INTRODUCTION
I break bread. I reach for the salt shaker.
The meal, Lord, bless!
How much live juice is in milk?
How much true love there is for life!
Milk is a product of everyday demand. Milk and its derivatives are consumed by people of all ages and nationalities. The authors of the project decided to find out how healthy the dairy products offered by Russian producers are.
TARGET:
determine the composition and quality of different types of milk
TASKS:
* Determine the composition of milk experimentally;
* Prove the presence of beneficial substances necessary for humans in milk;
* To study the need for milk consumption among primary school students;
* Make recommendations for the consumption of milk and dairy products.
CHAPTER 1. BIOLOGICAL VALUE OF MILK
1.1 Biological value
Milk is a biological fluid of complex chemical composition. It serves as a complete food for newborns, as well as a necessary food product for a person at any age. Milk is a high-calorie product. Ancient philosophers called it “the source of health,” “juice, life,” “white blood.” The great Russian physiologist I.P. Pavlov said that “milk is the easiest food for weak and sick stomachs and a host of other serious diseases” /1, p. 18/.
Since ancient times, milk has been used as a remedy for many diseases: in the treatment of the heart, kidneys and other organs. Helps treat poisoning with heavy metal salts, acids and alkalis, iodine and bromine.
What housewife doesn't drink milk? Even if none of your family drinks it, then you probably eat cheese, cottage cheese or sour cream!
In addition, milk is required to be added to many dishes. So, milk porridges are much tastier than those cooked in water. But since ancient times, truly supernatural properties have been attributed to dairy products!
In fairy tales, milk is often used as a means of achieving “eternal youth.” To do this you need to bathe in milk. It is also noted that a woman who washes her face with milk will look young and attractive for a long time. If you take milk baths, your skin will become soft and velvety, and your body will be filled with strength and vigor. This was used by the queen of Egypt, Cleopatra /7/.
Whey (buttermilk) is included in some creams, but it is more useful to use it in its natural form. Wipe your face and neck with it daily. After this procedure, look at yourself in the mirror and say: “I am beautiful”!
1.2 Chemical composition of milk
It has been established that milk contains over a hundred valuable components, many of which nature has not duplicated in any other product. It includes all the substances necessary for the functioning of the body: proteins, fats, carbohydrates, mineral salts, vitamins. These milk components are well balanced, making them easily and completely digestible. The digestibility of milk and dairy products ranges from 95 to 98%. Milk also aids in the absorption of other foods.
Milk consists of water (on average 87.5%) and dry matter (12.5%) /1, p. 218/.
Natural milk contains 25 types of fatty acids, 20 amino acids, more than 30 macro- and microelements and many other biologically active substances. The special importance of milk is that it gives a person complete protein of animal origin, the biological value of which significantly exceeds the value of protein from beef, pork and eggs. In terms of the amount of essential amino acids, which are not formed in the human body but must be supplied with food, cow's milk is superior to other food products.
Feed affects the quality of milk, cream, and the consistency of milk fat. Thus, green pasture gives a creamy-yellow color to milk, cream, and butter. Feed cabbage, silage, carrots and grass meal help preserve the color of milk even in winter.
Some feeds (rutabaga, turnips, cabbage, cabbage, tops, sugar beets and silage) can impart an unpleasant taste and odor to the milk, especially when fed in large quantities.
There are about thirty vitamins in milk. Dairy products play a particularly important role in supplying the body with vitamins. The most important of them:
vitamin A (retinol), B (thiamine), Bg (riboflavin), C (ascorbic acid), D (calciferol), E (tocopherol), H (biotin), PP (nicotinic acid)/2, p. 56/.
CHAPTER 2. EXPERIMENTAL
2.1 Research of milk quality according to data on packaging
Not all dairy products have the same composition and are equally healthy. To begin with, we determined the composition of dairy products based on the data on the packaging.
Target:
determine the quality of dairy products at home.
Tasks:
– Based on the data on the packaging, identify the presence of substances harmful to health;
– Determine the composition of dairy products;
- draw up a memo for the buyer.
Assumption:
Not all dairy products have the same composition and are equally healthy.
MILK happens:
* NORMALIZED;
* RESTORED;
* HOMOGENIZED;
* PASTEURIZED;
* DRINKING.
Normalized – that is, diluted, brought to a certain percentage of fat content.
Reconstituted – reconstituted by combining powder and water.
Homogenized - vegetable fats have been added to the milk
Pasteurized – disinfected by short-term heating
As a result, based on the data on the product packaging, the best and worst quality milk was determined.
Best quality
Worst quality
2.2 Determination of organoleptic indicators of milk quality
To carry out the experimental part of the work, we bought milk in the store with different percentages of protein and fat, and also took the milk that the children of our school drink.
Milk for experiment:
Determination of the appearance of milk.
To determine the appearance of milk, we poured it into a beaker to the middle of the volume. We carefully examined the milk and noted that it was free of various contaminants and impurities, and also noted its homogeneity.
Determining the color of milk.
We poured 50-60 ml of milk into a glass. They brought a white sheet of paper to the glass and compared the samples. We saw that the milk in all glasses has different shades of white (data in the table).
Determination of milk consistency.
To determine the consistency of milk, pour it into a test tube to the middle of the volume. Close the test tube and shake it slightly to wet the walls. The milk was allowed to drain for 1-2 minutes and then it was determined that the walls of the test tubes were not uniformly covered with milk.
Determination of the smell of milk.
They poured a little more than half of its volume into a test tube and closed it with a stopper. Then they vigorously shook and sniffed the milk.
The smell was determined by repeated short sniffs.
We determined that the milk in each test tube has a different smell.
Determination of the taste of milk.
We poured 10-20 ml of milk into a glass. Then they took a sip of milk into their mouth and held it for a while. After each milk sample, we rinsed our mouths with water and took short breaks between individual determinations. Thus, we determined that milk has a taste ranging from sweetish to tasteless.
2.3 Determination of physical and chemical parameters of milk
2.3.1 Determination of the pH of milk.
Substances contained in milk are of amphoteric nature, i.e. exhibit properties of both acids and bases, so the indicator should not change its color.
But experience shows that the universal indicator, when lowered into milk, changes color to pale green. This indicates that this milk has a slightly alkaline environment. Thus, we learned that soda is added to milk so that it does not go sour further, namely soda (NaHCO 3) and gives the milk a slightly alkaline environment. Soda is added to milk as a preservative.
