Contents:

What is protein and what functions does it perform in the body? What elements are included in its composition and what is the peculiarity of this substance.

Proteins are the main building material in the human body. Considered as a whole, these substances make up one fifth of our body. A group of subspecies is known in nature - the human body alone contains five million different variants. With its participation, cells are formed, which are considered the main component of living tissues of the body. What elements make up proteins and what is the peculiarity of the substance?

Subtleties of composition

Protein molecules in the human body differ in structure and take on certain functions. Thus, myosin is considered the main contractile protein, which forms muscles and guarantees the movement of the body. It ensures the functioning of the intestines and the movement of blood through human vessels. An equally important substance in the body is creatine. The function of the substance is to protect the skin from negative effects - radiation, temperature, mechanical and others. Creatine also protects against the entry of microbes from outside.

Proteins contain amino acids. Moreover, the first of them was discovered at the beginning of the 19th century, and the entire amino acid composition has been known to scientists since the 30s of the last century. It is interesting that of the two hundred amino acids that are discovered today, only two dozen form millions of proteins with different structures.

The main difference in the structure is the presence of radicals of different nature. Additionally, amino acids are often classified based on their electrical charge. Each of the components under consideration has common characteristics - the ability to react with alkalis and acids, solubility in water, and so on. Almost all representatives of the amino acid group are involved in metabolic processes.

Considering the composition of proteins, it is worth highlighting two categories of amino acids – nonessential and essential. They differ from each other in their ability to be synthesized in the body. The former are produced in the organs, which guarantees at least partial coverage of the current deficit, while the latter are supplied only with food. If the amount of any of the amino acids decreases, this leads to disturbances and sometimes death.

A protein that contains a complete set of amino acids is called “biologically complete.” Such substances are part of animal food. Some plant representatives, such as beans, peas and soybeans, are also considered useful exceptions. The main parameter by which the benefits of a product are judged is its biological value. If we consider milk as the base ( 100% ), then for fish or meat this parameter will be equals 95, for rice – 58 , bread (rye only) – 74 and so on.

Essential amino acids that make up protein are involved in the synthesis of new cells and enzymes, that is, they cover plastic needs and are used as the main sources of energy. Proteins contain elements that are capable of transformations, that is, the processes of decarboxylation and transamination. The reactions mentioned above involve two groups of amino acids (carboxyl and amine).

Egg white is considered the most valuable and beneficial for the body, the structure and properties of which are perfectly balanced. This is why the percentage of amino acids in a product is almost always used as a basis for comparison.

It was mentioned above that proteins consist of amino acids, and independent representatives play the main role. Here are some of them:

• Histidine- an element that was obtained in 1911. Its function is aimed at normalizing conditioned reflex work. Histidine plays the role of a source for the formation of histamine, a key mediator of the central nervous system involved in the transmission of signals to different parts of the body. If the remainder of this amino acid decreases below normal, the production of hemoglobin in the human bone marrow is suppressed.
• Valin- a substance discovered in 1879, but finally deciphered only 27 years later. If it is lacking, coordination is impaired and the skin becomes sensitive to external irritants.
• Tyrosine(1846). Proteins are made up of many amino acids, but this one plays one of the key functions. It is tyrosine that is considered the main precursor of the following compounds - phenol, tyramine, thyroid gland and others.
• Methionine synthesized only towards the end of the 20s of the last century. The substance helps in the synthesis of choline, protects the liver from excessive fat formation, and has a lipotropic effect. It has been proven that such elements play a key role in the fight against atherosclerosis and in regulating cholesterol levels. The chemical peculiarity of methionine is that it participates in the production of adrenaline and interacts with vitamin B.
• Cystine- a substance whose structure was established only in 1903. Its functions are aimed at participating in chemical reactions and methionine metabolic processes. Cystine also reacts with sulfur-containing substances (enzymes).
• Tryptophan– an essential amino acid that is part of proteins. It was synthesized by 1907. The substance is involved in protein metabolism and guarantees optimal nitrogen balance in the human body. Tryptophan is involved in the production of serum proteins and hemoglobin.
• Leucine– one of the “earliest” amino acids, known since the beginning of the 19th century. Its action is aimed at helping the body grow. Lack of the element leads to disruption of the kidneys and thyroid gland.
• Isoleucine– a key element involved in nitrogen balance. Scientists discovered the amino acid only in 1890.
• Phenylalanine synthesized in the early 90s of the 19th century. The substance is considered the basis for the formation of adrenal and thyroid hormones. Element deficiency is the main cause of hormonal imbalances.
• Lysine received only at the beginning of the 20th century. Lack of the substance leads to the accumulation of calcium in bone tissue, a decrease in muscle volume in the body, the development of anemia, and so on.

