Ministry of Education and Science Russian Federation

Federal Agency for Education

South Ural State University

Department of Commodity Science and Expertise of Consumer Goods

COURSE WORK

in the discipline "Commodity research, examination and standardization"

on the topic "Study of the elements of the chemical composition of food products (on the example of proteins)"

Completed:

Abidullina Eleonora

Group Kom-234

Checked by: Cherkasova Elvira Vyacheslavovna

Chelyabinsk

Introduction……………………………………………………………………….
1. Literature review
1.1. General concepts about proteins
1.1.1. The chemical nature of proteins……………………………….....
1.1.2. Classification of proteins………………………………………..
1.1.3. Properties of proteins……………………………………………….
1.2. The influence of proteins on the human body…………………………….
1.3. Changes in protein content during technological processing……………………………………………………………………...
1.4. Changes in protein content during storage…………………….
2. Practical part
2.1. Characteristics of quantitative methods for determining the content of proteins……………………………………………………………….
2.2. Characteristics of qualitative methods for determining the content of proteins…………………………………………………………………………….
3. Experimental part
3.1. Rationale for the choice of the object of study……………………….
3.2. Analysis of the results of own research…………………..
Conclusion…………………………………………………………………………...
Bibliography……………………………………………………………
Application……………………………………………………………………

Introduction

Proteins are the main plastic material for the growth, development and renewal of the body. They are the main structural elements of all tissues, are part of the liquid environment of the body. Food proteins are spent on the construction of red blood cells and hemoglobin, enzymes and hormones, and are actively involved in the development of protective factors - antibodies.

With insufficient protein content in the diet, severe disorders (hypotrophy, anemia, etc.) can develop in the body, more often acute respiratory diseases occur, which take a protracted course. However, too much protein can be detrimental to health. With prolonged use of high-protein foods, the function of the kidneys and liver suffers, nervous excitability increases, allergic reactions often appear, intoxications are possible due to incomplete breakdown and oxidation of proteins with the formation of toxic substances.

The most typical reason for the imbalance of diets is insufficient consumption of the main sources of complete animal protein (meat, fish, milk, eggs), vegetable oils, fresh vegetables and fruits.

Therefore, the study of the elements of the chemical composition of food products, and in particular proteins, is not only important, but also a very topical issue today.

The purpose of the work is to identify the importance of proteins for the human body and the main sources of proteins.

In the course of this work, the following main tasks are set: the study of the chemical composition of proteins, their effect on the human body, the problems of processing and storing proteins, their properties, the study of methods for studying the protein content in food products, checking whether the actual protein content in the product is normalized.

1. Literature review

1.1. General concepts about proteins

1.1.1. Chemical nature of proteins

Peptide bond

Proteins are irregular polymers built from amino acid residues, the general formula of which in an aqueous solution at pH values close to neutral can be written as NH3 + CHRCOO - . Residues of amino acids in proteins are interconnected by an amide bond between amino and carboxyl groups. A peptide bond between two amino acid residues is usually called a peptide bond, and polymers built from amino acid residues connected peptide bonds are called polypeptides. A protein as a biologically significant structure can be either a single polypeptide or several polypeptides that form a single complex as a result of non-covalent interactions.

Elemental composition of proteins

Studying the chemical composition of proteins, it is necessary to find out, firstly, what chemical elements they consist of, and secondly, the structure of their monomers. To answer the first question, the quantitative and qualitative composition of the chemical elements of the protein is determined. Chemical analysis showed the presence in all proteins of carbon (50-55%), oxygen (21-23%), nitrogen (15-17%), hydrogen (6-7%), sulfur (0.3-2.5%) . Phosphorus, iodine, iron, copper and some other macro- and microelements were also found in the composition of individual proteins, in various, often very small amounts.

The content of the main chemical elements in proteins can vary, with the exception of nitrogen, the concentration of which is characterized by the greatest constancy and averages 16%. In addition, the content of nitrogen in other organic substances is low. In accordance with this, it was proposed to determine the amount of protein by its constituent nitrogen. Knowing that 1 g of nitrogen is contained in 6.25 g of protein, the found amount of nitrogen is multiplied by a factor of 6.25 and the amount of protein is obtained.

To determine the chemical nature of protein monomers, it is necessary to solve two problems: to separate the protein into monomers and to find out their chemical composition. The breakdown of a protein into its component parts is achieved by hydrolysis - prolonged boiling of the protein with strong mineral acids (acid hydrolysis) or bases (alkaline hydrolysis). Boiling at 110°C with HCl for 24 hours is most commonly used. At the next stage, the substances that make up the hydrolyzate are separated. For this purpose, various methods are used, most often chromatography (for more details, see the chapter “Research methods ...”). Amino acids are the main part of the separated hydrolysates.

Amino acids

Currently, up to 200 different amino acids have been found in various objects of wildlife. In the human body, for example, there are about 60 of them. However, proteins contain only 20 amino acids, sometimes called natural ones.

Amino acids are organic acids in which the hydrogen atom of the carbon atom is replaced by an amino group - NH2. Therefore, by chemical nature, these are amino acids with the general formula:

From this formula, it can be seen that the composition of all amino acids includes the following general groups: - CH2, - NH2, - COOH. Side chains (radicals - R) of amino acids differ. The chemical nature of radicals is diverse: from a hydrogen atom to cyclic compounds. It is the radicals that determine the structural and functional features of amino acids.

All amino acids, except for the simplest aminoacetic to-you glycine (NH3 + CH2COO-) have a chiral Ca atom and can exist in the form of two enantiomers (optical isomers): L-isomer and D-isomer.

