What chemical elements are included in protein? Proteins: history of research, chemical composition, properties, biological functions. The theory of “carbon-nitrogen complexes” by A.Ya. Danilevsky

Chemical composition of proteins.

3.1. Peptide bond

Proteins are irregular polymers built from α-amino acid residues, the general formula of which in an aqueous solution at pH values close to neutral can be written as NH 3 + CHRCOO – . Amino acid residues in proteins are connected by an amide bond between the α-amino and α-carboxyl groups. Peptide bond between two-amino acid residues are usually called peptide bond , and polymers built from α-amino acid residues connected by peptide bonds are called polypeptides. A protein, as a biologically significant structure, can be either one polypeptide or several polypeptides that form a single complex as a result of non-covalent interactions.

3.2. Elemental composition of proteins

When 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 present in all proteins 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, in various, often very small quantities, were also found in the composition of individual proteins.

The content of basic chemical elements in proteins may vary, with the exception of nitrogen, the concentration of which is characterized by the greatest constancy and averages 16%. In addition, the nitrogen content of other organic matter is low. In accordance with this, it was proposed to determine the amount of protein by the nitrogen contained in it. 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: divide the protein into monomers and find out their chemical composition. The breakdown of protein into its component parts is achieved through hydrolysis - prolonged boiling of the protein with strong mineral acids (acid hydrolysis) or reasons (alkaline hydrolysis). The most commonly used method is boiling at 110°C with HCl for 24 hours. At the next stage, the substances included in the hydrolyzate are separated. For this purpose, various methods are used, most often chromatography (for more details, see the chapter “Research Methods...”). The main part of the separated hydrolysates are amino acids.

3.3. Amino acids

Currently, up to 200 different amino acids have been found in various objects of living nature. 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 - NH 2. Therefore, by chemical nature these are α-amino acids with the general formula:

H – C  – NH 2

From this formula it is clear that all amino acids include the following general groups: – CH 2, – NH 2, – COOH. Side chains (radicals - R) amino acids differ. As can be seen from Appendix I, the chemical nature of radicals is diverse: from the hydrogen atom to cyclic compounds. It is radicals that determine the structural and functional characteristics of amino acids.

All amino acids, except for the simplest aminoacetic acid glycine (NH 3 + CH 2 COO ) have a chiral C atom and can exist in the form of two enantiomers (optical isomers):

COO – COO –

NH3+ RR NH3+

L-isomerD-isomer

All currently studied proteins contain only L-series amino acids, in which, if we consider the chiral atom from the side of the H atom, the NH 3 +, COO  groups and the R radical are located clockwise. When constructing a biologically significant polymer molecule, the need to build it from a strictly defined enantiomer is obvious - from a racemic mixture of two enantiomers an unimaginably complex mixture of diastereoisomers would be obtained. The question of why life on Earth is based on proteins built specifically from L-, and not D--amino acids, still remains an intriguing mystery. It should be noted that D-amino acids are quite widespread in living nature and, moreover, are part of biologically significant oligopeptides.

Proteins are built from twenty basic α-amino acids, but the rest, quite diverse amino acids, are formed from these 20 amino acid residues already in the protein molecule. Among such transformations, we should first of all note the formation disulfide bridges during the oxidation of two cysteine residues in already formed peptide chains. As a result, a diaminodicarboxylic acid residue is formed from two cysteine residues cystine (See Appendix I). In this case, cross-linking occurs either within one polypeptide chain or between two different chains. As a small protein having two polypeptide chains, connected by disulfide bridges, as well as cross-links within one of the polypeptide chains:

GIVEQCCASVCSLYQLENYCN

FVNQHLCGSHLVEALYLVCGERGFYTPKA

An important example of modification of amino acid residues is the conversion of proline residues into residues hydroxyproline :

N – CH – CO – N – CH – CO –

CH 2 CH 2 CH 2 CH 2

CH2CHOH

This transformation occurs, and on a significant scale, with the formation of an important protein component of connective tissue - collagen .

Another very important type of protein modification is phosphorylation of hydroxyl groups of serine, threonine and tyrosine residues, for example:

– NH – CH – CO – – NH – CH – CO –

CH 2 OH CH 2 OPO 3 2 –

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

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

Acyclic. Monoaminomonocarboxylic amino acids They contain one amine and one carboxyl group; they are neutral in an aqueous solution. Some of them have common structural features, which allows us to consider them together:

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 acids, heme, and is necessary for the neutralization of toxic products in the liver. Alanine is used by the body in various processes of carbohydrate and energy metabolism. Its isomer -alanine is a component of vitamin pantothenic acid, coenzyme A (CoA), and muscle extractives.

Serine and threonine. They belong to the group of hydroxy acids, because have a hydroxyl group. Serine is a component 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.

Cysteine and methionine. Amino acids containing a sulfur atom. The importance 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 high oxidative capacity (in case of radiation injury, phosphorus poisoning). Methionine is characterized by the presence of a readily mobile methyl group, which is used for the synthesis of important compounds in the body (choline, creatine, thymine, adrenaline, etc.)

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

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

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

Cyclic. These amino acids have an aromatic or heterocyclic ring and, as a rule, are not synthesized in the human body and must be supplied with food. They actively participate in various metabolic processes. So

Phenyl-alanine serves as the main source for the synthesis of tyrosine, a precursor to a number of biologically important substances: hormones (thyroxine, adrenaline), and some pigments. Tryptophan, in addition to participating in protein synthesis, serves as a component of vitamin PP, serotonin, tryptamine, and a number of pigments. Histidine is necessary for protein synthesis and is a precursor of histamine, which affects blood pressure and gastric juice secretion.

Properties

Proteins are high molecular weight compounds. These are polymers consisting of hundreds and thousands of amino acid residues - monomers.

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

Proteins actively 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. To amino acid radicals, and Accordingly, molecular mass proteins ranges from 10,000 to 1,000,000. Thus, 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 17,000, and hemoglobin - 64,500 (574 amino acid residues). Other proteins have higher molecular weights: β-globulin (forms antibodies) consists of 1250 amino acids and has a molecular weight of about 150,000, and the molecular weight of the enzyme glutamate dehydrogenase exceeds 1,000,000.

Determination of molecular weight is carried out by various methods: osmometric, gel filtration, optical, etc. however, the most accurate is the sedimentation method proposed by T. Svedberg. It is based on the fact that during ultracentrifugation with acceleration up to 900,000 g, the sedimentation rate of proteins depends on their molecular weight.

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 are part of amino acid radicals. For example, the acidic properties of protein are imparted by the carboxyl groups of aspartic glutamic amino acids, and the alkaline ones are imparted by the radicals of arginine, lysine and histidine. The more dicarboxylic amino acids a protein contains, the more pronounced its acidic properties and vice versa.

These same groups also have electrical charges that form the overall charge of the protein molecule. In proteins where aspartic and glutamine amino acids predominate, the protein charge 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. Thus, 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 determining the behavior of a protein as a cation or anion is the reaction of the environment, 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 is equalized 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 minor 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 property of amphotericity underlies the buffering properties of proteins and their participation in the regulation of blood pH. The pH value of human blood is constant and ranges from 7.36 to 7.4, despite various substances of an acidic or basic nature that are regularly supplied with food or formed in metabolic processes - therefore, there are special mechanisms for regulating the acid-base balance of the internal environment of the body. Such systems include the one discussed in Chapter. “Classification” hemoglobin buffer system (p. 28). A change in blood pH by more than 0.07 indicates the development of a pathological process. A shift in pH to the acidic side is called acidosis, and to the alkaline side is called alkalosis.

Of great importance for the body is the ability of proteins to adsorb on their surface certain 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 transformation or neutralization.

Aqueous solutions of proteins have their own characteristics. Firstly, 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 hydration 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 water more easily and have a relatively large water shell, while globulins and fibrinogen bind water less well, and the hydration shell is smaller. Thus, the stability of an aqueous protein solution is determined by two factors: the presence of a charge on the protein molecule and the aqueous shell around it. When these factors are removed, the protein precipitates. This process can be reversible and irreversible.

Reversible protein precipitation(salting out) involves the precipitation of a protein under the influence of certain substances, after the removal of which it returns to its original (native) state. To salt out proteins, salts of alkali and alkaline earth metals are used (sodium and ammonium sulfate are most often used in practice). These salts remove the water coating (causing dehydration) and remove the charge. There is a direct relationship between the size of the water shell of protein molecules and the concentration of salts: the smaller the hydration shell, the less salts are required. Thus, globulins, which have large and heavy molecules and a small aqueous shell, precipitate when the solution is not completely saturated with salts, and albumins, which are smaller molecules surrounded by a large aqueous shell, precipitate when the solution is completely saturated.