It is worth highlighting the chemical composition of proteins. This is not surprising, because the substances in question belong to chemical compounds.

• carbon – 50-55%;
• oxygen – 22-23%;
• nitrogen – 16-17%;
• hydrogen – 6-7%;
• sulfur – 0,4-2,5%.

In addition to those listed above, proteins include the following elements (depending on the type):

• copper;
• iron;
• phosphorus;
• micro- and macrosubstances.

The chemical content of different proteins differs. The only exception is nitrogen, the content of which is always 16-17%. For this reason, the level of substance content is determined precisely by the percentage of nitrogen. The calculation process is as follows. Scientists know that 6.25 grams of protein contains one gram of nitrogen. To determine the protein volume, simply multiply the current amount of nitrogen by 6.25.

Subtleties of structure

When considering the question of what proteins are made of, it is worth studying the structure of this substance. Highlight:

• Primary structure. The basis is the alternation of amino acids in the composition. If at least one element is included or “falls out”, then a new molecule is formed. Thanks to this feature, the total number of the latter reaches an astronomical figure.
• Secondary structure. The peculiarity of the molecules in the protein is that they are not in an extended state, but have different (sometimes complex) configurations. Thanks to this, the life of the cell is simplified. The secondary structure has the form of a spiral formed from uniform turns. In this case, adjacent turns are characterized by close hydrogen bonding. In case of repeated repetition, stability increases.
• Tertiary structure is formed due to the ability of the mentioned spiral to fit into a ball. It is worth knowing that the composition and structure of proteins largely depends on the primary structure. The tertiary base, in turn, guarantees the retention of high-quality bonds between amino acids with different charges.
• Quaternary structure characteristic of some proteins (hemoglobin). The latter forms not one, but several chains that differ in their primary structure.

The secret of protein molecules is in a general pattern. The higher the structural level, the less well the formed chemical bonds are held together. Thus, secondary, tertiary and quaternary structures are exposed to radiation, high temperatures and other environmental conditions. The result is often a violation of the structure (denaturation). At the same time, a simple protein, if its structure changes, is capable of rapid recovery. If the substance has been subjected to negative temperature action or the influence of other factors, then the denaturation process is irreversible, and the substance itself cannot be restored.

Properties

Above we discussed what proteins are, the definition of these elements, structure and other important issues. But the information will be incomplete if the main properties of the substance (physical and chemical) are not highlighted.

Protein molecular weight – from 10 thousand to one million(a lot depends on the type here). In addition, they are soluble in water.

It is worth highlighting the common features of protein with colloidal solutions:

• Swelling ability. The higher the viscosity of the composition, the higher the molecular weight.
• Slow diffusion.
• The ability for dialysis, that is, the division of amino acid groups into other elements using semi-permeable membranes. The main difference between the substances under consideration is their inability to pass through membranes.
• Two-factor stability. This means that the protein is hydrophilic in structure. The charge of a substance directly depends on what the protein consists of, the number of amino acids and their properties.
• The size of each particle is 1-100 nm.

Also, proteins have certain similarities with true solutions. The main thing is the ability to form homogeneous systems. In this case, the formation process is spontaneous and does not require an additional stabilizer. In addition, protein solutions are thermodynamically stable.

Scientists highlight the special amorphous properties of the substances in question. This is explained by the presence of an amino group. If the protein is presented in the form of an aqueous solution, then there are equally different mixtures in it - cationic, bipolar ions, as well as anionic forms.