2.3.2. Determination of the presence of lactic acid.
Everyone knows that sour milk has a sour taste. Can this also be confirmed chemically? We left the milk warm for two days. A precipitate (yogurt) appeared in it, and the universal indicator changed color to red, which indicates the presence of lactic acid (CH3-CH-COOH)/OH in the milk
2.3.3. Determination of protein presence.
Protein is determined using color reactions:
XANTHOPROTEIN: when concentrated nitric acid is added to the protein and heated, a yellow precipitate is formed.
BIURET: when added to protein (milk), a blue precipitate of Cu(OH) 2 precipitates and a violet color appears.
2.3.4 Determination of the presence of carbohydrates.
Mammalian milk contains lactose (milk sugar), which is a disaccharide consisting of glucose and galactose molecules.
CH 22 O 11 + H 2 O = C 6 H 12 O 6 + C 6 H 12 O 3
Milk contains 4–6% lactose. It has a mild sweetness.
To prove the presence of carbohydrates in milk, we heated it together with Cu(OH) 2 - a blue precipitate and obtained a red precipitate, which confirms the presence of glucose.
CONCLUSION
1. Learned to determine the chemical properties of milk.
2. Studied the beneficial properties of dairy products.
3. We have drawn up practical recommendations for the consumption of this product and its derivatives.
Based on a study of the data on the packaging of the product, we determined that the best sample we purchased was the milk “Molochnoye Izobnosti” from the Engels Dairy Plant, and the worst sample was the snowball “Molochnoye Izobilie” from the same manufacturer.
Based on the determination of organoleptic indicators of milk quality and the study of physical and chemical indicators, it was determined that the best example is Koshkinskoye milk.
REFERENCES
1. Gorbatov. Biochemistry of milk and dairy products, - M.: Light industry, 1984, 344 p.
2. GOST 23454 – 79. Milk. Method for determining inhibitory substances, M.: publishing house of standards, 1989. – P.374 – 380.
3. Workshop on the biological foundations of agriculture: Proc. A manual for students of biology. Specialist. Ped. In – tov / I.M. Vashchenko, K.N. Lange, M.P. Merkulov, Ed. I.M.Vashchenko, - M.: education, 1982 – P.359 – 370
4. “Quality of dairy products” N.V. Barabanshchikov (Publishing house “Kolos”, 1980);
5. “Milk and sour products” V.P. Kugenev (Moscow, Peoples' Friendship University Publishing House)
6. Encyclopedia for children. Additional volume. Personal safety. - M., Avanta+, 2001 – 448 pp., illus.
7. materials from the magazine “Around the World”
8. www.vokrugsveta.ru,
9. www.prodpit.ru,
10. www.parents.ru/nutrition.html
11. Chemistry. 10: textbook for general education institutions/ X46 O.S. Gabrielyan, F.N. Maskaev, S.Yu. Ponomarev, V.I. Terenin - 4th ed., stereotype. - M. Bustard, 2003
12. Chemistry. 11: textbook for general education institutions/ X46 O.S. Gabrielyan, G.G. Lysova -4th ed., stereotype. - M. Bustard, 2004
THE WORK HAS BEEN DONE
8th grade students
Lyakhov Ivan, Polinsky Artyom, Torgashova Daria
Municipal educational institution
"Secondary school No. 33"
city of Engels, Saratov region
LEADERS
biology teacher Grankina Lyudmila Vasilievna,
Geography teacher Natalya Nikolaevna Solenkova,
biology teacher Chermashentseva Angela Sergeevna
RUSSIAN FEDERATION
KEMEROVSK TECHNOLOGICAL INSTITUTE
FOOD INDUSTRY
T.A.OSTROUMOVA
CHEMISTRY AND PHYSICS OF MILK
animal origin as a teaching aid
for students of higher educational institutions studying
in direction 655900 – Technology of raw materials and products
animal origin by specialty
271100 – Technology of milk and dairy products
Kemerovo 2004
UDC: 637.1.
Published by decision of the Editorial and Publishing Council of the Kemerovo Technological Institute of Food Industry
Reviewers: Head of the Department of Food Technology, Altai State Technical University. I. I. Polzunova, Doctor of Technical Sciences, Professor M. P. Shchetinin
Director of the State Scientific Institution Siberian Research Institute of Cheese Making, Siberian Branch of the Russian Academy of Agricultural Sciences,
Doctor of Technical Sciences A. A. Mayorov
Ostroumova T. A.
Chemistry and physics of milk: Textbook. -
Kemerovo Technological Institute of Food
industry. - Kemerovo, 2004.- 196 p.
ISBN 5-89289-250-6
The characteristics of milk components, their structure, composition, features of biosynthesis, physicochemical, chemical, organoleptic and technological properties are presented. The issues of equilibrium relationships between different phases of milk as a single polydisperse system are outlined. An analysis of changes in constituent components in the processes of obtaining, storing, transporting, processing milk and producing dairy products was carried out.
Intended for students of specialty 271100 – Technology of milk and dairy products.
