Physico-chemical properties of milk, characterizing its quality. Determination of the acidity of milk

Determination of the acidity of milk by the titrimetric method

Determination of milk acidity was carried out according to GOST 3624-92 “Milk and dairy products. Titrimetric methods for determining acidity.

The acidity determines the freshness of milk. The acidity of milk is expressed in Turner degrees. Acidity fresh milk due to the presence in it of proteins, phosphate and citrate salts, a small amount of dissolved carbon dioxide and organic acids. During the storage of milk as a result of the development of microorganisms that ferment milk sugar, lactic acid accumulates and the acidity of milk increases.

Method order. Pipette 10 ml of well-mixed milk into a 100 ml conical flask, add 20 ml of distilled water and 2-3 drops of phenolphthalein. The mixture is thoroughly mixed and titrated with a 0.1 N burette. alkali solution with continuous shaking. First, about 1 ml of alkali is immediately poured, and then drop by drop until a faint pink color appears, which does not disappear within 1 minute.

Titration should be carried out at the same speed, as a fast titration results in underestimated results compared to a slow one.

acidity of milk X in Turner degrees is determined by the formula:

where v - amount 0.1 n. sodium hydroxide solution used for titration 10 ml of milk, ml;

10 - coefficient for conversion to 100 ml of milk.

The discrepancy between parallel determinations should not exceed 2.6°T.

Determination of the mass fraction of fat in drinking milk

The determination was carried out according to GOST 5867-90 “Milk and dairy products. Methods for determining fat. The essence of the method: Fat is isolated in the form of a continuous layer, the volume of which is measured in special device- butyrometer. Fat in milk is in the form of fat globules, surrounded by a lipoprotein shell, which prevents their fusion and determines the high stability of the fat emulsion in milk. Therefore, to release fat, the protein shell is destroyed by the action of concentrated sulfuric acid, which converts the casein-calcium complex of milk into a double soluble compound of casein with sulfuric acid:

NH2R(COO)6Ca3 + 3H2SO4 >NH2--R--(COOH)6 + 3CaSO4

caseincalcium complex casein

NH2-- R--(COOH)6 + H2SO4 >H2SO4 NH2R(COOH)6

For faster release of fat, in addition to acid, isoamyl alcohol is introduced, which reduces the surface tension of fat globules and promotes their fusion.

Method order. In a clean dry butyrometer, trying not to wet the neck, 10 ml of sulfuric acid are measured with an automatic pipette and, carefully so that the liquids do not mix, add 10.77 ml of milk with a pipette, placing the tip of the pipette against the wall of the butyrometer neck at an angle. In this case, the level of milk in the pipette is set at the lower point of the meniscus. The milk should flow out of the pipette slowly. After emptying the pipette, take it away from the neck of the butyrometer no earlier than after 3 s. The pipette tip must not touch the sulfuric acid.

Blowing out the remaining drop of milk from the pipette is not allowed. Then 1 ml of isoamyl alcohol is measured into the butyrometer with an automatic pipette. While filling the butyrometer, the neck of the butyrometer must remain dry and clean. To neutralize the acid in case it gets on the neck of the butyrometer, the surface of the rubber stopper is treated with chalk and only after that the butyrometer is closed.

The cork is inserted into the neck in a helical motion slightly more than half of its length. While holding the cork with a finger, the butyrometer is shaken until the protein substances are completely dissolved, turning it over 5 times so that the liquids in it are completely mixed. Butyrometers may not have the same volume, as a result of which, with the same number of measured reagents in different butyrometers, the column of released fat may take a different position.

In order to measure the volume of released fat at the end of the analysis, its column after centrifugation must be in the graduated part of the butyrometer, and before centrifugation, the upper liquid level in the device must be within nine to ten divisions of the scale. This limit is determined by holding the stoppered butyrometer cap down. If the upper limit of the liquid is at the bottom of the scale, add to the butyrometer sulfuric acid. The addition of sulfuric acid does not affect the result of the determination. After checking the fullness of the butyrometer with liquid, it is put with the stopper down for 5 minutes in water bath with a temperature of 65±2°C. At this temperature, milk fat is in a molten state, which facilitates its separation during centrifugation. After removing from the bath, butyrometers are inserted into the centrifuge cartridges with the working part towards the center, placing them symmetrically one against the other. If there is an odd number of butyrometers, a butyrometer filled with water is added.

