Nutritional value of milk and dairy products. Introduction

Introduction

Milk and dairy products occupy an important place in human nutrition. They provide the body with favorably balanced and easily digestible proteins, fats, carbohydrates, minerals and vitamins.

Nutritional and biological value of milk

Squirrels- the most biologically valuable component. Milk proteins have lipotropic properties, regulating fat metabolism, increase the balance of food and the absorption of other proteins. With amphoteric properties, milk protein protects the body from toxic substances.

Milk sugar(lactose) is a source of energy for biochemical processes in the body, promotes the absorption of calcium, phosphorus, magnesium, barium.

Minerals milk play a significant role in the plastic processes of the formation of new tissue cells, enzymes, vitamins, hormones, as well as in the mineral metabolism of the body.

biological value milk is supplemented with the presence of almost the entire complex of vitamins known and necessary for the human body, the content of which varies depending on the diet of animal feeding; as a rule, it is increased in summer when livestock is kept on green pastures.

One liter of milk satisfies the daily requirement of an adult for animal fat, calcium, phosphorus; 53% in animal protein; 35% - biologically active non-essential fatty acids and vitamins A, C, thiamine; 12.6% in phospholipids and 26% in energy. The energy value of milk is 2720*10 J/kg.

The presence of all components in an optimal combination and easily digestible form makes milk an extremely valuable, indispensable product for dietary and nutritional needs. medical nutrition, especially when gastrointestinal diseases, diseases of the heart and blood vessels, liver, kidneys, diabetes, obesity, acute gastritis. It should be consumed daily as part of a balanced diet to maintain tone and as a factor in increasing life expectancy.

Milk is of exceptional importance in the nutrition of children, especially in the first period of their life. The shell protein of fat globules contains a significant amount of phospholipids, arginine and threonine - amino acids that normalize the processes of growth and development of the body. Milk is the main source of easily digestible phosphorus and calcium for building bone tissue.

The biological value of milk is complemented by the fact that it contributes to the creation acid environment in the intestinal tract and suppression of the development of putrefactive microflora.

Therefore, milk and dairy products are also widely used as a remedy for intoxication of the body with poisonous products of putrefactive microflora. The daily norm of milk consumption for an adult is 0.5 liters for a child 1 liter.

Dairy products are made from milk. It has long been believed that dairy products heal the body. With the development of microbiology, dietary, and with the discovery of antibiotics, the medicinal properties of these products were scientifically substantiated. A great merit in this belongs to the great Russian physiologist and microbiologist I. I. Mechnikov. Dealing with the problems of longevity, at the beginning of the 20th century, the scientist came to the conclusion that one of the causes of premature aging is the constant poisoning of the body with food decay products. “From here is the only conclusion,” wrote I. I. Mechnikov, “the more the intestines abound in microbes, the more it becomes a source of evil that shortens existence.”

To the history of the issue

Our distant ancestors knew how to process milk and use it not only in its natural form. Herodotus in the 5th century BC reported that the most favorite drink of the Scythians was mares' milk prepared in a special way - koumiss. Koumiss and curdled milk are mentioned in medical books of the 17th century as a cure for tuberculosis, typhoid fever and fever.

Man has long known the healing power of milk. Hippocrates, for example, prescribed milk to tuberculosis patients. He also believed that it was extremely useful in nervous disorders. Aristotle recognized mare's milk as the most valuable, then donkey's, cow's and, finally, goat's. Pliny the Elder isolated cow's milk. However, he also argued that in medicinal purposes You can also use pig's milk.

He actively healed various diseases with Avicenna's milk. He considered it useful for children and people "advanced in years." According to Avicenna, the most healing is the milk of those animals that bear the fetus for about the same time as a person. In this regard, he believed that cow's milk is most suitable for humans.

The outstanding Russian scientist S.P. Botkin called milk a “precious remedy” for the treatment of the heart and kidneys. Healing properties G. A. Zakharyin, the author of the “Russian method” of treating tuberculosis patients with koumiss, also highly appreciated milk. By all and always, I. P. Pavlov wrote, - milk is considered the lightest food and is given with weak and diseased stomachs and with a mass of severe general diseases.

At the end of the 19th century, the St. Petersburg doctor Karell used milk to treat diseases of the stomach, intestines, liver and other diseases. Moreover, he was the first to use skim milk, gradually increasing the dose from 3 to 12 glasses per day and not giving the patient other food for several days. This method of treatment fully justified itself and was approved by Botkin.

Almost everywhere, milk was actively used in folk cosmetics. Yes, in Ancient Rome donkey milk was considered the most suitable anti-wrinkle remedy. Pompey, the second wife of Nero, took baths from the milk of donkeys, during her travels she was usually accompanied by a herd of 500 of these animals. Avicenna claimed that milk reduces ugly spots on the skin, and if you drink it, it greatly improves the complexion. Especially if you drink with sugar. Curd whey, when rubbed into the skin, destroys freckles.

And yet, at all times, milk has been valued mainly for its amazing properties. nutritional properties. According to the apt expression of I. P. Pavlov, “milk is an amazing food prepared by nature itself.”

Milk

Cow's milk is a secretion product of the cow's mammary gland. It is a liquid white color with a yellowish tint and a specific slightly sweetish taste. Milk is formed in the mammary gland as a result of profound changes in the constituents of feed in the animal's body. The mammary gland of a cow consists of cells penetrated by nerves, a network of blood and lymphatic vessels that deliver the substances necessary for milk synthesis. The cells form small vesicles - alveoli, in which the formed milk is located. The alveoli are united into lobules and communicate with each other through thin tubules leading to a special cavity called the cistern, where milk accumulates.

The physiological process of milk formation is very complex, and many of its phenomena have not yet been sufficiently studied. It has been established that the main components of milk are synthesized in the mammary gland from substances brought in by the blood. Only a small part of the substances (mineral elements, vitamins, enzymes, hormones, immune bodies) pass into milk from the blood unchanged.

Cow's milk is mainly used directly for food and processing, less often mares, goats, sheep and deer.

1. NUTRITIONAL VALUE, COMPOSITION AND PROPERTIES OF BOvine

MILK

State standard “Natural raw cow's milk. Specifications»: GOST R.

Cow's milk is characterized by high nutritional value, which is due to the optimal content of proteins, fats, carbohydrates, mineral salts and vitamins in it, and the ratio and form in which the components are present in milk contribute to their good digestibility and assimilation. Currently, over 200 different components are known in milk. The main components include water, protein, fat, lactose and minerals. Milk also contains vitamins, enzymes, hormones, etc. Foreign substances may contain antibiotics, pesticides, detergents, toxic elements, radionuclides, aflatoxins, etc.

The chemical composition of milk, the degree of dispersion of its constituent parts determine the chemical and physical properties milk. The most important properties for milk processing processes are given in Table. 1.

Table 1. Chemical and physical properties of cow's milk

Index	Average value	Oscillation interval
Titratable acidity, °T
pH value"
Oxidation-reduction potential, mV
Density", kg/m3
Viscosity, Pa s		(1,1...2,5)-10-3
Freezing point, °С
Specific electrical conductivity, S/m
Heat capacity", J / (kg x K)
Thermal conductivity, W/(m x K)

Milk and dairy products are characterized by an energy value that complements the nutritional value of the product. It can be calculated using the following formula:

E \u003d (37.7F + 16.7B + 15.9L) x 10,

where E - energy value, kJ; W, B, L - respectively, the mass fraction of the content of fat, protein and lactose in the raw material or product,%; 37.7, 16.7 and 15.9 are coefficients.

1.1. Water and dry matter milk

As can be seen from the data in Table. 2, the main specific gravity in milk is water (moisture); the remaining components that make up the dry matter account for 10 ... 13% (with the exception of sheep and buffalo milk). Most of the moisture in milk (up to 85%) is in a free state and can pose a threat to the safety of dairy products, but it is relatively easy to remove during thickening and drying.

The average mass fraction of dry matter in cow's milk is 12.5%, but it can fluctuate during lactation, as well as depending on the age of the animals, feeding rations and other factors. The dry matter consists of fat, protein, milk sugar, minerals, vitamins, enzymes, etc. When subtracting the mass fraction of fat from the mass fraction of dry matter, dry skimmed milk residue (SOMO) is obtained, the content of which should be equal to 8% or higher. There are various formulas for calculating dry matter. Farrington formula:

Coll" href="/text/category/koll/" rel="bookmark">colloidal particles with a size of 50...300 nm and is characterized by high thermal stability.

Whey proteins presented B-lactoglobulin (0.4%), A-lactalbumin (0.1%), as well as immunoglobulins and serum albumin, totaling about 0.1%. Milk globulins and albumins are in a colloidal-dispersed state, have a particle size of 15 ... 50 nm and above, do not coagulate under the action of rennet, are thermolabile proteins (when milk is heated, they partially precipitate and, together with salts, form a "milk stone" ).

The biological value of whey proteins is higher than casein, so they are widely used in the production of children's and dietary products (albumin curd, various pastes, etc.). The yield of products in the production of cottage cheese, rennet cheeses, casein and milk protein concentrates depends on the protein content in the harvested milk.

1.4. Carbohydrates

In milk, carbohydrates are mainly represented by lactose - a carbohydrate characteristic only for milk, as well as glucose and galactose. Lactose is a disaccharide found in milk as a molecular dispersion. Lactose is present in almost all dairy products, participates in the formation of their properties, determines the nutritional and energy value of milk. In the human body, under the action of lactase and microorganisms of the gastrointestinal tract, lactose is fermented to lactic acid, creating an environment that prevents the development of putrefactive microorganisms. In milk, its average mass fraction is 4.7% (fluctuations from 4.5 to 5.3%). Milk sugar is a carbohydrate necessary for the nutrition of newborns in the first days of life; it is needed for normal metabolism, the work of the heart, kidneys and liver. The calorie content of 1 g of lactose is 3.8 kcal (15.909 kJ). IN pure form milk sugar is a white crystalline powder. The enterprises produce raw and refined milk sugar, which are used to produce lactulose and in the pharmaceutical industry. Lactose is a source of carbon for lactic acid bacteria, which ferment it under the action of enzymes - the production of fermented milk products, cheese, and sour cream butter is based on this property.

1.5. Minerals

Milk serves as a constant source of mineral substances entering the body, the most important of which are macronutrients - calcium, phosphorus, potassium, sodium and magnesium. More than half of all minerals are calcium and phosphorus salts. Calcium in milk is in a soluble state, and a significant part of it is associated with casein in the form of caseinate-calcium phosphate complex (CCPC), which makes it almost completely digestible. Phosphorus is part of the protein of all cells of the body, is a component of the nervous tissue and brain cells. Trace elements of milk (iron, copper, iodine, manganese, zinc, cobalt, etc.) are of great importance for normal metabolism in the body, the synthesis of vitamins, enzymes, hormones. Currently, the production of dairy products enriched with calcium, iron and iodine has begun.

1.6. vitamins

Milk contains all vital vitamins. Vitamins are divided into two groups: fat-soluble (A, D, E, K) and water-soluble (C, group B, biotin, etc.). There are functional differences between these groups of vitamins. So, fat-soluble vitamins are involved in redox reactions, transport of calcium and phosphorus, have antioxidant properties; water-soluble vitamin complexes are part of enzymes, including milk enzymes. Many vitamins are highly sensitive to high temperatures, light, acids, bases, and oxygen. Given the great importance of vitamins for the life of the body, the industry has established the production of various products enriched with vitamins.

1.7. Enzymes and hormones

A large number of enzymes of various origins have been found in milk. There are enzymes of native and bacterial origin. Depending on the specific action on various substrates, enzymes are divided into redox enzymes, transferases, hydrolases, cleavage enzymes, etc. For the dairy industry, they have importance milk enzymes belonging to the groups of oxidoreductases and hydrolases. Thus, oxidoreductases play an extremely important role in many technological processes in cheese making, in the production of fermented milk products, etc. The amount of certain enzymes, such as catalase, is a valuable indicator of the quality of milk. The concentration of lactoperoxidase determines the antibacterial activity of milk, and the results of peroxidase (and phosphatase) tests give an idea of the efficiency of milk pasteurization.