Ill. - 12, table - 3, library title - 12
ISBN-5-89289-250-6 © Kemerovo Technological
Institute of Food Industry
ABOUT THE CHAPTER
Introduction……………………………………………………………. 6
Topic 1. The role of domestic scientists in the development of science
“Chemistry and physics of milk”……………………….. 7
Topic 2. Current state of the dairy industry
technology, the main directions of development of technology
logy of dairy products and research problems
knowledge in the field of chemistry and physics of milk………… 10
Topic 3. The role of milk and dairy products in nutrition
person. Economic aspects of rational
extensive use of milk in production
dairy products……………………………. 12
Topic 4. General characteristics of the chemical composition
milk…………………………………………. 15
4.1. General characteristics of the components
nents of milk………………………………. 15
4.2. Comparative assessment of the composition of cow milk
moat with milk from other agricultural
animals and with human milk……… 21
4.3. The influence of zootechnical factors on the sow
tav and properties of milk………………………. 26
Topic 5. Milk proteins…………………………………….. 34
5.1. Modern nomenclature of milk proteins.
Characteristics of casein and whey fractions
mouth proteins……………………………. 35
5.2. Protein structure…………………………… 45
5.3. Protein composition: elemental and amino acids
lot……………………………………………………….. 53
5.4. Physico-chemical properties of proteins……… 55
5.5. Chemical properties of proteins………………. 62
5.6. Biosynthesis of proteins in the mammary gland……… 64
Topic 6. Milk lipids ………………………………….. 66
6.1. The importance of lipids. Classification………… 67
6.2. Glyceride composition of milk fat……… 69
6.3. Fatty acid composition of milk fat... 72
6.4. Physico-chemical properties of dairy
fat……………………………………………………… 76
6.5. Chemical properties of milk fat……… 79
6.6. Phospholipids, sterols and other lipids…… 82
6.7. Biosynthesis of lipids…………………………….. 84
Topic 7. Milk carbohydrates……………………………………. 90
7.1. General characteristics of milk carbohydrates. Know-
lactose reading…………………………………… 90
7.2. Structure of lactose, its isomeric forms and
physical properties……………………………. 91
7.3. Chemical properties of lactose…………………. 95
7.4. Biosynthesis of lactose………………………………. 97
Topic 8. Minerals of milk……………………… 98
8.1. General characteristics of mineral substances.
Salt composition of milk………………………….. 98
8.2. Salt balance of milk. Factors influencing
for salt balance……………………… 100
8.3. The role of macro- and microelements in milk and milk
local products………………………………… 103
Topic 9. Biologically active and other substances of milk... 106
9.1. Milk vitamins and their biological role……. 107
9.2. Characteristics of milk enzymes. Use
the use of enzyme properties in quality assessment
milk…………………………………………………………… 111
9.3. Hormones and gases…………………………………… 118
Topic 10. Milk as a polydisperse system………………. 120
10.1. General characteristics of disperse systems…… 120
10.2. Milk as a colloidal system………………. 122
10.2.1. The structure of casein micelles determines
defining the colloidal state of the sol…………….. 122
10.2.2. Conditions for destabilization of the colloidal system
melting of the sol and formation of a gel upon dis-
personal methods of coagulation…………… … 126
10.2.3. Co-precipitation of casein and whey
proteins during thermocalcium and thermo-
acid coagulation methods…………….. 130
10.3. Milk as an emulsion of fat in plasma…………… 131
10.3.1. Factors of aggregative stability of fat
howl of emulsion…………………………………… 131
10.3.2. Factors affecting fat stability
emulsions……………………………………….. 136
10.4. Milk as a true solution…………………. 140
Topic 11. Physico-chemical, organoleptic and technological
gical properties of milk…………………………… 143
11.1. Density………………………………………………………. 145
11.2. Titratable acidity………………………… 146
11.3. Active acidity and buffering properties... 147
11.4. Redox potential.. 151
11.5. Viscosity and surface tension………… 152
11.6. Osmotic pressure and temperature measured
knowledge…………………………………………………………….. 154
11.7. Electrical conductivity and thermophysical
properties…………………………………………. 155
11.8. Organoleptic properties………………….. 156
11.9. Technological properties………………….. 158
Topic 12. Physico-chemical changes in milk during its
storage and processing………………………………. 162
12.1. Changes during storage in low conditions
temperatures and transportation………………. 164
12.2. Changes due to mechanical influences... 166
12.3. Changes during heat treatment………….. 168
Topic 13. Physicochemical and biochemical changes
components of milk in the process of its transformation
boots and when storing dairy products………. 174
13.1. Changes in milk components
during thickening and drying………………………… 175
13.2. Biochemical changes in the constituent components
components of milk during its processing………. 178
13.2.1. Fermentation of milk sugar. Types of fermentation
nia……………………………………………………………… 178
13.2.2. The role of fermentation products in the formation
taste, aroma and consistency of dairy products
products……………………………………. 186
13.2.3. Proteolysis and formation of organoleptic
technical indicators…………………………… 189
13.2.4. Changes in lipid components………… 191
Bibliography……………………………………. 195
INTRODUCTION
“Chemistry and Physics of Milk” is a special cycle discipline that forms the professional knowledge of a dairy industry engineer-technologist. Along with others, this discipline provides a theoretical basis for the study of the technology of milk and dairy products.
The purpose of this course is to master the basics of chemistry and physics of milk to the extent necessary to solve production problems of the industry and in research activities.
The main objectives of the course are the acquisition of theoretical knowledge, practical skills and abilities for their further use in professional activities: in analyzing the composition and properties of milk, choosing directions for their improvement and adjustment, choosing and justifying technological parameters for processing and processing milk, justifying the economic feasibility of using milk for the production of certain dairy products.
As a result of studying the discipline, you should know and be able to:
chemical composition, physicochemical and organoleptic properties of milk;
characteristics of milk components, their structure, composition, physicochemical properties that determine the nutritional, biological value and technological properties of milk as a raw material for the dairy industry;
methods for adjusting the composition of milk necessary in production conditions;
the influence of various factors: zootechnical and technological on the composition and properties of milk;
the role of milk and its individual components in ensuring rational human nutrition;
equilibrium relationships between different phases of milk as a single polydisperse system;
physicochemical changes in milk during its storage and processing;
physical and chemical processes in the production of various groups of dairy products;
theoretical foundations of methods for studying the composition and properties of milk;
apply theoretical knowledge in specific production situations;
conduct research on the composition and properties of milk;
theoretically substantiate the choice of technological parameters for milk processing and processing.
Topic 1. ROLE OF DOMESTIC SCIENTISTS IN THE DEVELOPMENT OF THE SCIENCE “CHEMISTRY AND PHYSICS OF MILK”
The formation of the science “Chemistry and Physics of Milk” is directly related to the organization of first handicraft and then industrial production of dairy products.
The organization of industrial production of dairy products dictated the need to develop theoretical knowledge in the field of the composition and properties of milk, scientific explanations and justifications of technological processes, as well as the training of professional personnel.
Milk is a colloidal solution of fat in water. Under a microscope, it is clearly visible that it is heterogeneous: fat globules float in a colorless solution (serum).
Cow's milk usually contains from 3 to 6% fat (mainly esters of glycerol and saturated carboxylic acids - palmitic, stearic), about 3% proteins, as well as carbohydrates, organic acids, vitamins and minerals.
The casein protein in milk is present in a bound form - phosphate groups covalently attached to the amino acid serine form salts with calcium ions. When milk is acidified, these salts are destroyed, and casein is released in the form of a white curdled mass. In the human stomach, under the influence of special enzymes, a process called “casein curdling” occurs. Curdled casein precipitates and is eliminated from the body more slowly, and therefore is more fully absorbed. Casein is highly nutritious: it contains almost all the amino acids a person needs to build his own proteins. In its pure form, it is a tasteless white powder, insoluble in water. In addition to it, milk also contains other proteins, such as lactalbumin. When boiled, this protein turns into an insoluble form, forming a characteristic white film on the surface of boiled milk - foam.
The sugar lactose C 12 H 22 O 11 contained in milk is isomeric to sucrose. In the human body, under the action of the lactase enzyme, this sugar is broken down into monosaccharides glucose and galactose, which are easily digestible. Due to this, for example, infants replenish carbohydrate reserves. Interestingly, in many people (mainly representatives of the Mongoloid race), the body in adulthood loses the ability to break down lactose.