Also The properties of protein include:

• The ability to act as a buffer, that is, to react similarly to a weak acid or base. Thus, in the human body there are two types of buffer systems - protein and hemoglobin, which are involved in normalizing the level of homeostasis.
• Movement in an electric field. Depending on the number of amino acids in the protein, their mass and charge, the speed of movement of the molecules also changes. This function is used for separation using electrophoresis.
• Salting out (reverse precipitation). If ammonium ions, alkaline earth metals, and alkali salts are added to a protein solution, these molecules and ions compete with each other for water. Against this background, the hydration shell is removed, and the proteins cease to be stable. As a result, they precipitate. If you add a certain volume of water, it is possible to restore the hydration shell.
• Sensitivity to external influences. It is worth noting that in the event of a negative external influence, proteins are destroyed, which leads to the loss of many chemical and physical properties. In addition, denaturation causes the rupture of the main bonds that stabilize all levels of the protein structure (except the primary one).

There are many reasons for denaturation– the negative effect of organic acids, the effect of alkalis or heavy metal ions, the negative effect of urea and various reducing agents leading to the destruction of disulfide-type bridges.

• The presence of color reactions with different chemical elements (depending on the amino acid composition). This property is used in laboratory conditions when it is necessary to determine the total amount of protein.

Results

Protein is a key element of the cell, ensuring the normal development and growth of a living organism. But, despite the fact that scientists have studied the substance, there are still many discoveries ahead that will allow us to gain a deeper understanding of the secrets of the human body and its structure. In the meantime, each of us should know where proteins are formed, what their features are and for what purposes they are needed.

Squirrels- high molecular weight organic compounds consisting of α-amino acid residues.

IN protein composition includes carbon, hydrogen, nitrogen, oxygen, sulfur. Some proteins form complexes with other molecules containing phosphorus, iron, zinc and copper.

Proteins have a large molecular weight: egg albumin - 36,000, hemoglobin - 152,000, myosin - 500,000. For comparison: the molecular weight of alcohol is 46, acetic acid - 60, benzene - 78.

Amino acid composition of proteins

Squirrels- non-periodic polymers, the monomers of which are α-amino acids. Typically, 20 types of α-amino acids are called protein monomers, although over 170 of them are found in cells and tissues.

Depending on whether amino acids can be synthesized in the body of humans and other animals, they are distinguished: nonessential amino acids- can be synthesized; essential amino acids- cannot be synthesized. Essential amino acids must be supplied to the body through food. Plants synthesize all types of amino acids.

Depending on the amino acid composition, proteins are: complete- contain the entire set of amino acids; defective- some amino acids are missing in their composition. If proteins consist only of amino acids, they are called simple. If proteins contain, in addition to amino acids, a non-amino acid component (prosthetic group), they are called complex. The prosthetic group can be represented by metals (metalloproteins), carbohydrates (glycoproteins), lipids (lipoproteins), nucleic acids (nucleoproteins).

All amino acids contain: 1) carboxyl group (-COOH), 2) amino group (-NH 2), 3) radical or R-group (the rest of the molecule). The structure of the radical is different for different types of amino acids. Depending on the number of amino groups and carboxyl groups included in the composition of amino acids, they are distinguished: neutral amino acids having one carboxyl group and one amino group; basic amino acids having more than one amino group; acidic amino acids having more than one carboxyl group.

Amino acids are amphoteric compounds, since in solution they can act as both acids and bases. In aqueous solutions, amino acids exist in different ionic forms.

Peptide bond

Peptides- organic substances consisting of amino acid residues connected by peptide bonds.

The formation of peptides occurs as a result of the condensation reaction of amino acids. When the amino group of one amino acid interacts with the carboxyl group of another, a covalent nitrogen-carbon bond occurs between them, which is called peptide. Depending on the number of amino acid residues included in the peptide, there are dipeptides, tripeptides, tetrapeptides etc. The formation of a peptide bond can be repeated many times. This leads to the formation polypeptides. At one end of the peptide there is a free amino group (called the N-terminus), and at the other there is a free carboxyl group (called the C-terminus).

Spatial organization of protein molecules

The performance of certain specific functions by proteins depends on the spatial configuration of their molecules; in addition, it is energetically unfavorable for the cell to keep proteins in an unfolded form, in the form of a chain, therefore polypeptide chains undergo folding, acquiring a certain three-dimensional structure, or conformation. There are 4 levels spatial organization of proteins.

