Protein coagulation occurs at what temperature. Coagulation of protein substances. Thrombin functions in hemostasis

Properly conducted cooking tends to increase the nutritional value of food by improving its taste and digestibility. In addition, thermal exposure ensures the sanitary well-being of the food.

To recommend the most expedient method of heat treatment of a particular product and to obtain a finished culinary product with the desired properties, it is necessary to know what physicochemical changes occur in the products.

However, since food products are complex compositions consisting of many substances (proteins, fats, carbohydrates, vitamins, etc.), it is advisable to first consider the changes in each of them separately.

Protein changes

When foods are cooked, their protein systems undergo various changes.

Violation of the native secondary and tertiary structures of proteins is called "protein denaturation". Denaturation of proteins can occur due to heating, mechanical action (when whipping), an increase in the concentration of salts in the system (when freezing, salting, drying products) and some other factors.

The depth of disturbance in the structure of proteins depends on the intensity of the impact of various factors, the possibility of simultaneous action of several of them, the concentration of proteins in the system, the pH of the medium, and the effect of various additives.

Denaturation of proteins entails a change in their hydration properties - water-binding capacity, which determines the taste of the finished product.

When soluble proteins are denatured, their water-binding capacity decreases to varying degrees, which depends on the depth of denaturation changes. Correct regulation of the factors that determine the denaturation and hydration properties of proteins during the technological process makes it possible to obtain high quality culinary products.

So, in practice, the dependence of denaturation and water-binding capacity of proteins on the pH of the medium is often used. Denaturation of muscle proteins in meat and fish at a pH close to the isoelectric point occurs at lower temperatures and is accompanied by a significant loss of water.

Therefore, by acidifying protein systems in some methods of processing fish and meat (pickling, etc.), conditions are created to reduce the depth of denaturation of proteins during heat treatment.

At the same time, the acidic environment promotes denaturation and disaggregation of the connective tissue protein collagen and the formation of products with increased water-holding capacity. As a result, the cooking time of the products is reduced, and the finished products acquire juiciness and good taste.

Denaturation also changes the physical state of protein systems, which is usually defined by the term "protein folding". The folding of various protein systems has its own specifics.

In some cases, coagulated proteins are released from the system in the form of flakes or clots (the formation of foam when cooking broths, jam), in others, the protein system is compacted with a part of the water pressed out of it together with the substances dissolved in it (production of cottage cheese from yogurt) or an increase strength of the system without compaction and moisture release (curdling of egg whites).

Along with physical changes, when protein systems are heated, complex chemical changes occur in the proteins themselves and in the substances interacting with them.

Proteins of vegetables and fruits

The amount of protein substances in vegetables and fruits does not exceed 2-2,5%. Proteins are wasps ­ the main structural elements of the cytoplasm, its organelles and nuclei of plant cells.

During heat treatment, proteins of the cytoplasm coagulate and form flakes; the cell membrane structure is destroyed. Its destruction promotes the diffusion of substances dissolved in the cell sap into the broth or other liquid in which vegetables have been cooked or stored, and the penetration of substances dissolved in the broth or other liquid into them.

Proteins of grain and flour products

Peas, beans, lentils contain about 20-23% protein substances, soy - 30%. In cereals and NS the number reaches 11% , and in wheat flour of the highest and first grades - 10 - 12%.

In grain-and-flour products, proteins are in a dehydrated state, therefore, when soaking legumes, boiling cereals or kneading dough, they are able to absorb moisture and swell.

When heated to 50-70 ° C, the swollen proteins coagulate and squeeze out part of the absorbed moisture, which is bound by gelatinized starch.

Used in culinary practice, sautéing wheat flour with or without fat at a temperature of 120 ° C and above affects the proteins contained in it, which are denatured and lose their ability to swell and form gluten.