After inserting the butyrometers into the cartridges, the centrifuge is closed with a lid and centrifuged for 5 minutes at a speed of at least 1000 rpm. At the end of centrifugation, each butyrometer is removed from the cartridge and the movement of the rubber stopper adjusts the column of fat in the butyrometer so that it is in the graduated part of the device. Then the butyrometers are immersed with the stoppers down in a water bath, the water level in which should be slightly higher than the level of fat in the butyrometer. After 5 minutes, the butyrometers are removed from the water bath and the fat is quickly counted. When counting, the butyrometer is held vertically, the border of fat should be at eye level. By moving the plug up and down, the lower limit of the fat column is set on the whole division of the butyrometer scale and the number of divisions is counted from it to the lower point of the meniscus of the fat column. The interface between fat and acid should be clear, and the column of fat should be transparent. Cloudy or dark colored fat indicates misidentification

The acidity of milk is expressed in units of titratable acidity (in Turner degrees) and pH value at 20 °C.

titratable acidity. Titratable acidity according to GOST 13264-88 “Cow's milk. Requirements for harvesting” is a criterion for assessing the quality of harvested milk. The titratable acidity of milk and dairy products, except for butter, is expressed in conventional units - Turner degrees (°T). Turner degrees are understood as the number of milliliters of 0.1 N sodium hydroxide solution (potassium) required to neutralize 100 ml (100 g) of milk or product.

The acidity of freshly milked milk is from 16 to 18 °T. It is caused by acid salts - dihydrophosphates and dihydrocitrates (about 9-13 °T), proteins - casein and whey proteins (from 4 to 6 °T), carbon dioxide, acids (lactic, citric, ascorbic, free fatty, etc.) and others. milk components (in total they give about 1-3 °T).

When raw milk is stored, the titratable acidity increases as microorganisms develop in it, fermenting milk sugar with the formation of lactic acid. An increase in acidity causes undesirable changes in the properties of milk, such as a decrease in the resistance of proteins to heat. Therefore, milk with an acidity of 21°T is accepted as off-grade, and milk with an acidity above 22°T is not subject to delivery to dairies. m

Although titratable acidity is a criterion for assessing the freshness and naturalness of raw milk, it should be remembered that milk can have an increased (up to 26 °T) or low (less than 16 °T) acidity, but nevertheless it cannot be considered poor quality or adulterated, since it heat-resistant and withstands boiling or gives a negative reaction to the presence of soda, ammonia and impurities of inhibitory substances. The deviation of the natural (native) acidity of milk from the physiological norm in this case is associated with a violation of the feeding rations. Such milk is accepted as varietal based on the testimony of a stall sample (a sample taken during the control milking), confirming its naturalness. More precisely, the acidity of milk can be controlled using the pH method.

pH (active acidity). The hydrogen index of fresh milk, which reflects the concentration of hydrogen ions, varies (depending on the composition of milk) within a rather narrow range - from 6.55 to 6.75. Since in the current GOSTs and technological instructions acidity is expressed in units of titratable acidity, for comparison with them, the pH reading for milk and basic fermented milk products there are averaged ratios established by VNIMI and VNIIMS.

For example, for harvested milk, these ratios are as follows:

Table 1 - Average ratios of pH and titratable acidity

From the above data, it can be seen that when the titratable acidity of raw milk is above 18 °T, when lactic acid is formed, the pH decreases slightly. The slow change in pH is explained by the presence in milk of a number of buffer systems - protein, phosphate, citrate, bicarbonate, etc.

Buffer systems, or buffers, have the ability to maintain a constant pH of the medium when acids or alkalis are added. Buffer systems consist of a weak acid and its salt formed by a strong base, or a mixture of two acid salts of a weak acid. For example, a bicarbonate buffer includes H2CO3 and NaHCO3, a phosphate buffer includes NaH2PO4 and Na2HPO4, etc.

The buffering ability of milk proteins is explained by the presence of amine and carboxyl groups. Carboxyl groups react with hydrogen ions of the formed or added lactic acid:

Acid dissociation of proteins is negligible, so the concentration of hydrogen ions remains constant, while titratable acidity increases, since both active and bound hydrogen ions react with alkali when it is determined.

The buffering ability of phosphates consists in the mutual transition of hydrophosphates to dihydrophosphates and vice versa. With the formation of acid, part of the hydrophosphates passes into dihydrophosphates:

HPO42-+H+ > H2PO4-.

Since the H2PO4- anion weakly dissociates into H+ and HPO42- ions, the pH of the milk hardly changes, and the titratable acidity increases.