Proteins are built from the twenty basic amino acids, but the rest, quite diverse amino acids, are formed from these 20 amino acid residues already in the composition of the protein molecule. Among these transformations, first of all, the formation of disulfide bridges during the oxidation of two cysteine residues in the composition of already formed peptide chains should be noted. As a result, a diaminodicarboxylic acid cystine residue is formed from two cysteine residues. In this case, cross-linking occurs either within one polypeptide chain or between two different chains. As a small protein that has two polypeptide chains connected by disulfide bridges, as well as crosslinks within one of the polypeptide chains:

GIVEQCCASVCSLYQLENYCN

FVNQHLCGSHLVEALYLVCGERGFFYTPKA

Amino acids in an aqueous solution are in an ionized state due to the dissociation of amino and carboxyl groups that make up the radicals. In other words, they are amphoteric compounds and can exist either as acids (proton donors) or as bases (donor acceptors).

All amino acids, depending on the structure, are divided into several groups:

Acyclic. Monoamino monocarboxylic amino acids have one amino and one carboxyl group in their composition, they are neutral in aqueous solution. Some of them have common structural features, which allows them to be considered together:

1. Glycine and alanine. Glycine (glycocol or aminoacetic acid) is optically inactive - it is the only amino acid that does not have enantiomers. Glycine is involved in the formation of nucleic and bile to - t, heme, is necessary for the neutralization of toxic products in the liver. Alanine is used by the body in various carbohydrate and energy metabolism processes. Its isomer b-alanine is an integral part of the vitamin pantothenic to-you, coenzyme A (CoA), extractive substances of muscles.

2. Serine and threonine. They belong to the group of hydrohydroxy acids, because. have a hydroxyl group. Serine is part of various enzymes, the main protein of milk - casein, as well as many lipoproteins. Threonine is involved in protein biosynthesis, being an essential amino acid.

3. Cysteine and methionine. Amino acids containing a sulfur atom. The value of cysteine is determined by the presence of a sulfhydryl (-SH) group in its composition, which gives it the ability to easily oxidize and protect the body from substances with a high oxidizing ability (in case of radiation injury, phosphorus poisoning). Methionine is characterized by the presence of an easily mobile methyl group, which is used for the synthesis of important compounds in the body (choline, creatine, thymine, adrenaline, etc.)

4. Valine, leucine and isoleucine. They are branched amino acids that are actively involved in metabolism and are not synthesized in the body.

Monoaminodicarboxylic amino acids have one amino and two carboxyl groups and give an acidic reaction in aqueous solution. These include aspartic and glutamine to-you, asparagine and glutamine. They are part of the inhibitory mediators of the nervous system.

Diaminomonocarboxylic amino acids in aqueous solution have an alkaline reaction due to the presence of two amine groups. Related to them, lysine is necessary for the synthesis of histones and also in a number of enzymes. Arginine is involved in the synthesis of urea, creatine.

Cyclic. These amino acids have an aromatic or heterocyclic nucleus in their composition and, as a rule, are not synthesized in the human body and must be supplied with food. They are actively involved in a variety of metabolic processes. Thus, phenylalanine serves as the main source for the synthesis of tyrosine, a precursor of a number of biologically important substances: hormones (thyroxine, adrenaline), and some pigments. Tryptophan, in addition to participating in protein synthesis, is a component of vitamin PP, serotonin, tryptamine, and a number of pigments. Histidine is necessary for the synthesis of proteins, is a precursor of histamine, which affects blood pressure and secretion of gastric juice.

1.1.2. Protein classification

All proteins, depending on the structure, are divided into simple - proteins, consisting only of amino acids, and complex - proteins that have a non-protein proteistic group.

Proteins

Proteins are simple proteins, consisting only of the protein part. They are widely distributed in animals and flora. These include albumins and globulins, which are found in almost all animal and plant cells, biological fluids and perform important biological functions. Albumins are involved in maintaining the osmotic pressure of the blood (create oncotic pressure), transport various substances with the blood. Globulins are part of the enzymes that form the basis of immunoglobulins that act as antibodies. In the blood serum, there is a constant ratio between these two components - the albumin-globulin coefficient (A / G), equal to 1.7 - 2.3 and having an important diagnostic value.

Other representatives of proteins are protamines and histones - basic proteins containing a lot of lysine and arginine. These proteins are part of the nucleoproteins. Another major protein, collagen, forms the extracellular substance of the connective tissue and is found in the skin, cartilage, and other tissues.

Proteids

Proteins are complex proteins consisting of protein and non-protein parts. The name of the protein is determined by the name of its prosthetic group. So, nucleic acids are a non-protein part of nucleoproteins, phosphoric acid is part of phosphoproteins, carbohydrates are glycoproteins, and lipids are lipoproteins.

Nucleoproteins. They are important, because their non-protein part is represented by DNA and RNA. The prosthetic group is represented mainly by histones and protamines. Such complexes of DNA with histones are found in spermatozoa, and with histones - in somatic cells, where the DNA molecule is “wound” around histone molecules. Nucleoproteins by their nature are extracellular viruses - these are complexes of viral nucleic acid and a protein shell - capsid.

Chromoproteins. They are complex proteins, the prosthetic group of which is represented by colored compounds. Chromoproteins include hemoglobin, myoglobin (muscle protein), a number of enzymes (catalase, peroxidase, cytochromes), as well as chlorophyll.

Hemoglobin (Hb) consists of a globin protein and a non-protein part of the heme, which includes an Fe(II) atom connected to protoporphyrin. The hemoglobin molecule consists of 4 subunits: two a and two b and, accordingly, contains four polypeptide chains of two varieties. Each a-chain contains 141, and b-chain - 146 amino acid residues.

myoglobin. A chromoprotein found in muscles. It consists of only one chain, analogous to the subunit of hemoglobin. Myoglobin is the respiratory pigment in muscle tissue. It binds to oxygen much easier than hemoglobin, but it is more difficult to release it. Myoglobin creates oxygen reserves in the muscles, where its amount can reach 14% of the body's total oxygen. This is important, especially for the work of the muscles of the heart. A high content of myoglobin was found in marine mammals (seal, walrus), which allows them to stay under water for a long time.