Chicken egg whites

Egg white contains 11 -12% protein, yolk 15-16%. At a temperature of 50-55 ° C, the egg white begins to coagulate, which manifests itself in the form of local opacities, which, with a further increase in temperature, spread to the entire volume; upon reaching 80 ° C, the coagulated protein retains its shape.

Further heating increases the strength of the protein system, and is especially noticeable in the temperature range from 80 to 85 ° C. Upon reaching 95-100 ° C, the strength of the protein changes insignificantly over time.

Egg yolk curdles at higher temperatures. To increase its viscosity, the yolk must be heated to 70 ° C.

A mixture of protein with yolk manifests itself similarly to the yolk. Curled white, yolk, or a mixture of these holds the moisture bound and does not squeeze it out. The coagulation nature of the egg whites does not change if they are diluted with some water and the mixture is thoroughly mixed, however, the mechanical strength of the system decreases.

The ability of egg whites to bind moisture during clotting is used in culinary practice. The addition of eggs, water or milk to the proteins in the manufacture of omelets allows to reduce the mechanical strength of the protein systems and to obtain culinary products with a more delicate taste than products from natural eggs.

The mechanical properties of curdled egg whites are also used to structure (bond) some culinary products (vegetable cutlets, etc.).

Milk proteins

The main proteins of milk are casein (2.3-3.0%), lactalbumin (0.5-1.0%) and lactoglobulin (0.1%).

When milk with normal acidity is heated, noticeable changes are observed only with albumin, which coagulates and deposits in the form of flakes on the walls of the dishes. The process starts at 60 ° C and ends at almost 85 ° C.

Heating the milk has virtually no effect on the solubility of casein: only a small amount of it in an insoluble form is present in the froth formed on milk. In fermented milk, heating causes the casein to coagulate and separate the system into two fractions: curd (curdled casein) and whey.

Casein also curdles when heated milk with high acidity. When heated, cottage cheese releases some of the moisture. To connect it, cereals or flour are added to culinary products from cottage cheese.

Proteins of meat, poultry, fish

Technological processing of these products is largely due to the morphological structure and composition of their protein systems.

Features of the structure and composition of muscle tissue ... The bulk of the meat processed in culinary practice is skeletal musculature. Individual skeletal muscles are made up of muscle fibers connected into a single whole by connective tissue layers.

Muscle fiber is a specialized contractile cell, the length of which can reach 12 cm and more, and thickness up to 120 mm. The content of the fiber consists of two parts: liquid (homogeneous) - sarcoplasm and gelatinous (in the form of gelatinous filaments) - myofibrils. Outside, the fiber is covered with a sheath - sarcolemma (Fig. 3).

In the muscles, the fibers are collected in bundles: primary, consisting of muscle fibers; secondary, consisting of primary beams; higher order bundles that make up the muscle.

Proteins that make up the muscle fibers of meat, poultry, fish are called muscle proteins. Some of them in a liquid state are contained in the sarcoplasm, including the protein myoglobin, which stains the meat red, some in a gelatinous state are part of the myofibrils. The protein content in some meat and fish products is given in table. 12.

Muscle proteins have a high biological value: the ratio of essential amino acids in them is close to optimal. The content of muscle proteins in the skeletal muscles of cattle of the 1st category averages 13.4% with fluctuations from 6.1 to 14.3% in different parts of the carcass (Fig. 4).

Rice. 3. Diagram of the structure of muscle fiber:
1 - myofibril; 2 - sarcoplasm; 3 - core
Rice. 4. The content of muscle proteins in different parts of the carcass of cattle

The connective tissue of the muscle is called the misium. The part of it that connects the muscle fibers in the primary bundles is called the endomysium, which unites the bundles of muscle fibers with each other - the first from and it, and the outer shell of the muscle - the epimysium

Fibrillar proteins - collagen and elastin - are important components of connective tissue.

By means of X-ray structural analysis, it was found that the collagen molecule consists of three polypeptide chains (triplet) twisted together around a common axis.