Lipase, related to hydrolases, is formed in the body of an animal (native) and enters the mammary gland with blood, and then into milk. Bacterial lipase is produced by extraneous microflora - molds, micrococci, pseudomonads that enter milk. Lipase can be adsorbed on the surface of fat globules. Upon hydrolysis, it cleaves the ester bonds in triacylglycerols, resulting in the formation of fatty acids and glycerol.

Glycerides of low molecular weight acids are primarily affected by lipase. It can cause pronounced defects in the taste and smell of milk and dairy products. The maximum effect of lipase (native) is manifested at pH 8.8 and a temperature of 37 ° C, bacterial - at pH 7. In fresh milk milk fat usually not spontaneously affected by lipase. However, with strong mixing of milk with the formation of foam, with homogenization, pumping it with pumps, a rapid change in temperature, lipase is activated and causes lipolysis. Native lipase is inactivated at low temperatures (65...75°C), while bacterial lipase is completely destroyed at temperatures above 80°C.

Another hydrolase - phosphatase enters the milk from the secretory cells of the udder, and is also produced by some milk bacteria. It catalyzes the hydrolysis of phosphate esters. Milk contains acidic and - in larger quantities - alkaline phosphatase. Hydrolases also include proteases, lysozyme, and some other enzymes. native protease- plasmin passes into milk from blood serum, bacterial proteases are produced by foreign microflora. Plasmin shows specificity in relation to casein fractions - it is most sensitive to it. IN-casein. As a result of his actions, Y-caseins, while the yield of cottage cheese and cheese is reduced ( Y- we “lose” casein with whey) and bitter peptides can form. Lysozyme has antibacterial properties - destroys the cell walls of staphylococci and other pathogens of mastitis in cows. Milk hormones include prolactin, oxytocin, somatotropin, sex hormones, thyroxine, etc.

1.8. Toxic substances in milk

Toxic contaminants of milk and dairy products include pesticides, antibiotics, hormones, mycotoxins, heavy metals, etc. The source of pesticides is the use of poisons of chemical and biological origin in agricultural production to protect crop plants from weeds (herbicides), insects (insecticides), diseases (fungicides). Pesticides are also used in the special preventive treatment of animals from blood-sucking insects and certain types of diseases. The reason for the entry of antibiotics into milk may be non-compliance with the terms during which it is forbidden to use the milk of cows that have been treated for any diseases. In addition, sometimes in order to prevent milk from souring, it is falsified with antibiotics. Hormonal preparations can be found in milk only when they are specially used (for example, to increase the weight of animals), which is unacceptable in dairy production. The source of mycotoxins in milk is poor-quality feed and feed mixtures. In milk, the content of aflacotoxin M1 is normalized. A special group of toxic substances are heavy metals and arsenic (radionuclides - cesium-137, strontium-90 are also normalized). Sources of their entry into milk can be feed, drinking water for animals, air, as well as water used to reconstitute dry milk products.

*lead, cadmium, mercury, arsenic - which are highly toxic elements;

*Tin and chromium are polluting products when stored in tin and chrome containers. For these elements, the maximum allowable levels of their content in milk and dairy products have been established, as well as methods for their determination in food products, including dairy products, have been standardized.

1.9. Microflora of raw milk

Microorganisms enter milk directly from the udder or the external environment, from air, water, from the hands of attendants, from dishes, animal skin, etc. At any stage of production, processing, transportation and storage of milk, microorganisms can enter it. Bacteria, yeasts and molds have been found in milk. Milk containing only the microflora that came into it from the udder of a healthy cow is conditionally called aseptic. In 1 cm3 of such milk, there are from several hundred to several thousand microorganisms.

bacteria.

In milk, lactic acid, coliform, butyric, propionic and putrefactive bacteria are commonly found. Group lactic acid bacteria includes rods and cocci, which can form chains of various lengths. Lactic acid bacteria do not form spores, they are facultative anaerobes. Most of them die when heated to 70°C. Lactic acid bacteria use lactose as a carbon source, fermenting it to lactic acid, as well as acetic acid, carbon dioxide, and ethanol. Many of them are used in the production of dairy products. coliform bacteria(bacteria of the Escherichia coli group) are facultative anaerobes, their optimal development temperature is 30...37°C. They are found in the intestines, on the surface of the hands, in sewage, in contaminated water and on vegetation. Coliform bacteria ferment lactose to lactic acid and other organic acids, carbon dioxide and ethanol. In addition, they destroy milk proteins, resulting in a foreign smell. Certain types of bacteria cause mastitis in cows.

Coliform bacteria can cause significant harm in the production of cheese. In addition to the appearance of foreign odors as a result of increased gas formation during their life, the texture of the cheese is disturbed at an early stage of its ripening. The development of bacteria stops at a pH below 6, so their activity is observed precisely in the early stages of cheese ripening, when lactose is not yet fully fermented. Coliform bacteria, as a rule, die during pasteurization of milk.

Butyric acid bacteria- anaerobic spore-forming microorganisms, the optimum temperature for their development is 37°C. They do not develop well in milk, but they feel great in cheeses, where anaerobic conditions are observed. In fact, these bacteria are the "destroyers" of cheese. Butyric fermentation, accompanied by the formation of a large volume of carbon dioxide, hydrogen and butyric acid, which leads to the formation of a "torn" texture of the cheese and a rancid taste. Spores of butyric bacteria are not neutralized under pasteurization regimes. To remove them and suppress development, special operations are used: microfiltration, bactofugation, addition of saltpeter, salting of cheeses.

propionic acid bacteria do not form spores, the optimum temperature for their development is 30°C. Some species withstand pasteurization. Ferment lactates to propionic acid, carbon dioxide and other products. Pure cultures of propionic acid bacteria are used in the production of certain types of fermented milk products and cheeses.

putrefactive bacteria include a very large number of species of various forms, spore-forming and non-spore-forming, aerobic and anaerobic. They get into milk with feed, water, from the hands of workers, etc. Putrefactive bacteria produce enzymes that break down proteins; they can break them down completely to ammonia. This type of decomposition is known as putrefaction. Many of the putrefactive bacteria also produce the enzyme lipase, that is, they can decompose milk fat.

Yeast.

These are microorganisms of a round, oval or rod-shaped form. They reproduce by budding, sporulation, and sometimes division. Yeasts are about an order of magnitude larger than bacteria. Like all microorganisms, yeast develops under certain conditions. The acidity (pH) of their normal habitat is 3...7.5, at the optimum - 4.5...5. Optimum temperature for their development is 20...30°C. Yeasts are viable both in the presence and in the absence of atmospheric oxygen, i.e., they are facultatively anaerobic. In the presence of oxygen, they ferment sugar to carbon dioxide and water, in its absence, to alcohol and water.

Mold.

Develop only when exposed to air. The optimum temperature for mold development is 20...30°C (pH varies from 3 to 8.5, but many species prefer an acidic environment). As a rule, molds worsen the quality of dairy products, except for single species used in the production of cheeses such as Roquefort and Camembert.

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Introduction

Milk is complete and useful product nutrition. It contains all the nutrients necessary for life, needed to build the body. The natural purpose of milk in nature is to provide nutrition to the young organism after birth. The composition of the milk of various mammals is generally determined by the environmental conditions in which the growth of a young organism occurs. This is especially clearly manifested in the content of protein and fat, the more of them in the mother's milk, the faster her child grows.

So, an infant doubles its weight in about 180 days, a calf in 50 days, and a puppy in 9 days. The protein content in women's milk, compared with the milk of various animals, is the lowest - 1.6%, in cow's milk - 3.4%, and in dog's milk - 7.3% of protein. Milk fat serves primarily to meet the body's need for energy. In areas with a cold climate, the body's need for energy is higher than in areas with a temperate climate. That is why the milk of the female reindeer differs more high content fat - 19.7%. Milk has survived many civilizations before it became a food product and has its own purpose:

As a food product for the population,

Means for feeding young animals and feed in animal husbandry,

Raw materials for food production,

The source of obtaining individual components of milk, which, in turn, serve as raw materials for pharmacology and other industries.

The ever-increasing importance of milk as a complete food product and as a raw material has led to an increase in demand for it. As a result, milk production has become one of the most important branches of agricultural production. At present, milk makes up a significant share in the gross agricultural product of our country.

The nutritional value of 1 liter of milk is 685 kcal. Calorie content depends mainly on the content of fat, protein. Due to the content in milk of the most important nutrients, mainly protein, carbohydrates, vitamins, minerals, it is also a protective factor. In order to protect health in enterprises where there are harmful working conditions, workers receive milk.

Milk protein is an important protective factor, since, due to its alephoteric nature, it binds pairs of acids and alkalis, and also neutralizes toxic heavy metals (traces) and other substances harmful to health. Due to the content of calcium, phosphorus, and vitamins in milk, the development of beriberi is prevented. In addition to human nutrition, milk is used to feed farm animals: calves, pigs, birds.

With the help of physical and biochemical methods, dairy products are obtained from raw milk, which are partially fortified food products, due to which these products are characterized by an increased calorie content per 100 g. Processing of milk leads to a change in its nutritional value and palatability, therefore, it is necessary to take into account the properties of each individual component of milk. Raw materials for industry are such components of milk as casein and lactose. The definition of the substance of milk can be given from different points of view, taking into account, first of all, the purpose of the application. If we consider milk as a food product, then legislative, hygienic and economic requirements come to the fore, so that raw milk can be defined.

“Raw milk is the result of regular, complete milking of the udder of one or more cows from one or more milkings, a pure and then chilled product from which nothing has been removed and to which nothing has been added.”

Knowledge about the number of constituent parts of milk has constantly expanded over time. This can be explained by the purpose scientific research and the use of modern methods of analysis, which allow, without using the method of enrichment, to detect and quantify even those constituent parts of milk that are present in it in the form of traces. Currently, over 200 different components of milk are known.

The constituents of milk are all those components that are excreted from the udder during milking.

The chemicalization of agriculture, the treatment of diseases of cattle, as well as diseases of the udder with the help of chemotherapeutic agents, have led to an increase in the content of foreign substances in milk, which enter it in various ways.

1. Nutritional value and chemicalcomposition of milk from farm animals

The nutritional value of milk is due to its chemical composition. It is slightly different for milk different types and breeds of animals, may vary depending on the conditions of their feeding.

Proteins are the most valuable part of milk. They make up about 3.3%, including casein 2.7%, albumin 0.4%, globulin 0.12%. In recent years, a strong opinion has formed that proteins are the most valuable component of milk. Milk proteins are macromolecular compounds consisting of amino acids linked together by a peptide bond characteristic of proteins.

Milk proteins are divided into two main groups - caseins and whey proteins.

Casein refers to complex proteins and is found in milk in the form of granules, which are formed with the participation of calcium, phosphorus, etc. The size of casein granules depends on the content of calcium ions. With a decrease in the calcium content in milk, these molecules break down into simpler casein complexes.

Dry casein is White powder, tasteless and odorless. In milk, casein is bound to calcium and is found as a soluble calcium salt. Under the action of acids, acid salts and enzymes, casein coagulates (coagulates) and precipitates, which is used in the production of sour-milk drinks, cheeses, cottage cheese. After the removal of casein, soluble whey proteins (0.6%) remain in the whey, the main of which are albumin and globulin, which are blood plasma proteins.

Albumin is a simple protein, highly soluble in water. Under the action of rennet and acids, albumin does not coagulate, and when heated to 70 ° C, it precipitates.

Globulin - a simple protein - is present in milk in a dissolved state, coagulates when heated in a slightly acidic medium to a temperature of 72 ° C.

Globulin is the carrier of immune bodies. In colostrum, the amount of whey proteins reaches 15%. Whey proteins are increasingly being used as additives in the production of dairy and other products, since from the point of view of nutritional physiology they are more complete foam than casein, since they contain more essential acids and sulfur. The degree of assimilation of milk proteins is 96-98%.

Of the other proteins, the fat globule protein, which belongs to complex proteins, is of the greatest importance. The shells of fat globules consist of compounds of phospholipids and proteins (lipoproteins) and represent a lecithin-protein complex.