Passing through the digestive tract, lactose is not absorbed, but becomes a breeding ground for the development of various pathogens, which leads to general malaise. This is why the peoples of the Far East (Japanese, Chinese) practically do not consume dairy products in their food.
In industrial conditions, milk is subjected to heat treatment, the purpose of which is to suppress the development of microorganisms and extend its shelf life. To do this, the milk is pasteurized - held for 30 minutes at 65 °C, and short-term heat treatment is also used - heated for 10-20 s to 71 °C. Compared to pasteurization, heat treatment better preserves nutrients, especially vitamins. To prevent milk from separating into cream and whey, it is homogenized - passed under pressure through small holes. Fat globules are crushed, reduced in size, and the milk becomes more viscous.
A significant part of the milk is processed for the production of butter, cheese and fermented milk products (kefir, fermented baked milk, yogurt, sour cream).
To obtain kefir, milk is fermented - kept for 8-10 hours at 20-25 ° C, adding a seed of lactic acid bacteria. Under their influence, lactose breaks down into lactic acid:
It is lactic acid that determines the specific taste of kefir. As it accumulates in the solution, coagulation (clotting) of casein occurs, which is released in free form. Therefore, kefir has a thicker consistency than milk. Lactic acid fermentation of lactose is accompanied by alcoholic fermentation, which is why fermented milk products, in particular kefir, contain a small amount of alcohol (up to 0.03%). Fermented milk products also contain microorganisms that suppress the development of pathogenic bacteria and thereby improve digestion.
Cottage cheese is also produced by fermenting milk with lactic acid bacteria. Its main component is casein protein.
To prepare butter, the fat droplets that make up the milk must be separated from the whey. To do this, cream is churned - the upper, fattier layer formed when milk settles.
Casein is also included in cheese. They are made by adding a bacterial starter and special enzymes to milk, and then heating the mixture to a certain temperature. Enzymes are reintroduced into the released clot and heated. In this case, a partial change in the structure and composition of casein occurs. Then the mixture is laid out in molds and kept for a long time - up to six months - at a low temperature (not higher than 15 ° C). During ripening, casein is broken down by enzymes into polypeptides and free amino acids. Some amino acids are oxidized by atmospheric oxygen, resulting in the formation of ammonia, aldehydes, and keto acids, which give the cheese a characteristic aroma.
Souring of milk is a common example of protein denaturation.
Man's friend from the cradle, milk is a complete “comprehensive” food product. And it's not strange. After all, up to a certain age, a person, like other mammals, consumes only milk, which is so necessary for the nutrition, growth and development of his body.
Milk- one of the most important food products for humans, especially children, pregnant and lactating women, and the elderly. Milk and dairy products add variety to the diet, improve taste, increase the nutritional value of our food and are of great dietary importance. Milk contains physiologically highly valuable proteins, highly digestible fat, minerals, especially calcium and a number of important vitamins.
Composition and properties of cow's milk
Very interesting features can be noted when considering the average chemical composition of animal milk. For example, few people know that in terms of calorie content (in kilocalories per kilogram), the first places are occupied by the milk of a female deer (2725 kilocalories) and a rabbit (1708 kilocalories); compare with cow's milk, which has 713 kilocalories.
The same picture emerges when comparing fat and protein content. A female deer's milk contains 22.5 percent fat, a rabbit's milk contains 10.5 percent, while a cow's milk contains 3.7 percent. Sheep milk also contains a lot of fat - 6.7 percent. The protein in the milk of a female deer is 10.3 percent, in the milk of a female rabbit it is 15.5 percent, and in cow's milk it is only 3.3 percent. However, in terms of the content of milk sugar - lactose - cow's milk (4.8 percent lactose) is not far behind the milk of mare (6.7 percent lactose) and donkey (6.2 percent lactose).
Despite the fact that cow's milk contains up to 87 percent water, the so-called wateriness is not felt in its taste, just as milk sugar is not felt. This is explained by the fact that water and milk sugar are associated with proteins, phosphatides and other substances. However, the taste of milk that is frozen and thawed after some time changes dramatically: it becomes watery and sweet in taste. This is explained by the fact that after thawing, part of the water does not bind to proteins and milk sugar, that is, it remains in a free state and can be tasted.
Milk fat consists of triglycerides, which are esters of glycerol and fatty acids. Milk fat is found in milk in the form of tiny fat globules, about 2 microns in size (1 micron is equal to 0.001 parts of a millimeter). Fat is the lightest component of milk; when whole milk settles, it is released on the surface, forming cream. Cow's milk proteins are mainly represented by three types: casein, albumin and globulin. Casein alone accounts for 82 percent. Casein is bound to calcium and phosphorus.
If part of the calcium is “split off” from casein, it precipitates in the form of a flaky clot. This is what happens in milk when a large amount of lactic acid is formed (as a result of the development of lactic acid bacteria), when casein precipitates and the milk curdles. Milk contains approximately 6 percent globulin, and it is in a dissolved state. It is believed that globulin is the carrier of the antibiotic properties of milk. Albumin constitutes approximately 2 percent of milk proteins. The white sediment that remains on the walls and bottom of the container after boiling milk consists primarily of albumin. The more milk is boiled, the less valuable nutrients remain in it.
Milk proteins contain all the amino acids vital for humans. During the processing of milk into cheese and other fermented milk products, milk proteins undergo hydrolysis, that is, breakdown.
Milk sugar is what causes milk to taste sweet. With the development of lactic acid bacteria, milk sugar is converted into lactic acid, alcohol, esters, volatile acids and other compounds. Under the action of the enzyme lactase or strong solutions of organic acids, lactose is hydrolyzed, that is, it breaks down into monosaccharides - glucose and galactose.
Lactose plays an important role in the production of fermented milk products. As yeast develops, lactose also undergoes alcoholic fermentation, so part of it turns into alcohol. Typically, both of these types of fermentation - lactic acid and alcoholic - occur in parallel. The technology of very interesting and healthy drinks is based on them - kefir, kumis, ayran. Fermentation leads to the formation of gases, in particular carbon dioxide, which is responsible for the formation of eyes in the cheese.
Among the mineral salts in milk there are salts of calcium, phosphorus, magnesium, iron, sodium, potassium, citric, hydrochloric acids and others. Calcium, phosphorus and magnesium are part of bones, teeth, in addition, magnesium affects the functioning of the heart, and phosphorus is an integral part of nervous tissue and brain cells. All these salts are in milk in an easily digestible form - no food substance transfers calcium and phosphorus to the body better than milk.