Native protein molecule

Denatured protein molecule. The dashes indicate bonds in the native protein molecule that are broken during denaturation

Irreversible precipitation is associated with deep intramolecular changes in the structure of the protein, which leads to their loss of native properties (solubility, biological activity, etc.). Such a protein is called denatured, and the process denaturation. Denaturation of proteins occurs in the stomach, where there is a strongly acidic environment (pH 0.5 - 1.5), and this promotes the breakdown of proteins by proteolytic enzymes. Protein denaturation is the basis for the treatment of heavy metal poisoning, when the patient is given per os (“by mouth”) milk or raw eggs so that the metals denature the proteins of the milk or eggs.

They were adsorbed on their surface and did not act on the proteins of the mucous membrane of the stomach and intestines, and were also not absorbed into the blood.

The size of protein molecules lies in the range of 1 µm to 1 nm and, therefore, they are colloidal particles that 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.

The viscosity of a solution depends on the molecular weight and concentration of the solute. The higher the molecular weight, the more viscous the solution. Proteins, as high-molecular compounds, form viscous solutions. For example, a solution of egg white in water.

Water

colloidal particles do not pass through semi-permeable membranes (cellophane, colloidal film), since their pores are smaller than colloidal particles. All biological membranes are impermeable to protein. This property of protein solutions is widely used in medicine and chemistry to purify protein preparations from foreign impurities. This separation process is called dialysis. The phenomenon of dialysis underlies the operation of the “artificial kidney” device, which is widely used in medicine to treat acute renal failure.

Dialysis (large white circles – protein molecules, black – sodium chloride molecules)

Milk minerals

Milk ash contains minerals such as calcium, phosphorus, magnesium, potassium, sodium, chlorine, sulfur, and silicon. The amount of individual elements in milk is determined mainly by genetic factors. Feeding and other environmental factors have only a minor impact on their maintenance. The amount of minerals in milk remains constant even when individual elements are low in the diet. If the supply of minerals with food is insufficient, the body's reserves are mobilized and thus their concentration in milk is maintained at a certain level. If there is a significant deficiency of one or more elements, the mineral content per unit volume of milk remains more or less constant. However, milk productivity, and then the total amount of minerals in milk, decreases.

Minerals	Contains, g	Minerals

The total amount of microelements in milk is less than 0.15%. The content of microelements in milk is closely dependent on their presence in feed.

Structural and mechanical properties of oil.

According to Rehbinder, there are two main types of structures.

The first type is the coagulation structure- these are spatial networks that arise through the random adhesion of tiny particles of the dispersed phase or micromolecules through thin layers of a given medium.

The second type is a crystallization-condensation structure, formed as a result of the direct fusion of crystals with the formation of a polycrystalline solid.

The fatty bases of margarine belong to the coagulation type of structures. The consistency and plastic properties of margarine fat bases are mainly determined by the ratio of solid and liquid phases in a particular edible fat. This ratio of solid and liquid phases is characteristic of certain crystallization conditions (temperature, time, stirring). In this case, the composition of the continuous medium and the dispersed phase and the nature of the placement of the dispersed phase in a continuous liquid medium are important.

For some types of edible fat, at a certain temperature and crystallization conditions, the amount of solid dispersed phase may exceed the limit of the optimal phase ratio, and then such thin films of a continuous liquid medium are formed on the surface of the crystals that they cannot interfere with the massive chaotic fusion of crystals with each other. In this case, we will always have the greatest hardness of the fat base, crumbly consistency and the worst plastic properties.

If at room temperature the films of a liquid continuous medium are optimal in thickness, i.e. such that do not create conditions for the merging of crystals during storage, under mechanical or thermal influence on the system, then in this ideal case we will always obtain strengthened coagulation structures, which determine the best plastic properties of fatty bases.

In order to obtain strengthened coagulation structures with the best plastic properties, two types of lard with a melting point of 32°C and 42°C are often added to the fat base formulation abroad. In this case, a fairly significant amount of liquid vegetable oils is introduced. This, on the one hand, creates the best ratio of solid and liquid phases in the fat base, providing a consistency similar to butter, and on the other hand, creates conditions for the consistency of margarine over a fairly wide temperature range. Along with this, the introduction of high-melting fats into the fat base is in conflict with the requirements of physiologists for the composition of dietary fats.

First of all, it should be noted that only the presence of highly effective emulsifiers-stabilizers made it possible to create modern technology in the production of margarine and ensure the production of a high-quality edible fat product. Surface-active additives ensure the production of a finely dispersed emulsion into a strong connection of dispersed phase particles with a continuous medium (fat, solid at room temperature). The main issue in the production of margarine is the influence of surfactants on the structural and mechanical properties of margarine, and in particular on the ability to solubilize.

The adsorption layer of the emulsifier increases the stability of the emulsion, especially in cases where this layer is structured, forming a film of surface gel with greatly increased viscosity and strength.

These properties are of particular importance for the production of margarine, since the finished product is an emulsion of tiny liquid phase particles uniformly distributed in a continuous solid phase medium at room temperature.

Closely related to the problem of the strength of emulsions is the question of the type of emulsions formed with a given emulsifier. There is a possibility of formation of two types. The value of the ratio of phase volumes for a certain type of emulsion formed is explained by the fact that the coalescence and separation of an emulsion of this type occurs the more intensely, the smaller the volume of the dispersion medium and the larger the dispersed phase. If the emulsifier provides only one type of stable emulsion, then the volume ratio is no longer critical in determining the type of emulsion. Inversion depends not only on the ratio of phase volumes, but also on the concentration and chemical nature of the emulsifier.

Emulsifiers must have the following properties:

Reduce surface tension;
- adsorb quickly enough on the phase interface, preventing the merging of droplets;
- have a specific molecular structure with polar and non-polar groups;
- influence the viscosity of the emulsion.

The effectiveness of an emulsifier is a specific property that depends on its nature, the type of emulsifying substances, temperature, pH of the medium, concentration, emulsification time, etc.

The effectiveness and nature of the emulsifier determine the type of emulsion.

Hydrophilic emulsifiers, better soluble in water than in hydrocarbons, contribute to the formation of oil-water emulsions, and hydrophobic emulsifiers, better soluble in hydrocarbons, contribute to the formation of water-oil emulsions. The ratio of the sizes of the polar and non-polar parts of the emulsifier molecules is characterized by a special indicator - hydrophilic-lipophilic balance. If the HLB of the emulsifier is 3-6, a water-oil emulsion is formed; if the HLB value is 8-13, a predominantly oil-water emulsion is formed.

Margarine is a supercooled water-in-oil emulsion. In this case, the possibility of the formation of a mixed emulsion with a predominance of water-oil emulsion cannot be excluded.

Main functions of emulsifiers:

Creation of a stable highly dispersed emulsion;
- stabilization and prevention of separation of moisture and fat in the finished product;
- ensuring stability during storage;
- ensuring anti-spattering ability during frying;
- ensuring plasticity;
- ensuring the creation of a stable form of the crystal lattice in the process of structure formation;
- ensuring the specified functional properties of the finished product depending on the area of margarine use.

For many years, Ukraine has used emulsifiers produced in Russia and its own production, produced in semi-industrial production. These include emulsifiers:

T-1 is a product of glycerolysis of beef fat or lard;
- T-2 – glycerol polymerization product, esterified with stearic acid;
- T-F – a mixture of emulsifier T-1 and food phosphatide concentrate in a ratio of 2:1;
- PMD – food monodiglycerides;
- CE – combined emulsifier – a mixture of PMD and phosphatide concentrate in a ratio of 3:1.

A wide range of emulsifiers from the Nizhny Novgorod plant - various types of distilled monoglycerides. Currently, the production of a series of new emulsifiers based on lecithin has been mastered in Nizhny Novgorod. These are standard lecithins, fractionated lecithins - phosphaditylcholine and phosphaditylserine, as well as hydrolyzed lecithins.

In recent years, emulsifiers of various modifications of the Dimodan and Palsgaard series (at some Quest enterprises) have been predominantly used in Ukraine.

At different periods, the advantage in demand for these two types of emulsifiers shifted from one to the other. We can say that there is competition between quality and price.

Depending on the fat content of margarine and the scope of its application, emulsifiers Dimodan PVP (Dimodan HP), Dimodan OT (Dimodan S-T PEL/B), Dimodan CP are used. For margarines with a fat content below 40%, which are currently in demand among the population, additionally (in addition to Dimodan OT, or Dimodan CP., or Dimodan LS) esters of polyglycerol and ricinoleic acid are used - Grinsted PGPR90.

