Requirements for the quality of milk: GOST, physical and chemical indicators

Today, the dairy industry can be called one of the most important among all the processing industries of food production. It is armed with more than ten thousand units of modern technological and energy devices and equipment, production lines and means of mechanization of processes.

Milk processing technology is a reflection of progressive industrial methods for producing high-quality and high-grade products from it for the nutrition of children and adults. The requirements for the quality of milk and dairy products are a kind of incentive for the further development of this branch of food production.

Natural fresh cow's milk, fed from healthy animals, has a number of specific physicochemical, organoleptic and other indicators. By their values, it is possible to determine not only the breed and the state of health of the cows, but also to recognize the falsification. That is why the requirements for milk quality are given so much attention in various regulatory documents.

The role of milk in nutrition

It is no secret that milk is the most valuable food for humans, especially in the first years of life. By its nutritional value, it can replace almost any product, however, replacing milk with something is quite difficult. Milk contains the necessary nutrients for the human body (proteins, lipids, carbohydrates, vitamins, etc.) in a balanced ratio. Moreover, they are absorbed quite easily.

Proteins perform many functions in our body. So, antibodies have a protein nature, transport proteins carry out the transfer of substances throughout the body (for example, hemoglobin provides oxygen delivery), muscles are formed by proteins. As a result of the breakdown of proteins, various amino acids are formed, which are used to build cells, enzymes, hormones. And this is not a complete list. Especially high in amino acids in whey proteins.

Milk fats contain polyunsaturated fatty acids that are not synthesized in the body, but are well absorbed by it. Milk sugar (lactose) is a good source of energy required for biochemical processes. But, just as importantly, it contributes to the development of intestinal microflora, which suppresses the putrefactive environment due to the formation of lactic acid.

We all know that milk is a source of calcium. However, it contains other equally important elements: potassium, magnesium, phosphorus, sodium and many others. They are necessary for the synthesis of vitamins, hormones and enzymes. Whole milk and most dairy products have a very high energy value. So, one liter of milk satisfies the daily calorie needs of an adult. All this partly explains such high requirements for the quality of milk.

Separately, it is worth noting the role of milk in the nutrition of children, including the first year of life. Fat in milk is contained in the form of very small balls. And the amino acids contained in the proteins that form the shell of these fat droplets normalize the body's growth process and its development. The already mentioned calcium and phosphorus are necessary for the rapid growth of bone tissue.

Types of dairy raw materials

Certainly, the main raw material in the dairy industry remains whole milk. Its chemical composition is different even in the same animal. It varies depending on the period of lactation, the characteristics of feeding and maintenance, age and a number of other factors.

From the point of view of chemistry, milk is a complex colloidal system, the dispersion medium of which is water. Milk sugar and vitamins are dissolved in it. The dispersed phase is formed by proteins and fats. Many technological processes of milk processing include the stages of separation of it into its constituent components. As a result of the production of butter, cottage cheese, and cheese, by-products are also formed - buttermilk, skim milk, and whey, which are collectively called protein-carbohydrate raw materials.

Milk itself and various by-products formed during its processing are very valuable raw materials, which are suitable for many types of high-quality products. Therefore, the requirements for the quality of raw milk and milk product are somewhat different.

So, for medical purposes, requiring the dairy industry to obtain pure milk sugar for the cultivation of microorganisms, the immutability of lactose is important. For the production of canned milk , the ratio of components such as proteins and salts is of paramount importance. One of the main requirements for the quality of milk for the production of cheese is the content of casein, because the quality of the resulting cheese depends on its ability to curl under the influence of rennet.

In general, the quality of raw materials, including for the dairy industry, is understood to mean the entire combination of properties (physico-chemical, microbiological indicators, chemical composition), on which its suitability for further processing depends.

physical and chemical indicators

Since milk can be considered as a single physicochemical system, its properties are determined by the properties of individual components. Even small changes in their quantitative ratio and condition entail changes in the physicochemical properties of the entire system. Each of the constituent parts of milk has a definite effect on the totality of its physicochemical properties. So, the acidity and viscosity of milk are largely dependent on the mass protein content. Mineral substances in its composition significantly affect acidity and electrical conductivity.

The main physical and chemical indicators in the requirements for milk quality are:

• Mass fractions of fats and proteins. The most valuable is considered milk with increased mass fractions of proteins, fats and solids. It allows you to significantly improve the quality of dairy products, while reducing the consumption of raw materials. The values ​​of the mass fractions of these components must meet the requirements for milk quality in accordance with GOST. According to this regulatory document, the minimum mass fractions of fats and proteins should be 3.4% and 3.0%, respectively.
• Acidity. It is expressed in terms of titratable and active acidity. The first is determined in degrees Turner (T), that is, in the amount of milliliters of a 0.1 N NaOH solution spent on the neutralization of 100 ml of half-diluted milk. The titratable acidity is due to the presence of salts of citric and phosphoric acids, casein and whey proteins, as well as dissolved carbon dioxide in freshly milk. The value of titratable acidity should correspond to the range of 14-16 T. During storage of raw milk, its total acidity increases, and this leads to undesirable changes in properties (for example, the resistance of proteins to heat changes). Thus, titratable acidity is important for evaluating raw milk. Active acidity (pH) is an indicator characterizing the activity of H ⁺ ions. The main sources of hydrogen cations in dairy products and raw materials are a variety of acidic components in dissociated form. The value of the active acidity of freshly milk should be 6.6-6.7.
• The density of milk. It is determined by a hydrometer and characterizes the mass of milk at 20 ° C, enclosed in a unit volume. This parameter depends on temperature, as well as the percentage of milk, fat, protein, milk sugar and salt. Density should be measured 2 hours after the end of milking, when the structure of milk is stabilized due to solidification of the fat, removal of a certain part of the air, etc. The density of milk makes it possible to evaluate its naturalness. So, for example, dilution with water leads to a decrease in density, and skim milk, on the contrary, to increase.
• Freezing temperature. This parameter is the most important in determining the naturalness of milk, since it depends on the osmotic pressure, and more precisely on the concentration of lactose and salts dissolved in it. The requirements for the quality of milk according to this parameter in accordance with GOST TR 52054-2003 are as follows: the freezing temperature should not exceed minus 0.52 ° .