Glycoproteins. They are complex proteins whose prosthetic group is formed by derivatives of carbohydrates (amino sugars, hexuronic acids). Glycoproteins are part of cell membranes. Thus, the lung walls of bacteria are built from peptidoglycans, which are derivatives of linear polysaccharides bearing peptide fragments covalently linked to them. These fragments carry out crosslinking of polysaccharide chains with the formation of a mechanically strong network structure. For example, the cell wall of E. coli is built from polysaccharide chains formed by N-acetylglucosamine residues linked by b-(1®4) bonds, with each second residue carrying a fragment attached to it at the C3 atom, formed by lactic acid residues linked by amide bonds, L -alanine, D-glutamate (via g-carboxyl), mesodiaminonimelinate and D-alanine.

Glycoproteins are involved in the transport of various substances, in the processes of blood coagulation, immunity, are components of mucus and secretions of the gastrointestinal tract. In arctic fish, glycoproteins play the role of antifreezes - substances that prevent the formation of ice crystals inside their body.

Phosphoproteins. They have phosphoric acid as a non-protein component. Representatives of these proteins are milk caseinogen, vitellin (egg yolk protein), ichthulin (fish roe protein). This localization of phosphoproteins indicates their importance for the developing organism. In adult forms, these proteins are present in bone and nervous tissues.

Lipoproteins. Complex proteins, the prosthetic group of which is formed by lipids. By structure, these are small (150-200 nm) spherical particles, the outer shell of which is formed by proteins (which allows them to move through the blood), and the inner part - by lipids and their derivatives. The main function of lipoproteins is the transport of lipids through the blood. Depending on the amount of protein and lipids, lipoproteins are divided into chylomicrons, low-density lipoproteins (LDL) and high density(HDL), which are sometimes referred to as a- and b-lipoproteins.

Chylomicrons are the largest of lipoproteins and contain up to 98-99% lipids and only 1-2% protein. They are formed in the intestinal mucosa and ensure the transport of lipids from the intestine to the lymph, and then to the blood.

1.1.3. Protein Properties

Proteins have a high molecular weight, some are soluble in water, capable of swelling, are characterized by optical activity, mobility in an electric field, and some other properties.

Proteins are active enter into chemical reactions . This property is due to the fact that the amino acids that make up proteins contain different functional groups that can react with other substances. It is important that such interactions also occur inside the protein molecule, resulting in the formation of peptide, hydrogen disulfide, and other types of bonds. Various compounds and ions can attach to the radicals of amino acids, and hence proteins, which ensures their transport through the blood.

Proteins are macromolecular compounds. These are polymers consisting of hundreds and thousands of amino acid residues - monomers. Accordingly, the molecular weight of proteins is in the range of 10,000 - 1,000,000. So, ribonuclease (an enzyme that breaks down RNA) contains 124 amino acid residues and its molecular weight is approximately 14,000. Myoglobin (muscle protein), consisting of 153 amino acid residues , has a molecular weight of 17,000, and hemoglobin - 64,500 (574 amino acid residues). The molecular weights of other proteins are higher: g-globulin (forms antibodies) consists of 1250 amino acids and has a molecular weight of about 150,000, while the molecular weight of the glutamate dehydrogenase enzyme exceeds 1,000,000.

The most important property of proteins is their ability to exhibit both acidic and basic properties, that is, to act as amphoteric electrolytes. This is ensured by various dissociating groups that make up the amino acid radicals. For example, the acidic properties of the protein are imparted by the carboxyl groups of the aspartic glutamic amino acid, while the alkaline properties are imparted by the radicals of arginine, lysine, and histidine. The more dicarboxylic amino acids a protein contains, the stronger its acidic properties are and vice versa.

The same groupings also have electric charges that form total charge of a protein molecule. In proteins where aspartic and glutamine amino acids predominate, the charge of the protein will be negative; an excess of basic amino acids gives a positive charge to the protein molecule. As a result, in an electric field, proteins will move towards the cathode or anode, depending on the magnitude of their total charge. So, in an alkaline environment (pH 7 - 14), the protein donates a proton and becomes negatively charged, while in an acidic environment (pH 1 - 7), the dissociation of acid groups is suppressed and the protein becomes a cation.

Thus, the factor that determines the behavior of a protein as a cation or anion is the reaction of the medium, which is determined by the concentration of hydrogen ions and is expressed by the pH value. However, at certain pH values, the number of positive and negative charges equalizes and the molecule becomes electrically neutral, i.e. it will not move in an electric field. This pH value of the medium is defined as the isoelectric point of proteins. In this case, the protein is in the least stable state and, with slight changes in pH to the acidic or alkaline side, it easily precipitates. For most natural proteins, the isoelectric point is in a slightly acidic environment (pH 4.8 - 5.4), which indicates the predominance of dicarboxylic amino acids in their composition.

The ability of proteins is important adsorb on its surface, some substances and ions (hormones, vitamins, iron, copper), which are either poorly soluble in water or are toxic (bilirubin, free fatty acids). Proteins transport them through the blood to places of further transformations or neutralization.

Aqueous solutions of proteins have their own characteristics. First, proteins have a high affinity for water, i.e. They hydrophilic. This means that protein molecules, like charged particles, attract water dipoles, which are located around the protein molecule and form a water or hydrate shell. This shell protects the protein molecules from sticking together and precipitating. The size of the hydration shell depends on the structure of the protein. For example, albumins bind more easily to water molecules and have a relatively large water shell, while globulins and fibrinogen attach water worse and have a smaller hydration shell. Thus, the stability of an aqueous solution of a protein is determined by two factors: the presence of a charge on the protein molecule and the water shell around it. When these factors are removed, the protein precipitates. This process can be reversible and irreversible.

The size of protein molecules lies in the range of 1 µm to 1 nm and, therefore, they are colloidal particles which form colloidal solutions in water. These solutions are characterized by high viscosity, the ability to scatter visible light rays, and do not pass through semi-permeable membranes.