In the production of low-fat margarines, especially with a fat content of 25% and below, stabilizing systems are used - hydrocolloids (alginates, pectins, etc.).

It should be noted that manufacturing companies provide recommendations on the use of various types of emulsifiers and stabilizing systems, depending on the purpose of margarines. Compliance with these recommendations allows you to obtain high quality products

Muscle proteins

Poultry contains approximately 20-23% protein. Based on their solubility, muscle proteins can be divided into three groups: myofibrillar, sarcoplasmic and stromal proteins.

Myofibrillar, or salt-soluble squirrels insoluble in water, but most are soluble in solutions of table salt with a concentration of more than 1%. This group consists of approximately 20 individual proteins that make up the myofibrils of contractile muscle. Myofibrillar proteins can be divided into three groups depending on the function they perform: contractile, which are responsible for muscle contractions, regulatory, involved in controlling the contraction process, and cytoskeletal, which hold myofibrils together and help maintain their structural integrity.

Contractile proteins myosin and actin have a major influence on muscle protein functionality. Because actin and myosin are present as an actomyosin complex in stiff muscle, the functionality of myosin is altered in both emulsified and molded poultry products. The properties of the products also depend on the total ratio of actin and myosin and the ratio of myosin and actin in the free state. Sarcoplasmic proteins and stromal proteins, in turn, influence the functional properties of myofibrillar proteins.

Sarcoplasmic proteins soluble in water or in solutions with low ionic strength (

Stromal proteins, often called connective tissue proteins, serve as a scaffold that supports the structure of the muscle. The main protein of the stroma is collagen. Elastin and reticulin make up a small part of the stroma. All these proteins are insoluble in water and saline solutions. Meat tenderness generally decreases as animals age due to cross-linking and other collagen changes.

Blood and its fractions

Whole blood is used as the main raw material for the production of sausages, brawn, canned food and other food products, and also as an additive that gives traditional color to products when protein preparations are used in them (0.6-1.0%); For the same purpose, a hemoglobin preparation or a mixture of formed elements is used after hydration in water (1:1).

Compared to other types of protein-containing raw materials, whole blood is not widely used due to the presence of specific color and taste that modify the organoleptic characteristics of finished products. Currently, research is being conducted on blood clarification, however, for a number of reasons, the proposed methods have not found practical application in industry. The functional and technological properties of blood and its fractions (plasma, serum) primarily depend on their protein composition. Whole blood contains about 150 proteins with various physicochemical properties, the predominant of which are proteins of formed elements, albumins, globulins and fibrinogen. In this regard, on the basis of whole blood, it is advisable to prepare emulsions intended for introduction into meat product formulations and ensuring increased stability of meat systems, nutritional value and yield, improvement of organoleptic characteristics and structural and mechanical properties.

It is most advisable to use soy isolate or sodium caseinate as a protein preparation.

The level of introduction of emulsions prepared on the basis of whole blood into meat systems can be up to 30-40% by weight of the main raw material.

Blood plasma proteins have a unique PTS complex. Albumins easily interact with other proteins, can be associated with lipids and carbohydrates, and have high water-binding and foaming ability.

Globulins are good emulsifiers.

Fibrinogen - has a pronounced gel-forming ability, turning into fibrin under the influence of a number of factors (pH shift to isotochka, introduction of Ca++ ions into the plasma) and forming a spatial framework.

mixtures These properties of fibrinogen can be used in the production of multicomponent protein-containing, including PC, gel-like textures, in the process of secondary structure formation of meat emulsions in the production of boiled sausages.

All plasma proteins are characterized by good solubility, and as a result, high water-binding and emulsifying ability, and are capable of forming gels when heated. The introduction of table salt has a negative effect on the stability of emulsions based on blood plasma at pH 7.0. The most important property of plasma is its ability to form gels during heat treatment, and their strength and level of water-binding ability depend on the concentration of proteins in the system, pH value, the presence of salts, temperature and duration of heating.

The introduction of non-plasma proteins (egg albumin, soy isolate, sodium caseinate) into the plasma significantly increases both the strength of the gels and their water and fat absorption capacity after heat treatment.

Depending on the state of blood plasma and the conditions of primary processing, its composition and functional and technological properties and, accordingly, the area of use may change.

Systematization of currently available data on PC processing makes it possible to evaluate modern approaches to realizing the biological and functional-technological potential of the protein component of PC in food production.

The scheme gives an idea of the state, processing methods, composition and properties of protein preparations obtained on the basis of PC, determines the areas of their practical use, and the multifunctionality of the intended purpose of PC is reflected in the FTS formed during a particular processing method.

It should be noted that the level of individual FTS indicators given in Table 13 and used to decipher the symbols adopted in the scheme is relative due to the fact that the actual value of each characteristic depends decisively on the protein concentration, pH value in the system, and ambient temperature , ionic strength and a number of other factors.

Analysis of the classification scheme shows that one of the ways of technological use of blood plasma is its use in a liquid stabilized form (as well as after cooling and freezing) with a relatively low protein content and preserved native PTS.

In this case, PC proteins are characterized by a high level of BCC and emulsification, which is due to the presence of water-soluble proteins in it that can form gels when heated. The combination of these properties allows plasma to be widely used not only as a component that balances the overall chemical composition of finished products, but also as a functional additive in the production of emulsified meat products with a high final moisture content: boiled sausages, frankfurters, sausages, minced semi-finished products, canned minced meat, and ham products. The most rational is to introduce 10% plasma into the formulations instead of 3% beef or 2% pork; the introduction of 20% PC instead of water during cutting ensures an improvement in organoleptic, structural and mechanical characteristics and an increase in the yield of finished products by 0.3-0.5%. An excellent effect is achieved by using blood plasma as a medium for the hydration of protein preparations (3-4 parts PC per 1 part protein preparation).

PC is indispensable in the production of protein-fat emulsions, binders, multicomponent protein systems with a given composition and functional and technological properties, structured protein preparations.

Concentrating PC by methods of drying, ultrafiltration and cryoconcentration, while allowing a significant increase in protein content, leads to some modification of the drug's FTS.

Plasma drying has a particularly significant effect on the degree of change in the PTS, while dry PC concentrate subjected to ultrafiltration has very high functional properties.

The concentrates obtained by these methods are successfully used in the production of meat products along with liquid PC.

American experts believe that cattle blood plasma, thanks to its FTS, can successfully replace egg white.

Denaturation-coagulation precipitation, providing a combination of the processes of thermotropic structuring, flocculation (sedimentation) and concentration of PC proteins, makes it possible to obtain drugs with a relatively high protein concentration and extraordinary PTS, which allows their use in the formulations of semi-smoked, smoked baked, liver sausages, canned pate and semi-finished products having limited final moisture content and high fat absorption capacity. This group of drugs includes: “precipitated plasma protein”, “plasma protein precipitates”, Livex, “plasma cheese”, granulated PC.

The use of these types of blood plasma preparations in meat production practice is very limited.

Structuring blood plasma by recalcination significantly expands the possibilities of its technological use. The transfer of PC and multicomponent systems based on it into a gel form makes it possible to obtain structural matrices that imitate natural biological objects in appearance, composition and properties, creates the prerequisites for the regulation of FTS, ensures the involvement of low-grade raw materials in the production process, and makes it possible to approach the solution from a new perspective the issue of developing new types of food products. The complex use of PC and protein preparations (soy isolates, sodium caseinate, etc.) is especially effective. Structured forms of PC are used in the production of boiled sausages, chopped semi-finished products, casing ham, semi-smoked and liver sausages, pates, canned minced meat, textured recipe fillers , analogues of meat products.

MATURING OF MEAT

The issue of “ripening meat” has not yet received final coverage. From the observations of practitioners, it is known that after the death of an animal, physicochemical changes occur in the meat, characterized by rigor, then relaxation (softening) of muscle fibers. As a result, the meat acquires some flavor and is easier to cook. Its nutritional value increases. These changes in the soft tissues of the carcass are called "ripening" ("ageing") or "fermentation of meat".

To explain the process of meat ripening, the teaching of Meyerhoff, Embden, Palladin and Abdergalden on the dynamics and metabolism of carbohydrates in muscles during the life of an animal deserves great attention.

Meyerhof showed that the glycogen contained in the muscle is spent on the formation of lactic acid during muscle contraction. While relaxing
(rest) muscles, due to the supply of oxygen, glycogen is again synthesized from lactic acid

Lundsgrad showed that creatinophosphoric acid is located in muscle cells and, when they contract, is broken down into creatine and phosphoric acid (according to
Palladin), which combines with hexose (glucose). Adenosine phosphoric acid, found in muscle, is also broken down to form adenosine and phosphoric acid, which, when combined with hexose (glucose), promotes the formation of lactic acid (Embden and Zimmerman).

