Raw milk quality indicators. quality requirements

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 the "sanitary and veterinary rules 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 of nutrients in it. 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.

1) Acidity, for pasteurized milk should be no more than

21 °T 20 °T 19 °T

27) What is the mass fraction of fat contained in the Vologda oil?

28) How many natural milk needed to make 1 kg of cheese?

29) The contents of the stomach, what kind of animal is used for rennet?

2. Calf

3. Kid

30) Proteins of rennet-sluggish milk under the action of rennet poorly or do not coagulate at all. This is due to a lack of feed:

Soluble calcium salts. essential amino acids soluble phosphorus salts

31) Milk yield and fat content in milk are increased to:

6th calving 7th calving 8th calving

32) It is better to feed concentrates:

Before milking During milking After milking

33) In the gaps of the alveoli and small passages of the udder is:

90% milk 80% milk 70% milk

34) In the large milk ducts and cisterns of the udder is:

30% milk 20% milk 10% milk

35) When working out fermented milk drinks milk pasteurization temperatures are used:

85-87°C with 5-10 min hold or 90-92°C with 2-3 min hold 85-90°C with 5-10 min hold or 63-65°C with 2-3 min hold 85-90° C without exposure or 90-92 °C with exposure 2-3 min

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).

Storage raw milk titratable acidity increases with the development of microorganisms 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). Hydrogen indicator fresh milk, reflecting the concentration of hydrogen ions fluctuates (depending on the composition of milk) in 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, in order to compare 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 of a living organism from a possible sharp change in pH, which can adversely or detrimentally affect it. The buffering capacity of the constituent parts of milk plays an important role in the vital activity of lactic acid bacteria in the production of fermented milk products and cheeses.

The acidity of milk is used to judge its freshness. Acidity is necessary to know to establish the type of milk, as well as to determine the possibility of pasteurization and processing of milk into dairy products. Acidity can be determined using a pH meter (active acidity). The active acidity of milk is in the range of 6.5 - 6.7. Usually, titratable acidity is determined in conventional degrees or Turner degrees (o T).

Under the degree of Turner the number of milliliters is 0.1 n. alkali solution, which went to neutralize (titrate) 100 ml of milk, diluted twice with distilled water, with the indicator phenolphthalein.

The titratable acidity of fresh milk is in the range of 16 - 18 o T and is determined by:

1) acidic nature of proteins (5-6 o T);

2) phosphate, citrate salts and citric acid(10-11 about T);

3) dissolved carbon dioxide (1-2 o T).

1) Titration method. The method is based on the neutralization of the acids contained in the product with an alkali solution (NaOH, KOH) in the presence of the phenolphthalein indicator.

Definition technique. 10 ml of milk is measured into a flask with a graduated pipette, 20 ml of distilled water and 2-3 drops of a 1% alcohol solution of phenolphthalein are added. Water is added during the determination in order to more clearly capture the pink tint during titration. Then, while slowly shaking the contents of the flask, a decinormal (0.1N) solution of alkali (caustic soda) is poured from the burette until a faint pink color corresponding to the control color standard does not disappear within 1 minute. The amount of alkali used for titration (measured at the level of the lower meniscus), multiplied by 10 (that is, converted to 100 ml of milk), will express the acidity of milk in Turner degrees. The discrepancy between parallel determinations should be no more than 1 o T. If there is no distilled water, the acidity of milk can be determined without it. In this case, the reading results must be reduced by 2 o T.

2) Limiting acidity of milk. The method for determining the limiting acidity allows sorting during the mass acceptance of milk into conditioned (up to 19 - 20 o T) and not conditioned (over 20 o T). The method is based on the neutralization of the acids contained in the product with an excess amount of alkali (NaOH, KOH) in the presence of the phenolphthalein indicator. In this case, the excess of alkali and the color intensity in the resulting mixture are inversely proportional to the acidity of the milk.

