-bought milk

Option number 2: cottage cheese

Option #3: Loaf

Option #4: Peas

Option No. 5: Meat, Maggi bouillon cube

Option number 6: Buckwheat

Option number 7: Raw potatoes

Option No. 8 Sour cream

2 Groups of expert theorists :

Study the composition of the issued products indicated by the manufacturer, confirm or refute the conclusions of the laboratory technicians.

№p, p

Product name

Protein content per 100g of product, g

Discussion of results. Conclusions:

Chemistry teacher: (addresses the vocational cycle teacher) It turns out that animal foods are rich in protein. Maybe then give up vegetable proteins altogether and eat meat instead of cereal?

Vocational cycle teacher : No, this is where you are wrong! And what proteins are healthier for the body and how to prepare them correctly will soon be told to us by a future cook or pastry chef -……(information from a student) (presentation slide No. 7)

(Suggested answer: No. 1 Animal and plant proteins are absorbed differently by the body. If the proteins of milk, dairy products, eggs are absorbed by 96%, meat and fish - by 93-95%, then the proteins of bread - by 62-86%, vegetables - by 80%, potatoes and some legumes - by 70%. However, the mixture of these products is biologically more complete.Culinary processing of products is also important. With moderate heating of food products, especially those of plant origin, the digestibility of proteins increases slightly. With intensive heat treatment, digestibility decreases.Chemistry teacher: Thank you!

IV . Fastening:

1. Why is egg white used as an antidote when people are poisoned with salts of heavy metals: Hg, Ag, Cu, Pb, etc.?(Heavy metal ions that enter the body in the gastrointestinal tract bind to proteins into insoluble salts and are removed without having time to cause harm (cause denaturation) to the proteins from which the human body is built).

2. Why does the weight of the finished product decrease when cooking meat and fish?
( Under the influence of temperature, a change occurs in the secondary, tertiary and quaternary structures of the protein molecule (denaturation). The primary structure, and, consequently, the chemical composition of the protein does not change. During denaturation, proteins lose moisture (hydrogen bonds are destroyed), which leads to a decrease in the mass of the finished product.)

V . Reflection:

What did we find out?

What was the most interesting thing today?

Who wants to praise someone?

VI . Dz. Solve the problem : It is known that an adult needs 1.5 g of protein per 1 kg of body weight per day. Knowing your weight, determine the daily protein intake for your body.

In the experiments ahead of us, we will limit ourselves to simple qualitative reactions that will allow us to understand the characteristic properties of proteins.

One of the groups of proteins consists of albumins, which dissolve in water, but coagulate when the resulting solutions are heated for a long time. Albumins are found in chicken egg whites, in blood plasma, in milk, in muscle proteins and in general in all animal and plant tissues. It is best to use chicken egg white as an aqueous protein solution for experiments.

You can also use cow's or pig's blood serum. Carefully heat the protein solution to a boil, dissolve a few crystals of table salt in it and add a little dilute acetic acid. Flakes of coagulated protein fall out of the solution.

To a neutral or, better yet, an acidified protein solution, add an equal volume of alcohol (denatured alcohol). In this case, protein is also precipitated.

To the protein solution samples, add a small solution of copper sulfate, ferric chloride, lead nitrate or another heavy metal salt. The resulting precipitation indicates that heavy metal salts in large quantities are toxic to the body.

The problem of creating synthetic food not only for animals, but also for humans is one of the most important in modern organic chemistry. The most important thing is to learn how to get proteins, because agriculture provides us with carbohydrates, and we can increase the supply of dietary fats at least by refusing to use them for technical purposes. In our country, in particular, Academician A. N. Nesmeyanov and his colleagues are working in this direction. They have already managed to obtain synthetic black caviar, cheaper than natural caviar and not inferior in quality.

Strong mineral acids, with the exception of phosphoric acid, precipitate dissolved protein even at room temperature. This is the basis of the very sensitive Heller test, performed as follows. Pour nitric acid into the test tube and carefully add the protein solution along the wall of the test tube using a pipette so that both solutions do not mix. A white ring of precipitated protein appears at the boundary of the layers.

Another group of proteins is formed by globulins, which are insoluble in water, but dissolve more easily in the presence of salts. They are especially abundant in muscles, milk and many parts of plants. Plant globulins also dissolve in 70% alcohol.

