Causes of low acidity of milk in cows. Determination of the mass fraction of fat in drinking milk

Milk is characterized by the following basic physical and chemical parameters: titratable and active acidity, density, viscosity, surface tension, osmotic pressure, freezing point, electrical conductivity, dielectric constant, boiling point, light refraction.

By changing the physico-chemical properties, one can judge the quality of milk.

Total (titratable) acidity is the most important indicator of the freshness of milk. Titratable acidity reflects the concentration of milk components that have an acidic character. It is expressed in Turner degrees (°T) and for freshly milked milk is 16-18°T. The main components of milk, which determine the titratable acidity, are acidic phosphate salts of calcium, sodium, potassium, citrate salts, carbonic acid, and proteins. The proportion of proteins involved in creating the titratable acidity of milk accounts for 3-4 °T. When milk is stored, the titratable acidity increases due to the formation of lactic acid from lactose. However, the sour nature of milk is determined not only by hydrogen ions, which are formed as a result of the electrolytic dissociation of acids and acid salts contained in milk.

Active acidity is one of the indicators of milk quality. Active acidity (pH) is determined by the concentration of hydrogen ions. For fresh milk, the pH is in the range of 6.4-6.7, i.e. milk has a slightly acidic reaction.

The colloidal state of milk proteins, the growth of beneficial and harmful microflora, the thermal stability of milk, and the activity of enzymes depend on the pH value.

Milk has buffer properties due to the presence of proteins, hydrophosphates, citrates and carbon dioxide. This is proved by the fact that, despite the increase in titratable acidity, the pH of milk does not change up to a certain limit. The buffer capacity of milk is understood as the amount of 0.1 n acid or alkali necessary to change the pH of the medium by 1 unit. With the formation of lactic acid, the balance between the individual buffer systems shifts and the pH decreases. Lactic acid also dissolves colloidal calcium phosphate, which leads to an increase in the content of titratable hydrophosphates and an increase in the effect of calcium on the titration result.

Density of milk - is the ratio of the mass of milk at 20°C to the mass of the same volume of water at 4°C. Density of combined cow's milk is in the range of 1.027-1.032 g/cm 3 . The density of milk is influenced by all components, but first of all, proteins, salts and fat.

The density of milk fat is 0.931, protein - 1.451, lactose - 1.545, salts - 3. Thus, skimming fat increases density, dilution with water lowers it. When water is added to milk in an amount of 10%, the density decreases by 0.003 units, therefore it can be within the limits of milk density fluctuations. Reliably falsification of milk with water can be determined by density if 15% water is added.

Osmotic pressure of milk quite close to the osmotic pressure of the blood and is about 0.74 MPa. The main role in creating osmotic pressure is played by milk sugar and some salts. Fat does not participate in the creation of osmotic pressure, the protein plays an insignificant role.

The osmotic pressure of milk is favorable for the development of microorganisms. It is closely related to the freezing temperature (cryoscopic temperature). The freezing temperature, as well as the osmotic pressure of milk, practically does not change in healthy cows. Therefore, by cryoscopic temperature, one can reliably judge the falsification (dilution with water) of milk. The cryoscopic temperature of milk is below zero and averages -0.55-0.56 °C.

Viscosity of milk almost 2 times the viscosity of water and at 20 ° C for different types of milk it is 1.67-2.18 cP.

The amount and dispersion of milk fat and the state of proteins have the strongest influence on the viscosity index.

The surface tension of milk is approximately one third lower than the surface tension of water. It depends primarily on the content of fat, protein. Protein substances reduce surface tension and promote foam formation.

Optical properties are expressed by a refractive index, which is 1.348. The dependence of the refractive index on the dry matter content is used to control SOMO, protein and determine the iodine number by refractometric studies.

Dielectric constant milk and dairy products is determined by the amount and binding energy of moisture. For water, the dielectric constant is 81, for milk fat 3.1-3.2. The dielectric constant controls the moisture content in butter, dry dairy products.

The boiling point of milk is 100.2 °C.

The acidity of the milk of individual animals can vary over a fairly wide range. It depends on the state of metabolism in the body of animals, which is determined by feed rations, breed, age, physiological state, individual characteristics of the animal, etc. The acidity of milk changes especially strongly during the lactation period and when animals become ill.

So, in the first days after calving, the acidity of milk is increased due to the high content of proteins and salts, then, after a certain time (40-45 days), it decreases to the physiological norm. Milk before the end of lactation of cows has a low acidity.

When animals are sick, the acidity of milk, as a rule, decreases. It changes especially sharply in animals with mastitis.

Although titratable acidity is a criterion for assessing the freshness and naturalness of milk, it should be remembered that milk can have increased (up to 26°T) or low (less than 16°T) acidity, but nevertheless it cannot be considered poor quality or adulterated, since it is 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, confirming its naturalness. More precisely, the acidity of milk can be controlled using the pH method.

The observed increase (up to 23-26°T) in the acidity of milk obtained from individual animals and even the whole herd is the result of a serious violation of mineral metabolism in the animal body. It is caused, as a rule, by an insufficient amount of calcium salts in the feed. Such cases occur when animals are fed large amounts of acidic feed (green mass of cereals, corn, corn silage, beet pulp, bards) poor in calcium salts. Fresh milk with increased natural acidity is suitable for the production of fermented milk products, cheese and butter.

Decreased acidity of milk is mainly due to increased urea content, which can be caused by excessive consumption of proteins from green fodder, the use of significant amounts of nitrogen supplements in the diet of animals or nitrogen fertilizers in pastures. It is not advisable to process milk with low acidity into cheeses - it slowly coagulates with rennet, and the resulting clot is poorly processed.

Active acidity (pH).