When alkali is added to milk, proteins and phosphates react as follows:

When acid or alkali is added, citrates and bicarbonates react with H+ and OH- ions similarly to phosphates:

A change in the pH of milk when acid or alkali is added to it will occur if the buffer capacity of milk systems is exceeded. Under the buffer capacity of milk is understood the amount of acid or alkali that must be added to 100 ml of milk in order to change the pH value by one.

The presence of buffer systems in biological fluids is of great importance - it is a kind of protection for a living organism from a possible sharp change in pH, which can adversely or detrimentally affect it. The buffering capacity of milk constituents plays an important role in life lactic acid bacteria in the production of dairy products and cheeses.

When assessing the quality of milk, one should pay attention to its color, smell, taste, texture and other indicators. The color of normal milk from healthy cows is white or slightly yellowish. A yellowish tinge is more common in summer time When cows graze on pasture, this is due to the presence of carotene (provitamin A) contained in green grass. A bluish or bluish tint is acquired by skimmed milk. It is reddish because of the admixture of blood as a result of mastitis (inflammation of the udder) or damage to the nipples.

The smell should be pleasant, specific. It can vary from food, drugs, etc.

Milk sometimes acquires extraneous odors when it is carelessly stored: barn, ammonia, silo, fish, oil products, etc.

The taste of milk is pleasant, slightly sweet. It also depends on the composition of the food eaten. A salty taste is characteristic of the milk of old cows and those with mastitis. Milk acquires a metallic taste when stored in a rusty metal utensils. The consistency of normal milk is homogeneous, without the presence of mucus, flakes and non-viscous. Their presence indicates a disease of the mammary gland of the animal. Milk diluted with water, reverse, has an excessively liquid, watery consistency.

When assessing the quality of milk, when it is accepted from producers and from the population at collection points, in special laboratories, first of all, the fat content, density and acidity of milk are determined.

Fat content of milk set by mixing a milk sample with sulfuric acid and isoamyl alcohol (followed by centrifugation).

Milk density- a value showing how much its mass at a temperature of 20 ° C is greater than the mass of distilled water at 4 ° C in the same volume. It is determined by the specific gravity of the milk components, which is characterized by the following values: water - 1, milk fat - 0.92, proteins - 1.28. Density of normal milk usually ranges from 1.027-1.033, which is taken into account to establish natural milk. When water is added to milk, its density decreases. So, milk, the density of which is below 1.027, is considered diluted with water. At the same time, if the density of milk is higher than 1.033, then this indicates the removal of fat.

acidity of milk.

When assessing the quality of milk, its acidity is also checked. It is expressed in conventional degrees (Turner) and is 16-18°T for fresh milk, but not higher than 20°T. It is not allowed to sell milk with an acidity of 22°T and above, as it is sour, and milk with an acidity below 15°T is considered diluted with water. In laboratories, the density of milk is determined using a hydrometer (lactodensimeter). 200 ml of thoroughly mixed milk is poured into the cylinder (temperature 10-25 ° C), then the hydrometer is slowly immersed in the cylinder with milk and after 1-2 minutes a reading is made on the scale. The true density on the hydrometer scale can only be at a milk temperature of 20 ° C. If it is lower or higher, make the appropriate amendments.

The acidity of milk is determined by mixing it with distilled water and adding a few drops of phenolphthalein. This mixture is titrated with 0.1% sodium hydroxide solution until a persistent pale pink hue appears, corresponding to the paint standard. The acidity of the milk is then calculated.

acidity of milk different types animals is different. The normal acidity of sheep's milk is 22-24°T, goat's - 15-18 and mare's - 15-17°T.

The quality of milk is also assessed by purity and the degree of bacterial contamination. Purity is determined by passing milk through a filter and comparing it with a standard, establishing a purity group. There should be no impurities in the milk of the first group (clean filter), the second group has a slight sediment on the filter, and the third group has a noticeable sediment of mechanical impurities. Bacterial contamination is determined by the rate of discoloration of milk under the influence of methylene blue. Moreover, the faster the milk discolors, the more bacteria it contains. So, if milk becomes colorless in less than 20 minutes, it is believed that 1 ml of it contains more than 20 million bacteria. Such milk is classified as very poor in quality and class IV is assigned to it. If it takes more than 5.5 hours to decolorize milk, then 1 ml contains less than 0.5 million bacteria. This milk is considered very good and belongs to the I class. The second and third classes, respectively, are assigned the quality "satisfactory" and "poor" (the number of bacteria in 1 ml of milk is up to 4 and up to 20 million).