In conclusion, let us mention another group of proteins - scleroproteins, which dissolve only when treated with strong acids and at the same time undergo partial decomposition. They consist mainly of the supporting tissues of animal organisms, that is, these are the proteins of the cornea of ​​the eyes, bones, hair, wool, nails and horns.

Most proteins can be recognized using the following color reactions. The xanthoprotein reaction is that a sample containing protein, when heated with concentrated nitric acid, acquires a lemon-yellow color, which, after careful neutralization with a dilute alkali solution, turns orange. This reaction is based on the formation of aromatic nitro compounds from the amino acids tyrosine and tryptophan. True, other aromatic compounds can give a similar color.

When carrying out the biuret reaction, a diluted solution of potassium or sodium hydroxide (caustic potassium or caustic soda) is added to the protein solution, and then a solution of copper sulfate is added dropwise. A reddish color appears first, which turns into red-violet and then blue-violet.

Like polysaccharides, proteins, when boiled for a long time with acids, are broken down first into lower peptides and then into amino acids. The latter give many dishes a characteristic taste. Therefore, acid hydrolysis of proteins is used in the food industry for the production of seasonings for soups.

Grosse E., Weissmantel H.

Chemistry for the curious. Basics of chemistry and entertaining experiments.

Chapter 7 - continued

FATS - FUEL FOR THE BODY

We are already familiar with fats. They represent esters, formed by trihydric alcohol glycerin with saturated and unsaturated fatty acids, e.g. stearic, palmitic And oleic. We have already decomposed them with alkalis and obtained soap.
We also know that fats are the most important food products. They contain much less oxygen than carbohydrates. Therefore, fats have a significantly higher heat of combustion.
However, it would be unreasonable, based on this, to strive to provide your body only with fats, which are rich in energy but difficult to digest. At the same time, the body would wear out in the same way as an ordinary home stove if, instead of firewood, it was heated with much more high-calorie coal, or even more so with anthracite.
Based on their origin, fats are divided into vegetable And animals. They do not dissolve in water and thanks to my low density float on its surface. But they are highly soluble in carbon tetrachloride ( carbon tetrachloride), trichloromethane ( chloroform), on air and other organic solvents.
Therefore they can extract(extract) from crushed plant seeds or animal products with specified solvents when heated.
We will limit ourselves to finding fats in the kernels of nuts, poppy seeds, sunflowers or other plants. A small amount of the test sample must be ground, placed in a test tube, and a few milliliters of carbon tetrachloride added ( carbon tetrachloride) and heat for a few minutes.
(Carbon tetrachloride vapors are harmful to health and should not be inhaled! Conduct the experiment only outdoors or in a fume hood! Due to the risk of fire, never use flammable solvents such as ether or acetone!) Let's apply a few drops of the resulting solution to a piece of filter paper and get a beautiful thing - so unpleasant on clothes, but necessary in our experience - grease stain! If you heat the paper over the stove, the stain will remain - unlike essential oil stains, which will evaporate under such conditions.
Another unique way of detecting fat is based on the fact that it spreads in a thin layer on the surface of the water. If very small particles of camphor are applied to the surface of fat-free water, they begin to swirl - as if they are dancing. As soon as even the slightest trace of fat gets into the water, this dance immediately stops.
Alternatively, we can place a small amount of oil or a piece of fat in a test tube and quickly heat it over a high flame with a Bunsen burner. This produces yellowish-white smoke.
If we carefully sniff the test tube, we will feel irritation in our nose and tears in our eyes. This is explained by the fact that the decomposition of glycerol produces an unsaturated alkanal (aldehyde) acrolein, having the formula CH 2 =CH-CH=O. Its smell is all too familiar to many housewives whose roasts have burned. Acrolein exhibits a lachrymatory effect and is quite poisonous.
In everyday life, many fats are often used - sometimes in excessive abundance - for boiling, frying, baking and making sandwiches. In the latter case, only hard or semi-solid are suitable, mainly animal fats, such as butter and rendered fat. Some vegetable fats, such as coconut, are too hard to spread on bread, and liquid oils, of course, are not suitable for this either.
We owe it to the German chemist Norman that liquid fats can now be converted into solid fats by processing them into margarine.
Liquid vegetable oils contain unsaturated fatty acids, mainly oleic (octadecene). The latter differs from saturated stearic (octadecanoic) acid, which is part of solid fats, only in the absence of two hydrogen atoms in the molecule. Oleic acid contains a double bond - between the ninth and tenth carbon atoms:
CH 3 -(CH 2) 7 -CH=CH-(CH 2) 7 -COOH
In 1906, Norman managed to add hydrogen to oleic acid and thereby convert it into stearic acid. This hydrogenation reaction is accelerated in the presence of catalysts - finely divided platinum, palladium or nickel. Let's try to hydrogenate a small amount of fat ourselves.