1.2. The effect of proteins on the human body

The functions of proteins in the body are diverse. They are largely due to the complexity and diversity of the forms and composition of the proteins themselves. Protein is found in many foods, but the main sources are eggs, milk, and meat (Table 1).

Table 1 - Products containing proteins

Proteins are an indispensable building material. One of the most important functions of protein molecules is plastic. All cell membranes contain protein, the role of which is diverse here. The amount of protein in the membranes is more than half of the mass.

Many proteins have contractile function. These are, first of all, the proteins actin and myosin, which are part of the muscle fibers of higher organisms. Muscle fibers - myofibrils - are long thin filaments consisting of parallel thinner muscle filaments surrounded by intracellular fluid. It contains dissolved adenosine triphosphoric acid (ATP), which is necessary for the implementation of contraction, glycogen - a nutrient, inorganic salts and many other substances, in particular calcium.

The role of proteins in transport of substances in organism. Having different functional groups and a complex structure of the macromolecule, proteins bind and carry many compounds with the blood stream. This is, first of all, hemoglobin, which carries oxygen from the lungs to the cells. In muscles, another transport protein, myoglobin, takes over this function.

Another function of protein is spare. The storage proteins include ferritin - iron, ovalbumin - egg protein, casein - milk protein, zein - corn seed protein.

Regulatory function perform hormone proteins. Hormones are biologically active substances that affect metabolism. Many hormones are proteins, polypeptides, or individual amino acids. One of the best known protein hormones is insulin. This simple protein consists of only amino acids. The functional role of insulin is multifaceted. It reduces blood sugar, promotes the synthesis of glycogen in the liver and muscles, increases the formation of fats from carbohydrates, affects the metabolism of phosphorus, enriches cells with potassium.

The protein hormones of the pituitary gland, an endocrine gland associated with one of the parts of the brain, have a regulatory function. It secretes growth hormone, in the absence of which dwarfism develops. This hormone is a protein with a molecular weight of 27,000 to 46,000.

Vasopressin is one of the important and chemically interesting hormones. It inhibits urination and raises blood pressure. Vasopressin is a cyclic octapeptide.

The regulatory function is also performed by the proteins contained in the thyroid gland - thyroglobulins, the molecular weight of which is about 600,000. These proteins contain iodine in their composition. With the underdevelopment of the gland, metabolism is disturbed.

Another function of proteins is protective. On its basis, a branch of science called immunology was created.

Recently, proteins with receptor function. There are receptors for sound, taste, light, etc.

Mention should also be made of the existence of protein substances that inhibit the action of enzymes. Such proteins have inhibitory functions. When interacting with these proteins, the enzyme forms a complex and loses its activity, completely or partially. Many enzyme inhibitor proteins have been isolated in pure form and have been well studied. Their molecular weights vary widely; often they refer to complex proteins - glycoproteins, the second component of which is carbohydrate.

If proteins are classified only according to their functions, then such a systematization could not be considered complete, since new studies provide many facts that make it possible to distinguish new groups of proteins with new functions. Among them are unique substances - neuropeptides(responsible for the most important life processes: sleep, memory, pain, fear, anxiety).

1.3. Change in protein content during processing

Under the influence of processing, the proteins, fats, carbohydrates, vitamins, minerals and taste substances contained in the products change, which affects the digestibility, nutritional value, weight, taste, smell, color of the products used.

Squirrels coagulate(collapse) at temperatures above 70 ° C, lose their ability to swell, due to which, after heat treatment, the mass of meat and fish decreases.

Products such as meat, fish, eggs cannot be over-steamed, as this reduces their digestibility due to changes in protein molecules: collagen passes into glutin, softening the tissues.

Protein denaturation - this is a complex process in which, under the influence of external factors (temperature, mechanical action, the action of acids, alkalis, ultrasound, etc.), a change occurs in the secondary, tertiary and quaternary structures of the protein macromolecule, i.e. native (natural) spatial structure. The primary structure and, consequently, the chemical composition of the protein do not change. During cooking, denaturation of proteins is most often caused by heating. This process in globular and fibrillar proteins occurs differently. In globular proteins, when heated, the thermal movement of the polypeptide chains inside the globule increases, the hydrogen bonds that held them in a certain position break and the polypeptide chain unfolds and then folds in a new way. In this case, the polar (charged) hydrophilic groups located on the surface of the globule and providing its charge and stability move inside the globule, and reactive hydrophobic groups (disulfide, sulfhydryl, etc.) that are not able to retain water come to its surface. Denaturation is accompanied by changes in the most important properties of the protein: loss of individual properties (for example, a change in the color of meat when it is heated due to denaturation of myoglobin); loss of biological activity (for example, potatoes, mushrooms, apples and a number of other plant products contain enzymes that cause them to darken; when denatured, enzyme proteins lose their activity); increased attack by digestive enzymes (as a rule, heat-treated foods containing proteins are digested more completely and more easily); loss of ability to hydration (dissolution, swelling); loss of stability of protein globules, which is accompanied by their aggregation (folding, or coagulation, of the protein).

Aggregation- this is the interaction of denatured protein molecules, which is accompanied by the formation of larger particles. Outwardly, this is expressed differently depending on the concentration and colloidal state of proteins in solution. So, in low-concentration solutions (up to 1%), the coagulated protein forms flakes (foam on the surface of the broths). In more concentrated protein solutions (for example, egg whites), denaturation forms a continuous gel that retains all the water contained in the colloidal system.

Proteins, which are more or less watered gels (muscle proteins of meat, poultry, fish; proteins of cereals, legumes, flour after hydration, etc.), are compacted during denaturation, while their dehydration occurs with the separation of liquid into environment. The protein gel subjected to heating, as a rule, has a smaller volume, mass, greater mechanical strength and elasticity compared to the original gel of native (natural) proteins. The rate of aggregation of protein sols depends on the pH of the medium. Proteins are less stable near the isoelectric point.