The meat of a freshly killed animal (fresh meat) has a dense consistency, without a pronounced pleasant specific smell; when cooked, it produces a cloudy, non-aromatic broth and does not have high taste qualities. Moreover, in the first hours after the slaughter of an animal, the meat stiffens and becomes tough.
24-72 hours after the slaughter of the animal (depending on the ambient temperature, aeration and other factors), the meat acquires new quality indicators: its hardness disappears, it acquires juiciness and a specific pleasant smell, a dense film (drying crust) forms on the surface of the carcass, when when cooked, it gives a clear, aromatic broth, becomes tender, etc.
The processes and changes occurring in meat, as a result of which it acquires the desired quality indicators, are usually called meat ripening.

Meat ripening is a combination of complex biochemical processes in muscle tissue and changes in the physical-colloidal structure of the protein, occurring under the influence of its own enzymes.

The processes occurring in muscle tissue after the slaughter of an animal can be divided into the following three phases: post-mortem rigor, maturation and autolysis.

Post-mortem rigor mortis develops in the carcass in the first hours after the slaughter of the animal. In this case, the muscles become elastic and slightly shorten. This significantly increases their rigidity and resistance to the cut.
The ability of such meat to swell is very low. At a temperature of 15-20°C, complete rigor mortis occurs 3-5 hours after the slaughter of the animal, and at a temperature of 0-2°C, after 18-20 hours.

The process of post-mortem rigor mortis is accompanied by a slight increase in temperature in the carcass as a result of the release of heat, which is formed from chemical reactions occurring in the tissues. The rigor of muscle tissue observed in the first hours and days after the slaughter of animals is caused by the formation of an insoluble actomyosin complex from the proteins actin and myosin. The prerequisites for its formation are the absence of adenosine triphosphoric acid (ATP), the acidic environment of the meat and the accumulation of lactic acid in it. Biochemical changes in meat create these prerequisites.
The decrease and complete disappearance of ATP is associated with its breakdown as a result of the enzymatic action of myosin. The breakdown of ATP to adenosine diphosphoric (ADP, adenosine monophosphoric (AMP) and phosphoric acids itself leads to the appearance of an acidic environment in the meat. Moreover, already in this phase the breakdown of muscle glycogen begins , which leads to the accumulation of lactic acid, which also contributes to the formation of an acidic environment in it.

An acidic environment, which is a natural phenomenon of ATP breakdown and the beginning of the irreversible process of glycolysis (breakdown of muscle glycogen), increases muscle rigor. It has been noticed that the muscles of animals that died due to convulsions become numb faster. Rigor rigor without lactic acid accumulation is characterized by mild muscle tension and rapid resolution of the process.

However, long before the completion of the rigor rigor phase, processes associated with the phases of its own maturation and autolysis develop in meat.
They are driven by two processes - intensive breakdown of muscle glycogen, leading to a sharp shift in the pH value of meat to the acidic side, as well as some changes in the chemical composition and physical-colloidal structure of proteins.

Due to the fact that the muscles of the meat do not receive oxygen and the oxidative processes in them are inhibited, excess lactic and phosphoric acid accumulate in the meat. So, for example, with muscle fatigue of the body (during its life), a maximum of 0.25% of lactic acid is reached, and with post-mortem rigor it accumulates up to 0.82%. The active reaction of the medium (pH) in this case changes from 7.26 to 6.02. The accumulation of lactic acid causes a rapid contraction (rigidity) of the muscles, accompanied by protein coagulation (Saxl). In this case, actomyosin loses its solubility, proteins are stabilized, and calcium falls out of protein colloids and goes into solution (meat juice). Due to the excess content of lactic acid, swelling of the colloidal anisotropic substance (dark disk) of the muscle fibers first occurs (it is accompanied by shortening and rigor of the muscles); then, as the concentration of lactic acid increases and the protein coagulates, this substance softens. Collapsed proteins lose their colloidal properties, become unable to bind (retain) water and, to a certain extent, lose their dispersed medium (water): instead of the initial swelling, the cell colloids shrink (shrink), and the muscles become soft (rigidity resolution).

As a result of the accumulation of lactic, phosphoric and other acids in meat, the concentration of hydrogen ions increases, as a result of which by the end of the day the pH decreases to 5.8-5.7 (and even lower).

In an acidic environment, during the breakdown of ATP, ADP, AMP and phosphoric acid, a partial accumulation of inorganic phosphorus occurs. A strongly acidic environment and the presence of inorganic phosphorus are considered to be the cause of the dissociation of the actomyosin complex into actin and myosin. The disintegration of this complex relieves the phenomena of rigor and toughness of meat. Consequently, the rigor phase cannot be separated from other phases and must be considered one of the stages in the meat ripening process.

The scheme of biochemical changes during the ripening process of meat can be presented as follows.

The acidic environment itself acts bacteriostatically and even bactericidally, and therefore, when the pH shifts to the acidic side, unfavorable conditions are created in the meat for the development of microorganisms.

Finally, an acidic environment leads to some changes in the chemical composition and physical-colloidal structure of proteins. It changes the permeability of muscle membranes and the degree of protein dispersion. Acids interact with calcium proteinates and calcium is split off from proteins.
The transition of calcium into the extract leads to a decrease in the dispersion of proteins, as a result of which part of the hydration-bound water is lost. Therefore, meat juice can be partially separated from ripened meat by centrifugation.

The released hydrate-bound water, the action of proteolytic enzymes and the acidic environment create conditions for loosening the sarcolemma of muscle fibers, and primarily loosening and swelling of collagen. This greatly contributes to a change in the consistency of the meat and its more pronounced juiciness. Obviously, the swelling of collagen and then partial release of moisture from the surface of the carcass into the environment should be associated with the formation of a drying crust on its surface.

The phase of its own maturation largely determines the intensity of physical-colloid processes and microstructural changes in muscle fibers that occur in the autolysis phase. Autolysis during meat ripening is reduced in the broad sense of the word and is associated not only with the breakdown of proteins, but also with the process of breakdown of any constituent parts of cells. In this regard, the processes occurring in the phase of their own maturation cannot be separated or isolated from those during autolysis. Nevertheless, as a result of a complex of reasons (the action of proteolytic enzymes, a sharply acidic environment, products of autolytic breakdown of non-protein substances, etc.), autolytic breakdown of muscle fibers occurs into separate segments.

Meat ripening takes place within 24-72 hours at a temperature of +4°.
However, it is not always possible to keep meat at +4°. Sometimes you have to store it under normal conditions (not in cooling conditions) at a temperature of +6-8° and above; at elevated temperatures, the processes of rigor mortis and muscle resolution proceed faster. The speed of meat ripening also depends on the type and health status of the killed animal, its fatness and age; but these questions require further observation and study.

When meat ripens, some nucleides are broken down
(nitrogenous extractives). Volatile substances, esters and aldehydes are formed, which impart flavor to the meat. Adenylic and inosinic acids, adenine, xanthine, and hypoxanthine appear, on which the taste of meat depends. The reaction of the meat environment changes towards acidity (pH 6.2-
5.8). This promotes the swelling of protoplasm colloids, due to which the meat becomes soft, tender and lends itself well to cooking.
Meat of this quality is obtained after 1-3 days of storage at a temperature of 4 to 12° (depending on the capabilities of the enterprise).

The first stage of this process reveals segmentation in individual muscle fibers while maintaining the endomysium of the fibers. At the same time, the structure of the nuclei, transverse and longitudinal striations are preserved in the segments.

In the second stage, most muscle fibers undergo segmentation.
As at the first stage, the endomysium of the fibers, and in the segments the structure of the nuclei, transverse and longitudinal striations continue to be preserved. Finally, at the third stage (deep autolysis phase), the breakdown of segments into myofibrils and myofibrils into sarcomeres is detected.

Sarcomeres, when microscopying sections made from such Meat, are visible in the form of a granular mass enclosed in the endomysium.

Morphological and microstructural changes in tissues also cause softening and loosening of meat during its ripening, due to which digestive juices penetrate more freely into the sarcoplasm, which improves its digestibility. It should be noted that connective tissue proteins are almost not subject to proteolytic processes during meat ripening. Therefore, under equal ripening conditions, the tenderness of different cuts of meat of the same animal, as well as identical cuts of different animals, turns out to be unequal; The tenderness of meat containing a lot of connective tissue is low, and the meat of young animals is more tender than old ones.