Curing fats is not that easy!

Let's cure 2 g of pure olive or sunflower oil.
We'll need a catalyst. Let's prepare it as follows. From 0.5 to 1 g of methane ( formate) of nickel, the production of which was described earlier, will be placed in a test tube made of refractory glass and calcined for 15 minutes in the high-temperature zone of the flame of a Bunsen burner.
In this case, the salt decomposes and nickel metal is formed in the form of a very fine powder.
Let the test tube cool down, and during this time it should not be moved in order to reduce the contact of nickel with air as much as possible. It is best to immediately close the test tube after calcination by inserting a piece of asbestos cardboard into it with tweezers.
After cooling, pour 5 ml of pure alcohol (denatured alcohol is not good) or ether. Then add a solution of 2 g of oil in 15 ml of pure alcohol.
Let us connect the test tube, which serves as a reactor, with device for producing hydrogen. The end of the outlet tube through which hydrogen enters the test tube must be pulled back so that the gas is released in the form of small bubbles.
The hydrogen coming out of the gas separation device must be very well purified before entering the test tube so as not to poison the catalyst (In laboratory conditions, the purest hydrogen is obtained by electrolysis of water. However, hydrogen obtained by reacting aluminum with alkali solution. In this case, this method of preparation is preferable than from zinc and dilute (1 M) sulfuric acid - Transl.
To do this, let’s pass it through two more washing bottles. Pour a solution of potassium permanganate into the first, and a concentrated solution of caustic soda or caustic potassium into the second. Air should not enter the reactor. Therefore, hydrogen must first be passed only through a system where it is produced and purified, and thereby force the air out of it. Only after this will we connect this system to the reactor and pass hydrogen through the reaction mixture for at least an hour.
Gas should exit the reaction tube through the outlet tube. If he gives negative sample on explosive gas, it can be set on fire. And if you do not set it on fire, then the experiment can only be carried out in a fume hood or in the open air, and, of course, There should be no sources of heat nearby, much less open fire..
After the passage of gas is stopped, flakes fall out in the test tube, which are colored gray due to the presence of the catalyst. Let's dissolve them in heated carbon tetrachloride and separate the catalyst filtering through a double layer of filter paper as thick as possible. When the solvent evaporates, a small amount of white “grease” remains.
This lard, of course, is not margarine yet. But it is precisely this that serves as the raw material for the industrial production of margarine.
Hydrogenation of fats is carried out in the GDR at the Rodleben plant and is being expanded from year to year according to plan. Valuable vegetable oils, such as peanut and sunflower, cottonseed and rapeseed, are cured. By mixing coconut and palm fat, the best types of margarine are obtained - confectionery and butter. In addition, when making margarine, skim milk, egg yolk, lecithin and vitamins are added to the fats.
Thus, we see that margarine is a valuable food product that is made from vegetable oils and other food additives as a result of their “refinement” through chemical processing.

PROTEIN IS NOT ONLY IN EGGS

Life is a way of existence of complex protein bodies. Proteins are an important component of the protoplasm of all plant and animal cells. They are found in the cell sap of plants, in the muscles of animals, and in their nerve fibers, and in brain cells.
Proteins are the most complex chemical compounds. Their constituent parts have a simple structure. The German chemist Fischer, the founder of protein chemistry, as a result of many years of complex research, proved that proteins are built from amino acids.
The simplest amino acid is glycine, or aminoethanoic (aminoacetic) acid. It corresponds to the formula NH 2 -CH 2 -COOH.
It is characteristic that the glycine molecule includes an NH 2 group along with the COOH group inherent in carboxylic acids. Some amino acids also contain sulfur.
Amino acid molecules contain not only simple carbon chains, but also aromatic rings, including those with heteroatoms. In total, about 30 amino acids have been isolated from proteins and studied so far. Of these, at least ten are essential for human nutrition. The body needs them to build its proteins and cannot synthesize them itself.
Proteins of animal and especially plant origin usually do not contain all the amino acids necessary for life in sufficient quantities, so human protein nutrition should be as varied as possible. It turns out that our penchant for varied foods is scientifically based.
All amino acids are characterized by the ability to form peptide bonds. In this case, the NH 2 group of one amino acid molecule reacts with the COOH group of another molecule. As a result, water is split off and products of complex composition are obtained, called peptides.
For example, if two glycine molecules are connected to each other in this way, then the simplest peptide appears - glycyl-glycine:

NH 2 -CH 2 -CO-NH-CH 2 - COOH

If not two, but many molecules of different amino acids combine, then more complex molecules are formed proteins. These giant molecules, containing thousands or even millions of carbon atoms, are twisted into a ball or have a helical structure.
Remarkable advances have been made in protein synthesis in recent years. There were even production plans synthetic proteins on a large industrial scale as valuable animal feed (The problem of creating synthetic food not only for animals, but also for humans is one of the most important in modern organic chemistry. The most important thing is to learn how to obtain proteins, because agriculture provides us with carbohydrates, and to increase the supply of edible fats is possible at least by refusing to use them for technical purposes. In our country, academician A. N. Nesmeyanov and his colleagues worked in this direction. They have already managed to obtain synthetic black caviar, cheaper than natural one. and not inferior to it in quality. - Transl.).
Every day science is learning more and more about these important substances. Recently, we managed to unravel another mystery of nature - to reveal the secret of the “blueprints” according to which the molecules of many proteins are built. Step by step, researchers are persistently moving forward, revealing the essence of those chemical processes that occur in the body with the decisive participation of proteins.
Of course, there is still a lot of work to be done to overcome the long path leading us to a complete understanding of these processes and the synthesis of the simplest forms of life.

In the experiments ahead of us, we will limit ourselves to simple qualitative reactions that will allow us to understand the characteristic properties of proteins.
One of the groups of proteins consists albumins, which dissolve in water, but coagulate when the resulting solutions are heated for a long time. Albumin found in chicken egg whites, blood plasma, milk, muscle proteins and in general in all animal and plant tissues. It is best to use chicken egg white as an aqueous protein solution for experiments.
You can also use cow's or pig's blood serum. Carefully heat the protein solution to a boil, dissolve a few crystals of table salt in it and add a little diluted acetic acid. Flakes of coagulated protein fall out of the solution.
To a neutral or, better yet, acidified protein solution, add an equal volume of alcohol (denatured alcohol). In this case, protein is also precipitated.
To the protein solution samples, add a small solution of copper sulfate, ferric chloride, lead nitrate or another heavy metal salt. The resulting precipitates indicate that heavy metal salts are present in large quantities poisonous for the body.
Strong mineral acids, with the exception of phosphoric acid, precipitate dissolved protein even at room temperature. This is the basis for a very sensitive Teller test, performed as follows. Pour nitric acid into the test tube and carefully add the protein solution along the wall of the test tube using a pipette so that both solutions do not mix. A white ring of precipitated protein appears at the boundary of the layers.
Another group of proteins is formed globulins, which do not dissolve in water, but dissolve more easily in the presence of salts. They are especially abundant in muscles, milk and many parts of plants. Plant globulins also dissolve in 70% alcohol.
In conclusion, let us mention another group of proteins - scleroproteins, which dissolve only when treated with strong acids and undergo partial decomposition. They consist mainly of the supporting tissues of animal organisms, that is, these are the proteins of the cornea of ​​the eyes, bones, hair, wool, nails and horns.

Most proteins can be recognized using the following color reactions.
Xanthoprotein reaction is that a sample containing protein, when heated with concentrated nitric acid, acquires a lemon-yellow color, which, after careful neutralization with a dilute alkali solution, turns orange (This reaction is detected on the skin of the hands if nitric acid is handled carelessly. - Approx. transl. ).
This reaction is based on the formation of aromatic nitro compounds from amino acids tyrosine And tryptophan. True, other aromatic compounds can give a similar color.

When conducting biuret reaction a diluted solution of potassium or sodium hydroxide (caustic potash or caustic soda) is added to the protein solution and then a solution of copper sulfate is added dropwise. A reddish color appears first, which turns into red-violet and then blue-violet.
Like polysaccharides, proteins, when boiled for a long time with acids, are broken down first into lower peptides and then into amino acids. The latter give many dishes a characteristic taste. Therefore, acid hydrolysis of proteins is used in the food industry to make soup dressings.