Protein degradation. With prolonged heat treatment, proteins undergo deeper changes associated with the destruction of their macromolecules. At the first stage of changes, functional groups can be split off from protein molecules with the formation of such volatile compounds as ammonia, hydrogen sulfide, hydrogen phosphide, carbon dioxide, etc. Accumulating in the product, they participate in the formation of the taste and aroma of the finished product. During further hydrothermal treatment, proteins are hydrolyzed, while the primary (peptide) bond is broken with the formation of soluble nitrogenous substances of a non-protein nature (for example, the transition of collagen to glutin). The destruction of proteins can be a purposeful culinary treatment that contributes to the intensification of the technological process (the use of enzyme preparations to soften meat, weaken the gluten of the dough, obtain protein hydrolysates, etc.).

Foaming. Proteins are widely used as foaming agents in the production of confectionery (biscuit dough, protein-whipped dough), whipping cream, sour cream, eggs, etc. The stability of the foam depends on the nature of the protein, its concentration, and temperature.

1.4. Change in protein content during storage

During refrigerated storage and freezing of pure protein solutions, aggregation of protein molecules occurs. This process is usually preceded by protein denaturation. The data on the determination of the molecular weight, sedimentation constants, and diffusion rate of the protein particles formed during freezing and refrigerated storage indicate structural changes in this protein. According to some reports, in the process of refrigeration of fish, not only a decrease, but also an increase in protein solubility is possible. Thus, in the Baltic herring, protein solubility in the muscle tissue of frozen fish increased even during rigor mortis.

During the storage of meat, favorable conditions are created for the secondary interaction of lipids with proteins. This is because native proteins are rapidly destroyed during storage, the structural order of cell membranes is lost, and the spatial differentiation of the chemical components of cells is disturbed. In this case, both polar and neutral fats, as well as the products of their decomposition and oxidation, interact with proteins.

Interactions between lipids and proteins occur in foods and when stored frozen. The results of the study of meat and fish showed that the solubility of various protein fractions of muscle tissue, the content of sulfhydryl and disulfide groups in proteins, as well as the activity of a number of enzymes changed in waves.

The qualitative composition of amino acids during storage of the product is determined by many factors and depends on the activity of various enzymes in muscle tissue and individual transformations of amino acids, on the amino acid composition of degradable proteins, their quantity and degree of attack by enzymes, changes in pH, temperature and other interrelated factors.

2. Practical part

2.1. Characteristics of quantitative methods for determining the content of proteins

Methods for the quantitative determination of the protein fraction are based on the determination of the amount of total nitrogen. The most common is the determination by the Kjeldahl method, which allows nitrogen in the form of ammonia to be isolated only from amines and their derivatives, but some nitrogen-containing compounds under these conditions, along with ammonia, also form molecular nitrogen, which leads to underestimated data.

Kjeldahl method.

The Kjeldahl method is relatively simple, well reproducible, standardized and has several modifications.

The method includes three main steps: digestion, distillation and titration.

The method is based on the oxidation of organic substances to CO2, H2O, NH3 when heated with strong sulfuric acid. Ammonia reacts with excess H2SO4 conc and forms ammonium sulfate with it.

R-CHNH2COOH + H2SO4 → CO2 + H2O + NH3;

2NH3 + H2SO4 → (NH4)2SO4.

After the burning of the sample is completed, the excess acid is neutralized with alkali, and the ammonia bound in the form of ammonium sulfate is displaced by an excess of alkali.

(NH4)2SO4 + 2NaOH → Na2SO4 + 2NH4OH.

After burning the sample, nitrogen is determined colorimetrically by the optical density of colored solutions obtained by interaction with Nessler's reagent.

Ammonia and ammonium salts are able to form with Nessler's reagent (double salt of mercury iodide and potassium iodide, dissolved in caustic potassium). Mercurammonium iodide is a yellow-brown substance.

NH4OH + 2(HgI2KI) + 3KOH = OHg2NH2I + 7KI + 3H2O.

Method of formal titration.

Another quantitative method for determining protein content is the formal titration method, which is commonly used in dairies.

The method can only be used for the analysis of fresh raw milk with an acidity not higher than 22 ºT. Canned samples cannot be controlled by this method.

The method consists in blocking the NH2 groups of the product proteins with the introduced formalin with the formation of methyl derivatives of proteins, the carboxyl groups of which can be neutralized with alkali:

HOOC – R – NH2 + 2HCHO → HCHO – R – N(CH2OH)2;

HCHO – R – N(CH2OH)2 + NaOH → NaOH – R – N(CH2OH)2 + H2O.

The amount of alkali used for titration of acidic carboxyl groups is recalculated for the mass fraction of proteins.

The study is carried out according to the following scheme:

In a flask with a capacity of 100 cm³, 20 cm³ of the test product, 10-12 drops of 1% phenolphthalein solution are measured and titrated with 0.1 N sodium hydroxide solution until a pink color corresponding to the color of the standard appears. Then, 4 ml of neutralized 40% formalin are added with an automatic measuring device and titrated again with 0.1 N sodium hydroxide solution until the color of the standard is obtained. The amount of alkali used for the second titration (during the first titration, it is spent on neutralizing substances that cause the acidity of the product), is multiplied by a factor of 0.959 and the mass fraction of proteins in the product is obtained in percent.

A table can be used to convert the amount of sodium hydroxide solution to percent protein.

Consumption of 0.1N NaOH solution, ml	Mass fraction of protein, %	Consumption of 0.1N NaOH solution, ml	Mass fraction of protein, %

Table 2 - Dependence of the mass fraction of proteins on the volume of alkali solution used for titration of samples in the presence of formalin

2.2. Characteristics of qualitative methods for determining the content of proteins

Protein precipitation reactions

Proteins in solution and, accordingly, in the body are preserved in their native state due to stability factors, which include the charge of the protein molecule and the hydration shell around it. Removal of these factors leads to gluing of protein molecules and their precipitation. Protein precipitation can be reversible or irreversible, depending on the reagents and reaction conditions. In laboratory practice, precipitation reactions are used to isolate the albumin and globulin fractions of proteins, quantify their stability, detect proteins in biological fluids and release them in order to obtain a protein-free solution.

reversible precipitation.