The strength of the triple helix is ​​mainly due to hydrogen bonds. The individual molecules of collagen and elastin form fibers. In turn, bundles of collagen and elastin fibers, together with a substance that unites them into a single whole and consists of a protein-polysaccharide complex, form films of endomysium and perimisia.

Rice. 5. Microscopic specimen of the pectoral muscle of cattle. There are visible layers of endomysium between muscle fibers and layers of perimisium between their bundles

The structure of the endomysium practically does not depend on the contractile ability of the muscle and the nature of the work it does. Collagen in its composition forms very thin and slightly wavy fibers. Elastin in the endomysium is poorly developed.

The structure of the perimisium is greatly influenced by the nature of the work performed by the muscles. In the muscles that underwent small loads during the life of the animal, perimisium in structure is close to endomysium.

The perimisium of the muscles performing hard work has a more complex structure: the number of elastin fibers is increased, the collagen bundles are thicker, in the perimisium of some muscles the fibers are crossed and form a complex cellular weaving. The percentage of connective tissue is increased in the muscles.

Table 13.Approximate ratio (by tryptophan) of essential amino acids in muscle proteins of certain foods

Thus, the connective tissue of endomysium and perimisia forms a kind of skeleton or skeleton of muscle tissue, which includes muscle fibers. The nature of this skeleton determines the mechanical properties, or, as they say, the "toughness" or "tenderness" of the meat.

On average, most of the musculature of cattle contains from 2 to 2.9% collagen, but the amount of collagen in different parts of the carcass is very different (Fig. 6).

Rice. 6. Content of collagen (k) and elastin (e) in various parts of the carcass of cattle

In small livestock, the difference in the structure of perimisium in different parts of the carcass is expressed to a much lesser extent than in cattle, and, in addition, the perimisium has a simpler structure. The peculiarities of the anatomical structure of the muscular tissue of the bird include the low content and lability of the connective tissue.

The muscle tissue of fish also consists of muscle fibers and connective tissue, but it has its own characteristics. Her muscle fibers are united by perimisium into zigzag myocomes, which, with the help of connective tissue layers (septa), form the longitudinal muscles of the body. Septa are transverse and longitudinal (Fig. 7).

Like the muscle tissue of warm-blooded animals, the musculature of fish, which has an increased load (muscles adjacent to the head and tail), contains a more developed connective tissue, however, due to its low strength, fish is divided by varieties and culinary purposes, as is customary for meat of slaughter animals. ... The main protein of the connective tissue of fish is collagen (from 1.6 to 5.1%), there is very little elastin in it.

In addition to muscle tissue, collagen is found in significant quantities in the organic matter of cartilage, bones, skin and scales. So, its content in bones reaches 10-20%, in tendons -25-35%. The collagen found in bones is called ossein.

As a protein, collagen has a low biological value, since it is practically devoid of tryptophan and contains very little methionine; it is dominated by glycocol, proline and hydroxyproline.

The main components of meat of different types of animals are (in%): water -48-80, proteins-15-22, fats-1-37, extractive substances-1.5-2.8 and minerals-0.7-1, 5.

The amount of water depends on the age of the animal and the fat content of the meat. The younger the animal and the less fat in its meat, the more moisture in the muscles.

Most of the moisture (about 70%) is associated in the muscles with the proteins of the myofibrils. The sarcoplasm of muscle fibers contains less moisture with proteins, extractives and minerals dissolved in it. A certain amount of moisture is contained in the intercellular cavities of muscle tissue.

Extractive substances are metabolic products. They consist of amino acids, dipeptides, glucose, some organic acids, etc. Extractive substances and products of their transformation are involved in creating the taste and aroma characteristic of meat.