As a result of a complex of autolytic transformations of various components of meat during its ripening, substances are formed and accumulated that determine the aroma and taste of ripened meat. A certain taste and aroma is given to ripened meat by nitrogen-containing extractive substances - hypoxanthine, creatine and creatinine, formed during the breakdown of ATP, as well as accumulating free amino acids (glutamic acid, arginine, threonine, phenylalanine, etc.). Pyruvic and lactic acids apparently participate in the formation of a bouquet of taste and aroma.

I. A. Smorodintsev suggested that taste and aroma depend on the accumulation of easily soluble and volatile substances such as esters, aldehydes and ketones in ripened meat. Subsequently, a number of studies have shown that the aromatic properties of ripened meat improve as the total amount of volatile reducing substances accumulates in it. Currently, using gas chromatography and mass spectrometric analysis, it has been established that the compounds that cause the smell of cooked meat include acetaldehyde, acetone, m-ethyl ketone, methanol, methyl mercaptan, dimethyl sulfide, ethyl mercaptan, etc.

With an increase in temperature (up to 30 ° C), as well as with prolonged aging of meat (over 20-26 days) in conditions of low positive temperatures, the enzymatic ripening process goes so deep that the amount of protein breakdown products in the meat noticeably increases in the form of small peptides and free amino acids. At this stage, the meat acquires a brown color, the amount of amine and ammonia nitrogen in it increases, and a noticeable hydrolytic breakdown of fats occurs, which sharply reduces its marketable and nutritional qualities.

The biochemical processes that occur during ripening in the meat of sick animals differ from the biochemical processes in the meat of healthy animals.
With fever and fatigue, the energy process in the body is increased.
Oxidative processes in tissues are enhanced. Changes in carbohydrate metabolism during illness and fatigue are characterized by a rapid loss of glycogen in the muscles. Therefore, with almost any pathological process in the animal’s body, the glycogen content in the muscles is reduced. Since there is less glycogen in the meat of sick animals than in the meat of healthy animals, the amount of glycogen breakdown products (glucose, lactic acid, etc.) in the meat of sick animals is insignificant.

In addition, during severe diseases, intermediate and final products of protein metabolism accumulate in the animal’s muscles while the animal is still alive. In these cases, already in the first hours after the slaughter of the animal, an increased amount of amine and ammonia nitrogen is detected in the meat.

A slight accumulation of acids and an increased content of polypeptides, amino acids and ammonia are the reason for a smaller decrease in the concentration of hydrogen ions during the ripening of meat from sick animals. This factor affects the activity of meat enzymes. In most cases, the concentration of hydrogen ions established as a result of ripening the meat of sick animals is more favorable for the action of peptidases and proteases.

As a result, the accumulation of extractive nitrogenous substances in the meat of sick animals and the absence of a sharp shift in pH to the acidic side are considered conditions favorable for the development of microorganisms.

The changes that occur in the meat of sick animals have a different effect on the nature of the physical-colloidal structure of the meat. Less acidity causes a slight precipitation of calcium salts, which, in turn, causes a smaller change in the degree of protein dispersion and other changes characteristic of them during normal ripening of meat. A relatively high pH value, the accumulation of protein breakdown products and favorable conditions for the development of microorganisms predetermine the lower stability of meat from sick animals during storage. The listed signs are characteristic of the meat of every seriously ill animal; they are the reason for a certain uniformity in changes in the physicochemical parameters of meat obtained from animals killed during the pathological process, regardless of the nature of the disease. This position does not deny specific changes in the composition of meat during individual diseases, but gives grounds to talk about the general patterns of meat maturation during pathology in the animal body.

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Chemical compound and physical properties of sperm

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It is known that living matter is based on organic substances - proteins, fats, carbohydrates and nucleic acids. But the most important place among these substances is protein.

Most substances known to science change from solid to liquid when heated. But there are substances that, on the contrary, turn into a solid state when heated. These substances were combined into a separate class by the French chemist Pierre Joseph Macquet in 1777. By analogy with egg white, which coagulates when heated, these substances were called proteins. Proteins are otherwise called proteins. In Greek, protein (proteios) means “first place.” The protein received this name in 1838, when the Dutch biochemist Gerard Mulder wrote that life on the planet would be impossible without a certain substance, which is the most important of all substances known to science and which is necessarily present in absolutely all plants and animals. Mulder called this substance protein.

Protein is the most complex substance among all nutrients. Chemical reactions occur in every cell of the human body, in which protein plays a very important role.

What does protein consist of?

Proteins contain: nitrogen, oxygen, hydrogen, carbon. But other nutrients do not contain nitrogen.

Protein is a natural polymer. And polymers are substances whose molecules contain a very large number of atoms. Back in the 19th century, Russian chemist Alexander Mikhailovich Butlerov proved that if the structure of a molecule changes, then the properties of the substance also change. The main building blocks of proteins are amino acids. And proteins contain different combinations of amino acids. Consequently, a wide variety of proteins with different properties exist in nature. Through research, approximately 20 amino acids have been discovered that are involved in the creation of proteins.

How does the formation of a protein molecule occur?

Amino acids are added to each other sequentially. As a result of this process, a chain is formed, which is called a polypeptide. Subsequently, the polypeptides can fold into spirals or take on other shapes. The properties of a protein depend on the composition of amino acids, on how many amino acids are involved in synthesis, and in what order these amino acids are added to each other. For example, the synthesis of two proteins involves the same number of amino acids, which also have the same composition. But if these amino acids are located in different sequences, then we will get two completely different proteins.

If peptides contain no more than 15 amino acid residues, then they are called oligopeptides. And peptides containing up to several tens of thousands or even hundreds of thousands of amino acid residues are called proteins. The protein molecule has a compact spatial structure. This structure may be in the form of fibers. Such proteins are called fibrillar. They are building proteins. If a protein molecule has a spherical structure, then the proteins are called globular. These proteins include enzymes, antibodies, and some hormones.

Depending on which amino acids are included in proteins, proteins can be complete or incomplete. Complete proteins contain a full set of amino acids. Incomplete proteins lack some amino acids.

Proteins are also divided into simple and complex. Simple proteins contain only amino acids. In addition to amino acids, complex proteins also include metals, carbohydrates, lipids, and nucleic acids.

The role of proteins in the human body

Proteins perform various functions in the human body.

1.Structural. Proteins are part of the cells of all tissues and organs.

2. Protective. The interferon protein is synthesized in the body to protect against viruses.

3. Motor I. The protein myosin is involved in the process of muscle contraction.

4. Transport. Hemoglobin, which is a protein found in red blood cells, is involved in the transport of oxygen and carbon dioxide.

5. Energy I. As a result of the oxidation of protein molecules, the energy necessary for the functioning of the body is released.

6. Catalytic I. Enzyme proteins act as biological catalysts that increase the rate of chemical reactions in cells.

7. Regulatory I. Hormones regulate various body functions. For example, insulin regulates blood sugar levels.

There are a huge number of proteins in nature that can perform a wide variety of functions. But the most important function of proteins is to support life on Earth together with other biomolecules.

The basic properties of proteins depend on their chemical structure. Proteins are high-molecular compounds whose molecules are built from alpha amino acid residues, i.e. amino acids in which the primary amino group and the carboxyl group are connected to the same carbon atom (the first carbon atom counting from the carbonyl group).

19-32 types of alpha amino acids are isolated from proteins by hydrolysis, but usually 20 alpha amino acids are obtained (these are the so-called proteinogenic amino acids). Their general formula:

common part for all amino acids

R is a radical, i.e. a grouping of atoms in an amino acid molecule associated with an alpha carbon atom and not participating in the formation of the backbone of a polypeptide chain.

Among the hydrolysis products of many proteins, proline and hydroxyproline were found, which contain an imino group =NH, and not an amino group H 2 N- and are actually imino acids, not amino acids.

Amino acids are colorless crystalline substances that melt and decompose at high temperatures (above 250°C). Easily soluble, for the most part, in water and insoluble in ether and other organic solvents.

Amino acids simultaneously contain two groups capable of ionization: a carboxyl group, which has acidic properties, and an amino group, which has basic properties, i.e. amino acids are amphoteric electrolytes.

In strongly acidic solutions, amino acids are present in the form of positively charged ions, and in alkaline solutions - in the form of negative ions.

Depending on the pH value of the environment, any amino acid can have either a positive or a negative charge.

The pH value of the environment at which amino acid particles are electrically neutral is designated as their isoelectric point.