Fat in milk is contained in an amount of 2.8 to 5%. Milk is a natural emulsion of fat in water: the fatty phase is in the milk plasma in the form of small drops - fat globules, covered with a protective lecithin-protein shell. When the shell is destroyed, free fat forms lumps of fat, which impairs the quality of milk. To ensure the stability of the fat emulsion, it is necessary to minimize mechanical effects on the dispersed phase of milk during transportation, storage and processing, to avoid its foaming, to properly carry out heat treatment(prolonged exposure at high temperatures can cause denaturation of the structural proteins of the shell of fat globules and violation of its integrity), apply additional dispersion of fat by homogenization.

Milk fat is made up of a complex mixture of acylglycerols (glycerides). Of the several thousand triglycerides of milk fat, most are heteroacid, so the fat has a relatively low melting point and a uniform consistency.

Among saturated acids, palmitic, myristic and stearic acids predominate (60-75%), among unsaturated ones - oleic (about 30%). The content of stearic and oleic acids increases in summer, and that of myristic and palmitic acids in winter. Milk fat contains low molecular weight volatile saturated fatty acids - butyric, caproic, caprylic and capric (4-10%), which determine the specific taste of milk fat. A lower content of low molecular weight acids is a sign of falsification of milk fat by other fats. In addition to oleic acid, they are also found in large quantities unsaturated fatty acids - linoleic, linolenic and arachidonic (3-5%).

Unsaturated and low molecular weight fatty acids give milk fat low melting point (melting point - 27-34 ° C). These acids have more valuable biological properties than high-molecular and saturated ones. Low melting point and high dispersion ensure good digestibility of milk fat.

The disadvantages of milk fat include its low resistance to high temperatures, light rays, atmospheric oxygen, water vapor, solutions of alkalis and acids. Rancidity of fat occurs due to hydrolysis, oxidation, salting.

Associated substances in the composition of milk fat are 0.3 - 0.55%. Nasterins account for 0.2-0.4%. They are mainly represented by cholesterol in the free state or in the form of fatty acid esters, as well as ergosterol, etc. Along with simple lipids, milk fat includes a variety of phospholipids (lecithin, cephalin, etc.), which have an emulsifying ability, participate in the construction of ball shells fat. The yellow color of milk fat is due to the presence of carotenoids in it - tetraterpene hydrocarbons (carotenes) and alcohols (xanthophylls). The content of carotenes depends on the feed rations, the condition of the animals and the time of year (more in summer) and is 8-20 mg per 1 kg of milk fat.

Lactose (milk sugar) is the main carbohydrate of milk, monosaccharides (glucose, galactose, etc.) are present in it in a smaller amount, more complex oligosaccharides - in the form of traces.

The disaccharide lactose is the main source of energy for biochemical processes in the body (it accounts for about 30% of the energy value of milk), promotes the absorption of calcium, phosphorus, magnesium, and barium. In milk, lactose is in the free state in the form of a- and p-forms. A very small portion of lactose is associated with other carbohydrates and proteins. Milk sugar slowly penetrates through the intestinal wall into the blood, so it is used for nutrition by lactic acid bacteria, which heal the environment of the stomach. When milk is heated above 95 ° C, the color of milk changes from yellowish to brown due to the formation of melanoidins, which have a dark color, as a result of the reaction of milk carbohydrates with proteins and some free amino acids.

During hydrolysis, lactose is broken down into glucose and galactose, and during fermentation under the influence of enzymes, into acids (lactic, butyric, propionic, acetic), alcohols, esters, gases, etc.

Minerals. Mineral substances are understood as metal ions, as well as salts of inorganic and organic acids of milk. Milk contains about 1% of minerals. Most of these are medium and acidic salts of phosphoric acid. Of the salts of organic acids, there are mainly salts of caseic and citric acids.

Minerals are found in all tissues of the body, participate in the formation of bones, maintain the osmotic pressure of the blood, and are an integral part of enzymes and hormones.

Milk salts and trace elements, along with other main components, determine the high biological value of milk. An excess of salts entails a violation of the colloidal system of proteins, as a result of which they precipitate. This property of milk is used to accelerate protein coagulation in the production of curds and cheeses.

Depending on the concentration in milk, minerals are divided into macro- and microelements.

Macroelement composition of cow's milk

Trace elements are present in milk in the form of ions and are vital substances. They are part of many enzymes, activate or inhibit their action, can be catalysts for chemical transformations of substances that cause various defects in milk. Therefore, the concentration of trace elements should not exceed the permissible values.

Microelement composition of cow's milk

The human body has a high need for trace elements such as iron, copper, cobalt, zinc, iodine. Growing children's body especially needs calcium, phosphorus, iron, magnesium.

Milk enzymes catalyze many of the biochemical processes that take place in milk and in the production of dairy products. They are formed from the mammary gland of an animal (native enzymes) or secreted by microorganisms. An important role is played by such milk enzymes as lactase, phosphatase, reductase, peroxidase, lipase, protease, amylase.

Lactase (galactosidase) breaks down milk sugar into glucose and galactose and is secreted by microorganisms.

Phosphatase (phosphomonoesterase) is of animal (native) and microbiological origin. The effectiveness of pasteurization of milk is judged by the presence of phosphatase.

Reductase is formed due to the development of foreign microorganisms. Reduct gas test indicates the purity class of milk according to bacterial contamination.

Peroxidase - an enzyme of animal origin, is destroyed by short-term heating to 75-80 ° C. The effectiveness of milk pasteurization is judged by the presence of the peroxidase enzyme in milk.

Lipase (glycerol ester hydrolase) can be of native and microbiological origin. Its presence in high-fat dairy products is undesirable, as it breaks down milk fat into glycerol and fatty acids, resulting in a rancid taste. Lipase is destroyed at temperatures of 80-85°C.

Thus, milk enzymes play a positive or negative role, their activity depends on temperature, pH value, concentration of milk solids, the amount of the enzyme itself, etc.

Vitamins are present in milk fat-soluble (A, D, E, K) and water-soluble (groups B and ascorbic acid).

Vitamin A (retinol) is formed in the intestinal mucosa of animals from carotenes (a-, p- and y-forms) of feed. In cows, part of the carotenes is absorbed in the intestines without being transformed into vitamin A and then found in milk. The daily human requirement for vitamin A is 1 mg. In milk, on average, it contains 0.24 mg / kg, in kefir 0.41 mg / kg; since retinol is a fat-soluble vitamin, it is most abundant in sour cream (5.55 mg/kg), cheese (2.5 mg/kg), butter (4.9 mg/kg); summer milk is richer in this vitamin than winter milk. Vitamin A well withstands heating (up to 120 ° C) without air access. Storage of milk leads to a decrease in the content of vitamin A, it is destroyed by oxygen and light.

Vitamin D (calciferol) is formed from stearins under the action of ultraviolet rays, therefore, it accumulates much more in summer milk than in winter. The daily requirement is 25 mg. Milk contains on average up to 1.5 mcg/kg of vitamin D. During the processing of milk, it is not destroyed and, together with fat, passes into dairy products.

Vitamin E (tocopherols) is found in milk in a small amount(0.7-0.9 mg/kg). The milk of cows fed green fodder is richer in tocopherols than cows fed dry fodder. Tocopherols are resistant to prolonged heating. They are natural antioxidants that protect fats from oxidative damage. When dairy products are stored under the influence of oxygen, tocopherols are destroyed and their antioxidant properties are violated.

Vitamin B1, (thiamine) is found in milk in an amount of about 0.5 mg / kg with a daily requirement of 2 mg. In fermented milk products, the content of thiamine increases due to the synthesis of certain races of lactic acid bacteria. During the heat treatment of milk (pasteurization and drying), vitamin B is slightly destroyed. Decomposes in an alkaline environment.

Vitamin B2 (riboflavin) is found in milk in the amount of 1.5-2 mg/kg with a daily requirement of 2 mg. Pasteurization of milk almost does not reduce the content of vitamin B2. In fermented milk products, the content of vitamin B2 increases. Its cheese contains from 2.3 to 6.8 mg/kg.

Vitamin B12 is found in milk at about 7.5 mg/kg with a daily requirement of about 1 mg, so milk is considered a rich source of this vitamin. This vitamin is stable when milk is heated to 120 °C.

Vitamin B6 (pyridoxine) is found in milk in free form and associated with proteins; stimulates the development of lactic acid streptococcus, is resistant to heat. The content in milk is 0.2-1.7 mg/kg.

Vitamin PP (nicotinic acid) is found in milk in the amount of 1.5 mg/kg at a daily rate of 150 mg. It is stable in milk, does not break down during oxidation, under the influence of light and alkalis. In fermented milk products, it is somewhat less than in the original milk, since lactic acid bacteria consume nicotinic acid.

Vitamin C is ascorbic acid, the daily requirement of which is 75-100 mg. Milk and dairy products are poor in vitamin C. In freshly milked milk, the content of vitamin C reaches 10–25 mg/kg, but during storage, its amount rapidly decreases. Vitamin C is sensitive to oxidation, the action of metals (copper, iron), light and heat. Pasteurization of milk, especially long and open, destroys vitamin C up to 30%. Fermentation of milk with lactic acid bacteria increases the content of vitamin C, which is most likely due to the greater ability of lactic acid bacteria to synthesize this vitamin.

Vitamin composition of cow's milk.

vitamins
fat soluble
A (retinol)
P-carotene (provitamin L) A)
D (calciferol)
E (tocopherol)
K (phylloquinone)	60 µg/cm3 (traces)
water soluble
B, (thiamine)
B2 (riboflavin)
B4 (choline)
B6 (iiridoxine)
B3 (pantothenic acid)
B8 (inositol)
B12 (cyanocobalamin)	0.7 µg/cm3
B6, (folic acid)	0.1 µg/cm3
PP (nicotinic acid)
H (biotype)	5.0 µg/cm3
C (ascorbic acid)

Hormones are protein substances that accelerate the course of biochemical reactions in the body (synthesis and breakdown of individual compounds, etc.). Milk contains enzymes such as lipase, lactase, phosphatase, catalase, peroxidase. So, lipase breaks down fats, lactase regulates the breakdown of milk sugar, phosphatase is involved in hematopoiesis, bone formation, motor function of muscles, including cardiac, regulates metabolism.

It is present only in raw milk, as pasteurization destroys it. Catalase protects the body from the toxic effects of hydrogen peroxide, which is formed during metabolism. The amount of catalase in the milk of healthy cows is insignificant, but with inflammation of the mammary gland, its content rises sharply, which is used to identify sick animals. Peroxidase stimulates oxidation reactions that are very important for the body. When milk is heated to 8°C and above, it is destroyed. This serves as a reliable way to monitor the effectiveness of milk pasteurization.

Hormones are secreted by the endocrine glands and, together with the blood, enter the glandular apparatus of the udder, from where they pass into milk. They have a regulatory effect on metabolic processes in the body. In addition, they stimulate the processes of milk formation and milk flow. The following hormones are found in milk - adrenaline, insulin, thyroxine, oxytocin, prolactin, etc.

Water, which accounts for almost 9/10 of the composition of milk, serves as a medium in which all its constituent parts are in various physical states. It is very important for newborns - in the first weeks of life they are provided with water only through milk. However, despite such a large amount of water in milk, its taste is natural milk is not felt. But if you add raw water to milk or taste frozen and then thawed milk, you will find that it has become sweetish and watery. This is explained by the fact that the water in natural milk is not like ordinary milk. drinking water- it is associated with proteins, milk sugar and other substances. After thawing, the bonds of water with these parts of the milk are broken and free water is obtained in the milk, which tastes exactly the same as poured into it from a water tap.

Milk also contains many other beneficial substances that are involved in the metabolic process, increase the body's resistance to infections and fight against harmful intestinal microorganisms. These include antibiotic substances, immune bodies, lysozymes, opsonins, etc.

Gases dissolved in milk have a level of 60-80 ml/1 l in fresh milk.

In this volume of carbon dioxide 50-70%, oxygen 5-10%, and nitrogen 20-30%, there is also a certain amount of ammonia. During storage, due to the development of microorganisms, the amount of ammonia increases, and oxygen decreases. An increase in the oxygen content during pumping, transporting milk gives it an oxidized taste. During pasteurization, the content of oxygen and carbon dioxide is reduced.