Rice. 7. Diagram of the structure of the muscle tissue of fish: 1 - muscle fibers (their direction is shown by strokes); 2 - myocomma; 3 - transverse septa; 4 - longitudinal septa

So, solutions of glutamic acid and its salts have a meaty taste, therefore monosodium glutamate is used as one of the components of dry soups, sauces and other concentrates. Amino acids such as serine, alanine, glycine have a sweet taste, leucine is slightly bitter, etc.

When heated, extractive substances undergo various chemical changes - reactions of melanoid formation, oxidation, hydrolytic cleavage, etc. The resulting substances are also considered to be extractive: their taste, smell and color affect the organoleptic characteristics of the finished product.

The extractive substances of fish muscle tissue differ significantly in composition from the extractive substances of meat. It has little glutamic acid and more histidine, phenylalanine, tryptophan, cystine and cysteine. It is believed that the taste and smell of fish are mainly due to nitrogenous bases of extractive substances, which are especially abundant in sea fish and little or not at all in the meat of land animals.

Among the mineral substances of the muscle tissue of land animals and fish, a significant proportion is accounted for by the salts of sodium, potassium, calcium and magnesium.

Protein changes during heat treatment

During heat treatment, muscle and connective tissue proteins undergo significant changes.

Muscle proteins of meat and fish begin to denature and coagulate at a temperature of about 40 ° C. At the same time, the contents of muscle fibers become denser, since moisture is released from them with mineral, extractive substances dissolved in it and soluble proteins not denatured at a given temperature.

The release of moisture and the compaction of muscle fibers increases their strength: they are more difficult to cut and chew.

If meat or fish is heated in water, then the proteins that have passed into it, upon reaching the appropriate temperatures, denature and coagulate in the form of flakes, forming the so-called foam.

About 90% of soluble proteins in meat and fish are denatured at temperatures of 60-65 ° C. At these temperatures, the diameter of muscle fibers in beef is reduced by 12-16% of the original value. The subsequent increase in temperature entails additional moisture loss, thickening of muscle fibers and an increase in their strength.

When meat is cooked, the protein myoglobin is denatured, which determines the color of the meat. Denaturation of myoglobin is accompanied by a change in the color of muscle tissue, which makes it possible to indirectly judge the culinary readiness of meat.

Meat retains its red color at temperatures up to 60 ° С, at 60-70 ° С it turns pink, and at 70-80 ° С it turns gray. When cooked, the meat remains gray or brown in color.

Heating the connective tissue causes disaggregation of the collagen contained in it and changes the structure of the tissue itself. The initial stage of this process is collagen denaturation and disruption of the fibrillar structure of the protein, which is defined by the term "collagen fusion".

The temperature of denaturation or boiling of collagen is the higher, the more it contains proline and hydroxyproline. For meat, cooking is observed at a temperature of about 65 ° C, for fish, about 40 ° C.

At these temperatures, there is a partial rupture of cross-links between the polypeptide chains of fibrillar protein molecules. As a result, the chains contract and take on an energetically more favorable folded position.

In collagen fibers isolated from the connective tissue, collagen is welded at certain temperatures and has the character of a jump. Collagen welding in perimisia films is extended in the temperature range. The process begins at the temperatures indicated above and ends at higher temperatures, and the higher the temperature, the more complex the structure of the connective tissue.

Changes at the molecular level entail changes in the structure of collagen fibers and connective tissue layers. Collagen fibers are deformed, bent, their length is reduced and they become more elastic and transparent-vitreous.

The structure of the connective tissue layers themselves also changes: they also deform, increase in thickness, become more elastic and transparent vitreous.

Collagen welding is accompanied by the absorption of a certain amount of moisture and an increase in the volume of connective tissue layers. Compression of the connective tissue layers greatly contributes to the squeezing out of the muscle tissue of the fluid released during denaturation and coagulation of muscle proteins.

With further heating of the connective tissue, a partial or complete rupture of cross-links between the polypeptide chains of denatured collagen occurs, and some of them pass into the broth, forming a gelatin solution; the structure of the connective tissue layers is largely disturbed, and their strength decreases.