Under the influence of precipitation factors, proteins precipitate, but after the termination of the action (removal) of these factors, the proteins again become soluble and acquire their native properties. One type of reversible protein precipitation is salting out.

salting out. The albumin fraction of proteins precipitates with a saturated solution of ammonium sulfate, and the globulin fraction with a semi-saturated solution.

The essence of the reaction is the dehydration of protein molecules.

Definition progress. 30 drops of an undiluted sample are poured into a test tube and an equal amount of a saturated ammonium sulfate solution is added. Mix the contents of the tube. A semi-saturated solution of ammonium sulfate is obtained, while the globulin fraction precipitates, and the albumin fraction remains in solution. The latter is filtered off, then mixed with ammonium sulfate powder until the dissolution of the salt stops, and a precipitate forms - globulins.

Irreversible precipitation of proteins.

Irreversible precipitation of proteins is associated with profound disturbances in the structure of proteins (secondary and tertiary) and the loss of their native properties. Such changes in proteins can be caused by boiling, the action of concentrated solutions of mineral and organic acids, salts of heavy metals.

Precipitation at boiling. Proteins are thermolabile compounds and when heated above 50-60 degrees C, they are denatured. The essence of thermal denaturation is the destruction of the hydration shell, the breaking of the bonds stabilizing the protein globule, and the deployment of the protein molecule. The most complete and fastest precipitation occurs at the isoelectric point (when the charge of the molecule is zero), since the protein particles are the least stable in this case. Proteins with acidic properties precipitate in a slightly acidic environment, and proteins with basic properties - in a slightly alkaline one. In strongly acidic or strongly alkaline solutions, the protein denatured when heated does not precipitate, since its particles are recharged and carry a positive charge in the first case, and a negative charge in the second, which increases their stability in solution.

Definition progress. Add 10 drops of sample solution to 4 numbered tubes. Then the 1st tube is heated to boiling, while the solution becomes cloudy, but since the denatured protein particles carry a charge, they do not precipitate. This is due to the fact that egg white has acidic properties (its isoelectric point is 4.8) and is negatively charged in a neutral environment; 1 drop of 1% acetic acid solution is added to the second tube and heated to boiling. The protein precipitates, because. its solution approaches the isoelectric point and the protein loses its charge (one of the factors of protein stability in solution); add 1 drop of 10% acetic acid solution to the 3rd tube and heat to boiling. A precipitate is not formed, since in a strongly acidic medium the protein particles acquire a positive charge (one of the factors of protein stability in solution is preserved); 1 drop of NaOH solution is poured into the 4th tube, heated to a boil. No precipitate is formed, since the negative charge of the protein increases in an alkaline environment.

Precipitation with concentrated mineral acids. Concentrated acids (sulphuric, hydrochloric, nitric, etc.) cause protein denaturation by removing protein stability factors in solution (charge and hydration shell). However, with an excess of hydrochloric and sulfuric acid, the precipitated precipitate of denatured protein dissolves again. Apparently, this occurs as a result of the recharging of protein molecules and their partial hydrolysis. When an excess of nitric acid is added, the precipitate does not dissolve. This is why nitric acid is used to detect small amounts of protein in the urine in clinical studies.

Definition progress. 5 drops of concentrated sulfuric, hydrochloric and nitric acids are poured into three test tubes. Then, tilting the test tube at an angle of 45 degrees, the same volume of sample is carefully layered along the wall. At the boundary of the two layers, a protein precipitate appears in the form of a white ring. Shake the test tubes carefully, observe the dissolution of the protein in the test tubes with sulfuric and hydrochloric acids; no protein dissolution occurs in the test tube with nitric acid.

Precipitation by organic acids. Trichloroacetic acid precipitates only proteins, and sulfosalicylic acid precipitates not only proteins, but also high-molecular peptides.

Definition progress. Add 5 drops of the sample solution into two test tubes. 2 drops of sulfosalicylic acid are added to one of them, and 5 drops of trichloroacetic acid to the other. Protein precipitates in test tubes.

Precipitation of protein by salts of heavy metals. When interacting with salts of lead, copper, mercury, silver and other heavy metals, proteins are denatured and precipitated. However, with an excess of some salts, dissolution of the initially formed precipitate is observed. This is due to the accumulation of metal ions on the surface of the denatured protein and the appearance of a positive charge on the protein molecule.

Definition progress. Add 5 drops of sample to three test tubes. In the first add 1 drop of lead acetate, in the third - 1 drop of silver nitrate. Precipitation occurs in all test tubes. Then 10 drops of silver nitrate are added to the first test tube - there is no dissolution of the precipitate.

Color reactions for proteins

Color reactions are used to establish the protein nature of substances, identify proteins and determine their amino acid composition in various biological fluids.

Biuret reaction for a peptide bond. It is based on the ability of peptide bonds (-CO-NH-) to form colored complex compounds with copper sulfate in an alkaline medium, the color intensity of which depends on the length of the polypeptide chain. The protein solution gives a blue-violet color.

Definition progress. Add 5 drops of the sample solution, 3 drops of NaOH, 1 drop of Cu(OH)2 to the test tube, mix. The contents of the tube acquire a blue-violet color.

Ninhydrin reaction. The essence of the reaction is the formation of a blue-violet colored compound consisting of ninhydrin and amino acid hydrolysis products. This reaction is characteristic of amino groups in the -position present in natural amino acids and proteins.

Definition progress. Add 5 drops of the sample solution to the test tube, then 5 drops of ninhydrin, heat the mixture to a boil. A pink-violet color appears, turning blue-violet over time.

xantoprotein reaction. When concentrated nitric acid is added to the protein solution and heated, a yellow color appears, which turns orange in the presence of alkali. The essence of the reaction is the nitration of the benzene ring of cyclic amino acids with nitric acid to form nitro compounds that precipitate. The reaction reveals the presence of cyclic amino acids in the protein.