Non-protein nitrogenous substances. From non-protein nitrogenous substances, milk contains urea, amino nitrogen, creatine, creatinine and uric acid.

Milk contains choline and methylguanidine.

Lemon acid. In milk, citric acid is partly in the free state, partly in the form of potassium and sodium salts. Its content in milk averages 0.15--0.2%.

Milk pigments. Milk contains pigments that give it (with a significant amount) a somewhat yellowish tint. Lactoflavin is a substance identical to riboflavin.

Milk also contains pigments of plant origin, which enter the bloodstream with food, and then into milk. This group of pigments includes carotene and xanthophyll. Xanthophyll can be considered as a product of carotene oxidation. The coloring ability of carotene and xanthophyll is very significant, as a result of which even a relatively very small content of them in milk gives the latter an intense color. These pigments are highly soluble in fats, so they are concentrated in the fat during the manufacture of butter, turning it yellow. The color intensity of the oil depends on the amount of pigment in the feed. In summer green fodder it is much more than in winter concentrated fodder. That's why summer oil usually has a more intense yellow color than winter.

Foreign chemicals can get into the milk as a result of feeding, increased radiation in the area where animals are kept, etc. Substances harmful to humans include impurities of antibiotics, pesticides, heavy metals, nitrates and nitrites, residues of disinfectants, bacterial and plant poisons, and radioactive isotopes.

Factors that shape the quality are associated with the processing of milk, which is carried out immediately after milking. It is filtered and cooled to the lowest possible positive temperatures. Timely cooling of milk helps to extend its shelf life.

The milk received at the dairy plant is checked for organoleptic characteristics, acidity and fat content. The received milk is purified from mechanical impurities, then normalized for fat, i.e. reduce or increase the fat content, using skimmed milk (skim) or cream for this.

During the separation and pumping of milk, a partial destabilization of the fat emulsion occurs - the release of free fat on the surface of the fat globules, their sticking together and the formation of lumps of fat. To increase the degree of dispersion of the fatty phase, increase its stability, improve the consistency and taste of milk, it is homogenized. To do this, heated milk is sent to homogenizers, where it is passed under high pressure through a narrow slot, as a result of which the fat globules are crushed - their diameter is reduced by 10 times.

Heat treatment of milk (pasteurization and sterilization) is necessary to destroy microorganisms and destroy enzymes in order to obtain products that are hygienically safe and have a longer shelf life. At the same time, the nutritional and biological value of milk should be preserved to the maximum, and there should be no undesirable changes in its physical and chemical properties.

Pasteurization can be long-term (at a temperature of 63 ° C, milk is kept for 30 minutes), short-term (at a temperature of 72 ° C for 15-30 minutes) and instant (high-temperature at 85 ° C and above without exposure). In the process of heating, whey proteins are denatured (structural changes in molecules) and the milk acquires the taste of a boiled product or the taste of pasteurization. As a result of pasteurization and sterilization, the amount of calcium in milk decreases due to the formation of poorly soluble calcium phosphate (precipitates in the form of a milk stone or burn along with denatured proteins). This impairs the ability of milk to rennet coagulation; in the production of cottage cheese and cheese, calcium chloride is added to pasteurized milk.

Sterilization of milk causes the decomposition of lactose with the formation of carbon dioxide and acids - formic, lactic, acetic, etc. Due to the denaturation of the protein of the shells of fat globules, during the sterilization of milk, rendering of fat is observed. Sterilization of milk in bottles consists in processing it in autoclaves under the following conditions: at 104 ° C for 45 minutes; at 109 °C for 30 min; at 120 °C for 20 min. Sterilization of milk in the flow is carried out at ultrasonic temperatures (UT) of 140-142 °C with exposure for 2 s and subsequent cooling and bottling under aseptic conditions. With ultrasonic sterilization, more vitamins are stored in milk than with sterilization in bottles. Most of all, vitamin C is lost (10-30%).

Insufficient heat treatment leads to incomplete inactivation of milk enzymes, which cause undesirable biochemical processes in milk and dairy products. The result can be a reduction in the quality, taste and nutritional value of products. Thus, lipases contribute to the rancidity of dairy products, and proteinases of bacterial origin cause coagulation of the U-milk.

As a result of pasteurization and sterilization, such physicochemical and technological properties of milk as viscosity, surface tension, acidity, ability to settle cream, ability of casein to rennet coagulation. Milk acquires a specific taste, smell and color, its constituent parts change.

Features of the composition of milk of various farm animals.

Not only cow's milk is used for food and for the production of various dairy products, but also the milk of a number of other farm animals. So, high-quality cheese is obtained from sheep's milk, koumiss - from mare's.

Characteristics of animal milk of various species

milk sterilization separation value

Type of milk		Acidity, °T
	dry matter





buffalo
camel
Zebu milk

Goat's milk is closest to cow's milk in composition and properties. It is characterized by a sweetish taste and a characteristic smell. Goat milk contains more fat, calcium, phosphorus, milk fat has a higher dispersion.

Sheep milk has a white color with a grayish tint, due to the absence of carotene, although the content of vitamin A is significant.

Mare's milk has a sweet, slightly tart taste and smell, more viscous, white with a bluish tint. Compared to cow's milk, it contains less fat, protein, minerals; albumin and globulin predominate in its proteins. Milk is rich in vitamins, especially vitamin C (5-7 times more than in cow's milk). Mare's milk has a bactericidal effect. Fat in mare's milk is more dispersed than in cow's.

Donkey milk in terms of chemical composition and organoleptic characteristics slightly differs from mare's milk.

When coagulated, donkey's milk forms a flocculent clot, has a high biological value and is classified as a medicinal food.

Buffalo milk has a pleasant taste and smell, more viscous than cow's milk, due to the significant content of fat and SOMO.

Camel milk is characterized by a sweetish taste, viscous texture, increased content phosphate and calcium salts.

Conclusion

Literature

1. Drummers N.V., Shuvarikov A.S. Dairy business. - M.: MSHA, 2000. - 347 p.

2. Pavlov V.A., Pavlova V.V. Production of milk and dairy products (Sanitary and hygienic requirements). - M.: Informagrotekh, 199. - 160 p.

3. Technology of milk and dairy products./ G.V. Tverdokhleb, Z.Kh. Dilanyan, L.V. Chekulaeva and others - M .: Agropromizdat, 1991. - 463 p.

4. Commodity science and examination of edible fats, milk and dairy products: Textbook for higher. textbook institutions /M. S. Kastornykh, V. A. Kuzmina, Yu. S. Puchkova and others - M .: Publishing Center "Academy", 2003.

5. Borovkov M.F. - Veterinary and sanitary expertise with the basics of technology and standardization of livestock products: a textbook. - St. Petersburg: Lan publishing house, 2007.

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Nutritional value and chemical composition

Milk - biological fluid formed in the mammary gland of mammals and intended for feeding a newborn cub. This is a complete and healthy food product containing all the necessary elements for building the body. It contains over 200 different components: 20 fatty acid glycerides, more than 20 amino acids, 30 macro- and microelements, 23 vitamins, 4 sugars, etc. The composition of the milk of various mammals depends on the environmental conditions in which the young organism grows, and may change as a result of animal diseases, microbiological and other processes occurring in it.

Water. Milk consists of 85 ... 89% of water, which takes part in various reactions occurring in the body of animals: hydrolysis, oxidation, etc. Its main source is blood, and only a part is formed during the synthesis of triglycerides, while three water molecules are released.

Water in milk is in a free and bound state. There is much more free water (83...86%) than bound water (3.0...3.5%). It takes part in biochemical reactions and is a solution of various organic and inorganic substances. Milk sugar, water-soluble vitamins, minerals, acids, etc. dissolve in free water. It can be easily removed by thickening, drying milk. Free water freezes at 0°C.

Bound water (adsorption-bound water) is held near the surface of colloidal particles (proteins, phospholipids, polysaccharides) by molecular forces. Hydration of protein molecules is due to the presence of polymeric groups (hydrophilic centers) on their surface. These include carboxyl, hydroxyl, amine and other groups. As a result, dense hydrated (water) shells are formed around the particles, preventing their connection (aggregation). The properties of bound water differ from free water in milk. It freezes at temperatures below 0 ° C, does not dissolve sugar, salts and other substances, and is difficult to remove when dried.

A special form of bound water is chemically bound water. This water is crystalline and crystallized. It is associated with milk sugar crystals C 12 H 22 O m H 2 0 (lactose).

Dry substances. Dry matter (DM) in milk contains an average of 12.5%, they are obtained as a result of drying milk at

102... 105 °С. The composition of solids includes all components of milk except water. nutritional value milk is determined by its dry matter content. Raw material consumption per 1 kg finished products when processing milk into cottage cheese, cheese, canned food, etc. also depends on the amount of dry matter.

The productivity and breeding quality of animals is evaluated not only by the content of fat in milk and milk yield, but also by the content of solids in it.

Milk proteins. Protein is the most valuable component of milk. It contains a variety of proteins that differ in structure, properties and play a strictly defined role. The mass fraction of proteins in milk is 2.1 ... 5%.

From a chemical point of view, proteins are high-molecular compounds that are part of all living structures of cells, tissues and the body as a whole. Proteins are a building energy material that performs various functions: transport, protective, regulatory. They are built according to the same principle and consist of four main elements: carbon, oxygen, hydrogen and nitrogen. All proteins contain a small amount of sulfur, and some contain iron, calcium, phosphorus, zinc, etc. The structural blocks of proteins are amino acid residues arranged in a certain order and interconnected in a chain. A protein molecule consists of more than 20 amino acids.

The composition of acids includes amine (NH 2) and carboxyl (COOH) groups. The amine group is in the ^-position with respect to the carboxide. Amino acids can contain an equal number of carboxyl and amine groups (serine, alanine, cysteine, glycine, phenylalanine, etc.) - they are neutral, but there are amino acids containing two carboxyl groups (glutamic acid) or two amino groups (lysine); their aqueous solutions show an acidic or alkaline reaction, respectively.

A protein is a long chain of various amino acid residues. The connection of amino acids into a protein polymer occurs as follows: the amino group of one amino acid reacts with the carboxyl group of another amino acid, while water molecules are released and a peptide bond -CO-NH- is formed.

Amino acids, connecting in different combinations, form long polypeptide chains with R groups in the form of branches. The sequence of the polypeptide chain of amino acid residues is specific for each protein. Protein molecules have a certain flexibility. In water, hydrophobic regions are in contact with each other, while hydrophilic regions are in contact with water and the molecule. When bending, the molecule folds in such a way that all hydrophobic side chains are inside the globule, and hydrophilic side chains are on its surface, closer to water.

The primary structure is an elongated thread, the secondary is a spiral, the tertiary is a globule, when the globules combine into one whole, a quaternary structure is formed. In proteids (complex proteins), in contrast to proteins ( simple proteins) in addition to the protein part, there is also an additional component of a non-protein nature (phosphoric acid residues in phosphoproteins, fats, carbohydrates, etc.), which affects the properties of the protein. In water, the protein forms a stable colloidal solution.

Milk contains more than 20 different proteins, but the main ones are casein and whey proteins: albumin, globulin, etc. The nutritional value of whey proteins is higher than that of casein.

Casein is the main protein of milk, its content ranges from 2 to 4.5%. In milk, casein is present in the form of colloidal particles (micelles).

The structure of casein. On the surface of micelles, there are charged groups (negative sign) and a hydration shell; therefore, they do not stick together and do not coagulate when approaching each other. The casein particles in fresh milk are fairly stable. Like other animal proteins, casein contains free amino groups (NH 2) and carboxyl groups (COOH): the first - 83, the second - 144, therefore it has acidic properties and has an isoelectric point at pH 4.6 ... 4, 7. In addition, casein contains -OH groups of phosphoric acid, being not a simple, but a complex phosphoprotein protein. In milk, casein is combined with calcium salts and forms a caseinate-calcium phosphate complex, which in freshly milked milk forms micelles capable of binding a significant amount of water. Casein formula:

Casein isolated from milk consists of the following fractions: a, b, c, p. They differ in physicochemical properties, sensitivity to calcium ions and solubility. So, A- and ^-casein are sensitive to calcium ions and precipitate under their action, are unstable and are located inside micelles; c-casein is insensitive to calcium ions and is located on the surface. Under the action of rennet, all three fractions of casein are precipitated; the fourth fraction - p-casein - is not part of micelles and does not precipitate under the action of rennet, therefore, in the production of cottage cheese and cheese by the rennet method, it is lost with whey.

properties of casein. Casein isolated from milk and treated with alcohol is an amorphous white powder, tasteless and odorless, with a density of 1.2...1.3 g/cm 3 . It dissolves well in some salt solutions, worse in water; completely insoluble in ether and alcohol.