The weakening of the perimisium strength is one of the factors that determine the readiness of the meat. Once cooked, meat should not offer significant resistance to cutting or nibbling along the muscle fibers.

Like the welding temperature, the rate of collagen disaggregation depends on the structure of the perimisium. So, for 20 min boiling in the psoas muscle, the perimisium of which is poorly developed, disaggregated and passed into broth 12.9% of collagen, and in the pectoral muscle with coarser perimisium, under the same conditions, only 3.3% of collagen was disaggregated.

Over 60 min boiling, these figures increased: for the psoas muscle up to 48.3%, for the pectoral muscle - only up to 17.1% The temperature at which the heat treatment process is carried out has an insignificant effect on the rate of collagen disaggregation and softening of perimisia.

For example, when boiling the shoulder muscle at a temperature of 120 ° C (in an autoclave), the amount of disaggregated collagen is twice the content in a similar muscle that was cooked in the usual way at a temperature of 100 ° C.

However, it should be noted that with an increase in the cooking temperature, simultaneously with a reduction in the period of heat treatment, excessive compaction of muscle proteins occurs, which negatively affects the consistency and taste of the meat.

When used for frying muscles with a complex perimizne, the meat is treated with acids (pickling) or enzyme preparations. For pickling, citric or acetic acid is usually used. Disaggregation of collagen and weakening of perimisia are noticeably accelerated in pickled meat.

Fried the products are juicy, with good taste.

Proteolytic enzymes of plant, animal and microbial origin are successfully used as meat softeners: ficin (from figs), papain (from melon tree), trypsin (of animal origin), etc.

Enzyme preparations are powders, pastes or solutions that are used to treat meat in one way or another (moisten, spread, inject). Often the meat is loosened before being processed with enzymes.

Heat treatment slightly reduces the strength of elastin fibers, therefore, muscle tissue with a high content of elastin (neck, flank) remains tough after heat treatment and is mainly used for making cutlet mass.

Usage: agriculture, namely, the production of animal feed. The essence of the invention: electrocoagulation of the protein is carried out by direct current in the chamber, the anodic and cavod regions of which are separated by a membrane. In the process of current flow, the pH value of the medium is recorded and when its value 5 is reached, the process is stopped. As the coagulum is removed, the remainder of the protein-containing material is fed from the cathode region to the anode one. The temperature of the material does not exceed 39 - 40 o C. 2 h. p. f-ly, 1 tab.