All protein-derived amino acids, with the exception of glycine, are optically active, since they contain an asymmetric carbon atom in the alpha position.

Of the 17 optically active protein amino acids, 7 are characterized by right /+/ and 10 by left /-/ rotation of the plane of the polarized beam, but all of them belong to the L-series.

D-series amino acids have been found in some natural compounds and biological objects (for example, in bacteria and in the antibiotics gramicidin and actinomycin). The physiological significance of D- and L-amino acids is different. D-series amino acids, as a rule, are either not absorbed by animals and plants at all, or are poorly absorbed, since the enzyme systems of animals and plants are specifically adapted to L-amino acids. It is noteworthy that optical isomers can be distinguished by taste: L-series amino acids are bitter or tasteless, and D-series amino acids are sweet.

All groups of amino acids are characterized by reactions in which amino groups or carboxyl groups, or both, take part. In addition, amino acid radicals are capable of a variety of interactions. Amino acid radicals react:

Salt formation;

Redox reactions;

Acylation reactions;

Esterification;

Amidation;

Phosphorylation.

These reactions, leading to the formation of colored products, are widely used for the identification and semi-quantitative determination of individual amino acids and proteins, for example, the xanthoprotein reaction (amidation), Millon reaction (salt formation), biuret reaction (salt formation), ninhydrin reaction (oxidation), etc.

The physical properties of amino acid radicals are also very diverse. This concerns, first of all, their volume and charge. The diversity of amino acid radicals in chemical nature and physical properties determines the multifunctional and specific features of the proteins they form.

The classification of amino acids found in proteins can be carried out according to various criteria: the structure of the carbon skeleton, the content of -COOH and H 2 N groups, etc. The most rational classification is based on differences in the polarity of amino acid radicals at pH 7, i.e. at a pH value corresponding to intracellular conditions. In accordance with this, the amino acids that make up proteins can be divided into four classes:

Amino acids with non-polar radicals;

Amino acids with uncharged polar radicals;

Amino acids with negatively charged polar radicals;

Amino acids with positively charged polar radicals

Let's look at the structure of these amino acids.

Amino acids with non-polar R-groups (radicals)

This class includes four aliphatic amino acids (alanine, valine, isoleucine, leucine), two aromatic amino acids (phenylalanine, tryptophan), one sulfur-containing amino acid (methionine), and one imino acid (proline). A common property of these amino acids is their lower solubility in water compared to polar amino acids. Their structure is as follows:

Alanine (α-aminopropionic acid)

Valine (α-aminoisovaleric acid)

Leucine (α-aminoisocaproic acid)

Isoleucine (α-amino-β-methylvaleric acid)

Phenylalanine (α-amino-β-phenylpropionic acid)

Tryptophan (α-amino-β-indolepropionic acid)

Methionine (α-amino-γ-methyl-thiobutyric acid)

Proline (pyrrolidine-α-carboxylic acid)

2. Amino acids with uncharged polar R‑groups (radicals)

This class includes one aliphatic amino acid - glycine (glycocol), two hydroxy amino acids - serine and threonine, one sulfur-containing amino acid - cysteine, one aromatic amino acid - tyrosine, and two amides - asparagine and glutamine.

These amino acids are more soluble in water than amino acids with nonpolar R groups because their polar groups can form hydrogen bonds with water molecules. Their structure is as follows:

Glycine or glycocol (α-aminoacetic acid)

Serine (α-amino-β-hydroxypropionic acid)

Threonine (α-amino-β-hydroxybutyric acid)

Cysteine (α-amino-β-thiopropionic acid)

Tyrosine (α-amino-β-parahydroxyphenylpropionic acid)

Asparagine

Ministry of Education and Science of the Russian Federation

Federal Agency for Education

South Ural State University

Department of Commodity Research 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 (using the example of proteins)”

Completed:

Abidullina Eleonora

Group Kom-234

Checked by: Elvira Vyacheslavovna Cherkasova

Chelyabinsk

Introduction……………………………………………………………………………….
1. Literature review
1.1. General concepts about proteins
1.1.1. 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. Change in protein content during technological processing………………………………………………………………………………...
1.4. Change in protein content during storage…………………….
2. Practical part
2.1. Characteristics of quantitative methods for determining protein content……………………………………………………….
2.2. Characteristics of qualitative methods for determining protein content………………………………………………………………………………….
3. Experimental part
3.1. Justification for choosing the research object……………………….
3.2. Analysis of the results of our own research…………………..
Conclusion…………………………………………………………………………...
Bibliography……………………………………………………………
Application……………………………………………………………………

Introduction

Proteins are the main plastic material for growth, development and renewal of the body. They represent the main structural elements of all tissues and are part of the fluid environment of the body. Food proteins are used to build red blood cells and hemoglobin, enzymes and hormones, and take an active part in the production of protective factors - antibodies.

If the protein content in the diet is insufficient, the body may develop severe disorders (hypotrophy, anemia, etc.), and acute respiratory diseases that take a protracted course often occur. However, excess protein can have a negative impact on health. With prolonged use of high-protein foods, kidney and liver function suffers, nervous excitability increases, allergic reactions often appear, and intoxication is possible due to incomplete breakdown and oxidation of proteins with the formation of toxic substances.

The most common cause of imbalance in diets is insufficient consumption of 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 pressing 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: studying the chemical composition of proteins, their effect on the human body, problems of processing and storing proteins, their properties, studying methods for studying the protein content in food products, checking the compliance of the actual protein content in the product with the standardized one.

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 – . Amino acid residues in proteins are connected by an amide bond between the 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 joined by peptide bonds are called polypeptides. A protein, as a biologically significant structure, can be either one polypeptide or several polypeptides that form a single complex as a result of non-covalent interactions.

Elemental composition of proteins

When 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 of carbon (50-55%), oxygen (21-23%), nitrogen (15-17%), hydrogen (6-7%), sulfur (0.3-2.5%) in all proteins . Phosphorus, iodine, iron, copper and some other macro- and microelements, in various, often very small quantities, were also found in the composition of individual proteins.

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

Amino acids

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 is clear that all amino acids include the following general groups: – CH2, – NH2, – COOH. The side chains (radicals - R) of amino acids differ. The chemical nature of radicals is diverse: from the hydrogen atom to cyclic compounds. It is radicals that determine the structural and functional characteristics of amino acids.

All amino acids, except for the simplest aminoacetic acid 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 twenty basic amino acids, but the rest, quite diverse amino acids, are formed from these 20 amino acid residues already in the protein molecule. Among such transformations, we should first of all note the formation of disulfide bridges during the oxidation of two cysteine residues in the composition of already formed peptide chains. As a result, a cystine diaminodicarboxylic acid 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 having two polypeptide chains, connected by disulfide bridges, as well as cross-links within one of the polypeptide chains:

GIVEQCCASVCSLYQLENYCN

FVNQHLCGSHLVEALYLVCGERGFFYTPKA

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

Acyclic. Monoaminomonocarboxylic amino acids contain one amine and one carboxyl group; they are neutral in an aqueous solution. Some of them have common structural features, which allows us to consider them 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 acids, heme, and is necessary for the neutralization of toxic products in the liver. Alanine is used by the body in various processes of carbohydrate and energy metabolism. Its isomer b-alanine is a component of vitamin pantothenic acid, coenzyme A (CoA), and muscle extractives.

2. Serine and threonine. They belong to the group of hydroxy acids, because have a hydroxyl group. Serine is a component 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 importance 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 high oxidative capacity (in case of radiation injury, phosphorus poisoning). Methionine is characterized by the presence of a readily 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 actively participate in metabolism and are not synthesized in the body.

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

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

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

1.1.2. Protein classification

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

Proteins

Proteins are simple proteins consisting of only the protein part. They are widespread in the animal and plant world. 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 (creating oncotic pressure) and transport various substances with the blood. Globulins are part of the enzymes that form the basis of immunoglobulins, which perform the functions of antibodies. In the blood serum, there is a constant ratio between these two components - the albumin-globulin ratio (A/G), equal to 1.7 - 2.3 and having important diagnostic value.

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

Proteids

Proteids are complex proteins consisting of protein and non-protein parts. The name of a protein is determined by the name of its prosthetic group. Thus, nucleic acids are the non-protein part of nucleoproteins, phosphoric acid is part of phosphoproteins, carbohydrates are glycoproteins, and lipids are part of 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 - they are complexes of viral nucleic acid and a protein shell - the 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 the globin protein and the 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 types. Each a-chain contains 141 and each b-chain contains 146 amino acid residues.