Definition progress. Add 3 drops of nitric acid to 5 drops of the sample solution and (carefully!) heat it up. A yellow precipitate appears. After cooling, add (preferably to the precipitate) 10 drops of NaOH, an orange color appears.

Adamkevich's reaction. The amino acid tryptophan in an acidic environment, interacting with acid aldehydes, forms red-violet condensation products.

Definition progress. 10 drops of acetic acid are added to one drop of the sample. Tilting the tube, carefully add 0.5 ml of sulfuric acid drop by drop along the wall so that the liquids do not mix. When the test tube is standing, a red-violet ring appears at the boundary of the liquids.

Fohl reaction. Amino acids containing sulfhydryl groups - SH, undergo alkaline hydrolysis with the formation of sodium sulfide Na2S. The latter, interacting with sodium plumbite (formed during the reaction between lead acetate and NaOH), forms a black or brown precipitate of lead sulfide PbS.

Definition progress. 5 drops of Fohl's reagent are added to 5 drops of the sample solution (an equal volume of 30% NaOH solution is added to a 5% lead acetate solution until the formed precipitate dissolves). and boil for 2-3 minutes. After settling 1-2 min. a black or brown precipitate appears.

3. Experimental part

3.1. Rationale for the choice of the object of study

I chose a chicken egg as the object of my research, as it is the main source of protein and many substances necessary for the human body, and the egg is included in the diet of every person.

Every year, about a billion, that is, thousands of billions of eggs are consumed in the world. Each person eats an average of 200 eggs a year. But eggs are not just an ordinary food item.

Eggs are not only a rich cocktail of nutrients, thanks to eggs your culinary imagination will have no limits. Germans love soft-boiled eggs for breakfast, Americans call their eggs "sunny side up", Spaniards are in love with their tortilla, Italians prefer fritata, a type of omelet, and gourmet Japanese dip raw meat into freshly laid eggs.

Perhaps no other product is used in the kitchen as often as a fresh egg. In pies, desserts, ice cream, gourmet sauces or everyone's favorite egg pasta - everywhere eggs give out their golden yolk color.

The highest quality of protein and the combination of various vital elements make eggs an extremely valuable food product. A large egg contains about nine grams of protein, eight grams of fat, the valuable element lecithin, as well as other minerals and vitamins - with the exception of vitamin C. Vitamins are hidden mainly in the yolk.

The most important vitamin is vitamin A and its provitamins - carotenoids. The so-called "eye vitamin" improves vision. It is needed in the retina of the eye both for the perception of light and darkness, and for color discrimination. Vitamin A also plays an important role in the immune system, promoting the growth and strengthening of hair, skin and teeth.

Chicken eggs are also a source of vitamin B, which is responsible for the smooth metabolism, cell respiration and the formation of red blood cells - erythrocytes.

One egg covers a person's daily requirement for folic acid by 26 percent. This especially unstable vitamin creates new cells and activates growth. Folic acid deficiency is one of the most common forms of vitamin deficiencies and often occurs together with iron deficiency. But eggs are also a real pantry of minerals: calcium, magnesia, potassium, iron, zinc, iodine and fluorine make the egg one of the most nutritious foods on Earth.

Eggs - good source protein, so in the table below, they are used as a basis for comparison with other products. Eggs are assigned a conditional value of 100.

The figures given are for eggs as a whole, not for whites or yolks. Nowadays, it is fashionable to eat only proteins, as they do not contain fat. In fact, the yolks contain no less protein. And the content of vitamins and minerals is even higher.

Based on the data in the table, we can conclude that eggs are the main source of protein.

Compared to other animal products, a chicken egg contains the most complete protein, which is almost completely absorbed by the body. Egg protein contains all the essential amino acids in the most optimal ratios.

Below is a table that shows the weight content of protein in some protein sources and the percentage of that protein that can actually be absorbed by our body.

Table 4 - weight content of protein in products,%

The table shows that, for example, eggs contain only 12% protein, but due to a certain composition of amino acids, 94% of the protein can be absorbed by the body. On the other hand, protein makes up 42% of soy flour, but the composition of this protein allows you to absorb only 61% of this amount.

Based on the data in the table, we can conclude that there is a huge difference between the total protein content of foods (what we read on the labels) and the amount that the body actually uses.

If you look at the list in the table, you can see that foods such as rice, beans, and potatoes contain much less healthy protein than eggs. The reason for this is the too low content of the necessary amino acids necessary for the complete absorption of protein by the body.

Accordingly, proteins that lack essential amino acids are called incomplete; those in which there are enough essential amino acids are complete, egg proteins are complete.

Thus, we can conclude that a chicken egg, compared to other animal products, contains the most complete protein, which is almost completely absorbed by the body. Egg protein contains all the essential amino acids in the most optimal ratios.

According to current Russian standards, marking should be on every egg produced at a poultry farm.

The first character in the label indicates the permissible shelf life:

The letter "D" - denotes a dietary egg, such eggs are sold within 7 days.

The letter "C" - denotes a table egg, which is sold within 25 days.

The second sign in the marking means the category of the egg, depending on its weight:

Selected egg (O) - from 65 to 74.9 g.

Characteristics of the object of study

As an object of study, I chose three samples - chicken eggs produced at Chelyabinsk Poultry Farm OJSC (CHEPFA).

Chelyabinsk Poultry Farm OJSC is one of the five largest poultry enterprises in Russia. The main activity is the production, processing, storage and sale of agricultural products. The main product of the poultry farm is a high-quality chicken egg obtained from the Lohmann LSL-classic cross-country bird. Today JSC Chelyabinsk Poultry Farm unites five structural subdivisions: Chelyabinsk Poultry Farm, Yemanzhelinsky Breeding Farm, Petropavlovsk Grain Complex, Yemanzhelinsky Grain Reception Center and Kurochkino Sanatorium.