The invention relates to agriculture, namely the production of animal feed. The known method of thermal coagulation of protein from potato juice, which consists in heating it with steam to 70-100 about C. The disadvantages of this method are low protein yield (70-80%), high energy consumption (0.5 MJ / kg). There is a method of chemical coagulation, which consists in the precipitation of a protein without heating while acidifying it with acids or heavy metal salts to the isoelectric point (pH 4.8-5.2). The disadvantage of this method is the low yield of protein (40-50%), the need to neutralize the medium. The closest to the proposed method is the method of electrothermal treatment, in which the protein-containing medium is heated with an electric current of industrial frequency up to 70-100 o C. The electric field strength between the electrodes located in the coagulated medium is (5-25) 10 2 V / m. The protein yield reaches 80-84%, the energy content is 0.12 MJ / kg. The purpose of the invention is to increase the yield of protein, to reduce the energy consumption of the process. To achieve this goal, the protein is coagulated in a chamber separated by a membrane partition that is permeable to inorganic compounds (mainly H + and OH- ions) and practically impermeable to protein ions due to their "large" size. When a direct current flows, for example, through a potato juice from the positive electrode to the negative electrode, the H + ions move to the cathode, and the OH hydroxyl group ions move to the anode. This leads to a decrease in the pH at the anode and an increase at the cathode. The acidic environment at the anode coagulates the protein. In addition, the electric current passing through the potato juice activates the mass transfer and the rate of chemical reactions without causing significant heating. Due to this, the temperature of the juice rises only to 30-40 o C. Thus, due to the thermochemical action of the electric current, the protein coagulates at temperatures much lower than with the known thermal methods, which reduces the energy consumption of the process to 0.05 MJ / kg. The combined chemical and thermal action of the electric current increases the protein yield up to 97%. The spent fraction from the cathode region is introduced into the anode one in a proportion that does not disturb the coagulation process. EXAMPLE Potato juice (pH 6.6-6.8) is placed in the working chamber of the coalescer, the anode (A) and cathode (K) spaces of which are separated by a membrane partition in the ratio A: K 4: 1, practically impermeable to juice components in the absence of electric current ... A direct current with an electric field strength in the interelectrode space (3-5) 10 2 V / m is supplied to the chamber electrodes from the rectifier, under the influence of which the pH drops to 2.5-5. When coagulation proceeds, the temperature is recorded. When reaching 30-40 about C, the process is stopped. In the process of coagulation, the processed product from the cathode region is fed to the anode one, mixing it with "fresh" juice. The processing time depends on the strength of the electric field and the initial temperature of the juice. The coagulated protein is isolated from the juice by conventional methods. The table shows a comparative assessment of various methods of coagulation, obtained in the laboratory of transport and regulation of plant metabolism of the Academy of Sciences of the Republic of Belarus. Studies have shown that the proposed method increases the yield of protein by 10-15%; reduces energy consumption by 2-3 times; At the same time, the density of direct current during coagulation does not exceed 8000 A / m 2, which makes it possible to reduce the processing temperature.

Claim

1. METHOD OF PROTEIN COAGULATION, including placing a protein-containing material in a chamber, the anode and cathodic regions of which are separated by a membrane partition, and passing a direct electric current between the electrodes located in these regions, characterized in that during the current flow, the pH value of the processed material in the anode the area of ​​the chamber and at a pH value of not more than 5, the current is stopped. 2. A method according to claim 1, characterized in that after removing the coagulant from the anode region of the chamber, the protein-containing material remaining in the cathode region of the chamber is transferred to the anode region and both regions are supplemented to the working level with new protein-containing material. 3. The method according to claim 1, characterized in that the direct current density in the process of coagulation is not more than 8000 A / m 2.

Coagulation(from lat. Coagulatio- coagulation, thickening), adhesion of particles of a colloidal system during their collisions in the process of thermal (Brownian) motion, mixing or directional movement in an external force field.

Blood clotting- This is the most important stage of the hemostasis system, which is responsible for stopping bleeding in case of damage to the vascular system of the body. The set of various factors of blood coagulation interacting with each other in a very complex way form a blood coagulation system.

Blood clotting is preceded by the stage of primary vascular platelet hemostasis... This primary hemostasis is almost entirely due to vasoconstriction and mechanical blockage by platelet aggregates of the site of damage to the vascular wall. The characteristic time for primary hemostasis in a healthy person is 1-3 minutes. Blood clotting itself (hemocoagulation, coagulation, plasma hemostasis, secondary hemostasis) is called the complex biological process of the formation of fibrin protein filaments in the blood, which polymerizes and forms blood clots, as a result of which the blood loses its fluidity, acquiring a curdled consistency. Blood clotting in a healthy person occurs locally, at the site of the formation of the primary platelet plug. The characteristic time for the formation of a fibrin clot is about 10 minutes. Blood clotting is an enzymatic process.