Thanks to casein, the color of milk is also white. Casein does not precipitate when heated, but coagulates under the action of rennet, acids and salts. These properties are used in the production of fermented milk products and cheese. The concentration of casein and the size of its particles determine the rate of settling and the strength of protein clots. The thermal stability of milk depends on the size of the particles: the larger they are, the less thermally stable it is. Hydrophilic properties of casein, i.e. its ability to bind and retain moisture determines the quality of the resulting acid and rennet clots, as well as the consistency of finished fermented milk products and cheese. The nature of the interaction of casein with water depends on its amino acid composition, the reaction of the medium and the concentration of salts in it.

When proteins are precipitated with acid, rennet, after mechanical and heat treatment, the hydrophilic properties of casein change as a result of a change in the structure of protein particles and the redistribution of hydrophobic and hydrophilic groups on their surface. The hydrophilic properties of casein are greatly influenced by whey proteins of milk, since during the heat treatment they interact with its particles. Whey proteins bind water more actively than casein; while increasing its hydrophilic properties. These properties are taken into account when choosing milk pasteurization modes. Under the action of acids, rennet, calcium chloride, casein precipitates, and the colloidal protein solution turns into a clot, or gel; protein particles are connected to each other in chains and form spatial networks.

Serum proteins (albumin and globulin). Their milk contains significantly less than casein (0.2...0.7%), i.e.

15 ... 22% of the mass of all proteins. Albumin and globulin contain more sulfur than casein, they are soluble in water and do not coagulate under the action of acids and rennet, but precipitate when heated, and together with salts form a "milk stone".

Albumin and globulin are of great importance for a newborn animal. Immunoglobulins that pass from the animal's blood into milk are antibodies that neutralize foreign cells, i.e. play a protective role in the body. Especially a lot of these proteins in colostrum. Thus, the content of albumin can reach 10...12%, globulin - up to 8...15%.

Whey proteins are contained in milk in the form of small particles compared to casein, on the surface of which there is a total negative charge. The particles are surrounded by a strong hydration shell, so they do not coagulate even at the isoelectric point. When milk is heated to 70...75 °C, albumin precipitates, and globulin precipitates by heating to 80 °C. By heating milk to 90-95 °C, albumins and globulins can be isolated from whey. Whey proteins can be isolated by combined heat, calcium, or acid treatment. The resulting protein mass is used in the production of protein products, processed cheeses, children's and diet food. The shell protein makes up about 70% of its mass. This complex protein is a mixture of protein and phospholipids. The fatty globules of the protein shell contain a fat-like substance called lecithin. Unlike other milk proteins, whey proteins contain less nitrogen, no phosphorus, calcium, magnesium.

Milk fat. It is a compound of esters of glycerol and fatty acids. Glycerin, which is part of triglycerides, is a trihydric alcohol.

Fatty acids contain a carboxyl group (COOH) and a radical, at the end of which there is a methyl group (CH 3) and an unequal number of carbon atoms (from 0 to 24), forming carbon chains of different lengths. Carbon can be present in the form of saturated methylene (-CH 2 -) compounds - in this case, fatty acids will be saturated (limited) - or unsaturated ethylene compounds (-CH \u003d) - acids will be unsaturated (unsaturated).

The mass fraction of fat in milk averages 3.8%. Fat is synthesized from feed, which includes proteins, carbohydrates and fats. These substances, getting into the gastrointestinal tract of the animal, undergo complex changes. In the stomachs of ruminants (in the rumen), during fermentation, acetic acid and other volatile fatty acids (propionic, butyric, etc.) are formed, which are precursors of fat: the more acetic acid is formed, the fatter the milk. If the amount of propionic acid increases, then the fat content decreases, and the amount of protein in milk increases. The listed volatile fatty acids are absorbed first into the lymph, then into the blood, which transfers them to the mammary gland, where fat is synthesized. The source of milk fat can also be neutral blood fat formed in the liver.

The mass fraction of fat in milk depends on the breed, productivity, age and diet of the animal. IN fresh milk fat is present in a liquid state and forms an emulsion in the water part. In cold milk, the fat is solid and is in the form of a suspension. The fat in milk is in the form of balls (Fig. 1) with a strong elastic shell, so they do not stick together. The ball diameter is 3...4 µm (dimensions range from 0.1 to 10 µm, in some cases up to 20 µm). 1 ml of milk contains from 1 billion to 12 billion, on average from 3 billion to 5 billion fat globules. The content of fat globules in milk changes during the lactation period: at the beginning of lactation, they are larger and smaller, and vice versa towards the end of lactation. Fat globules of small size float faster, as they stick together into lumps.

The physical stability of fat globules in milk and dairy products depends mainly on the composition and properties of their shells. The shell of the fat globule consists of two layers: the outer one is loose (diffuse), easily desorbs during the technological processing of milk; internal-thin, tightly adjacent to the crystalline layer of high-melting triglycerides of the fat globule (see Fig. 1).

The composition of the shell substance includes proteins, phospholipids, sterols, 6-carotene, vitamins A, D, E, minerals Cu, Fe, Mo, Mg, Se, Na, K, etc.

Rice. 1.

1 - fat globule: 2 - inner layer; 3 - outer layer

Rice. 2.

1 - hydrophilic shell: 2 - lipophilic shell: 3 - fat: 4 - water

The inner layer includes lecithin and a small amount of cephalin, sphingomyelin. Phospholipids are good emulsifiers, their molecule consists of two parts: lipophilic, similar to fat, and hydrophilic - attaches water of hydration.

The protein components of the shell include two fractions: soluble in water and poorly soluble in water. The water-soluble protein fraction contains a high-carbohydrate glycoprotein and enzymes: phosphatase, cholinesterase, xanthine oxidase, etc.

The poorly water-soluble fraction contains 14% nitrogen, more arginine than in milk, and less leucine, valine, lysine, ascorbic and glutamic acids. It also contains a significant amount of glycoproteins containing hexoses, hexosamines and sialic acid. The outer layer of the shell of the fat globule consists of phosphatides, shell protein and water of hydration. The composition and structure of the shells of fat globules change after cooling, storage and homogenization of milk and cream.

The protein shell of the balls is also destroyed during mechanical and chemical attack. In this case, fat is released from the shell and forms a continuous mass. These properties are used in the production of butter and in determining the fat content of milk.

As a result of the technological processing of milk, the outer layer of the shell changes first of all due to an uneven, rough, loose surface and a rather large thickness after mixing, shaking and storage. The shells of fat globules become smoother and thinner as a result of desorption of lipoprotein micelles from the shells into the plasma. Simultaneously with the desorption of micelles, sorption of proteins and other components of milk plasma occurs on the surface of the membrane of fat globules. These two phenomena - desorption and sorption - cause a change in the composition and surface properties of the shells, which leads to a decrease in their strength and partial rupture.

Already in the process of heat treatment of milk, partial denaturation of membrane proteins occurs, which contributes to a further decrease in the strength of the shells of fat globules. They can be destroyed quite quickly and as a result of a special mechanical effect: during the production of oil, as well as under the action of concentrated acids, alkalis, amyl alcohol.

The stability of the fat emulsion is primarily due to the appearance of an electric charge on the surface of the fat droplets due to the content of polar groups on the surface of the shell of the fatty globule - phospholipids, COOH, NH 2 (Fig. 2). Thus, a total negative charge is formed on the surface (isoelectric point at pH 4.5). Calcium, magnesium, etc. cations are attached to the negatively charged groups. As a result, a second electric layer is formed, the repulsive forces of which exceed the attractive forces, so the emulsion does not separate. In addition, the fat emulsion is further stabilized by the hydration shell that forms around the polar groups of the membrane components.

The second factor in the stability of the fat emulsion is the formation of a structural-mechanical barrier at the phase boundary, due to the fact that the shells of fat globules have increased viscosity, mechanical strength and elasticity, i.e. properties that prevent ball fusion. Thus, to ensure the stability of the fat emulsion of milk and cream during the production of dairy products, it is necessary to strive to keep the shells of fat globules intact and not reduce their degree of hydration. To do this, it is necessary to minimize the mechanical effects on the dispersed phase of milk during transportation, storage and processing, avoid foaming, properly conduct heat treatment, since prolonged exposure at high temperatures can cause significant denaturation of the structural proteins of the shell and damage to its integrity.

Additional dispersion of fat by homogenization stabilizes the fat emulsion. If during the development of some dairy products, the process engineer is faced with the task of preventing the aggregation and opalescence of fat globules, then when obtaining oil, on the contrary, it is necessary to destroy (demulsify) the stable fat emulsion and separate the dispersed phase from it.

Milk fat differs from other types of fats in that it is easier to digest and absorb. It contains more than 147 fatty acids. Animal and vegetable fats contain

5 ... 7 low molecular weight fatty acids with the number of carbon atoms from 4 to 14.

Milk fat has a pleasant taste and aroma, but under the influence of light, high temperature, oxygen, enzymes, solutions of alkalis and acids, it can acquire an unpleasant odor, rancid taste, and a taste of fat. Such changes occur during hydrolysis, oxidation and rancidity of fat.

Fat hydrolysis is the process of action of water on triglycerides at elevated temperature, as a result of which triglycerides are broken down into glycerol and fatty acids. Hydrolysis increases the acidity of the fat. The origin and method of obtaining milk fat can affect the rate of hydrolysis. If milk fat is obtained by rendering at 65°C, hydrolysis proceeds faster than at 85°C. Hydrolysis proceeds more slowly at a lower temperature (4 °C) and in sealed packaging.

Fat oxidation occurs under the action of sunlight, elevated temperature or catalysts, as a result of which hydrogen and oxygen are added at the place of double bonds. In the process of oxidation of milk fat, as a result of discoloration of carotenoids, the fat also becomes discolored, as well as the smell and taste change. Fat oxidation occurs as a result of the transition of liquid unsaturated acids to solid saturated ones. Rancidity of fat leads to the appearance of a bitter taste and a specific smell in milk fat, due to the formation of peroxide, aldehydes, etc. The process of rancidity occurs under the influence of enzymes, oxygen, heavy metals, microorganisms.

All these changes occurring in fat are difficult to distinguish, since they occur together and are accompanied by side processes, therefore, under production conditions, the physicochemical constants of fat are determined, which depend on its quantitative and qualitative composition. These include acid number, Reichert-Meissl number, iodine number (Hübl number), saponification number (Kettstorfer), pour point and boiling point.

Carbohydrates. In milk, they are represented by lactose - milk sugar and are made up of carbon, hydrogen and oxygen. Lactose refers to disaccharides (C | 2 H 22 O p) and includes the remains of two simple sugars - galactose and glucose. The average mass fraction of lactose is 4.7%.

Carbohydrates are necessary for metabolism, the work of the heart, liver, kidneys; are part of enzymes.

Lactose is formed in the glandular tissue of the mammary gland by combining galactose, glucose and a water molecule. Milk sugar is found only in milk. Pure lactose is a white crystalline powder, 5-6 times less sweet than sugar (sucrose). Lactose is less soluble in water than sucrose.

Lactose is present in milk in two forms: a and b, which differ in physical and chemical properties and can change from one to another at a rate that depends on temperature. In a supersaturated solution, lactose forms crystals of more or less regular shape.

Crystalline lactose is obtained from whey. Crystallization of lactose also occurs during the production of sweetened condensed milk.

When milk is heated to a temperature above 150 ° C, a reaction takes place in it between lactose and proteins or some free amino acids. As a result, melanoidins are formed - dark-colored substances, with pronounced odor and taste. When heated to 110 ... 130 ° C, lactose loses water of crystallization, and when heated to 185 ° C, it caramelizes. The decomposition of milk sugar in solutions begins at temperatures above 100 ° C, with the formation of lactic and formic acids.