Among the trace elements found in milk: cobalt, copper, zinc, bromine, manganese, sulfur, fluorine, aluminum, lead, tin, titanium, vanadium, silver and others. Of course, their number amounts to hundred thousandths or even millionths of a percent. It would seem that substances in such insignificant quantities cannot be important, however, as we have already said, their absence or deficiency in food can cause various disturbances in the functioning of the body. 
Vitamins, the need for which is calculated in thousandths of a gram, are presented quite fully in milk. We can safely say that milk contains almost all fat-soluble and water-soluble vitamins known in nature. Vitamin A and carotene (provitamin A) are dissolved in the fat of milk, so they are absent in skim milk. The vitamin A content in milk is 30-40 gamma percent (gamma is a thousandth of a milligram). Summer and autumn milk contains 2-5 times more vitamin A than winter and spring milk. There is several times more vitamin D in summer milk than in winter milk. Milk contains approximately 90 gamma percent vitamin E, the amount of which does not change significantly throughout the year. Vitamin K in milk is 3-4 gamma percent.
Of the water-soluble vitamins in milk, there is vitamin B1, or thiamine, vitamin B2, or riboflavin, vitamin B6, or pyridoxine, vitamin B12, or cyanocobalamin. Vitamin C in milk contains 1000-1500 gamma percent. Winter milk contains less vitamin C than summer milk. Evening milk contains 15-20 percent more vitamin C than morning milk. But vitamin C is the least stable; it is easily oxidized by atmospheric oxygen and loses its properties. To preserve it longer, it is necessary to immediately cool the milk after milking to a temperature below 8 degrees and subsequently store it, without shaking, at a low temperature, avoiding light shining on the milk.
In addition, milk contains vitamin PP, or nicotinic acid, vitamin H, or biotin, folic acid, which is involved in hematopoiesis, pantothenic acid, which promotes the normal development of the nervous and circulatory system and skin, and choline.
Milk enzymes play a very important role. Milk contains numerous enzymes, in particular hydrolyzing enzymes - galactase, lactase, lipase, phosphatase and redox enzymes. In early childhood, milk enzymes may be important for the processes of transformation of nutrients in the gastrointestinal tract. However, boiling milk destroys its enzymes.
An important role is played by the immune bodies contained in milk, which increase the body’s resistance to infectious diseases, which is especially important for children who have not had childhood illnesses.
About the milk of other animals
The population of various countries widely uses in their diet, in addition to cow's milk, the milk of other farm animals: goats, sheep, mares, donkeys, camels, and deer. 
Goat's milk is higher in biological value than cow's milk, since it contains more highly dispersed proteins, and when it coagulates, more delicate flakes are formed. It contains more cobalt salts, which is part of vitamin B12. There is a prejudice that when consuming goat milk, children develop anemia - this is completely unfounded.
Sheep milk is 1.5 times more nutritious than cow milk. There are 2-3 times more vitamins A, B1 and B2 in sheep's milk than in cow's milk. Sheep milk is widely used for making yogurt, kefir, cheese, butter and other products. Residents of Italy, Greece and the Middle East consume a lot of sheep and goat milk. The least fatty milk is mare's milk, but it contains many vitamins, especially vitamin C. It has great medicinal value and is used for the production of kumis.
Donkey milk is close in composition and properties to human milk. Camel milk has a specific taste, which contains a lot of fat, phosphorus and calcium salts. In desert and semi-desert areas, the local population consumes camel milk fresh and prepares a nutritious, refreshing fermented milk product from it - shubat.
The most high-calorie milk known to the northern peoples is reindeer milk. It is four times more caloric than cow's. In India, Indonesia and Egypt, buffalo milk is consumed mainly. It is thicker than cow milk, twice as fat.
Variety of fermented milk products
There is a great variety of fermented milk products. Yogurt and Varenets in Russia, matsun in Armenia, matsoni in Georgia, katyk in Azerbaijan and Central Asia, chal in Turkmenistan, kurunga in Northeast Asia, jugurt, ayran and kefir in the North Caucasus, kumis in Bashkiria, Kazakhstan, Tataria, fermented baked milk in Ukraine, leben in Egypt, yagurt (or yaurt) in Bulgaria, Romania, Turkey, Greece, funeral milk in Norway, etc.
What are the characteristics of national types of yogurt (sour milk)?
Ukrainian curdled milk, or ryazhenka, the taste and consistency resembles sour cream, and the sweetish aftertaste resembles stewed milk. The fat content of fermented baked milk is 6 percent. To prepare it, pure cultures of lactic acid streptococcus are used. The calorie content of fermented baked milk is significantly higher than the calorie content of yogurt of other varieties.
Varenets produced from baked or sterilized (steamed) milk. In this case, some evaporation of moisture from the milk and its thickening occurs. Varenets is thick, slightly viscous in consistency, and its sour taste has a sweetish aftertaste.
Matsoni, matsun, katyk- different names for the same type of southern sour milk produced from cow, buffalo, sheep or goat milk. The main microflora of these products is Bulgarian bacillus and heat-loving lactic acid streptococci. Milk is fermented at elevated temperatures (48-55 degrees) and fermented in a device that retains heat.
Dzhugurt produced in the North Caucasus (Kabardino-Balkaria). This is pressed sour milk that looks like thick sour cream or paste. It contains 12-13 percent fat, and no more than 70 percent water. Various dishes are prepared from this pressed sour milk. It can be stored for a long time for consumption during the winter months in the form of a creamy product called “brnats-matsun”.
Ayran- mixed liquid yogurt, which is prepared in the household for future use. For better storage, the whey is partially removed from the mixed curd and salted.
Yogurt, or yagurt, or yaurt, has become widespread in Europe and America. It has long been known in Bulgaria. In some countries, yogurt is made from partially evaporated milk or from whole milk to which powdered milk is added.
Shubat (in Kazakhstan), or chal (in Turkmenistan)- a highly foaming fermented milk drink with a pronounced sour-milk taste and yeasty smell made from camel milk. The initial starter for preparing the drink is sour camel milk - katyk.
Fermented milk drink kurunga common among the Buryats, Mongols, Tuvans, Khakassians, Oirots, etc. It is a product of lactic acid and alcoholic fermentation, pleasant to the taste, and not much different in consistency from kumiss. Milk wine is obtained by distillation of kurungi. container -
sung and semi-liquid nutritional drink Arsu.