Coagulation (coagulation)- a spontaneous process, which, in accordance with the laws of thermodynamics, is a consequence of the desire of the system to move to a state with a lower free energy. However, such a transition is difficult, and sometimes practically impossible, if the system is aggregatively stable, that is, it is able to resist consolidation. (aggregation) particles. Protection from Coagulation (coagulation) in this case, there may be an electric charge and (or) an adsorption-solvation layer on the surface of the particles, which prevents their approach. Aggregative stability can be disturbed, for example, by increasing the temperature (thermocoagulation), stirring or shaking, introducing coagulating substances (coagulants) and other types of external influence on the system. The minimum concentration of an injected substance, electrolyte or non-electrolyte that causes Coagulation (coagulation) in a system with a liquid dispersion medium, it is called the coagulation threshold. The adhesion of homogeneous particles is called homocoagulation, and dissimilar - heterocoagulation or adagulation.

The founder of the modern physiological theory of blood coagulation is Alexander Schmidt... In scientific research of the 21st century, conducted on the basis of Hematological Research Center under the direction of F.I. Ataullakhanova, it was convincingly shown that blood coagulation is a typical autowave process, in which the effects of bifurcation memory play a significant role.

To isolate whey proteins, it is necessary to change the native protein structure. With this change (denaturation), its structure is violated. The protein globule unfolds during denaturation. The process is accompanied by a change in the configuration, hydration and state of aggregation of the particles. The protein globule becomes less stable during denaturation.

The stability of whey protein globules is due to the particle conformation, charge and the presence of a hydration shell (solvation layer). To isolate proteins, it is necessary to upset the balance of three or at least two of these stability factors.

In fresh whey, protein particles are in a native state. When the native state of the protein changes (denaturation), first of all, its structure is disturbed. The protein globule unfolds during denaturation, for which it is necessary to break from 10 to 20% of the bonds involved in its formation. The denaturation process is accompanied by a change in the configuration, hydration and state of aggregation of the particles. The protein globule becomes less stable as a result of denaturation.

To overcome potential barriers to the stability of protein particles, various denaturation methods can be used: heating, irradiation, mechanical action, the introduction of desolvating substances, oxidants and detergents, and a change in the reaction of the medium. The introduction of some substances into solutions promotes thermal denaturation.

The classification of serum coagulation methods considered in this work is shown in the diagram (Fig. 3).

Rice. 3.

Ultimately, the release of proteins is caused by secondary phenomena after denaturation, such as the association of unfolded globules and their chemical change. Here, the formation of intermolecular bonds and aggregation comes to the fore, in contrast to the intramolecular processes that occur during denaturation.

In general, the process of isolating whey proteins can be characterized as coagulation.

Taking into account the expediency of the extraction and use of proteins, the coagulation of whey proteins must be fixed in order to avoid the process of renaturation (restoration of the native structure of proteins), as well as to limit the decomposition of the formed aggregates as much as possible.

However, it should be borne in mind that as a result of thermal denaturation, in addition to the rupture of hydrogen bonds of the protein particle, their dehydration occurs, which facilitates the subsequent aggregation of the protein particles. Coagulant ions (calcium, zinc, etc.), being actively sorbed on the surface of the protein particle, provide coagulation, and at significant doses can lead to salting out of proteins.

Coagulation of milk is nothing more than its transformation into a gel (clot), that is, its coagulation.

It is a bound solid fraction of milk proteins with the presence of dissolved fats, which can then be easily separated from the liquid (whey).

Coagulation of milk protein is latent and true. With latent coagulation, micelles do not bind to each other with the entire surface, but only in some of its areas, forming a spatial fine-mesh structure, which is called a gel.

When all or most of the particles of the dispersed phase are destabilized, the gel covers the entire volume of the dispersed medium (original milk).

Latent coagulation is simply called coagulation, gelling, or coagulation.

True coagulation consists in the complete fusion of colloidal particles and the precipitation of a dispersed phase or floating.

Coagulants are substances that perform several functions, but most importantly - they form a jelly-like clot - they separate dense fractions of milk from liquid ones.

For this purpose, previously used only, which is obtained from the stomachs of calves.

It is this enzyme in the stomachs of calves (chymosin) that helps them ferment mother's milk for nutrition.