Under the action of the lactase enzyme secreted by lactic acid and other bacteria, lactose is split into simple sugars. The process of breakdown of lactose under the action of microorganisms is called fermentation. Up to the stage of formation of pyruvic acid (C 3 H 4 0 2), all types of fermentation proceed in the same way. Further transformation of the acid proceeds in different directions. As a result, various products are formed: acids (lactic, acetic, propionic, butyric, etc.); alcohols (ethyl, butyl, etc.); carbon dioxide, etc.

There are the following types of fermentation: lactic acid, alcohol, propionic acid, butyric.

Lactic acid fermentation is caused by lactic acid bacteria (streptococci and bacilli). During fermentation, pyruvic acid is reduced to lactic acid. From one sugar molecule, four molecules of lactic acid are formed:

After the accumulation of a certain amount of lactic acid during fermentation, lactic acid bacteria die. For sticks, the limit of accumulation of lactic acid is higher than for coccal forms. The lactic acid formed during the fermentation process is of great importance for the coagulation of casein in the production of most fermented milk products - it gives the product a sour taste. The yield of lactic acid depends on the type of lactic acid bacteria that make up the starter culture.

Along with lactic acid, lactic acid fermentation produces volatile acids (formic, propionic, acetic, etc.), alcohols, acetaldehyde, acetone, acetoin, diacetyl, carbon dioxide, etc. Many of them give the finished product a specific sour-milk taste and smell. To improve these properties, in addition to lactic acid bacteria, aroma-forming microorganisms are also used, which from pyruvic acid form aromatic substances - acetoin, acetaldehyde, diacetyl. The accumulation of diacetyl requires the presence of citric acid, which is added to milk, which improves the taste and aroma of the product. In the production of fermented milk products, different combinations of lactic acid bacteria, as well as flavoring and aromatic substances are used.

Alcoholic fermentation is caused by yeast contained in bacterial starter cultures (kefir fungi). Under the action of these starter cultures, pyruvic acid is broken down to acetaldehyde and carbon dioxide. Acetic aldehyde is then reduced to ethanol. As a result, four molecules of alcohol and carbon dioxide are formed from one molecule of lactose:

The resulting products, in which 0.2 ... 3% alcohol accumulates, give fermented milk products (kefir, koumiss, ayran) a sharp refreshing taste.

Propionic acid fermentation occurs in ripening cheeses under the action of enzymes that are secreted by propionic acid bacteria. This fermentation begins after the formation of lactic acid in the presence of lactic acid bacteria. The products of propionic acid fermentation include propionic and acetic acid, carbon dioxide, water:

Butyric fermentation. This process is caused by spore-forming butyric acid bacteria that secrete enzymes. This type of fermentation is undesirable in the production of fermented milk products. Cheeses acquire an unpleasant taste, smell and swell.

Butyric acid bacteria enter milk from soil, manure, dust and withstand pasteurization. Their presence is the result of non-compliance sanitary regulations obtaining raw materials.

Minerals. Milk is a constant source of minerals in the body. Depending on the content, they are divided into macro- and microelements. On average, milk contains 0.7% in the form of salts of inorganic and organic acids.

Macronutrients. Of this group, calcium, phosphorus, potassium, sodium, magnesium, sulfur and chlorine are important. In milk, they are present in the form of inorganic and organic salts (medium and sour) and in the free state. Acid salts, along with other substances, determine the acidity of freshly milked milk. The main part of the salts is found in milk in the ionic and molecular state, and phosphoric acid salts form colloidal solutions. The average content of macronutrients in milk: sodium - 50 mg%, potassium -145, calcium -120, magnesium -13, phosphorus-95, chlorine - 100, sulfate - 10, carbonate -20, citrate (in the form of a citric acid residue) - 175 mg%.

The salt composition of milk can be judged by the content and ratio of macronutrients. Mostly in milk there are salts of potassium, calcium and sodium, as well as inorganic and organic acids: phosphate (phosphates), citrates (citrates), chlorides (chlorides). Calcium ions strengthen the hydration shell, as they are adsorbed on the surface of casein micelles and thereby increase their stability. Phosphates, citrates and carbonates take part in the buffer system of milk.

Calcium is of great importance for milk processing processes. Its content in milk ranges from 112 to 128 mg%. About 22% of all calcium is associated with casein, and the rest is represented by phosphate and citrate salts. The low content of calcium in milk causes slow rennet coagulation of casein during the production of cheese and cottage cheese, and its excess causes the coagulation of milk proteins during sterilization. When milk soured, almost all calcium passes into whey, since under the action of lactic acid it is split off from the casein complex. The properties and quality of dairy products depend on the calcium content in milk. An important role belongs to calcium in the production of processed cheese. It binds melting salts, passes from calcium caseinate to plastic sodium caseinate. In the latter, the fat emulsifies better, and the characteristic texture of the cheese is formed. The quality of the resulting condensed milk and the solubility of milk powder in the production of reconstituted milk also depend on the calcium content.

Phosphorus in milk is part of the caseinate-calcium phosphate complex. The resistance of a protein to the effects of proteolytic enzymes depends on the phosphorus content. Phosphorus gives stability to the shell of fat globules. The development of microorganisms in milk in the production of fermented milk products is associated with phosphorus.

Microelements. 19 trace elements were found in milk. 1 kg of milk contains approximately (mg): copper -0.067 ... 0.205; manganese-0.1 16...0.365; molybdenum - 0.015...0.090; cobalt-0.001...0.009; zinc - 0.082...2.493; magnesium -84.05 ... 140; iron-2.55...77.10; aluminum - 1.27...22.00; nickel-0.017...0.323; lead - 0.017...0.091; tin - 0.004...0.071; silver - 0.0002...0.11; silicon - 1.73...4.85; iodine-0.012...0.020; titanium, chromium, vanadium, antimony and strontium - decimals and traces. The content of trace elements in milk depends on the diet, lactation stage of animals and other factors. In colostrum, some trace elements, such as iron, copper, iodine, cobalt, zinc, are much larger than in milk. Trace elements are part of vitamins and enzymes.

Trace elements play an important role in the human body. So, manganese acts as a catalyst in oxidative processes and is necessary for the synthesis of vitamin C, as well as vitamins B! and D. Cobalt is a component of vitamin B 12 . Iodine stimulates the activity of the thyroid gland. Some trace elements contribute to the formation of defects in milk, as they catalyze chemical reactions. Excess copper leads to fat oxidation, and the milk acquires an oxidized flavor; its lack slows down the process of lactic acid fermentation.

Vitamins. Almost all of the vitamins contained in milk pass into it from the feed eaten by animals, and are also synthesized by the microflora of the rumen. Their number depends on the season, breed, individual characteristics of animals. Lack or lack of vitamins leads to metabolic disorders and the occurrence of diseases such as rickets, scurvy, beriberi, etc.

Vitamins serve as metabolic regulators, since many of them are part of various organic compounds: acids, alcohols, amines, etc. The sensitivity of vitamins to high temperature, the action of acids, oxygen and light was noted. Most vitamins dissolve in water, some in fats, ether, chloroform, etc. In this regard, vitamins are divided into water-soluble and fat-soluble.

Water-soluble vitamins include vitamins B, B 2 , B 6 , B 12 , PP, choline, and folic acid.

Vitamin B /(thiamine) in its pure form is a white crystalline powder. 1 kg of milk contains about 500 mg of thiamine and its amount depends on the season of the year, as well as on the microflora of the gastrointestinal tract. In alkaline solutions, the vitamin decomposes, in acidic it is stable. During drying, up to 10% of thiamine is destroyed, while thickening, up to 14%.

Vitamin B stimulates the growth of microorganisms, including lactic acid bacteria, as it is a dicarboxylase coenzyme. In this regard, the amount of this vitamin in fermented milk products increases by 30%. IN skimmed milk the content of vitamin B increases and reaches 340 mg / kg, in serum - 270, buttermilk - 350 mg / kg. The daily human need for thiamine is 1...3 mg.

Vitamin B 2(riboflavin) is synthesized in the gastrointestinal tract of the animal. Its milk contains 1.6 mg/kg; in colostrum -6; in cheese -3.07 mg/kg; traces in oil. Riboflavin is resistant to high temperatures, pasteurization, in fermented milk products its amount increases to 5% compared to the original milk, and only when dried it becomes less by 10 ... 15%. Vitamin B 2 is part of enzymes and takes part in carbohydrate and protein metabolism; the redox potential of milk depends on it.

Riboflavin imparts a greenish-yellow color to whey and a yellow color to raw sugar. With a lack of vitamin B 2, growth retardation, eye diseases, etc. are observed. The daily requirement for vitamin B 2 for adults is 1.2 ... 2 mg.

Vitamin B 3(pantothenic acid) stimulates the development of lactic acid bacteria, is part of coenzyme A, which is involved in the synthesis of fatty acids, styrene and other components. Its milk contains 2.7 mg/kg; in whey - 4.4; in buttermilk -4.6; in skimmed milk -3.6 mg/kg. Vitamin B 3 is destroyed during sterilization.

Vitamin B 6(pyridoxine) in milk is contained in a free and protein-bound state. In the free state, its amount in milk is 1.8 mg/kg; bound - 0.5; in oil -2.6; in condensed milk with sugar - 0.33 ... 0.4 mg / kg. Pyridoxine stimulates the growth of microorganisms, resistant to high temperatures. Lack of vitamin B 6 in the body leads to diseases of the nervous system and intestines.

Vitamin B /2(cobalamin) is synthesized by the microflora of the gastrointestinal tract. The content in milk is 3.9 mg/kg. In spring and summer, milk contains significantly less vitamin B 12 than in autumn. A decrease in the vitamin content also occurs when milk is treated with high temperatures (sterilization), losses can be 90%. In the production of kefir, the amount of cobalomin decreases by 10 ... 35% due to the fact that it is used by lactic acid bacteria.

Cobalomin takes part in metabolic processes, catalyzes circulatory reactions.

Vitamin C(ascorbic acid) - a crystalline compound, easily soluble in water with the formation of acidic solutions. Content: in raw milk -3...35 mg/kg; in serum -4.7; in dry milk -2.2; in condensed -3.9; in cheese -1.25 mg/kg.

Vitamin is synthesized in the body, participates in redox processes, inactivates toxins, improves the absorption of hormones. Lack of vitamin causes gum disease, with a lack of it, the body becomes less resistant to infectious diseases. When raw milk is stored, the content of vitamin C is significantly reduced. Prolonged pasteurization, as well as thickening, reduces the content of vitamin C by up to 30%.

Vitamin PP(nicotinic acid, or inacin) is synthesized by the intestinal microflora. Raw milk contains 1.51 mg/kg (range 1.82...1.93 mg/kg). A lot of vitamin PP in powdered milk - 4.8 mg / kg; in cottage cheese -1.5; in cream -1.0; in sour cream -0.9; in cheese-0.37 mg/kg. In curdled milk, it is less by 27...73%, and in the production of condensed milk, the content of inacin is reduced by 10%.

Vitamin H(biotin) is resistant to high temperatures both during pasteurization and sterilization. The content in milk is 0.047 mg/kg. In summer, the amount of biotin in milk doubles. When drying and thickening milk, the vitamin content is reduced by 10 ... 15%. Biotin favorably affects the growth of microorganisms (yeast, etc.).

Choline is part of the lecithin-protein shell of the fatty globule. Content: in milk - 60 ... 480 mg / kg, in colostrum - 2.5 times more, in dried milk - 1500, in cheese - 500 mg / kg. Choline is unstable to high temperatures; during pasteurization, losses reach 15%. In the production of fermented milk products, the content of choline increases in yogurt by 37%, in kefir - by 2 times.

Folic acid found in raw milk in the amount of 0.5...2.6 mg/kg. It is synthesized by lactic acid bacteria, so the content in fermented milk products folic acid increases by 50%. Pasteurized milk contains 6-7% more folic acid than raw milk (due to the release of bound forms of the vitamin).