Cow's milk when purchasing from households and the population, it is assessed in accordance with the requirements of GOST. It must be fresh, whole, obtained from healthy cows, filtered, chilled, clean, homogeneous, not frozen, without foreign tastes and odors, white or slightly yellow in color, without precipitation and flakes.

Depending on the quality, cow's milk (according to GOST) is divided into two grades: the first grade - milk with an acidity of 16-18 ° T, class I in terms of bacterial contamination and the first group in terms of purity; the second grade - milk with an acidity of 16-20 ° T, class II in terms of bacterial contamination and the second group in terms of purity.

In all cases, the density of milk must be at least 1.027, acidity - at least 15°T, fat content must comply with the standards established for the given region, republic. Milk with indicators below the first and second grade is considered non-grade.

In addition to the cow population receives, uses and sells for sale sheep, goat and mare's milk. The requirements for this product category are as follows. Sheep milk It has a white color, a thick, homogeneous texture without flakes, a pleasant specific taste and smell. The fat content in it is not lower than 5%, the density is 1.034-1.038, the acidity is not more than 24°T. Goat- according to organoleptic parameters close to the cow. It is allowed to sell it with a weak specific "goat" smell, fat content of at least 4.4%, density of 1.027-1.038, acidity of not more than 15°T. Mare's milk sweetish, slightly tart taste, with specific smell color is white with a bluish tint. Fat content - not less than 1%, density - 1.029-1.033, acidity - not more than 17°T. As we have seen, milk is very tender, perishable product, requiring for its preservation at home the adoption of a wide variety of measures.

Milk enters the state trade usually pasteurized, packaged in bags or bottles with a capacity of 0.5 and 1 l, and whole (flask), which must be pasteurized.

The acidity of milk and dairy products (except butter) is expressed in Turner degrees.

The Turner degree indicates the number of milliliters of 0.1 N. sodium hydroxide solution (or potassium hydroxide) required to neutralize 100 ml or 100 g of the product. The true acidity of milk is pH 6.5-6.8, the total acidity is 15.99-20.99°T. If the milk value drops below pH 6.5, this may indicate that the animal is infected. If it drops to pH 4.4, the animal is seriously ill.

Table of the ratio of acidity in degrees Turner and pH

Milk purchased by processors must be collected from healthy cows on farms that are free from infectious diseases and in accordance with the rules of veterinary legislation.

In terms of quality, milk must meet the requirements of the standard; it must be filtered and cooled after milking; its storage with manufacturers must comply with the requirements of "sanitary and veterinary regulations for dairy farms of collective farms, state farms and subsidiary farms”, approved in the prescribed manner.

The shelf life of milk before sale should not exceed 24 hours at a temperature not exceeding 4 ° C; 18 hours - at a temperature not higher than 6 ° C; 12 hours - at a temperature not higher than 8°C.

Milk conductivity measurement

Conductivity (or electrolytic conductivity) is defined as the ability of a substance to conduct an electric current. It is the inverse of the resistance value.

*These values ​​depend on the geographical area, breed and other factors.

The conductivity of milk varies depending on the concentration of ions in it, in the following relationship:

The addition of water, sugar, proteins, insoluble salts - reduces the concentration of ions and therefore reduces the conductivity of milk.

Addition of salts - increases the concentration of ions and therefore increases the conductivity of milk.

Exceptionally high readings (6.5 - 13.00mS/cm (18°C) - indicate the presence of mastitis. The infection has penetrated the tissues of the udder. This allows sodium and chloride ions in the blood to penetrate into the milk. The concentration of ions in the milk increases and it is easier to conduct electric current, therefore its conductivity increases

Mastitis is a disease of the mammary gland and is most often provoked by a bacterial infection of the tissues of the udder. Mastitis leads to changes in the electrical conductivity of milk, mainly due to changes in the concentration of sodium, potassium and chloride ions. Therefore, conductivity measurement can help

If, using its conductivity measurement option, you get exceptionally high conductivity readings (6.5 - 13.00 mS/cm (18°C)), this is an indicator of the development of mastitis.

Determination of milk density

The density of milk varies between 1.030 - 1.034, which depends on the composition nutrients in him. The density of skimmed milk increases and can reach 1.037. Milk diluted with water has a low density (1.018), since the percentage of solids in it decreases.

If the temperature of the milk at the time of measurement was above or below 20°C, the results of the reading must be checked against the table.

In the absence of tables, the calculation method is used. It has been established that a change in temperature by 1 degree changes the density of milk by 0.2 divisions of the lactodensimeter, or by 0.0002 units of density.