Myoglobin. Chromoprotein found in muscles. It consists of only one chain, similar to the hemoglobin subunit. Myoglobin is the respiratory pigment of muscle tissue. It binds with oxygen much more easily than hemoglobin, but releases it more difficult. 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 functioning of the heart muscles. A high content of myoglobin has been 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 carbohydrate derivatives (amino sugars, hexuronic acids). Glycoproteins are part of cell membranes. Thus, the pulmonary walls of bacteria are built from peptidoglycans, which are derivatives of linear polysaccharides carrying peptide fragments covalently linked to them. These fragments crosslink polysaccharide chains to form 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, and every second residue carries a fragment attached to it at the C3 atom, formed by amide-linked lactic acid residues, L -alanine, D-glutamate (via g-carboxyl), mesodiaminone melinate and D-alanine.

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

Phosphoproteins. They have phosphorus 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 nerve tissue.

Lipoproteins. Complex proteins whose prosthetic group is formed by lipids. In structure, these are small-sized (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 is formed 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 lipoproteins (HDL), which are sometimes referred to as a- and b-lipoproteins.

Chylomicrons are the largest of the 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 into the blood.

1.1.3. Properties of proteins

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

Proteins actively 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 therefore proteins, which ensures their transport through the blood.

Proteins are high molecular weight 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. Thus, 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 is 64,500 (574 amino acid residues). Other proteins have higher molecular weights: g-globulin (forms antibodies) consists of 1250 amino acids and has a molecular weight of about 150,000, and the molecular weight of the enzyme glutamate dehydrogenase 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 are part of amino acid radicals. For example, the acidic properties of protein are imparted by the carboxyl groups of the aspartic glutamic amino acid, and the alkaline ones are imparted by the radicals of arginine, lysine and histidine. The more dicarboxylic amino acids a protein contains, the more pronounced its acidic properties and vice versa.

These same groups also have electrical charges that form net charge of a protein molecule. In proteins where aspartic and glutamine amino acids predominate, the protein charge 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. Thus, 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.

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

Aqueous solutions of proteins have their own characteristics. Firstly, 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 hydration 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 water more easily and have a relatively large water shell, while globulins and fibrinogen bind water less well and have a smaller hydration shell. Thus, the stability of an aqueous protein solution is determined by two factors: the presence of a charge on the protein molecule and the aqueous 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 varied. They are largely due to the complexity and diversity of the forms and composition of the proteins themselves. Protein is found in a variety of foods, but the main sources are eggs, milk, and meat (Table 1).

Table 1 - Products containing proteins

Proteins are an irreplaceable building material. One of the most important functions of protein molecules is plastic. All cell membranes contain a protein, the role of which is varied. The amount of protein in the membranes is more than half 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 contraction, glycogen - a nutrient, inorganic salts and many other substances, in particular calcium.

The great role of proteins in transport of substances in organism. Having various functional groups and a complex macromolecule structure, proteins bind and transport many compounds through the bloodstream. This is, first of all, hemoglobin, which carries oxygen from the lungs to the cells. In muscles, this function is taken over by another transport protein - myoglobin.

Another function of protein is spare. 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 most well-known hormone proteins is insulin. This simple protein consists of only amino acids. The functional role of insulin is multifaceted. It reduces blood sugar, promotes glycogen synthesis in the liver and muscles, increases the formation of fats from carbohydrates, affects phosphorus metabolism, and enriches cells with potassium.

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.

One of the important and chemically interesting hormones is vasopressin. It suppresses urine production and increases blood pressure. Vasopressin is a cyclic octapeptide.

A regulatory function is also performed by proteins contained in the thyroid gland - thyroglobulins, whose molecular weight is about 600,000. These proteins contain iodine. When the gland is underdeveloped, metabolism is disrupted.

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

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

It should also be mentioned that there are 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 proteins - enzyme inhibitors - are isolated in pure form and are 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 by their functions, then such systematization could not be considered complete, since new studies provide many facts that make it possible to identify new groups of proteins with new functions. Among them are unique substances - neuropeptides(responsible for the most important life processes: sleep, memory, pain, feelings of fear, anxiety).

1.3. Changes in protein content during processing

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

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

Products such as meat, fish, eggs cannot be overcooked, as this reduces their digestibility due to changes occurring in protein molecules: collagen turns into gluten, softening the tissue.

Denaturation of proteins - this is a complex process in which, under the influence of external factors (temperature, mechanical stress, the action of acids, alkalis, ultrasound, etc.), a change occurs in the secondary, tertiary and quaternary structures of the protein macromolecule, i.e. the native (natural) spatial structure. The primary structure, and therefore the chemical composition of the protein, does not change. During cooking, protein denaturation is most often caused by heat. This process occurs differently in globular and fibrillar proteins. 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 are broken and the polypeptide chain unfolds and then folds in a new way. In this case, polar (charged) hydrophilic groups located on the surface of the globule and ensuring its charge and stability move inside the globule, and reactive hydrophobic groups (disulfide, sulfhydryl, etc.) that are unable 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; upon denaturation, enzyme proteins lose activity); increased attackability by digestive enzymes (as a rule, heat-treated foods containing proteins are digested more fully and easily); loss of ability to hydrate (dissolve, swell); loss of stability of protein globules, which is accompanied by their aggregation (coagulation, or coagulation, of the protein).

Aggregation- this is the interaction of denatured protein molecules, which is accompanied by the formation of larger particles. Externally, this is expressed differently depending on the concentration and colloidal state of the proteins in solution. Thus, in low-concentrated solutions (up to 1%), the coagulated protein forms flakes (foam on the surface of the broth). 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.), become denser during denaturation, and their dehydration occurs with the separation of liquid into the environment. A protein gel subjected to heating, as a rule, has a smaller volume, weight, 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.

Destruction of proteins. With prolonged heat treatment, proteins undergo more profound changes associated with the destruction of their macromolecules. At the first stage of changes, functional groups can be split off from protein molecules to form volatile compounds such 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. With further hydrothermal treatment, the proteins are hydrolyzed, and 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 method of culinary processing that contributes to the intensification of the technological process (the use of enzyme preparations to soften meat, weaken the gluten of dough, obtain protein hydrolysates, etc.).

Foaming. Proteins are widely used as foaming agents in the production of confectionery products (sponge dough, egg whites), 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. These determinations of molecular weight, sedimentation constants, and diffusion rates of protein particles formed during freezing and refrigerated storage indicate structural changes in this protein. According to some data, during the process of refrigeration of fish, not only a decrease, but also an increase in protein solubility is possible. Thus, in Baltic herring, protein solubility in the muscle tissue of frozen fish increased even during rigor mortis.

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

Interactions between lipids and proteins occur in foods and during frozen storage. 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 product storage is determined by many factors and depends on the activity of various muscle tissue enzymes and individual transformations of amino acids, on the amino acid composition of proteins being broken down, 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 protein content

Methods for quantitative determination of the protein fraction are based on determining the amount of total nitrogen. The most common is the determination by the Kjeldahl method, which allows the isolation of nitrogen in the form of ammonia 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, highly 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 combustion of the sample is completed, excess acid is neutralized with alkali, and ammonia bound in the form of ammonium sulfate is displaced by excess alkali

(NH4)2SO4 + 2NaOH → Na2SO4 + 2NH4OH.

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

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

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

Formol titration method.

Another quantitative method for determining protein content is the formol 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 exceeding 22 ºT. Canned samples cannot be controlled using this method.

The method consists in blocking the NH2 groups of the product proteins with added formalin to form 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 the titration of acidic carboxyl groups is recalculated to the mass fraction of proteins.

The study is carried out according to the following scheme:

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

To convert the amount of sodium hydroxide solution into percent protein, you can use the table.

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

Table 2 - Dependence of the mass fraction of proteins on the volume of alkali solution spent on titrating samples in the presence of formalin

2.2. Characteristics of qualitative methods for determining protein content

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 the gluing of protein molecules and their precipitation. Precipitation of proteins can be reversible or irreversible depending on the reagents and reaction conditions. In laboratory practice, precipitation reactions are used to isolate albumin and globulin fractions of proteins, quantitatively characterize their stability, detect proteins in biological fluids and free them from them in order to obtain a protein-free solution.

Reversible deposition.

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

Salting out. The albumin fraction of proteins is precipitated with a saturated solution of ammonium sulfate, and the globulin fraction is precipitated with a semi-saturated solution.

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

Progress of determination. 30 drops of undiluted sample are poured into a test tube and an equal amount of saturated ammonium sulfate solution is added. The contents of the test tube are mixed. 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, then mixed with ammonium sulfate powder until the salt stops dissolving, and a precipitate - globulins - precipitates.

Irreversible precipitation of proteins.