Primary protein structure- the sequence of arrangement of amino acid residues in the polypeptide chain that makes up the protein molecule. The bond between amino acids is a peptide bond.

If a protein molecule consists of only 10 amino acid residues, then the number of theoretically possible variants of protein molecules that differ in the order of alternation of amino acids is 10 20. Having 20 amino acids, you can make even more diverse combinations from them. About ten thousand different proteins have been found in the human body, which differ both from each other and from the proteins of other organisms.

It is the primary structure of the protein molecule that determines the properties of the protein molecules and its spatial configuration. Replacing just one amino acid with another in a polypeptide chain leads to a change in the properties and functions of the protein. For example, replacing the sixth glutamic amino acid with valine in the β-subunit of hemoglobin leads to the fact that the hemoglobin molecule as a whole cannot perform its main function - oxygen transport; In such cases, the person develops a disease called sickle cell anemia.

Secondary structure- ordered folding of the polypeptide chain into a spiral (looks like an extended spring). The turns of the helix are strengthened by hydrogen bonds that arise between carboxyl groups and amino groups. Almost all CO and NH groups take part in the formation of hydrogen bonds. They are weaker than peptide ones, but, repeated many times, impart stability and rigidity to this configuration. At the level of secondary structure, there are proteins: fibroin (silk, spider web), keratin (hair, nails), collagen (tendons).

Tertiary structure- packing of polypeptide chains into globules, resulting from the formation of chemical bonds (hydrogen, ionic, disulfide) and the establishment of hydrophobic interactions between the radicals of amino acid residues. The main role in the formation of the tertiary structure is played by hydrophilic-hydrophobic interactions. In aqueous solutions, hydrophobic radicals tend to hide from water, grouping inside the globule, while hydrophilic radicals, as a result of hydration (interaction with water dipoles), tend to appear on the surface of the molecule. In some proteins, the tertiary structure is stabilized by disulfide covalent bonds formed between the sulfur atoms of two cysteine ​​residues. At the tertiary structure level there are enzymes, antibodies, and some hormones.

Quaternary structure characteristic of complex proteins whose molecules are formed by two or more globules. The subunits are held in the molecule by ionic, hydrophobic, and electrostatic interactions. Sometimes, during the formation of a quaternary structure, disulfide bonds occur between subunits. The most studied protein with a quaternary structure is hemoglobin. It is formed by two α-subunits (141 amino acid residues) and two β-subunits (146 amino acid residues). Associated with each subunit is a heme molecule containing iron.

If for some reason the spatial conformation of proteins deviates from normal, the protein cannot perform its functions. For example, the cause of “mad cow disease” (spongiform encephalopathy) is the abnormal conformation of prions, the surface proteins of nerve cells.

Properties of proteins

The amino acid composition and structure of the protein molecule determine it properties. Proteins combine basic and acidic properties, determined by amino acid radicals: the more acidic amino acids in a protein, the more pronounced its acidic properties. The ability to donate and add H + is determined buffering properties of proteins; One of the most powerful buffers is hemoglobin in red blood cells, which maintains blood pH at a constant level. There are soluble proteins (fibrinogen), and there are insoluble proteins that perform mechanical functions (fibroin, keratin, collagen). There are proteins that are chemically active (enzymes), there are chemically inactive proteins that are resistant to various environmental conditions and those that are extremely unstable.

External factors (heat, ultraviolet radiation, heavy metals and their salts, pH changes, radiation, dehydration)

can cause disruption of the structural organization of the protein molecule. The process of loss of the three-dimensional conformation inherent in a given protein molecule is called denaturation. The cause of denaturation is the breaking of bonds that stabilize a certain protein structure. Initially, the weakest ties are broken, and as conditions become stricter, even stronger ones are broken. Therefore, first the quaternary, then the tertiary and secondary structures are lost. A change in spatial configuration leads to a change in the properties of the protein and, as a result, makes it impossible for the protein to perform its inherent biological functions. If denaturation is not accompanied by destruction of the primary structure, then it may be reversible, in this case, self-recovery of the conformation characteristic of the protein occurs. For example, membrane receptor proteins undergo such denaturation. The process of restoring protein structure after denaturation is called renaturation. If restoration of the spatial configuration of the protein is impossible, then denaturation is called irreversible.