Fat-soluble vitamins include vitamins A, D, K, E, and F.

Vitamin A(retinol) is formed in the liver of animals from provitamin (N-carotene) supplied with feed under the action of carotenoses. When splitting one molecule of carotene, two molecules of vitamin A are formed, which enters first into the blood and then into milk. Thus, the content of vitamin A in milk is completely dependent on the content of carotene in the feed.

In the spring-summer period, more carotene is supplied with feed than in the autumn-winter period.

Raw milk contains 0.15 mg / kg of vitamin A, colostrum contains 5 ... 10 times more, oil - 4 mg / kg. In pasteurized powdered milk of spray drying and during storage, the content of vitamin A decreases to 15%, and in fermented milk products it rises to 33%.

Lack of the vitamin causes eye damage ("night blindness") and dryness of the cornea. The presence of vitamin A in the diet increases the body's resistance to infectious diseases, promotes the growth of young animals, etc. The daily human need for vitamin A is 1.5 ... 2.5 mg.

Vitamin D(calciferol) is formed under the action of ultraviolet rays. Its milk contains an average of 0.5 mg / kg; in colostrum - 2.125 mg / kg on the first day and 1.2 mg / kg on the second; in melted butter - 2.0 ... 8.5; in sweet cream butter (summer) - up to 2.5 mg/kg. Grazing cows increases the amount of vitamin D.

Vitamin takes part in mineral metabolism, i.e. in the exchange of calcium salts. With a prolonged lack of vitamin D, the bones become soft, brittle, and rickets occurs.

Vitamin E(tocopherol) is an antioxidant in milk fat and contributes to better assimilation vitamin A. The content in milk depends on its content in the feed. In milk, it is 0.6 ... 1.23 mg / kg; in oil -3.4...4.1; in dry milk - 6.2; in colostrum-4.5; in sour cream -3.0; in curdled milk -0.6 mg/kg. With pasture keeping of cows, the amount of vitamin E increases, with stall keeping, it decreases. By the end of lactation, the content of tocopherol in milk reaches 3.0 mg/kg. Long-term storage of milk at temperatures below 10 ° C leads to a decrease in the content of the vitamin.

Vitamin K synthesized by green plants and some microorganisms, biologically similar to vitamin E.

Vitamin F normalizes fat and water metabolism, prevents liver diseases and dermatitis. Its milk contains approximately 1.6 ... 2.0 mg / kg.

Enzymes. Milk contains various biological catalysts - enzymes that speed up chemical reactions and promote the breakdown of large food molecules into simpler ones. The action of enzymes is strictly specific. They are sensitive to changes in temperature and the reaction of the environment. There are more than 20 true, or native, enzymes in milk, as well as enzymes that are produced by microorganisms that enter milk. One part of the native enzymes is formed in the cells of the mammary gland (phosphatase, etc.), the other passes from the blood into milk (peroxidase, catalase, etc.). The content of native enzymes in milk is constant, but their increase indicates a violation of secretion. The amount of enzymes produced by bacteria depends on the degree of contamination of milk.

Enzymes are divided into groups depending on their specific action on various substrates: hydrolases and phosphorylases; cleavage enzymes; redox.

From hydrolases and phosphorylases for dairy business, lipase, phosphatase, protease, carbohydrase, etc. are of the greatest interest.

Lipase catalyzes the hydrolysis of milk fat triglycerides, with the release of fatty acids. Milk contains native and bacterial lipases. There is more bacterial lipase, less native.

Native lipase is associated with casein, and a small part of it is adsorbed on the surface of the shells of fat globules. The milk fat of fresh milk is usually not spontaneously attacked by lipase.

The hydrolysis of fat by the action of lipase is called lipolysis. Lipolysis of milk occurs under mechanical action (homogenization, pumping milk with a pump, strong mixing, as well as during freezing and thawing, rapid temperature changes).

Highly active bacterial lipase is secreted by molds and bacteria that can cause rancid taste in milk, butter and other foods.

Native lipase is inactivated at a pasteurization temperature of 80 °C, while bacterial lipase is more resistant to high temperatures.

Protease- the result of the vital activity of lactic acid bacteria. This enzyme is active at 37...42 °C, is destroyed at 70 °C for 10 minutes or at 90 °C for 5 minutes. There is a lot of protease in cheeses, which is formed in them during ripening. It gives cheeses their characteristic taste and smell, but in milk and butter it can cause taste defects.

Carbohydrases include amylase and lactase. Amylase is produced by cells of the glandular tissue and from them enters the milk. There is a lot of it in the first portions of colostrum, and the amount of amylase increases with inflammation of the mammary gland. The enzyme is not resistant to high temperatures. At a temperature of 65 ° C for 30 minutes, it is destroyed. It is believed that glycogen is converted to lactase in the mammary gland.

Phosphotase synthesized by secretory cells of the udder and some microorganisms of milk. It catalyzes the elimination of phosphoric acid residues from phosphate esters. Milk contains acid and alkaline phosphatases. The latter is larger, and it enters the milk from the cells of the mammary gland. Alkaline phosphatase is sensitive to heat; it is completely destroyed when milk is heated to 74 °C and exposed for 15–20 s. This property of phosphatase underlies the method for monitoring the efficiency of milk pasteurization. Acid phosphatase is resistant to heat and is destroyed when milk is heated above 100 °C.

Of the cleavage enzymes, the most interesting for the dairy business is catalase. In milk, it is formed from the secretory cells of the mammary gland and as a result of the activity of putrefactive bacteria. Lactic acid bacteria do not secrete catalase. When hydrogen peroxide is added, it decomposes under the action of catalase into molecular oxygen and water.

Catalase is identified by adding hydrogen peroxide to milk.

Redox enzymes include reductase and peroxidase. With their help, the quality of milk and the results of pasteurization are determined.

reductase unlike other enzymes, it is secreted only by microorganisms and is a product of their vital activity. The mammary gland does not synthesize reductase. Aseptic milk does not contain reductase, so its presence indicates bacterial contamination of the product.

The reductase test evaluates the quality of milk. There are very few microbes in freshly milked milk. As they accumulate, the content of reductase increases. When a redox dye (methylene blue or resazurin) is added to milk, it is restored: the more enzyme in the milk, the faster it becomes discolored.

Peroxidase is produced by the mammary gland and is used to determine the pasteurization of milk.

Hormones. They are necessary for the normal functioning of the body, as well as for regulating the formation and excretion of milk, into which they enter from the blood.

Prolactin stimulates milk secretion and is produced by the anterior pituitary gland.

Luteosterone inhibits the action of prolactin and milk secretion, is a hormone of the corpus luteum, is activated during deep pregnancy of lactating animals.

Folliculin stimulates the development of the glandular tissue of the udder in first-calf heifers and dry cows, and is formed in the tissues of the ovary.

Thyroxine is a thyroid hormone. Regulates fat, protein and carbohydrate metabolism in the body, contains iodine. Milk also contains other hormones: insulin (pancreatic hormone), adrenaline (adrenal hormone), etc.

Pigments. These include carotenoids, which provide the creamy color of milk. Their content in milk depends on the season of the year, feed, breed of cows.

immune bodies. Immune bodies include agglutinins, antitoxins, oxonins, precipitins, etc. Colostrum contains much more of them than milk. The bacterial and bactericidal properties of milk depend to some extent on immune bodies. The milk of animals that have had any diseases contains more immune bodies than the milk of healthy ones. The content of immune bodies in colostrum provides immunity to the calf.

Gases. Freshly milked milk contains gases, including carbon dioxide, which are present in the blood of animals. They are easily adsorbed during milking, handling and storage. Oxygen in milk - 5 .. L 0%, nitrogen - 20 ... 30, carbon dioxide - 55 ... 70%. The latter dissolves in plasma and is one of the components that provide its acidity. At the time of filtering milk through filters, the oxygen content increases to 25%, nitrogen - up to 50%, carbon dioxide - decreases to 25%. When heated, the amount of gases in milk decreases.

We have all heard about the usefulness of products made from milk since childhood, but not every person has a sufficient understanding of the role that they play in the life of our body.

Perhaps no one will deny that we simply do not think about the merits of dairy products. And in fact, drinking a glass of milk or eating curd cheese, we do not think about their composition and usefulness.

And yet, every person needs to be imbued with the consciousness that milk occupies an exceptional place in our diet, that without dairy products our diet would be depleted, deprived of many valuable and scarce substances, and, finally, that dairy food is an obligatory and indispensable part of our nutrition. That is why information about useful properties milk and products from it is necessary for each consumer of these products.

So, what is milk, this secretory fluid secreted by the mammary glands of mammals and intended for feeding young animals? From the point of view of nutrition, it is a natural product that is unique in nutritional value and importance for the body, which a person, in the process of conscious activity, has adapted to his needs.

For its high nutritional value, milk is called the "elixir of life", "white blood", "gift of nature", and I. P. Pavlov called it an amazing food prepared by nature itself, and noted that it occupies "an exceptional position among the varieties of human food" .

Milk and products obtained from it are not only amazing food in terms of their digestibility and usefulness, but they are also universal, diverse, and everyday. It is universal because, firstly, it contains almost all the substances necessary for the body, which are also favorably balanced, and secondly, it is equally necessary for children and adults, sick and healthy. Diverse because it has many dozens of types and names of products. Everyday because it is used every day.

Dairy products also have medicinal properties and are successfully used in therapeutic and prophylactic and dietary nutrition.

If all the substances necessary for the body and found in food are divided (conditionally, of course) into energy, satisfying energy needs, plastic, from which cells and tissues are “built”, and regulatory, involved in metabolic processes, then it will be noted that in milk contains both the first (carbohydrates and partly fat), and the second (protein and mineral substances) and the third (trace elements, vitamins, enzymes).

The value of milk as a food product is characterized by the following factors: the richest and most favorably balanced composition of components, the high digestibility of all nutrients in milk.

According to its chemical composition, milk is a unique food product, since it contains all those substances without which the human body cannot develop normally. There are already over 200 different substances in milk, and research is ongoing.

For industrial processing, we use cow's milk in the largest quantities, the average content of the main substances of which is given below.

Of course, in addition to these basic substances, milk also contains other substances: acids, vitamins, enzymes, etc. Some of them will be discussed further. First, let's take a closer look at the meaning and properties of the main components of milk.

Based on modern ideas about nutrition and from the analysis of the actual consumption of nutrients, the most deficient component of food today is proteins, especially complete proteins, and these are, as a rule, proteins of animal origin. Therefore, the consideration of the constituent parts of milk is best to start with proteins.

The total protein content in milk (we will only talk about cow's milk) averages 3.2%. Milk proteins are heterogeneous. They are composed of casein, albumin and globulin. The content of casein is 2.7%, albumin - 0.4%, globulin and other proteins - 0.1%. Casein is of the greatest practical importance, and not only because it accounts for 80-83% of all milk proteins, but also because it is released from milk during the manufacture of cottage cheese and cheese, while albumin and globulin remain in whey (they are called hence whey proteins.

Casein is a specific protein and is found only in milk, where it is combined with calcium and phosphorus in a soluble form. If calcium is split off from casein, then, being insoluble in an aqueous medium, casein coagulates, i.e., forms a clot. Casein itself is heterogeneous; several fractions are distinguished in it, differing from each other in the content of phosphorus.

In milk, casein is in the form of a colloidal solution and is the smallest spherical particles - globules. They are so small that they cannot be seen with a conventional microscope, and only an electron microscope, which gives an increase of 20-30 thousand times, allows you to see its spherical particles. Their size is approximately one hundred thousandth of a millimeter.

Unlike many other proteins, casein is heat stable. Even short-term heating, for example, of an egg leads to the coagulation of its proteins, to coagulation. We can boil milk, but the coagulation of proteins does not occur. This very important property of casein allows milk to be heated to destroy microorganisms in it without a significant change in the properties of the product.

But casein is very sensitive to the action of acids. Everyone had to observe that if milk is left in a warm place or leaven is added to it, then lactic acid fermentation quickly occurs in it. At the same time, milk sugar is converted by microbes into lactic acid, and we see how a clot forms after a few hours. It coagulated the casein. This property of casein is the basis for the production of kefir, curdled milk, cottage cheese and other fermented milk products.