Irreversible protein precipitation 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, and salts of heavy metals.

Boiling precipitation. Proteins are thermolabile compounds and are denatured when heated above 50-60 degrees C. The essence of thermal denaturation is the destruction of the hydration shell, the breaking of the bonds stabilizing the protein globule and the unfolding of the protein molecule. The most complete and rapid deposition occurs at the isoelectric point (when the charge of the molecule is zero), since the protein particles are the least stable. Proteins with acidic properties precipitate in a slightly acidic environment, and proteins with basic properties precipitate in a slightly alkaline environment. 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.

Progress of determination. 10 drops of sample solution are poured into 4 numbered test tubes. Then the 1st test tube is heated to boiling, and 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; Add 1 drop of 1% acetic acid solution to the second test tube and heat 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 test tube and heat to boiling. No precipitate is formed, since in a strongly acidic environment the protein particles acquire a positive charge (one of the protein stability factors in solution is retained); 1 drop of NaOH solution is poured into the 4th test tube and heated to boiling. A precipitate does not form because the negative charge of the protein increases in an alkaline environment.

Precipitation with concentrated mineral acids. Concentrated acids (sulfuric, 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 denatured protein dissolves again. Apparently, this occurs as a result of the recharging of protein molecules and their partial hydrolysis. When adding excess nitric acid, the precipitate does not dissolve. This is why nitric acid is used to determine small amounts of protein in urine in clinical studies.

Progress of determination. 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, carefully layer the same volume of sample along the wall. At the border of the two layers, a protein sediment appears in the form of a white ring. Shake the test tubes carefully, observe the dissolution of the protein in test tubes with sulfuric and hydrochloric acids; in a test tube with nitric acid, protein dissolution does not occur.

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

Progress of determination. Add 5 drops of sample solution into two test tubes. Add 2 drops of sulfosalicylic acid to one of them, and 5 drops of trichloroacetic acid to the other. A protein precipitate appears in the test tubes.

Precipitation of protein by salts of heavy metals. Proteins, when interacting with salts of lead, copper, mercury, silver and other heavy metals, are denatured and precipitate. However, with an excess of certain 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.

Progress of determination. Add 5 drops of sample into three test tubes. Add 1 drop of lead acetate to the first, 1 drop of silver nitrate to the third. A precipitate forms in all test tubes. Then 10 drops of silver nitrate are added to the first test tube - the precipitate does not dissolve.

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

Progress of determination. Add 5 drops of sample solution, 3 drops of NaOH, 1 drop of Cu(OH)2 into the test tube and mix. The contents of the test 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.

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

Xanthoprotein reaction. When concentrated nitric acid is added to a 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.

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

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

Progress of determination. Add 10 drops of acetic acid to one drop of sample. Having tilted the test tube, carefully add 0.5 ml of sulfuric acid dropwise along the wall so that the liquids do not mix. When the test tube stands at the boundary of the liquids, a red-violet ring appears.

Foll reaction. Amino acids containing sulfhydryl groups - SH, undergo alkaline hydrolysis to form 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.

Progress of determination. To 5 drops of the sample solution add 5 drops of Foll's reagent (an equal volume of 30% NaOH solution is added to a 5% lead acetate solution until the precipitate that forms is dissolved). and boil for 2-3 minutes. After settling for 1-2 minutes. a black or brown precipitate appears.

3. Experimental part

3.1. Justification for choosing the research object

I chose a chicken egg as the object of my research, since 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 on average about 200 eggs per year. But eggs are not just an ordinary food product.

Eggs not only contain a rich cocktail of nutrients, but eggs will allow your culinary imagination to have no limits. In Germany, they love soft-boiled eggs for breakfast, Americans call their scrambled eggs “sunny side up,” the Spaniards are in love with their tortilla, the Italians prefer frittata, a type of omelette, and the gourmet Japanese dip raw meat in 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 - eggs everywhere give themselves away with the golden color of the yolk.

The highest quality of protein and the combination of various vital elements make eggs an extremely valuable food product. A large egg contains approximately 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 necessary in the retina of the eye both for the perception of light and darkness, and for distinguishing color. 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 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 particularly unstable vitamin creates new cells and activates growth. Folic acid deficiency is one of the most common forms of vitamin deficiency and often occurs together with iron deficiency. But eggs are also a real treasure trove of minerals: calcium, magnesium, potassium, iron, zinc, iodine and fluorine make eggs one of the most nutritious foods on Earth.

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

The data given refers to eggs as a whole, not whites or yolks. These days 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 greater.

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

A chicken egg, compared to other animal products, contains the most complete protein, almost completely absorbed by the body. Egg white contains all the essential amino acids in the most optimal proportions.

Below is a table that shows the protein content by weight of some protein-supplying foods and the percentage of that protein that can actually be absorbed by our bodies.

Table 4 – weight protein content in products, %

The table shows that, for example, eggs contain only 12% protein, but thanks 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 soybean flour, but the composition of this protein allows only 61% of this amount to be absorbed.

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 labels) and the amount that the body actually uses.

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

Accordingly, proteins that lack essential amino acids are called incomplete; those that contain enough essential amino acids are complete; egg whites are complete.

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

According to current Russian standards, every egg produced at a poultry farm must be marked.

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

The letter "D" means a dietary egg; such eggs are sold within 7 days.

The letter "C" stands for a table egg, which is sold within 25 days.

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

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

Characteristics of the research object

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

OJSC Chelyabinsk Poultry Farm 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 high-quality chicken eggs obtained from Lohmann LSL-Classic cross birds. Today, Chelyabinsk Poultry Farm OJSC unites five structural divisions: the Chelyabinsk poultry farm, the Yemanzhelinsky breeding facility, the Petropavlovsk grain complex, the Yemanzhelinsky grain collection point and the Kurochkino sanatorium.

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

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

Sample No. 3 is a selective table egg (SD), produced on March 26, 2009, weighing 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 sample 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.

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 to the mark. Having mixed the contents of the flask well, take a 10 ml sample and accurately titrate with 0.5 N NaOH against phenolphthalein to determine the amount of alkali required for neutralization.

After this, take a sample of the same solution in 10 ml and transfer it to another 100 ml volumetric flask, add a specified amount of 0.5 N NaOH to neutralize the acid. After this, add water to the mark and shake well. This liquid is used to prepare colored solutions.

Preparation of colored solutions. To do this, prepare working and standard solutions in two 100 ml volumetric flasks. 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 is added and adjusted to the mark.

Then the optical density of the resulting colored solutions is determined.

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 standard working solution;

Dm is the optical density of the working solution;

Dm is the optical density of the standard solution;

m – mass of a sample 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 – Amount of protein content in the studied samples

The most protein is contained in a dietary egg of the first category (D1) (Sample No. 1). This is explained by the fact that a dietary egg is the freshest egg, laid no more than a week ago. According to research, microbiological processes continue to occur in the egg throughout the 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 according to the literature, the egg white of a dietary egg white should contain about 19% protein, and the yolk about 18%, and the study revealed that the protein content in the white is 18.7%, and in the yolk 17.6% . We can conclude that the deviations in protein content are small, but still exist, which is explained by improper storage of the egg.

Selected table eggs (SS) (Sample No. 3) contain less protein than dietary eggs, 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 °C. If you maintain optimal air humidity and carbon dioxide content, you can store eggs for up to 9 months. But at the same time, denaturation and aggregation of the protein in the egg occurs. According to the literature, the white of a table egg should contain about 17% protein, and the yolk about 16%, and the study revealed that the protein content in the white is 16.5%, and the yolk is 15.7%. We can conclude that deviations in protein content are small, but still exist, which is explained by the fact that all necessary conditions are not met during storage.

In a table egg of the first category (C1) (Oratz No. 2), the protein content does not differ much from the protein content in a selected table egg, which is explained by the fact that a table egg of the first category differs from a selected 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.

During 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 proteins. Based on the results of the study, we can conclude that the quality of eggs from modern producers and the protein content in them corresponds to the standardized indicators, but with small deviations, which is explained by the duration of storage and possible inconsistency in the egg storage regime.

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 plant origin, such as peas, beans, buckwheat and pearl barley, millet, rice; and it has also been determined that proteins are necessary and vital elements of the chemical composition of food products that perform many functions - plastic, contractile, storage, regulatory and protective.

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

Bibliography

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

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

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

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

5. http://www.chepfa.ru

Annex 1

Diary of calculations

Sample No. 1. Dietary egg of the first category

Protein: optical density of the test sample – 0.237

sample weight – 0.0465 g

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

Yolk: optical density of the test sample – 0.220