If the temperature of the milk is above 20 ° C, then its density will be less than at a temperature of 20 ° C, therefore, 0.0002 must be added to the density value found for each degree of temperature.

If the temperature of the milk under study is below 20 ° C, then its density is higher than at a temperature of 20 ° C, i.e., 0.0002 must be subtracted from the density found for each degree of temperature.

When assessing the quality of milk, the following are determined: organoleptic indicators (taste, color, smell, texture), physicochemical indicators (density, acidity, freezing point, heat resistance, SOMO), mass fraction of fat and protein, sanitary and hygienic indicators.

Organoleptic indicators of milk quality. The color, smell, taste and consistency of milk depend on its composition. White color with a yellowish tint and opacity whole milk due to the presence of colloidally dissolved compounds of casein with phosphorus-calcium salts and emulsified fat. Carotene and lactoflavin give the milk a yellowish tint.

The taste and smell of natural milk is influenced by proteins (tasteless in pure form), lipids, milk sugar, acids, mineral salts, vitamins and other substances. Fat gives tenderness, milk sugar - sweetness, protein and minerals form the taste of milk. Free low molecular weight fatty acids, carboxylic compounds, and their oxidation products determine the flavor of milk.

Deviations in organoleptic properties are classified as milk defects, which are of feed, bacterial, technical and physico-chemical origin. Feeding defects can be detected immediately after milking. They occur when cows eat sorrel, chamomile, wormwood, colza, garlic, wild onion, buttercup, containing a large amount essential oils. Introduction to cabbage diets large quantities leads to the appearance of cabbage taste and smell in milk.

Milk can adsorb feed odors. Volatile carbohydrates, esters, acids, alcohols found in feed are absorbed by milk and give it feed flavors and odors.

Defects of bacterial origin (viscous milk, blue, red, excessively yellow) are detected during storage. As a result of protein proteolysis

Putrefactive, cheesy and musty flavors appear in milk with enzymes of putrefactive bacteria. Under the action of enzymes of a variety of microflora, carbohydrates can be decomposed with the formation of butyric and other carboxylic acids, volatile carbonyl compounds, and alcohols that cause defects in milk.

When storing milk, an oxidized taste may appear associated with peroxides, aldehydes formed during the oxidation of unsaturated acids contained in milk. milk fat and phospholipids. Fat is prone to oxidation at high concentrations of copper and iron in milk, as well as when it is stored in the light under the influence of sunlight.

The most common defects in the consistency of milk: viscous, slimy, frothy, watery, curdled, sandy. Color defects: blue and blue, excessive yellow, bloody. Smell defects: ammonia, cabbage, beet, medicinal, acetone, tobacco, butyric, sour, yeast, alcohol, putrid, musty, stable. Taste defects: bitter, fishy, ​​rancid or tart-salty, salty, soapy, fodder, turnip, radish, garlic, onion, beetroot, grass, metallic, taste of petroleum products.

Physical and chemical indicators of milk quality. The most important indicator of the physicochemical properties of milk is density.

Density. This is the mass of a substance at 20 °C enclosed in a unit volume (kg/m3). The density of milk determines its naturalness. In our country, the density of whole cow's milk is 1030 kg/m3 with fluctuations from 1027 to 1033 kg/m3. The density of fresh, freshly milked milk is lower than chilled and standing for 2-3 hours. This is due to the volatilization of carbon monoxide in milk, the transition of fat to a solid state and the hydration of proteins.

The density of milk is determined by a special hydrometer (lactodensimeter) at a temperature of 20 °C. It is allowed to determine the density at 15-25 ° C, bringing it through an amendment to 20 ° C, which is 0.2 ° A for each temperature degree. If the temperature is more than 20 °C, the correction will be with a plus, if it is less than 20 °C - with a minus. The degree of lactodensimeter (°A) means the third and fourth signs of the density indicator. For example, a density of 1029 kg/m3 in laktodensimeter degrees would be 29 °A.

When water is added, the density of milk decreases by about 2.5-3 °A for every 10% of added water.

Freezing point. Freezing point is the temperature at which milk becomes solid. It is set using a Beckmann thermometer. Normal cow's milk freezes at -0.54°C. Depending on the composition of milk, this indicator can vary from -0.525 to -0.565 ° C. The freezing point of colostrum ranges from -0.57 to -0.58 °C. The dependence of the freezing point on the concentration of truly soluble parts of milk can be used in practice to determine the adulteration of milk and calculate the added water. The addition of 1% water leads to an increase in the freezing point by an average of 0.005 °C.