Organoleptic indicators

Milk is evaluated according to the following indicators from this group: appearance and consistency, color, taste and smell. In its appearance, milk should have a uniform structure, not include sediment or flakes. Its color is allowed from white to light yellow.

Milk has a specific smell and corresponding taste, due to the presence of carbohydrates (sugars), lipids, proteins and salts. The sweetness of lactose is 6 times less than that of sucrose, so the requirement for the quality of fresh milk is a barely perceptible sweet taste.

Lipids provide milk with a delicate taste, but proteins and salts practically do not affect the taste of fresh milk. However, it is worth noting that old-milk contains several more salts, which means its taste is slightly brackish.

It is obvious that if there are any defects in organoleptic indicators in raw milk, then they will also appear in the finished product, and this will lead to a decrease in its quality. Properly performed control of taste, color and smell in accordance with the requirements for the quality of milk is of paramount practical importance.

Technological performance

The main technological indicators of milk quality include heat resistance and rennet coagulation. Thermal stability is understood to mean the ability of milk to maintain the initial colloidal-dispersed properties of the proteins contained in it at elevated temperatures (115-140 C). Typically, milk is stable at pasteurization temperature or heating of about 100 ° C for tens of minutes. However, already at 130 ° C, the duration of its heating to coagulation of proteins and their deposition in various samples can vary from 2 to 60 minutes. This requirement for milk quality is especially important for the production of sterilized milk, baby food, and canned milk.

Rennet coagulation is understood as the ability of milk proteins to coagulate from the action of rennet, which leads to the formation of a fairly dense clot. For standard conditions, the clotting time should be at least 10-15 minutes. If this time period is too long, milk is called rennet-lethargic. This indicator is most important in the production of cheese.

Sanitary indicators

It is known that milk is one of the biological fluids, which means that it is necessary to take into account that the level of hygiene in the process of its production, which affects the presence of mechanical impurities and bacteria, is important. Mechanical contamination is determined by filtering milk with subsequent comparison of the precipitate with the standard. Next, a purity group is established.

The total bacterial contamination, taking into account the presence of all available types of microorganisms in the milk sample, is determined by seeding on a solid medium with KMAFAnM counting exactly after 72 hours. Not only taste properties, but also physicochemical parameters depend on the amount of bacteria contained in raw milk. Since milk can contain not only beneficial bacteria, but also harmful organisms, it is also important to qualitatively determine their composition.

Since mastitis is one of the common diseases in cows, determining the number of somatic cells is also important. With an increase in leukocytes, physical and chemical characteristics, organoleptic and technological properties deteriorate. In the milk of healthy cows, the number of somatic cells does not exceed 500 thousand / cm ³ . This requirement for milk quality is extremely important, since pathogenic microflora (staphylococci, streptococci, Escherichia coli, pseudomonas) increase in milk of animals with mastitis.

Naturalness indicators of milk

Milk is considered to be falsified when any components are added to it or fat is removed.

Varieties of "Wrong" Milk

Abnormal milk is called such a raw material or product, physico-chemical parameters, as well as bacterial contamination of which differ from normal values. It is colostrum, mastitis and old-fashioned milk, rennet-sluggish or with a modified salt composition. Products obtained from such milk will certainly have any defects.

By colostrum is understood that milk which is received in the first few days after calving. It has a yellow-brown tint, brackish taste and a peculiar smell, thick and viscous in its consistency. Despite the fact that it contains more proteins, fats, salts and less sugar, it is not suitable for processing. This is due to the fact that colostrum coagulates upon the slightest heating, almost does not coagulate from rennet, and is also characterized by small fat globules. Thus, it does not meet the requirements for the quality of milk and cream.

By “old-fashioned” we mean milk that is obtained from cows before they are launched. Its taste becomes bitter-brackish. This is due to an increase in the amount of fatty acids released from the action of lipases and chlorides on fats. It coagulates poorly from rennet, contains small balls of fat and casein micelles.

GOST requirements

So still, what are the requirements for the quality of fresh milk? The normative documents describe in detail the values ​​of indicators for various varieties of milk.

It is important that the milk is natural, not subjected to the extraction and addition of components. Primary treatment is allowed, including purification from mechanical impurities, as well as cooling to 4 ° C. The requirements for the quality of milk and cream in butter production are correlated with the values ​​of physical and chemical indicators presented to raw milk.

Powdered milk

Dry milk, as well as dry cream, refers to such dairy products that are obtained by the partial removal of water from raw materials - milk or cream, respectively.

As you can see, the requirements for the quality of milk powder are clearly delineated depending on its type.