Definition technique. To prepare a working solution of alkali, measure into a 1 liter volumetric flask right amount(table) 0.1 n. alkali solution (NaOH), 10 ml of 1% phenolphthalein solution and add distilled water to the mark.

Determination of the maximum acidity of milk

10 ml of caustic soda (potassium) prepared to determine the corresponding degree of acidity is poured into a series of test tubes. 5 ml of the test milk is poured into each tube with the solution, and the contents of the tube are mixed by inverting. If the contents of the tube become discolored, the acidity is higher than the value corresponding to this solution.

Instead of the above NaOH solution, another solution can be used. To do this, measure 10 ml of distilled water into test tubes, add 2-3 drops of phenolphthalein and 0.1 n. Na OH solution, corresponding to a certain acidity of milk, in the following amount:

1.1 ml of NaOH corresponds to an acidity of 22 o T

1.0 ml of NaOH corresponds to an acidity of 20 o T

0.95 ml NaOH corresponds to an acidity of 19 o T

0.90 ml of NaOH corresponds to an acidity of 18 o T

0.85 ml of NaOH corresponds to an acidity of 17 o T

0.80 ml of NaOH corresponds to an acidity of 16 o T

In large factories, the method of establishing the limiting acidity of milk is used to sort it in the flow automatically into fresh and sour.

3) Boiling test. This test is used to distinguish really fresh milk from mixed milk, in which milk with hyperacidity. The freshness of milk is determined by boiling a small portion in a test tube. Usually, milk coagulates when boiled if its acidity is higher than 25 o T. But a mixture of milk with an acidity of 27 o T and 18 o T will also curdle when boiled, although the titratable acidity of such a mixture may not exceed 22 o T. Due to the simplicity of this method, it is desirable when assessment of milk quality. delivered to dairies.

4) Acid-boiling test. It is used to judge both the acidity and the state of milk proteins.

Definition technique. To 10 ml of normal fresh milk, you can add up to 0.8 - 1 ml of 0.1 N. sulfuric acid solution, hold the mixture for 3 minutes in boiling water, and it will not curdle. If milk coagulates when less acid is added, then the protein in it has changed mainly under the influence of microflora.

5) Determination of milk freshness. The freshness of milk is expressed in degrees, which is understood as the sum of degrees of acidity and the number of coagulation of milk. Collapse number- the number of milliliters 0.1 n. sulfuric acid solution needed to coagulate 100 ml of milk.

Degree of freshness normal milk should not be lower than 60. If the milk has changed, mainly under the influence of putrefactive bacteria, then less acid will be required to coagulate the milk. In such milk, the degree of freshness will be less than in normal.

Example. When determining acidity, 1.8 ml of 0.1 N. NaOH solution, that is, the acidity is 18 o T. 3.0 ml of 0.1 n. sulfuric acid solution, therefore, the coagulation number is 30.

Degrees of freshness 18 + 30 = 48, which means that the milk is of poor quality, since with a low titratable acidity, relatively little acid was required to precipitate casein.

A decrease in the acidity of milk may be associated with high content urea, which may be the result of excessive intake of proteins from green fodder, exceeding the norms for the intake of urea as a dietary nitrogen supplement, or high content nitrogenous fertilizers on the pasture. Such milk, due to low acidity, coagulates more slowly. rennet and emerging

i curd is worse processed when making cheeses.

pH (active acidity) - the concentration of hydrogen ions, depending on the composition of milk, varies within narrow limits - from 6.55 to 6.75. When the titratable acidity of raw milk is above 18oT, when the formation of lactic acid is already taking place, the pH decreases slightly. This is due to the presence of a number of buffer systems in milk - protein, phosphate, citrate, bicarbonate lactate, etc. The buffer capacity of milk is understood as the amount of a 1 n acid or alkali solution that must be added to 100 cm3 of milk to shift the pH by one. The buffer capacity of fresh normal milk for acid is 1.7 - 2.6, and for alkali - 1.2 - 1.4. The buffer properties of milk constituents are of great importance for the functioning of lactic acid bacteria. The minimum pH value for the development of thermophilic lactic acid bacilli is 3.5 - 4.25, for lactococci - 4.75. Due to the buffering properties of milk, the pH of kefir at the end of fermentation at a titratable acidity of 75-80oT is only 4.85-4.75, and the pH of cottage cheese at an acidity of 58-60oT is 5.15-5.05.