In addition to the mentioned drinks, other interesting things, not to mention ordinary yogurt, Mechnikovskaya curdled milk(it differs from the ordinary one in its more sour taste and dense clot) and southern curdled milk(slightly viscous, with a pinching, refreshing taste).
MINISTRY OF EDUCATION OF THE RUSSIAN FEDERATION
State educational institution of higher professional education "Orenburg State University"
Department of Milk and Meat Processing Technology
O.V. BOGATOVA, N.G. DOGAREVA
CHEMISTRY AND PHYSICS OF MILK
Recommended by the Academic Council of the state educational institution of higher professional education "Orenburg State University" as a teaching aid for students enrolled in higher professional education programs in the specialty "Technology of Milk and Dairy Products"
Orenburg 2003
BBK 36.95ya73 B 73
UDC 637.1 (0758)
Reviewer: Candidate of Agricultural Sciences, Professor V.S. Antonova
Bogatova O.V., Dogareva N.G.
B73 Chemistry and physics of milk: Textbook. - Orenburg: State Educational Institution OSU,
This manual contains a series of lectures on the discipline "Chemistry and Physics of Milk", covering the main sections of the course in accordance with the requirements of the approved program.
The textbook is intended for students enrolled in higher professional education programs in specialty 271100
Dogareva
© GOU OSU, 2004
Introduction
Biological chemistry, or biochemistry, is a science that studies the chemical composition of organisms and the chemical processes underlying their life activity.
One of the most important components of biological chemistry, which deals with the study of biochemical processes occurring in raw materials of plant and animal origin during storage and processing, is technical biochemistry, in particular the biochemistry of milk, meat, grain, etc.
The production of dairy products is based on biochemical transformations of the main components of milk. In this regard, in the course on the biochemistry of milk and dairy products, a significant place is devoted to the study of the composition of milk, considering the chemical nature, structure, biological value, functional properties, as well as biochemical changes in the components of milk during its storage and processing. When describing the processes occurring in milk, attention is paid to both purely biochemical and related chemical and physicochemical processes. Dairy products are formed as a result of the joint passage of these processes, and it is not always possible to establish the boundary where one ends and another begins. Therefore, the discipline is called “Chemistry and Physics of Milk”. When studying the biochemistry of milk and dairy products, the achievements of related sciences are used, such as organic, physical and colloid chemistry, physiology, animal husbandry, nutritional biochemistry, etc. At the same time, the biochemistry of milk serves as a scientific basis for the subsequent study of the technology and microbiology of milk and dairy products.
Stages and prospects for the development of milk chemistry and physics Great influence on the development of milk biochemistry as a science about milk
contributed to the research of the great Russian scientists I.P. Pavlov and I.I. Mechnikov. I. P. Pavlov (1849-1936) was the first to give a scientific explanation of the easy digestibility and digestibility of the constituent parts of milk and dairy products; he is responsible for the well-known definition of the nutritional value of milk as a product prepared by nature itself. I. I. Mechnikov (1845-1916), dealing with the issues of longevity, was the first to draw attention to the extremely valuable dietary and medicinal properties of fermented milk products, which have now been confirmed and fully explained.
The systematic study of the properties of milk and dairy products was started by A.A. Kalantar - the founder of the domestic dairy business. A.A. Kalantar (1859-1937) organized the first dairy laboratory in Russia at the Edimonovo Dairy School, where he studied the production process of Swiss cheese, the use of calcium salts in its production, the development of formulas for calculating milk solids, etc. A.A. Kalantar actively participated in public life
nor the country, he carried out extensive pedagogical work, first at the Edimonov School, then at the Moscow Agricultural Academy named after K. A. Timiryazev and the Yerevan Zooveterinary Institute.
Biochemistry of milk (milk chemistry) as a science was created in Soviet times by professors G.S. Inikhov and Ya.S. Zaikovsky. G.S. Inikhov carried out numerous studies on the study of the composition and properties of milk and dairy products, the development of methods for quality control of raw materials and finished products, etc. He wrote (1922-1926) the first textbooks “Chemistry of Milk” and “Analysis of Milk”. Subsequently, his textbooks on the biochemistry of milk and dairy products for technical schools and universities and practical guides on methods for analyzing milk and dairy products were reprinted many times. G.S. Inikhov paid great attention to pedagogical work. For many years he worked at the Vologda Dairy Institute and the Moscow Technological Institute of Meat and Dairy Industry, where he trained many candidates and doctors of science.
Scientific and pedagogical activities of Professor Y.S. Zaikovsky started at the Vologda Dairy Institute, then worked for many years at the Omsk Agricultural Institute. His works were devoted to the study of the composition, physicochemical properties of milk, the chemistry of rennet coagulation, the development of the theory of oil formation, etc. The work of Ya.S. Zaikovsky “Chemistry and Physics of Milk and Dairy Products”, published in 1930 and reprinted in 1938 and 1950.
Professor S.V. made a significant contribution to the development of milk biochemistry. Parashchuk (1873-1950). He has done a lot of work to study the influence of feed on the composition and properties of milk and butter, the properties of rennet and pepsin. He developed the fundamentals of the technology for children's medicinal and dietary dairy products and for the first time in the USSR organized their production. For many years he trained process engineers at the Leningrad Institute of Dairy Engineers, where from 1931 to 1949 he headed the department of milk and dairy products technology.
The development of the biochemistry of milk and dairy products was also facilitated by the work of A.P. Belousova, N.P. Brio, D.A. Granikova, R.B. Davidova, 3.X Dilanyan, P.F. Dyachenko, M.M. Kazansky, I.I. Klimovsky, M.S. Kovalenko, A.I. Ovchinnikova, A.I. Chebotareva and others.
IN currently huge Research work in the field of milk biochemistry is carried out by teams of employees of the All-Union Scientific Research Institute of the Dairy Industry (VNIMI), the All-Union Scientific Research Institute of Butter and Cheese-Making Industry (VNIIMS) of NPO "Uglich", the Ukrainian Research Institute of Meat and Dairy Industry (Ukr-NII-myasomolprom ) n scientists from a number of higher educational institutions.
IN In recent years, milk biochemistry as a science has been experiencing a period of rapid development. This was largely facilitated by the use of such modern biochemical research methods as gas-liquid and thin-layer chromatography, electrophoresis, spectroscopy, electron micro-
copy and a number of others.
Advances in the development of milk biochemistry have made it possible to improve existing technological processes, develop new areas of milk processing, and increase the nutritional, biological value and taste of dairy products. In connection with the increasing influence of milk biochemistry on the technology of milk production and processing, the importance of studying this discipline for a specialist in the dairy industry becomes obvious. Only a deep knowledge of the basics of milk biochemistry will allow him to understand the essence of the biochemical processes occurring during the production and storage of dairy products, critically approach the choice of technological modes for processing and processing milk, storage conditions for dairy products, use raw materials more rationally, prevent the occurrence of various defects, etc. .