Place 50 g of dried and crushed pieces of beef or cottage cheese into a 250 ml wide-neck Erlenmeyer flask. Then pour concentrated hydrochloric acid there so that all the protein is completely saturated (about 30 ml). We will heat the contents of the flask in a boiling water bath for exactly one hour. During this time, the protein will partially break down and a thick dark brown broth will form.
If necessary, after heating for half an hour, you can add 15 ml of half-diluted concentrated hydrochloric acid. It is advisable to take exactly as much acid as is needed to hydrolyze the protein, because if there is too much of it, then after neutralization there will be a lot of salt in the broth.
In a second flask or clay pot, mix finely chopped or mashed vegetables and spices, for example 20 g of celery, 15 g of onions or leeks, a little nutmeg and black or red pepper, with 50 ml of 10% hydrochloric acid. We prepare the latter by diluting 1 volume of concentrated acid with 2.5 volumes of water. We will also heat this mixture in a water bath until a brown color appears (usually this happens after about 20 minutes).
Then place both mixtures in a heat-resistant glass crystallizer or large porcelain evaporation cup and mix thoroughly. Add 50 ml of water and neutralize the acid by gradually adding sodium bicarbonate (baking soda). This should be done gradually, in small portions, with a wooden or plastic spoon. The mixture must be thoroughly mixed all the time.
In this case, a lot of carbon dioxide will be released, and sodium chloride will be formed from hydrochloric acid, or, more simply, table salt, which will remain in the broth. Thanks to salt, the broth is better preserved. The end of neutralization is easy to notice by the cessation of foam formation when adding another small portion of baking soda. It must be added so much that the finished mixture exhibits a very slightly acidic reaction when tested with litmus paper.
Of course, the resulting concentrate can be used to prepare soup only if completely pure hydrochloric acid was used to hydrolyze the protein, i.e., pure for analysis or used for medical purposes (The latter can be purchased at a pharmacy. - Transl.) , because technical acid may contain admixtures of toxic arsenic compounds (!).
The quality and taste of this soup may vary depending on what products we used to prepare it. However, if the given recipe is strictly followed, it can be eaten.
In industry, food concentrates for soups are supplemented with: protein hydrolysates, obtained in a similar way from wheat bran (Often other proteins, mainly of plant origin, are used for this - from waste from processing oilseeds, as well as milk protein - casein. The resulting hydrolysates have a pleasant meat or mushroom taste. You can even get a hydrolyzate that tastes just as good as chicken broth. - Approx. transl.).
In recent years, one of the amino acids has been used as an additive that improves the taste of food, as well as a strengthening agent - glutamine, which is found in abundance in globulins. It is used in a free state or as a sodium salt - monosodium glutamate. Let's add to our concentrate a little pure monosodium glutamate or glutamic acid itself, tablets of which can be bought at the pharmacy. This will give the concentrate a stronger flavor. Glutamic acid itself has only a mild taste, but it stimulates the taste buds and thus enhances the characteristic taste of food.

WHAT IS TURNING INTO WHAT?

Can you imagine what a giant chemical plant looks like? Huge chimneys emit clouds of black, poisonous yellow or brown smoke into the air. Huge distillation columns, refrigeration units, gas tanks and large production buildings give the chemical plant its unique shape.
If we get to know the plant better, we will be captivated by the intense rhythm of its continuous work. We will stop in front of huge boilers, walk along pipelines, hear the noise of compressors and the sharp, initially frightening sound of steam escaping from safety valves.
However, there are also chemical plants that do not smoke or make noise, where there are no equipment and where, day after day, old workshops are destroyed, giving way to new ones. Such chemical enterprises are living organisms.