Active acidity is expressed by the pH value. It characterizes the concentration of free hydrogen ions (activity) in milk and is numerically equal to the negative decimal logarithm of the concentration of hydrogen ions (H +), expressed in moles per 1 liter.

The pH value of whole milk averages 6.7-6.5 and ranges from 6.3 to 6.9, which indicates a slightly acid reaction of milk.

Since in the current GOSTs and technological instructions, acidity is expressed in units of titratable acidity, there are established average ratios for comparing pH readings for milk and basic fermented milk products with them. For example, for harvested milk, these ratios are as follows:

There is no complete correspondence between active and titratable acidity, since titratable acidity does not indicate the content of any alkalis in milk, but a shift in pH from 6.3 to 8.2-8.5. This is established by the appearance of a red color of phenolphthalein introduced into milk. Freshly milked milk may have a high titratable acidity, but a low active one, and vice versa. With an increase in titratable acidity as a result of the formation of acid during the development of microorganisms, the pH does not change for some time due to the buffer properties of milk, characterized by the presence of proteins, phosphates, and nitrites in it. If, instead of acid, a certain amount of alkali is added to milk, then the pH will not change, and the titratable acidity will change. Only when the acid and amide groups of the amino acids of proteins are neutralized does a sharp change in active acidity occur.

The pH index is of great importance, since it determines the stability of the polydisperse system of milk, the conditions for the growth of microflora and its influence on the processes of maturation of cheese, the speed of formation of components that determine the taste and smell of dairy products, the thermal stability of milk proteins, and the activity of enzymes. The pH value evaluates the quality of raw milk and dairy products.

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 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

Titratable acidity, in T	pH limits
16	6.75-6.72
17	6.71-6.67
19	6.60-6.55
20	6.54-6.49
21	6.48-6.44
22	6.43-6.39
23	6.38-6.34
24	6.33-6.29
25	6.28-6.24
26	6.23-6.19
27	6.18-6.14

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.

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 o 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, the required amount (table) of 0.1 N is measured into a 1-liter volumetric flask. 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 high acidity has been added. 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.

The acidity of milk is determined in Turner degrees. For 1 degree of acidity, take 1 ml of 0.1 N sodium hydroxide solution used to neutralize acids in 100 ml of milk or 100 g of a dairy product .

normal fresh milk has an acidity of 16-19 degrees; fairly fresh milk has 20-22 degrees, stale milk- 23 degrees or more. Milk diluted with water or mixed with soda has an acidity below 16 degrees.

Progress:

To determine the acidity, 10 ml of milk is poured into the flask, 20 ml of distilled water and 3-4 drops of a 1% alcohol solution of phenolphthalein are added, mixed well and titrated with 0.1 N sodium hydroxide solution until a slightly pink color does not disappear within 2 minutes.

The number of ml of 0.1 N sodium hydroxide solution consumed, multiplied by 10 (for conversion to 100 ml of milk), will show the number of degrees of milk acidity.

Example: Let's say that 2 ml of a 0.1 N alkali solution was used to titrate 10 ml of milk, then the acidity of milk is (2 times 10) 20 degrees.

Determination of fat content in milk.

8 ml of a 10% soda solution, 10 ml of test milk and 3-3.5 ml of an alcohol mixture consisting of 1 part of amyl alcohol, 6 parts of ethyl alcohol and a few drops of phenolphthalein solution are poured into the Gerber butyrometer. After that, the butyrometer is closed with a stopper and the contents are shaken well until the gelatinous lumps formed at the beginning are completely dissolved and the mass turns into a uniform liquid. Then put the butyrometer with the stopper down for 4-5 minutes in a water bath at 65-70 0 C, after which it is transferred to a centrifuge and rotated for 4 minutes. At the end of centrifugation, the butyrometer is carefully removed, holding the stopper down so as not to mix the contents, which as a result of centrifugation is divided into 2 layers: the upper one is transparent, amber in color, the lower one is red (for better peeling, the butyrometer is again placed in the bath for 3-4 minutes ). The upper layer is fat, and the calculation of its amount is carried out in the same way as in the original Gerber method (butyrometer), one large division of the butyrometer corresponds to 1% fat.

Note: after filling the butyrometer, it is necessary to check that its contents, when positioned with the stopper down, reach the first or second division of the scale. If the liquid level is lower, which may be due to fluctuations in the volume of the butyrometer, then you need to add the missing amount of soda solution.

The fat content of milk is normally 3.2-3.6%.

Definition of adulteration of milk.

Definition of soda in milk: Approximately the same amount of 0.2% solution of rosolic acid in 96% alcohol is added to 1/3 test tubes of the milk under study and shaken. In the presence of soda, the mixture turns pink. Soda is added to milk to delay its sourness. From a hygienic point of view, the addition of soda to milk, according to current sanitary legislation, is not allowed.

End of work -

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Transportation of foodstuffs must be carried out on special, suitably equipped vehicles, kept clean and not used for other needs. Meat and fish are transported to

Food storage
Public catering establishments should have separate rooms for storing bread and dry products, for vegetables and perishable products. Bread is stored on the shelves with

The composition of the premises of the food block
The food block, in addition to storage rooms, should include the following groups of rooms: 1) a dining room with utility rooms for serving visitors (wardrobe, lavatory with wash

Personal hygiene of food block personnel
All employees of the food unit must undergo a medical examination and be tested for acute intestinal diseases, helminths and tuberculosis before they start work. In the future

Temporary food outlets in rural areas
Food points for agricultural workers are organized on a clean, elevated place at a distance of at least 100 m from places where fuel, pesticides are stored and at least 25 m from latrines and roadways.

Evaluation and research of dishes
Utensils used for preparing and storing food must meet the following general requirements: - be smooth inside and out and be shaped to allow easy washing and cleaning; -