Nutritional value and role of milk in human nutrition Among the huge number of different animal and plant products
of bodily origin the most perfect, i.e. The most valuable in nutritional and biological terms are milk and dairy products. Milk is the only food product that provides the body of mammals with all the necessary nutrients. I.P. Pavlov pointed out three main properties of milk as a food product: easy digestibility, the ability to stimulate the digestive organs, and better absorption of the nitrogen in milk compared to the nitrogen in other products. The digestibility of milk and dairy products ranges from 95 to 98% Pavlov wrote: “Milk is an amazing food created by nature itself.”
The high nutritional value of milk is due not only to the content of proteins, fat, carbohydrates, mineral salts and their favorable ratio, but also to the specific composition of these components. There is virtually no other food product that has the same nutritional value as milk. 1 liter of milk contains: 32 g of protein, which corresponds to the amount in four to five chicken eggs, 32 g of milk fat, which corresponds to 36 g of butter, 48 g of milk sugar, which is equivalent to the calorie content of 12 pieces of sugar, as well as mineral salts and almost all known vitamins necessary for the human body of any age.
As you know, animal proteins play an important role in a balanced diet. In terms of digestibility and balanced amino acid composition, milk proteins are among the most biologically valuable. Their digestibility (digestibility) ranges from 96 to 98%.
It is important to note that the main protein of milk - casein - is easily “attacked” and digested in its native undenatured state by proteolytic enzymes of the digestive tract.
A comparison of the composition of essential amino acids in milk proteins with the composition of the “ideal” protein indicates the virtual absence of amino acids that limit the biological value of proteins.
Those amino acids that limit the biological value of proteins are considered
acids, the velocity of which is less than 100%. The amino acid score shows the percentage of each amino acid in the protein under study relative to their content in the “ideal” protein. One gram of “ideal” protein according to the FAO/WHO scale (adopted in 1973) contains (in mg): isoleucine - 40, leucine - 70, lysine - 55, sulfur-containing amino acids (methionine + cystine) - 35, aromatic (phenylalanine + tyrosine) - 60, threonine - 40, tryptophan - 10, valine - 50.
Some deficiency of sulfur-containing amino acids, mainly cystine, has been noted for casein, but whey proteins are rich in them. Whey proteins are also high in the two other most deficient amino acids: lysine and tryptophan. Therefore, the introduction of whey milk proteins into food products, especially of plant origin, contributes to a sharp increase in their biological value, which is associated with an improvement in the degree of balance of the amino acid composition.
Milk fat has a certain value in human nutrition. Compared to fats of animal origin, it is better absorbed in the human body. This is facilitated, firstly, by the relatively low melting point of fat (from 28 to 33 ° C); secondly, it is found in milk in a finely dispersed form. The digestibility coefficient of milk fat ranges from 97 to 99%. Milk fat contains relatively few essential polyunsaturated fatty acids. However, when consuming 0.5 liters of milk, about 20% of a person’s daily need for these acids is covered. The presence in milk fat of deficient arachidonic acid, short-chain fatty acids, as well as significant amounts of phospholipids and vitamins (A, D, E) increases its biological value. In addition, the ratio of fat and protein in milk is close to optimal.
An important component of milk is lactose. Unlike other sugars, it is relatively poorly soluble in water, is slowly absorbed in the intestine and thereby stimulates the development of lactic acid bacilli, which, forming lactic acid, suppress putrefactive microflora and promote better absorption of calcium and phosphorus. The role of lactose in the nutrition of infants is especially important.
Minerals are of great importance in human nutrition. First of all, it should be noted that milk and dairy products contain high levels of calcium and phosphorus, which perform a number of important functions in the human body. Both elements are found in milk in well-balanced proportions, which makes them relatively highly digestible. Thus, the ratio between calcium and phosphorus in milk is 1:1 - 1.4:1 (in cottage cheese and cheese 1:1.5-1:2), while in meat and fish it is 1:13 and 1:11. About 80% of a person's daily calcium requirement is met through milk and dairy products.
At the same time, milk is relatively poor in some microelements: iron, copper, manganese, iodine, fluorine. Currently doing -
There have been attempts to introduce iodine and fluorine compounds into milk, while in the production of baby food products, iron salts are usually added to the milk base.
Milk and dairy products are a constant source of almost all vitamins. They are especially rich in riboflavin, which is relatively scarce in food products - about 50% of a person’s daily need for the vitamin is met through milk and dairy products.
The biological value of milk is supplemented by a variety of enzymes, hormones, antibodies, antibiotics and other biologically active substances.
Thus, the nutritional and biological value of milk is indisputable, and it should be an indispensable human food product at all periods of his life. It is not for nothing that, according to ancient legend, Hercules in infancy fed on milk that flowed at the behest of Zeus from the Olympian heights. After this, the milk spilled throughout the universe formed the Galaxy or Milky Way. Ancient philosophers called milk “the source of health,” “white blood.”
Various dairy products also play a very important role in nutrition - fermented milk products, cheeses, butter, etc. Fermented milk products, along with high nutritional and biological value, have very important dietary properties, therefore they are especially recommended for feeding children, the elderly and the sick. Like milk, they contain all the essential nutrients in a well-balanced form, as a result of which they are easily digested in the gastrointestinal tract and quickly absorbed by the human body. At the same time, many of them contain proteins in a finely dispersed, partially split state, which makes them especially easy to digest. Due to the accumulation of carbon dioxide, lactic acid and other flavoring substances, fermented milk products stimulate appetite, stimulate the secretion of gastric juice, and improve metabolism. The presence in their composition of living microorganisms that can take root in the intestines and suppress putrefactive microflora, leads to inhibition of putrefactive processes and the cessation of the formation of toxic protein breakdown products - phenol, indole, skatole, etc.
Thanks to the high content of the valuable amino acid - methionine, cottage cheese has a lipotropic and anti-sclerotic effect and is used for diseases of the liver, kidneys and cardiovascular system. It is also one of the important sources of easily digestible proteins, calcium, phosphorus, and acidophilus-yeast cottage cheese - vitamins B1 and B12.
Acidophilus fermented milk products (acidophilus milk, acidophilus, acidophilus paste and acidophilus-yeast milk) have antibiotic properties and are used in the treatment of gastrointestinal diseases: ulcerative colitis, gastritis, childhood dyspepsia, etc.