METABOLISM

“Combustion” of food in the body occurs in cells. The oxygen required for this is provided through respiration and in many living organisms is carried by a special liquid - blood. In higher animals, blood consists of plasma and red and white blood cells suspended in it.
Red blood cells, erythrocytes, which give blood its color, consist of 79% complex protein hemoglobin. This protein contains a red dye. heme attached to colorless protein globin, from the group globulins.
The composition of hemoglobin varies greatly among different animals, but the structure of heme is always the same. From heme you can get another connection - hemin.
Anatomist Teichmann was the first to isolate hemin crystals and thereby find a reliable method for recognizing blood. This reaction makes it possible to detect the slightest traces of blood and is successfully used in forensic examination in the investigation of crimes. Using a glass rod, apply a drop of blood to a glass slide, smear it and air dry it. Then apply a thin layer of table salt, crushed to the finest powder, to this glass, add 1-2 drops glacial acetic acid(in extreme cases, you can use high concentration acetic acid instead) and put a cover glass on top. Heat the slide with a weak (!) flame until the first bubbles form (glacial acetic acid boils at 118.1 °C).
Then, with careful heating, completely evaporate the acetic acid. After cooling, examine the sample under a microscope with 300x magnification. We will see red-brown diamond signs ( prisms). If such crystals have not formed, then we again apply acetic acid to the interface of the glasses, let it seep inside and heat the slide again.
This reaction makes it possible to detect traces of dried blood on fabric. To do this, treat such a stain with water containing carbon dioxide, for example mineral water, filter the extract, evaporate the filtrate on a glass slide and then process the sample in the same way as indicated above.
The German chemist Hans Fischer was the first to synthesize and break down hemin in 1928. Comparison of the formula of hemin (or heme) with the formula of the green plant pigment chlorophyll indicates the amazing similarity of these compounds: A benzidine test can also detect a small amount of blood. First, let's prepare the reagent. To do this, dissolve 0.5 g of benzidine in 10 ml of concentrated acetic acid and dilute the solution with water to 100 ml. To 1 ml of the resulting solution add 3 ml of a 3% solution peroxide(peroxide) hydrogen and immediately mix with a very diluted aqueous blood extract. We will see a green color that quickly turns blue.
In 5 liters of blood contained in the human body, there are 25 billion red blood cells, and they contain from 600 to 800 g of hemoglobin.
About 1.3 ml of oxygen can be added to 1 g of pure hemoglobin. However, not only oxygen can attach to hemoglobin. Its affinity for carbon monoxide (carbon monoxide) is 425 times greater than for oxygen.
The formation of a stronger compound of carbon monoxide with hemoglobin leads to the fact that the blood loses its ability to carry oxygen, and the poisoned person suffocates. That's why Let's be careful with household gas and other gases containing carbon monoxide!
We now know that in metabolism, blood plays the most important role as a vehicle. Transfer of gases, removal of foreign substances, wound healing, transport of nutrients, metabolic products, enzymes and hormones are the main ones functions blood. All food that a person eats is subjected to chemical processing in the stomach and intestines. These transformations are carried out under the influence of special digestive juices - saliva, gastric juice, bile, pancreatic and intestinal juice.
The active principle of digestive juices is mainly biological catalysts- the so-called enzymes, or enzymes.
For example, enzymes pepsin, trypsin And erepsin, as well as rennet chymosin, acting on proteins, they break them down into simple fragments - amino acids, from which the body can build its own proteins. Enzymes amylase, maltase, lactase, cellulase participate in the breakdown of carbohydrates, while bile and group enzymes lipases promote the digestion of fats. The effect of bile on the digestion of fats can be confirmed by the following experiment. Insert glass funnels into two identical flasks or Erlenmeyer flasks. In each funnel, lightly moisten a strip of filter paper with water.
Then in one of the funnels we soak the paper with bile (cow, pork or goose) and pour a few milliliters of edible vegetable oil into both funnels.
We will see that the oil penetrates only into the strip of paper that was treated with bile. The fact is that bile acids cause emulsification of fats, breaking them into small particles. Therefore, bile helps enzymes in the body that help digest fat. This is especially evident in the following experiment. If you can find a pork stomach, you need to turn it out, rinse it with water and scrape off the mucous membrane with a blunt knife into a beaker. Pour four times the amount of 5% ethanol into it and leave the glass for 2 days.
Filter the resulting water-alcohol extract through a piece of cloth. Filtration can be significantly accelerated by using suction on a suction filter with a water jet pump.
Instead of preparing such an extract, you can buy powdered pepsin at the pharmacy and dissolve it in 250 ml of water.
Finally, grate chicken egg white, hard-boiled (boil for 10 minutes), and mix it in a beaker with 100 ml of water, 0.5 ml of concentrated hydrochloric acid and a prepared extract containing pepsin, or with 50 ml of commercial pepsin solution.