Casein passes into an insoluble form, forming a clot, and under the action of rennet. However, rennet milk clot does not have sour taste, it tastes the same as fresh milk. This method of precipitation of milk proteins is used in practice in the manufacture of cheeses and some types of cottage cheese.

IN Lately A third type of coagulation of milk proteins is also becoming more and more widely used: under the action of calcium ions. This method was developed and theoretically substantiated by Professor P. F. Dyachenko. Calcium ions, as it were, connect the casein globules, forming “bridges” between them and causing protein coagulation. We will talk about the practical application of all these methods of coagulation of casein and other milk proteins a little later, considering the technology for the production of some dairy products.

One more property of casein should be mentioned - its ability to swell. According to P. F. Dyachenko, 1 g of casein binds about 0.7 g of water. Due to this property, dairy products such as cheese, cottage cheese, with apparent "dryness" contain a significant amount of water. For example, cheese, which has a hard elastic consistency, contains 40-45% water.

Albumin and globulin are simple proteins. They are soluble in water, as well as in weak acids and alkalis. Like casein, they are found in milk in a colloidal solution. However, their molecules are even smaller than casein, and are not visible even in an electron microscope at normal magnification. Unlike casein, these proteins are not thermostable, and already at temperatures above 75 ° C they coagulate. In this case, they do not form a clot, but fall out in the form of a fine suspension. But acids and rennet do not cause their coagulation, and they remain in the whey during the production of cottage cheese and cheese. This gave reason to call them whey proteins.

Until recently, whey proteins remaining in whey after the manufacture of rennet cheeses and cottage cheese were used in food extremely insufficiently, and meanwhile, in terms of their amino acid composition, whey proteins are not only not inferior to casein, but even surpass it. For example, most. the amino acid lysine deficient in nutrition in albumin and globulin of milk contains almost 1.5 times more than in casein, almost 4 times more in milk albumin and tryptophan. Whey proteins are also rich in an amino acid such as cystine. In albumin, it is almost 19 times more than in casein. Of course, the loss of these proteins is undesirable, therefore, at present, dairy industry enterprises extract them from whey, obtaining albumin curd, and curds, pastes and other milk-protein products are produced from it.

In addition to the technological properties noted here, milk proteins also have very important biological properties. All protein substances of milk are easily and quickly broken down by the digestive enzymes of the body. As the protein is broken down, it gradually breaks down into simpler elements, down to amino acids. The latter are the "bricks" of which proteins are composed.

It has been established that in terms of digestibility, milk proteins are in the first place, ahead of the proteins of meat, fish, and cereals. The digestibility of milk proteins is 95-97%.

But the greatest advantage of milk proteins is their biological usefulness, due to the amino acid composition of proteins.

Milk proteins contain all the amino acids needed by the human body. Among the two dozen amino acids in the composition of proteins, there are those that the body can synthesize on its own, and those that are not synthesized, but must come "in ready-made» with food. The former are called interchangeable, the latter are irreplaceable. Naturally, proteins that contain all the essential amino acids are more valuable in nutrition. Therefore, milk proteins are considered complete because they contain all the essential amino acids and in a favorable ratio. Moreover, milk proteins are rich in the most deficient essential amino acids, which are often deficient in the human diet. These amino acids include lysine, tryptophan, methionine. And without these amino acids or with a lack of them, the body cannot synthesize “own” proteins and “build” its cells, tissues, enzymes, antibodies, hormones and other structural and physiological elements from them. In addition, a lack of lysine in food leads to a violation of blood formation, tryptophan is necessary for growth processes, methionine normalizes the activity of the liver, and is necessary for the prevention of atherosclerosis.

The biological value of milk proteins can be illustrated by data that shows and compares the content of essential amino acids in low-fat cottage cheese, category I beef, buckwheat and wheat flour (the protein content in these products is relatively high and amounts to 18.0; 18.6; 12.6; 10.6%, respectively).


Essential amino acids	low-fat cottage cheese	buckwheat	wheat flour

Isoleucine


Methionine

tryptophan
Phenylalanine
Total Essential Amino Acids

Of the four very common and commonly consumed foods greatest content essential amino acids, as we see, falls on cottage cheese. It contains more than other products, methionine, threonine, isoleucine and leucine. In meat, only two amino acids (valine and lysine) are superior in content to cottage cheese, cereals and flour, and the total amount of essential amino acids in meat is 11% lower than in cottage cheese.

Fat in milk, depending on the breed of cattle and lactation period, contains from 3 to 5%. Milk fat is easily digested and well absorbed by the human body (by 96-97%) due to the fact that its melting point is several degrees lower than the human body temperature (28-33°C). The composition of milk fat includes more than 20 fatty acids, among them butyric, caproic, caprylic, etc., which determine the value of milk fat in terms of nutritional physiology, since thanks to them milk fat is very easily digested in the body. Contained here, however, in a small amount (up to 4%) and the so-called essential fatty acids: linoleic, linolenic, arachidonic.

In milk, fat is in the form of a fat emulsion. Fat globules are generally 2-4 microns in size. Considering that a micron is one thousandth of a millimeter, one can imagine what a thin fat emulsion milk is. Due to their small size, fatty particles are easily accessible to the action of digestive juices.

Under the action of enzymes in the gastrointestinal tract, fat is broken down with the release of fatty acids, which are absorbed into the blood.

In milk, fat particles do not merge together, since each ball is surrounded by a strong lecithin-protein shell that prevents this.

Milk fat contains phosphatides, sterols, fat-soluble vitamins A, D, E, K and other related substances, so milk fat should be considered not only as a source of energy, but also as a product of high biological value, rich in biologically active substances.

Like all other fats, milk fat has a high energy value (calorie content). When “burning” in the body, 1 g of fat is released 9 kcal, 1 g of protein - 4 kcal, 1 g of carbohydrates - 3.75 kcal. Therefore, 1 g of fat provides the body with 2.4 times more energy than carbohydrates and 2.25 times more than proteins. This means that the more fat a product contains, the higher its calorie content and the higher the calorie content of the diet in which this product is included.

Is it good or bad? It all depends on many factors - we will talk about them ahead.

Phosphatides, sterols play an important role in the body: they are part of tissues and physiological fluids, participate in metabolic processes, etc. Of the phosphatides, lecithin is of the greatest importance in nutrition. It contains organic phosphorus and the nitrogenous substance choline, which determine the high physiological activity of lecithin. These substances contribute to the normalization of fat and cholesterol metabolism in the body. Phosphatides prevent excessive deposition of fat in the liver and thereby disrupt its most important functions. Phosphatides. they also have an anti-sclerotic effect, since they are involved in the regulation of cholesterol metabolism processes.

Carbohydrates in milk are represented mainly by milk sugar - lactose (4.5-5%). In water, lactose dissolves much worse than sucrose (beet sugar), and is 5-6 times less sweet. This explains the fact that, being present in milk in almost the same amount as beet sugar, for example, in sweet tea, milk sugar does not give the milk a pronounced sweet taste. However, like other carbohydrates, milk sugar is well absorbed by the body and has a high energy value. Milk sugar, like beet sugar, belongs to disaccharides; in the intestine, under the action of enzymes, it is broken down into glucose and galactose and, in this form, is absorbed into the blood. In the intestine, lactose serves as a nutrient medium for lactic acid microorganisms that suppress the putrefactive microflora.

Lactose under the influence of lactic acid microorganisms is fermented with the formation of lactic acid. This property is widely used in the production of many fermented milk products: kefir, curdled milk, sour cream, cottage cheese, etc. Being a nutrient medium for lactic acid microflora, milk sugar is thereby involved in the technological processes for producing many dairy products.

Under the influence of high temperatures, milk sugar caramelizes, while the color of the product becomes slightly brownish. If such conditions are created in a solution containing casein, then melanoidins are formed during the interaction of sugars and amino acids. The appearance of a brownish color in sterilized and baked milk, fermented baked milk is explained precisely by these reactions.

As for minerals, figuratively speaking, we can say that almost the entire periodic table is concentrated in milk. Milk contains both macroelements - sodium, potassium, calcium, phosphorus, magnesium, etc., and microelements - copper, aluminum, zinc, tin, arsenic, cobalt, manganese, chromium, etc. Both the first and the second are involved in the construction cells and tissues of the body, and many trace elements are regulators of metabolic processes. The total amount of minerals in milk is 0.6-0.7%. In milk, there are mainly salts of phosphoric, as well as caseic and citric acids. Lack or excess of salts leads to an imbalance, and proteins can precipitate. This property of milk is used in the production of fermented milk products and cheeses.

More than half of the total amount of minerals in milk falls on two elements: calcium and phosphorus. No other foods contain calcium in such large quantities as dairy products, especially cheeses and cottage cheese. Studies have established that their combination with milk protein is especially favorable for the absorption of calcium and phosphorus. It is in milk that both of these elements are associated with the casein molecule and, therefore, are in the most acceptable form for the body. Calcium is included in large quantities in the composition of teeth, together with phosphorus, it forms the basis of bone tissue, participates in a number of metabolic processes.

Microelements are also of great importance for the human body. As catalysts for many biochemical processes, they are essentially mineral "vitamins". So, cobalt is involved in blood formation, zinc affects the function of reproduction, fluorine promotes the formation of bone and dental tissue, etc.

Already enumeration physiological significance a small part of the elements contained in milk indicates their most important role in the human body.

In terms of vitamin content, milk cannot be considered a high-vitamin product, but since dairy products are a daily food product, milk provides the body with a significant proportion of these essential nutritional factors. Milk contains almost all known water- and fat-soluble vitamins: vitamin C (ascorbic acid), PP (nicotinic acid), B 1 (thiamine), B 2 (riboflavin), B 6 (pyridoxine), B 12 (diancobalamin ), A (retinol), D (calciferol), E (tocopherol), K (phylloquinone), etc. Together with other food products, milk is involved in providing the human body with these biologically active substances that regulate the vital functions of the body. The level of vitamin content in milk and dairy products is significantly influenced by the conditions of animal feeding, lactation period, technological processing of milk and other factors. Under the influence of high temperatures and during long-term storage of products, some vitamins are destroyed.

So, we noted that milk contains a variety of chemicals that play an important role in the human body, each of the components of milk has one or another importance in nutrition, and in quantitative terms, most of them correspond to a balanced nutrition formula, which indicates a high nutritional and biological value of milk and products of its processing.

Another factor characterizing the nutritional value of milk is the easy digestibility and assimilation of its main constituents. It is explained by the fact that all components are in milk in the form of tiny particles, due to which they are quickly and completely broken down by digestive enzymes. The size of these smallest particles can be judged by the following fact: 1 ml of milk contains an average of up to 3 billion fat globules! What can we say about the size of the elementary particles of proteins and other components, if they cannot even be seen with a conventional microscope? Naturally, thanks to such a highly dispersed system as milk, it is quickly absorbed by the human body.

The third factor characterizing the nutritional value of milk, although not as significant as the first two, is the favorable ratio of its main nutrients.

It is known that in the human diet, the main nutrients, i.e. proteins, fats and carbohydrates, should be in the ratio 1:1:4. Naturally, this is achieved due to their total content in a set of various food products. But if we talk about individual products, then only milk has the closest to the optimal ratio of the main nutrients, i.e. 1:1:1.5. This, of course, is not an ideal ratio, but if we consider that in all other types of natural products it deviates much more from the optimum, then it should be recognized that milk has the closest ratio of these nutrients to the desired one.

In addition to cow's milk, goat's, sheep's, mare's milk is also used in various regions of our country, in the desert areas of Central Asia - camel's milk, in the mountainous regions of the Caucasus - buffalo, and in the Far North - deer's milk. Although each of these types of milk has its own characteristics and retains its individuality, their general properties, composition and main factors of nutritional value are close to cow's milk.

The table compares data on the degree of satisfaction of a person's daily need for basic nutrients and energy from certain dairy products and meats.

Nutrients	The degree of satisfaction of a person's daily needs
	500 g milk	100 g fat cottage cheese	100 g Russian cheese

Including:
animals
deficient amino acids
tryptophan

methionine

Minerals




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Nutritional value of milk and dairy products. Introduction

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