The high nutritional and biological value of cheeses, like cottage cheese, is due to the content of a large amount of easily digestible proteins and products of their enzymatic breakdown, minerals (calcium and phosphorus).
handicap), vitamins, organic acids, etc. Thanks to their pungent taste and specific aroma, cheeses stimulate the appetite and promote the active secretion of gastric and intestinal juices. At the same time, traditional high-fat cheeses (Swiss, Soviet, Dutch, etc.) have a high energy value.
Butter, along with high organoleptic characteristics (specific taste and aroma, plastic consistency) and good digestibility by the human body, is characterized, like cheeses, by high energy value, but a less balanced chemical composition.
The exceptionally high nutritional and biological value of milk and dairy products makes them indispensable in the diet of people of various age categories. In order to more rationally use dairy products, dairy industry workers must solve the problem of further expanding the range of low-fat products for feeding the elderly and obese, dietary and medicinal products intended for people suffering from intolerance to certain components of milk, etc. But now, every person can choose dairy products that meet the requirements of a balanced diet, their physical needs, tastes and habits.
The physiologically based consumption rate of milk and dairy products is 434 kg per year per person. However, actual consumption of dairy products has declined sharply in recent years. So, if in 1990 it was 386 kg per year, then in 1996 it was only 206 kg per year or about 53% of the recommended norm.
The traditions of consuming milk and dairy products in Russia go back to ancient times. In addition, milk is one of the archetypes in the Russian popular consciousness - a symbol of health, prosperity, and abundance. Suffice it to recall, for example, “milk rivers with jelly banks” in Russian folk tales, the expression “blood with milk” as a synonym for good physical shape, as well as ancient ladies’ beauty recipes - washing with milk and milk baths. Today's catastrophic decline in the level of consumption of milk and dairy products has many reasons (economic, social, etc.). One of them is the promotion of the American way of life. Young people choose Pepsi, which dissolves an iron nail in three days. By the way, the incidence of osteoporosis among Americans raised on carbonated drinks is one of the highest in the world. The Americans quickly realized their mistake and now even in their schools they have vending machines selling milk cartons, and on TV they constantly play videos where the younger generation chooses milk instead of beer. Thus, dairy industry specialists have a very important role to play in improving the nutritional structure of the country's population by increasing the consumption of dairy products, the range of which should constantly expand.
1 Milk and its composition
1.1 Chemical composition of milk
Milk is a biological fluid that is formed in the mammary gland of mammals and is intended for feeding a newborn.
Milk has a complex composition. It contains more than a hundred different components. Typically, in widespread practice, the chemical composition of milk is characterized by the most important substances, the amount of which is not strictly constant. It varies depending on various factors. On average, milk has the following composition (percentage):
Water - 87.5;
- dry matter – 12.5. Including:
a) milk fat – 3.8; b) proteins 3.3 (casein – 2.7, albumin – 0.5, globulin – 0.1); c) milk sugar – 4.7;
d) minerals – 0.7.
Deviations in milk composition are explained by the influence of many factors
– breed of livestock, its feeding, stages of lactation, age, condition of the animal, seasons of the year and other reasons.
The most valuable part of milk is the dry residue. When producing dairy products, they strive for maximum preservation. Dry residue is everything that remains after drying the milk.
at a temperature of 102 to 105 ° C. It includes all the components of milk, with the exception of water and substances that volatilize during drying. The most variable part of the dry residue is fat, so in practice the dry non-fat residue (DFR) indicator is often used. Dry substances are found in milk in a finely dispersed and dissolved state, i.e. in the most favorable form for assimilation; fat - in the form of a thin emulsion, proteins - in the form of colloidal solutions, milk sugar - in a molecular state, mineral salts - in a colloidal molecular and ionic state.
The more finely and evenly dispersed a particular component of milk is, the less its content varies: thus, the fat content is subject to greater changes than the content of protein substances. The most constant parts of milk in terms of quantitative content are lactose and salts.
The largest specific gravity in milk is water.
Milk contains from 86 to 89% water, most of which (from 83 to 86%) is in a free state, and a smaller part (from 3 to 3.5%) is in bound form. Free water is a solvent for organic and inorganic compounds in milk (lactose, mineral elements, acids, aromatic substances, etc.). As a solvent, free water participates in all biochemical processes occurring in milk during heating.
processing of dairy products. It can be easily removed by condensing, drying and freezing the milk.
Bound water differs significantly in its properties from free water. It does not freeze at low temperatures (-40 °C), does not dissolve electrolytes, has a density twice the density of free water, is not removed from the product upon drying, etc. Bound water, unlike free water, is inaccessible to microorganisms. Therefore, to suppress the development of microflora in food products, free water is completely removed or converted into bound water by adding moisture-binding components (sugar, salts, polyhydric alcohols, etc.).
The main part of the bound water is adsorption water, which is retained by molecular forces near the surface of colloidal particles (proteins, phospholipids, polysaccharides). A special form of bound water is chemically bound water. This water is crystalline hydrates, or water of crystallization. It is almost never found in the components of milk, with the exception of milk sugar, which crystallizes with one molecule of water (C12 H22 O11 H2 O)
1.2 The influence of various factors on the chemical composition of milk. Changes in the composition of milk during lactation
Lactation is the process of formation and secretion of milk, as well as the time during which a cow lactates. A cow's lactation lasts an average of 305 days, and during this time the composition and properties of milk change most significantly three times, and therefore three stages of lactation are distinguished: colostrum, when the cow produces colostrum, main, when the cow produces normal milk corresponding to the quality of natural milk, and the old milking period, when the cow produces milk shortly before drying off.
Colostrum period lasts from 7 to 10 days after the cow calving. Colostrum differs significantly from normal milk but has a specific taste and smell, a more viscous consistency, a light yellow color, and increased density (on average from 40 to 50 ºA). Colostrum is characterized by increased acidity, especially in the first day (from 30 to 50 ºT), then sharply decreasing (from 22 to 25 ºT) by the end of the colostrum period. Colostrum contains 2 times more dry matter (25% instead of 12.5% in normal milk).
An increase in dry matter occurs due to an increase in proteins, and whey proteins, which are of great importance for a newborn calf. The albumin content in colostrum can reach from 10 to 12%, and globulin from 8 to 15%. Moreover, immune globulins in the first milk yield account for an average of 70% of all whey proteins. Colostrum contains 1.5-2 times more minerals and significantly more vitamins. Colostrum has excellent bactericidal properties that protect the newborn’s body from diseases and various nutritional disorders. It has an increased number of somatic cells. Colostrum area