Such pH values ​​allow the development of lactic acid streptococci, which accumulate aromatic substances.

When developing hard cheeses The pH of the cheese mass is 5.2 - 5.6 with a very high titratable acidity up to 200oT, which is associated with a significant buffer capacity of proteins.(2)

Density of milk. The density or volumetric mass of milk at 20 °C ranges from 1027 to 1032 kg/m 3. The density of the harvested milk is 1028.5 kg/m or 28.5 degrees hydrometer. The density of milk depends on temperature (decreases with increasing) and on chemical composition(decreases with an increase in fat content and increases with an increase in the content of proteins, sugar and salts). The density of milk must be determined no earlier than 2 hours after milking, since the density of freshly milked milk is lower due to the content of gases in milk and changes in the density of milk fat.

Colostrum and milk obtained from animals with mastitis significantly differ in density from normal milk. The density of milk changes when adulterated - it decreases when water is added and increases when cream is raised or diluted with skim milk.

The density of dairy products depends on their composition: cream 8 - 10% fat - density 1024, cream 20% fat - 1018, cream 35% fat - 998, condensed milk with sugar - 1270 - 1295, whey 1019 - 1027, skimmed milk- 1032 - 1035, buttermilk 1031 - 1033.(16)

Table 2. Average amount of vitamins in milk.

Regulation of milk secretion. It has been established that the nervous and endocrine systems take part in the regulation of the activity of the glandular epithelium. Afferent impulsation is due to the presence of a rich receptor apparatus - mechano-, thermo- and chemoreceptors are widely represented in the mammary gland. The afferent impulsation that has arisen in the receptors of the mammary gland enters the spinal cord, where a short reflex arc is formed - the interaction of sensitive and effector neurons develops, as a result of which the so-called segmental reflex to the mammary gland is carried out.

Along with this, afferent impulses reach the medulla oblongata and hypothalamus through the conduction system of the spinal cord - the dorsal longitudinal bundle and spinothalamic pathways. The mammary gland has a wide representation in the hypothalamic structures, which are responsible for the production of releasing factors (liberins) and inhibitory factors (statins) that determine the production of lactogenic hormones. From the hypothalamus, excitation goes to the cerebral cortex, where a community of nerve centers is formed that controls the intensity of the lactation process and a special state of the body "lactation dominant" is created.

1.3 Rules for milking cows. Hygiene of dairy equipment

The excretion of milk is not carried out spontaneously, but only in the presence of certain specific effects on the gland - sucking or milking. The secretion of secretion components in the alveolar epithelium proceeds cyclically - the phases of the secretory cycle, including the transport of precursors, the synthesis and formation of the sector product and its excretion outside the cell, are completed in a period of time that takes from 55 to 70 minutes. Several secretory cycles may occur in the secretory epithelium between suckling and milking, and with the accumulation of excess amounts of milk in the alveolar epithelium, inhibition of the secretory process is observed. (5)

It is customary to divide milk in the capacitive system of the organ into cisternal and alveolar portions. The alveolar portion of the secret fills the cavity of the alveoli and small interalveolar ducts and ranges from 25 to 48% of a single milk yield. By the time of milking, the tank contains about 25% of milk yield, but with full pre-milking preparation, massage, washing of the udder, the bulk of the milk (85 - 97%) moves into the tank. This rather conditional division of milk yield is necessary to describe the phases of the milk excretion reflex: nervous and neurohumoral.