Sample No. 1 - dietary egg of the first category (D1), produced on March 26, 2009, having a mass of 62 grams.

Sample No. 2 - table egg of the first category (C1), produced on March 26, 2009, having a mass of 59 grams.

Sample No. 3 is a table egg of choice (CO), produced on March 26, 2009, having a mass of 68 grams.

Method for estimating protein content

As part of the work, the Kjeldahl-Golub micromethod was used as a method for assessing the protein content in the product.

The study is carried out according to the following scheme:

A weighed portion of the test product in a volume of 0.04 g, taken with an accuracy of ±0.0001, is placed in a test tube. Then 2 ml of H2SO4 (specific gravity 1.84) and 1...2 drops of H2O2 (33%) are sequentially introduced. Mineralization is carried out by heating the test tube in a water bath at a temperature of 85 degrees.

In this case, easily oxidized substances are completely oxidized within 1–2 minutes, and the discolored liquid remains colorless upon further heating.

At the end of oxidation, the contents of the test tube are transferred quantitatively into a 100 ml volumetric flask up to the mark. After mixing the contents of the flask well, take a sample of 10 ml and accurately titrate with 0.5 N NaOH against phenolphthalein to determine the amount of alkali needed for neutralization.

After that, a sample of the same solution in 10 ml is taken and transferred to another 100 ml volumetric flask, a prescribed amount of 0.5 N NaOH is added to neutralize the acid. Then make up to the mark with water and shake well. This liquid is used to prepare colored solutions.

Preparation of colored solutions. For this, working and standard solutions are prepared in two volumetric flasks with a capacity of 100 ml. 10 ml of the test solution is poured into one, both flasks are topped up three-quarters with water, after which 4 ml of Nessler's solution are added and brought to the mark.

Then determine the optical density of the obtained colored solutions.

Based on the analysis data, the protein content (%) is calculated using the formula:

where 0.002 is the amount of mg of nitrogen in 1 ml of the standard working solution;

Dm is the optical density of the working solution;

Dm is the optical density of the standard solution;

m is the weight of the weighed portion of the test substance, g;

K - conversion factor of nitrogen to protein, equal to 6.25 for products of animal origin; for products of plant origin 5.7.

3.2. Analysis of the results of our own research

Figure 1 - Protein content in the studied samples

Table 5 - The amount of protein content in the studied samples

Most of the protein is found in the dietary egg of the first category (D1) (Sample No. 1). This is because the diet egg is the freshest egg laid no more than a week ago. According to studies, microbiological processes continue to occur in the egg for a week, i.e. it lives. During a week of storage, the qualitative and quantitative composition of protein and amino acids in eggs does not have time to change much. But in accordance with the literature data, the egg white of a dietary egg protein should contain about 19% protein, and about 18% in the yolk, and the study revealed that the protein content in the protein is 18.7%, and in the yolk 17.6% . It can be concluded that the deviations in the protein content are small, but still there, due to improper storage of the egg.

The selected table egg (CO) (Sample No. 3) contains less protein than a dietary egg, which is explained by the shelf life of the egg. The egg must be stored in a cool, but not too dry place; the best temperature is 0 - +5 °С. If you maintain optimal humidity and carbon dioxide content in it, eggs can be stored for up to 9 months. But at the same time, denaturation and aggregation of the protein in the egg occurs. In accordance with the literature data, the egg white of a table egg should contain about 17% protein, and about 16% in the yolk, and the study revealed that the protein content in the protein is 16.5%, and in the yolk 15.7%. It can be concluded that the deviations in the protein content are small, but still exist, which is explained by the fact that all the necessary conditions are not met during storage.

In the table egg of the first category (C1) (Orazets No. 2), the protein content does not differ much from the protein content in the table egg, which is explained by the fact that the table egg of the first category differs from the table egg only in weight. In the protein of Sample No. 2, the protein content is 16.5%, and in the yolk 15.7%, which corresponds to the literature data, but with some deviations.

In the course of this work, it was revealed that proteins are organic substances of animal or plant origin that provide support for the cellular structure of the human body. Their main element is numerous amino acids.

Amino acids are found in all products of plant and animal origin, but their content and ratio in products is different.

The object of the study was the chicken egg as the main source of protein. Based on the results of the study, it can be concluded that the quality of the eggs of modern producers and the protein content in them correspond to the normalized indicators, but with slight deviations, which is explained by the duration of storage and the possible inconsistency of the egg storage regimen.

In the course of the work, the main goal was achieved: the main sources of proteins were identified - these are products of animal origin - milk, meat, fish, eggs (contain essential amino acids in the most favorable ratios) and vegetable origin, such as peas, beans, buckwheat and pearl barley, millet, rice; and it was also determined that proteins are necessary and vital elements of the chemical composition of food products that perform many functions - plastic, contractile, reserve, regulatory and protective.

Proteins are the basis of a healthy and proper diet, so it is necessary to improve the nutrition culture of the country's population and promote a healthy lifestyle.

Bibliography

1. Potoroko I.Yu., Kalinina I.V. Theoretical foundations of commodity science and examination of consumer goods: Laboratory workshop. - Chelyabinsk: Publishing house of SUSU, 2005. - 97 p.

2. Merchandising of meat and egg products. Commodity science of dairy products and food concentrates: Proc./G. N. Kruglyakov, G. V. Kruglyakova.-M.: Marketing, 2001.

3. Chemical composition of Russian food products / Ed. I. M. Skurikhin, V. A. Tutelyan; Ros. acad. honey. Sciences, Institute of Nutrition.-M.: DeLi print, 2002.

4. http://ru.wikipedia.org/wiki/Proteins

5. http://www.chepfa.ru

Annex 1

Calculation diary

Sample #1. Dietary egg of the first category

Protein: optical density of the test sample - 0.237

sample weight - 0.0465 g

X \u003d (0.002x0.237x100x6.25) / (0.35x0.0465) \u003d 18.1%

Yolk: optical density of the test sample - 0.220