In the modern world, to form a clot (also called kalya), they use:

• Veal rennet (rennet), made from the stomachs of calves (milk-clotting enzyme - chymosin).
  It can be powdery, pasty and liquid. It is chymosin (from calf rennet or cultured chymosin) that is best suited for the production of hard and semi-soft cheeses.
• Pepsins are extracts from the stomachs of other pets. Mostly used is bovine or pork and chicken pepsins are also commercially available, however they are very sensitive to acidity and are unstable. Their use is not recommended.
  Cow pepsin (especially when mixed with chymosin) can be used for the production of brine cheeses (feta cheese, suluguni). It is not recommended to use pepsins for the production of soft, semi-soft and hard cheeses.
• Microbial rennin (microbial pepsin) - Certain yeasts, molds, and fungi naturally produce enzymes suitable for coagulation. The most widely used enzymes are those obtained from the microscopic fungus Rhizomucor meihei (formerly called Mucor meihei). It is a vegetarian coagulant. An example of such a coagulant is.
• Chymosin obtained by fermentation (recombined chymosin) - the calf chymosin gene was introduced into the genome of several host microorganisms (Kluyveromyces lactis, Aspergilleus niger, Escherichia), as a result of which they became capable of producing a protein completely identical to calf chymosin during fermentation.
  This enzyme has proven itself to be excellent in all types of cheeses where veal rennet is commonly used. It is a vegetarian coagulant.

For the preparation of fresh cheeses, cottage cheese, pickled cheeses, you can use any coagulant.

However, for semi-soft and hard cheeses, only chymosin (animal rennet or recombined chymosin) is suitable, since it, together with lactic acid bacteria (ferments), participates in the formation of the texture of the cheese, its taste and ability to preserve for a long time.

During the coagulation of proteins, milk fat and water with solutes (whey) are sufficiently firmly captured by the formed gel; during the precipitation of proteins, only a small amount of milk fat and the aqueous phase can be mechanically retained by the sediment.

The production and maturation of rennet cheeses is carried out at low temperatures and active acidity, called physiological, in order to ensure the possibility of biological transformation of milk components with minimal loss of nutritional value.

When using the thermoacid method, the fat phase of the milk is separated by separation, the proteins of skim milk are precipitated and mixed with cream.

Precipitation consists in the rapid acidification of milk to a level lower than the isoelectric point by adding acid whey, sour milk, lemon juice, acetic acid and heating it to high temperatures (90-95 ° C).

Thus, during enzymatic coagulation, casein and milk fat are concentrated simultaneously, with thermoacid coagulation - as a result of two processes: centrifugal and precipitation.

The acidic method consists in curdling milk at the isoelectric point of casein (pH 4.6) by slowly forming acids by microorganisms or adding acids (usually hydrochloric) or acidogens (for example, glucolactone) to milk; it is used in the production of fresh or short-maturing cheeses.

The enzymes involved in the maturation of rennet cheeses are inactive in acidic cheeses due to the low pH. The degree of transformation of proteins and lipids of milk in fermented milk cheeses is lower, the flavoring bouquet is narrower than in rennet cheeses.

The acid-enzymatic method is a variant of acid coagulation, with the introduction of a small amount of milk-clotting enzymes into the milk, which is insufficient for enzymatic coagulation at the pH of fresh milk.

In this case, milk coagulation occurs at a pH of 5.1-5.4 (in the isocule of paracasein). The addition of milk-clotting enzymes has a beneficial effect on the clotting rate, the strength of the curd and the release of whey, however, at the pH of the acid-rennet coagulation of milk, radical changes in the casein micelles occur, which sharply changes the structure of the curd and cheese in comparison with those with rennet clotting.

The curd formed during the production of cheeses by the acid-enzymatic method is closer in its properties to an acid curd, the quality of the products is closer to fermented milk cheeses.

Concentration of milk by ultrafiltration has gained a certain distribution in the production of brine and some other cheeses.