Hydrochloric acid must be added because pepsin acts only in an acidic environment - at a pH of 1.4 to 2. The pH value of gastric juice, due to the presence of hydrochloric acid in it, ranges from 0.9 to 1.5.
Let the glass be kept for several hours at a temperature of approximately 40 °C in a warm place - at home near a stove or oven, or in a laboratory in a drying cabinet. During the first quarter of every hour, we will stir the contents of the glass with a glass rod.
After just 2 hours we will notice that the amount of protein has decreased significantly. After 6-8 hours, all the protein will dissolve and a small amount of white skin with a slight yellowish tint will form. In this case, egg white, which has a complex structure, is hydrolyzed by water and converted into a mixture of compounds of a simpler structure - egg white peptone. What a chemist can achieve only with the help of concentrated acids, we were able to achieve in our artificial stomach under extremely mild conditions.
The unpleasant sour smell of the contents of the glass is close to the smell of incompletely digested food. Now let’s conduct a few more test tube experiments on our own related to the study of food digestion. Some of them deserve a brief explanation.
The breakdown of starch can be carried out in a test tube using saliva to liquid starch paste (37 °C, 30 minutes -1 hour). The resulting sugar is detected using Fehling's reagent. The same result can be obtained by heating 10 ml of starch paste with 5 ml of cow pancreas extract for 15 minutes in a water bath at 40 0C. The extract is prepared by rubbing the pancreas with a small amount propanetriol(glycerol).
This paste from the pancreas is also useful for studying the digestion of fats. For this purpose, add a 0.5% solution of soda (sodium carbonate) to a test tube half filled with whole milk until a red color with phenolphthalein appears. If you now add the gruel from the pancreas and heat it in a water bath to 40 ° C, the red color will disappear again. In this case, free fatty acids are formed from the fat of natural milk.
In conclusion, using rennet (rennet starter) or a strip of purified veal stomach mucosa, we can isolate the protein from raw milk casein. Chemists and biologists have discovered hundreds of interesting reactions that reveal a wide variety of substances found in the body. We'll look at some of these reactions. Cholesterol present in all organs, but most of all it is found in the brain, bile and ovaries. This important substance belongs to the group of polycyclic alcohols sterols, to which some sex hormones also belong. In addition, cholesterol is very close in structure to ergosterol, an intermediate substance from which vitamin D is obtained.
Cholesterol was originally found in gallstones and is therefore called “hard bile.” Later they were opened sterols of plant origin. Previously, cholesterol was found only in vertebrates, including humans. Therefore, its presence was considered a sign of a high level of development of living beings. However, GDR scientists were the first to discover cholesterol in bacteria.
Extract cholesterol from egg yolk with diethyl ether.
Then mix 0.5 ml of glacial acetic acid and 2 ml of concentrated sulfuric acid, heat for 1 minute and finally cool thoroughly. In a test tube, under a layer of egg yolk extract, carefully introduce a cooled mixture of acids - so that the contents do not mix. Let's leave the test tube for a while. After some time, several zones with different colors form in it.
Above the colorless acid layer we will see a red layer, and above it a blue layer. Even higher is a yellowish hood, and above it is a green layer. Readers will likely enjoy this beautiful play of colors. The reaction carried out is called the Lieberman reaction.
(Cholesterol is often determined using the beautiful Liebermann-Burkhard color reaction. To a solution of 5 mg of cholesterol in 2 ml of chloroform add 1 ml of acetic anhydride and 1 drop of concentrated sulfuric acid. When shaken, a pink color is formed, quickly changing to red, then blue and finally green - Translator's note).
Cholesterol can also be detected using another color reaction - the Salkovsky method. In this case, a few milliliters of the extract are mixed with an equal volume of dilute (approximately 10%) sulfuric acid. Acid layer fluoresces green, and the hood acquires a color from yellow to intense red.
(Both reactions - Lieberman and Salkovsky - may not work the first time if the ratios of the reagents are poorly chosen. Salkovsky's test is easier. If, for example, an extract is obtained by diluting 6 ml of yolk to 50 ml with ether, then it is best to add 1 ml of such an extract 2 ml of 10% sulfuric acid. - Transl.).
A beautiful color reaction is also obtained when bile pigment is detected in the urine. To do this, nitric acid is carefully added dropwise to a test tube half filled with urine along the wall. As a result, a green zone is formed at the bottom of the test tube, which turns into blue, purple and red.
The presence of bile pigment in the urine indicates a human disease. In general, when recognizing some diseases, reliable conclusions can be obtained through the analysis of urine and feces - the end products of metabolism in a living organism. These are waste products that the body does not need and therefore must be excluded from metabolism. However, we know that these substances do not disappear uselessly, but as a necessary link are included in the cycle of substances in nature.