Functions of proteins

Function	Examples and explanations
Construction	Proteins are involved in the formation of cellular and extracellular structures: they are part of cell membranes (lipoproteins, glycoproteins), hair (keratin), tendons (collagen), etc.
Transport	The blood protein hemoglobin attaches oxygen and transports it from the lungs to all tissues and organs, and from them transfers carbon dioxide to the lungs; The composition of cell membranes includes special proteins that ensure the active and strictly selective transfer of certain substances and ions from the cell to the external environment and back.
Regulatory	Protein hormones take part in the regulation of metabolic processes. For example, the hormone insulin regulates blood glucose levels, promotes glycogen synthesis, and increases the formation of fats from carbohydrates.
Protective	In response to the penetration of foreign proteins or microorganisms (antigens) into the body, special proteins are formed - antibodies that can bind and neutralize them. Fibrin, formed from fibrinogen, helps stop bleeding.
Motor	The contractile proteins actin and myosin provide muscle contraction in multicellular animals.
Signal	Built into the surface membrane of the cell are protein molecules that are capable of changing their tertiary structure in response to environmental factors, thus receiving signals from the external environment and transmitting commands to the cell.
Storage	In the body of animals, proteins, as a rule, are not stored, with the exception of egg albumin and milk casein. But thanks to proteins, some substances can be stored in the body; for example, during the breakdown of hemoglobin, iron is not removed from the body, but is stored, forming a complex with the protein ferritin.
Energy	When 1 g of protein breaks down into final products, 17.6 kJ is released. First, proteins break down into amino acids, and then into the final products - water, carbon dioxide and ammonia. However, proteins are used as a source of energy only when other sources (carbohydrates and fats) are used up.
Catalytic	One of the most important functions of proteins. Provided by proteins - enzymes that accelerate biochemical reactions occurring in cells. For example, ribulose biphosphate carboxylase catalyzes the fixation of CO 2 during photosynthesis.

Enzymes

Enzymes, or enzymes, are a special class of proteins that are biological catalysts. Thanks to enzymes, biochemical reactions occur at tremendous speed. The speed of enzymatic reactions is tens of thousands of times (and sometimes millions) higher than the speed of reactions occurring with the participation of inorganic catalysts. The substance on which the enzyme acts is called substrate.

Enzymes are globular proteins, structural features enzymes can be divided into two groups: simple and complex. Simple enzymes are simple proteins, i.e. consist only of amino acids. Complex enzymes are complex proteins, i.e. In addition to the protein part, they contain a group of non-protein nature - cofactor. Some enzymes use vitamins as cofactors. The enzyme molecule contains a special part called the active center. Active center- a small section of the enzyme (from three to twelve amino acid residues), where the binding of the substrate or substrates occurs to form an enzyme-substrate complex. Upon completion of the reaction, the enzyme-substrate complex breaks down into the enzyme and the reaction product(s). Some enzymes have (except active) allosteric centers- areas to which enzyme speed regulators are attached ( allosteric enzymes).

Reactions of enzymatic catalysis are characterized by: 1) high efficiency, 2) strict selectivity and direction of action, 3) substrate specificity, 4) fine and precise regulation. The substrate and reaction specificity of enzymatic catalysis reactions are explained by the hypotheses of E. Fischer (1890) and D. Koshland (1959).

E. Fisher (key-lock hypothesis) suggested that the spatial configurations of the active center of the enzyme and the substrate must correspond exactly to each other. The substrate is compared to the “key”, the enzyme to the “lock”.

D. Koshland (hand-glove hypothesis) suggested that the spatial correspondence between the structure of the substrate and the active center of the enzyme is created only at the moment of their interaction with each other. This hypothesis is also called induced correspondence hypothesis.

The rate of enzymatic reactions depends on: 1) temperature, 2) enzyme concentration, 3) substrate concentration, 4) pH. It should be emphasized that since enzymes are proteins, their activity is highest under physiologically normal conditions.