Thermal stability of milk. This is its resistance to high temperatures (up to 140 ° C) without protein coagulation. Under production conditions, the heat resistance group of milk is determined by the formation of protein flakes in a Petri dish when mixing 2 ml of milk with 2 ml ethyl alcohol different concentration: 80% (heat resistance group I), 75% (group II), 72% (group III), 70% (group IV), 68% (group V).

titratable acidity. The acidity of milk determines its freshness. Freshly milked milk has an amphoteric, that is, acidic and alkaline reaction, since proteins contain amine and acid groups. Titratable acidity is expressed in conventional degrees, or Turner degrees. The Turner degree is understood as the amount of milliliters of a 0.1 n alkali solution (KOH or NaOH) required to neutralize 100 ml of milk diluted twice with distilled water, with the indicator phenolphthalein. Sometimes titratable acidity is converted to lactic acid. To do this, the number of Turner degrees is multiplied by 0.009 (the number of grams of lactic acid equivalent to 1 ml of 0.1 n alkali).

The titratable acidity of fresh milk is 16-18 °T. During the storage of milk, microorganisms developing in it ferment milk sugar, which contributes to the accumulation of lactic acid, which increases the titratable acidity. The acidity of milk depends on a number of factors: breed, individual characteristics of animals, feeding conditions, stage of lactation of cows. In the first month of lactation of cows, it is 20 °T, in the tenth month - 15-13 °T, sometimes it drops to 6 °T. As cows age, the acidity of milk decreases.

The low acidity of milk indicates that it is obtained from sick animals. Milk with hyperacidity unsuitable for the manufacture of dairy products and may curdle during pasteurization.

In addition to titratable acidity, they also determine active acidity. This indicator is expressed by the value pH, on average it is 6.5 (ranging from 6.3 to 6.9), which indicates a slightly acid reaction of milk.

In the technical regulations for milk, the indicator of dry skimmed milk residue (SOMO) is regulated.

SOMO. This indicator is determined by subtracting the fat content from the dry residue. The dry residue contains all the chemical constituents of milk (fat, proteins, milk sugar, minerals vitamins, enzymes, etc.). Depending on the stage of lactation, age, diet and other factors, it can vary significantly - from 11 to 14%. SOMO - the value is more constant. It is used to judge the naturalness of milk: if the SOMO is below 8%, then the milk is probably diluted with water.

When assessing the quality of milk, additional indicators are also determined that are not regulated by regulatory documents: viscosity, surface tension, boiling point, electrical conductivity, specific heat capacity, thermal conductivity, redox potential, refractive index, osmotic pressure. These indicators are determined when determining the naturalness of milk and during its processing.

Sanitary and hygienic indicators of milk quality. They are judged by the purity, content of bacteria and somatic cells, the nature of the microflora, the presence of pathogens, chemical pollutants. The technical regulations for milk and dairy products regulate the following indicators of milk safety:

Microbiological indicators: the number of mesophilic aerobic and facultative anaerobic microorganisms(QMAFAnM), bacteria of the Escherichia coli group (CGB), sulfite-reducing clostridia, S. aureus pathogenic microorganisms, including salmonella and Listeria monocytogenes,

Toxic elements (lead, arsenic, cadmium, mercury);

Pesticides - hexachlorocyclohexane (a, R\at- isomers), LCT and its metabolites;

Mycotoxins (aflatoxinMO;

Antibiotics (levomycetin, tetracycline group, streptomycin, penicillin);

Radionuclides (cesium-137 and strontium-90);

inhibitory substances.

Requirements for milk safety indicators are given in Chapter 5.

Purity. This indicator characterizes sanitary conditions receiving milk. Contamination of milk with various mechanical impurities (wool, particles of feed or bedding, dust, etc.) indicates a lack of proper care for animals, non-compliance with elementary sanitary and hygienic rules. Sources of contamination can be: udder, skin and hair of the animal, barnyard air, dairy utensils and equipment, feed, bedding, attendants.

According to the degree of purity, milk is divided into three groups: the first - pure milk, good quality; the second - satisfactory and the third - polluted.

Microorganisms in raw milk. They can be conditionally divided into three groups: useful for human health (lactic acids, widely used in the dairy industry), harmful to health (causative agents of diseases) and worsening the hygienic properties of milk (butyric, putrefactive).

The content of bacteria in milk is determined on reductase test. Bacteria that have entered the milk secrete enzymes, in particular reductase. In fresh, freshly milked milk, reductase is absent. Reductase decolorizes methylene blue or resazurin solutions added to milk. When a solution of methylene blue is added to milk, the mixture turns blue, when resazurin is added, it turns grayish-lilac, and then becomes colorless under the action of reductase. The color fades the faster, the more reductase in the milk. Having established the duration of the discoloration of methylene blue or resazurin, using special tables, the number of bacteria in it is determined.

The nature of the microflora determined by a fermentation test. With the natural souring of milk, a clot is formed. The nature of the clot depends on the predominance of one or another type of bacteria. According to the quality of the clot, milk is classified into one or another class.

The milk of cows with mastitis has a high bacterial contamination. In mastitis milk, the content of somatic cells increases.

somatic cells. They are represented mainly by leukocytes, the epithelium of the milk alveoli and the milk ducts and are common elements of normal milk. When animals become sick with mastitis, the migration of leukocytes to the focus of inflammation increases, which leads to an increase in the number of somatic cells in milk. AT working conditions the number of somatic cells is determined using the surfactant "Mastoprim" using milk-control plates PMK-1, devices "ISKM-1", "Somatos", etc.

Requirements for the quality of raw milk, raw skimmed milk and cream intended for processing are regulated by the Federal Law of June 12, 2008 No. 88-FZ "TR for milk and dairy products", as well as GOST R 52054-2003 "Natural cow's milk - raw materials. Specifications”, GOST R 53503-2009 “Skimmed milk - raw material. Specifications” and GOST R 53435-2009 “Cream-raw materials. Specifications".

Standardization and conformity assessment of milk

In accordance with the requirements of the TR, raw milk must be obtained from healthy farm animals in a territory free from infectious and other diseases common to humans and animals. It is not allowed to use raw milk obtained during the first seven days after the calving of animals and within five days before their launch (before their calving) and (or) from sick and quarantined animals.

The manufacturer must ensure the safety of raw milk. It should not contain residual amounts of inhibitory, detergent, disinfectant and neutralizing substances, animal growth stimulants and drugs.

The mass fraction of dry fat-free substances (SOMO) in cow's milk should be at least 8.2%. The density of cow's milk with a fat content of 3.5% must be at least 1027 kg/m3 at a temperature of 20°C, or at least the equivalent value for milk with a different fat content.

Indicators of chemical, radiation, microbiological safety, the content of somatic cells, regulated by TR, are given in Chapter 5.

In the TR, the requirements for the quality of raw milk are differentiated depending on its intended purpose. The most stringent requirements are set for the quality of milk intended for the production of products baby food milk based. The purity index must not be lower than the first group, the thermal stability index according to the alcohol test - in accordance with the requirements of the national standard - not lower than the second group, QMAFAnM must not exceed the level established for raw milk of the highest and first grades, the number of somatic cells - established for milk premium.

raw milk cow's milk intended for the production of sterilized milk, including concentrated milk or condensed milk, must correspond to the temperature stability indicator for an alcohol test of at least the third group.

Milk intended for the production of cheese must meet the following requirements: rennet-fermentation test of the 1st and 2nd classes; the level of bacterial contamination according to the reductase test of the 1st and 2nd classes; QMAFAnM not more than 1x10 b unit/cm3; the number of spores of mesophilic anaerobic lactate-fermenting butyric microorganisms for cheeses with a low temperature of the second heating - no more than 13000 spores / dm3, s high temperature- 2500 spores/dm3; acidity not more than 19 °T; mass fraction of protein is not less than 2.8%.

In milk intended for the production of products diet food, QMAFAnM should not exceed 5 * 105 units / cm3, the number of somatic cells - 5x105 in 1 cm3, the thermal stability index should not be lower than group 2.

GOST R 52054-2003 applies to natural cow's milk - raw materials produced domestically and imported into Russia, intended for further processing. In accordance with the standard, milk, depending on microbiological, organoleptic and physical and chemical indicators subdivided into grades: the highest, the first, the second and non-grade (tab. 14.2).

The basic all-Russian norm of the mass fraction of fat in milk established by the standard is 3.4%, protein 3%.

If inhibitory substances are found in milk, it is classified as non-varietal if, according to other indicators, it meets the requirements of the standard. Acceptance of the next batch of milk received from the farm is carried out after receiving the results of the analysis, confirming the absence of inhibitory substances.

Milk with a density of 1026 kg / m3, acidity of 15 °T or 21 °T is allowed to be accepted on the basis of a control (stall) sample as the second grade, if it meets the requirements of the standard in terms of organoleptic, physico-chemical and microbiological indicators.