Most enzymes can only work at temperatures between 0 and 40°C. Within these limits, the reaction rate increases approximately 2 times with every 10 °C increase in temperature. At temperatures above 40 °C, the protein undergoes denaturation and enzyme activity decreases. At temperatures close to freezing, enzymes are inactivated.

As the amount of substrate increases, the rate of the enzymatic reaction increases until the number of substrate molecules equals the number of enzyme molecules. With a further increase in the amount of substrate, the speed will not increase, since the active centers of the enzyme are saturated. An increase in enzyme concentration leads to increased catalytic activity, since a larger number of substrate molecules undergo transformations per unit time.

For each enzyme, there is an optimal pH value at which it exhibits maximum activity (pepsin - 2.0, salivary amylase - 6.8, pancreatic lipase - 9.0). At higher or lower pH values, enzyme activity decreases. With sudden changes in pH, the enzyme denatures.

The speed of allosteric enzymes is regulated by substances that attach to allosteric centers. If these substances speed up a reaction, they are called activators, if they slow down - inhibitors.

Classification of enzymes

According to the type of chemical transformations they catalyze, enzymes are divided into 6 classes:

1. oxireductases(transfer of hydrogen, oxygen or electron atoms from one substance to another - dehydrogenase),
2. transferases(transfer of methyl, acyl, phosphate or amino group from one substance to another - transaminase),
3. hydrolases(hydrolysis reactions in which two products are formed from the substrate - amylase, lipase),
4. lyases(non-hydrolytic addition to the substrate or detachment of a group of atoms from it, in which case C-C, C-N, C-O, C-S bonds can be broken - decarboxylase),
5. isomerases(intramolecular rearrangement - isomerase),
6. ligases(the connection of two molecules as a result of the formation of C-C, C-N, C-O, C-S bonds - synthetase).

Classes are in turn subdivided into subclasses and subsubclasses. In the current international classification, each enzyme has a specific code, consisting of four numbers separated by dots. The first number is the class, the second is the subclass, the third is the subsubclass, the fourth is the serial number of the enzyme in this subclass, for example, the arginase code is 3.5.3.1.

Go to lectures No. 2"Structure and functions of carbohydrates and lipids"

Go to lectures No. 4"Structure and functions of ATP nucleic acids"

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 administered 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 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 makes it possible to widely use plasma 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 FCS, 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 rigor 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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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.

Squirrel rich in vitamins and minerals such as: vitamin B2 - 11.7%, vitamin PP - 20%, potassium - 12.2%, phosphorus - 21.5%, iron - 26.1%, selenium - 16.9%

Why is Belka useful?

• Vitamin B2 participates in redox reactions, helps to increase the color sensitivity of the visual analyzer and dark adaptation. Insufficient intake of vitamin B2 is accompanied by impaired condition of the skin, mucous membranes, and impaired light and twilight vision.
• Vitamin PP participates in redox reactions of energy metabolism. Insufficient vitamin intake is accompanied by disruption of the normal condition of the skin, gastrointestinal tract and nervous system.
• Potassium is the main intracellular ion that takes part in the regulation of water, acid and electrolyte balance, participates in the processes of conducting nerve impulses and regulating pressure.
• Phosphorus takes part in many physiological processes, including energy metabolism, regulates acid-base balance, is part of phospholipids, nucleotides and nucleic acids, and is necessary for the mineralization of bones and teeth. Deficiency leads to anorexia, anemia, and rickets.
• Iron is part of proteins of various functions, including enzymes. Participates in the transport of electrons and oxygen, ensures the occurrence of redox reactions and activation of peroxidation. Insufficient consumption leads to hypochromic anemia, myoglobin deficiency atony of skeletal muscles, increased fatigue, myocardiopathy, and atrophic gastritis.
• Selenium- an essential element of the antioxidant defense system of the human body, has an immunomodulatory effect, participates in the regulation of the action of thyroid hormones. Deficiency leads to Kashin-Beck disease (osteoarthritis with multiple deformities of the joints, spine and limbs), Keshan disease (endemic myocardiopathy), and hereditary thrombasthenia.

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