The standard provides labeling requirements, milk acceptance rules, control methods, transportation and storage conditions. The following frequency of monitoring quality indicators when receiving milk has been established: organoleptic indicators, temperature, titratable acidity, mass fraction of fat, density, purity group, freezing point, heat resistance group should be determined daily in each batch; bacterial contamination, the content of somatic cells, the presence of inhibitory substances at least once every 10 days; mass fraction of protein at least twice a month.

Requirements for skimmed milk in terms of taste, smell, appearance and consistency in accordance with GOST R 53503-2009 are similar to the requirements for raw milk. The color should be white with a slightly bluish tinge, the mass fraction of fat is not more than 0.5%, the mass fraction of protein is not less than 2.8%, the acidity is from 16 to 21 °T, the density is not less than 1030 kg/m3.

Cream-raw materials according to GOST R 53435-2009, depending on the quality, are divided into 3 grades: the highest, the first and the second. Cream of the highest grade should have a pronounced creamy, clean, sweet taste and smell, homogeneous homogeneous consistency, heat resistance according to the alcohol test - the first group, titratable acidity not more than 17-13 °T, depending on the mass fraction of fat. The cream of the 1st grade has a sweetish taste, the smell is creamy with a slightly pronounced fodder flavor, for the cream of the 2nd grade - the smell is not sufficiently pronounced creamy, not clean enough and (or) with a fodder flavor, the consistency of cream of both varieties is homogeneous, homogeneous or with single lumps of fat, heat resistance of cream of the 1st and 2nd grades, respectively, of the second and third groups and the fourth and fifth groups, titratable acidity - no more than 19-14 and 21-15 °T. The color of cream of all varieties is white, with a cream tint, uniform throughout the mass, the temperature is not higher than 10 ° C. Cream density (at a temperature of 20 ° C) with a mass fraction of fat from 9 to 20% ranges from

Standardization and conformity assessment of milk

1020 to 1008 kg/m3; from 20 to 30 - from 1008 to 997; from 30 to 40 - from 997 to 987; from 40 to 50 - from 987 to 976 and from 50 to 58% - from 976 to 968 kg/m3.

14.3. Requirements to primary processing,
transportation and storage of raw milk

Raw milk after milking must be purified from mechanical impurities. To purify milk on farms, filter-strainers or separators-milk cleaners are used. In accordance with the requirements of TR, within 2 hours after milking, the milk must be cooled to a temperature of (4±2) °C. At this temperature, it is allowed to store raw and raw skimmed milk by the manufacturer for no more than 36 hours, taking into account the time of transportation, and milk intended for the production of baby food - 24 hours. Flasks, tanks, cooling tanks are used to store milk.

The manufacturer can carry out heat treatment, including pasteurization of raw and raw skimmed milk, in the following cases: its acidity is from 19 to 21 °T, raw cream from 17 to 19 °T; storage of raw milk and cream for more than 6 hours; transportation of raw milk, the duration of which exceeds the permissible period of its storage, but not more than 25%. Mode heat treatment must be specified in the accompanying documentation.

Agricultural producers in the production of raw milk, raw skimmed milk and raw cream must use equipment and materials approved for contact with dairy products.

During the transportation of chilled milk raw materials to the place of processing, its temperature should not exceed 10 °C. Raw milk that does not meet these requirements must be processed immediately.

Milk is transported by specialized vehicles in containers with tight-fitting lids. Vehicles must be equipped with refrigeration systems to maintain the temperature.

The storage and transport of raw milk and raw cream must be accompanied by a declaration of conformity and consumer information. Raw milk, raw cream sold by legal entities or individuals for processing must be accompanied by shipping documents containing the following information: product name and grade, identification indicators (except for the mass fraction of milk solids), batch number, name and location of the manufacturer , volume (in liters) or mass (in kilograms), date and time (hours, minutes) of shipment of products, temperature during shipment.

raw milk, raw cream, non-industrial milk processing products sold by individuals, including individual entrepreneurs in the markets, must be accompanied by information about the place of production, the name of the product and the date of production.

14.4. Identification and conformity assessment of milk
requirements technical regulations

Milk identification is carried out by the certification body in assessing and confirming compliance with the requirements of the TR, as well as in the conduct of State control (supervision) by the federal executive body exercising the functions of control and supervision in the field of veterinary medicine. The body for State control (supervision)

conducts identification in order to establish the compliance of milk with the information contained in the information for consumers, the declaration of conformity. Indicators of identification of raw cow's milk are given in table. 14.3.