1) Acidity, for pasteurized milk should be no more

21 ° T 20 ° T 19 ° T

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

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

29) Stomach contents of what kind of animal is used for rennet?

2. Calf

3. Kid

30) Proteins of dry-flaccid milk under the influence of rennet are poorly or not at all coagulated. This is due to the lack of feed:

Soluble calcium salts. essential amino acids of soluble phosphorus salts

31) Milk yield and fat content in milk increase to:

6th calving 7th calving 8th calving

32) Concentrates are best fed:

Before milking during milking after milking

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

90% milk 80% milk 70% milk

34) In large milk ducts and udder tanks there is:

30% milk 20% milk 10% milk

35) When working out fermented milk drinks use milk pasteurization temperatures:

85-87 ° C with exposure for 5-10 minutes or 90-92 ° C with exposure for 2-3 minutes 85-90 ° C with exposure for 5-10 minutes or 63-65 ° C with exposure for 2-3 minutes 85-90 ° With no exposure or 90-92 ° C with exposure for 2-3 minutes

When assessing the quality of milk, the following are determined: organoleptic indicators (taste, color, odor, consistency), physical and chemical indicators (density, acidity, freezing point, heat resistance, SNF), mass fraction of fat and protein, sanitary and hygienic indicators.

Organoleptic indicators quality of milk. 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 colloidal dissolved compounds of casein with phosphorus-calcium salts and fat in an emulsified state. Carotene and lactoflavin give 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 gives sweetness, protein and minerals form the taste of milk. Free low molecular weight fatty acids, carboxylic compounds, their oxidation products determine the aroma of milk.

Deviations in organoleptic properties are classified as milk defects, which are of fodder, bacterial, technical and physicochemical origin. Forage defects can be detected immediately after milk is milked. They arise when cows eat sorrel, chamomile, wormwood, colza, garlic, wild onion, buttercup, containing a large amount essential oils... An introduction to cabbage diets in large quantities ah leads to the appearance of cabbage taste and smell in milk.

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

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

putrefactive, cheesy and musty aftertastes appear in milk by enzymes of putrefactive bacteria. Under the influence of enzymes of various microflora, decomposition of carbohydrates can occur with the formation of butyric and other carboxylic acids, volatile carbonyl compounds, alcohols that cause milk defects.

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

The most common defects in milk consistency: stringy, slimy, frothy, watery, cheesy, sandy. Color defects: blue and cyan, excessive yellow, bloody. Odor defects: ammonia, cabbage, beet, medicinal, acetone, tobacco, butyric acid, sour, yeast, alcohol, putrid, musty, barnyard. Flavor flaws: bitter, fishy, ​​rancid or tart-salty, salty, soap, feed, turnip, radish, garlic, onion, beet, grass, metallic, petroleum flavor.

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

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

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

Freezing point. Freezing point refers to the temperature at which milk becomes solid. It is installed using a Beckmann thermometer. Normal cow's milk freezes at -0.54 ° C. Depending on the composition of milk, this indicator can range 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 establish milk falsification 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 concentrations: 80% (group I of heat resistance), 75% (group II), 72% (group III), 70% (group IV), 68% (group V).

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

Titratable acidity fresh milk 16-18 ° T. In the process of storing 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.

Low acidity of milk indicates that it was obtained from sick animals. Milk with high acidity is not suitable for the manufacture of dairy products and can curdle during pasteurization.

In addition to titratable acidity, and active acidity. This indicator is expressed by the value NS, on average it is 6.5 (ranges from 6.3 to 6.9), which indicates a slightly acidic reaction of milk.

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

SOMO. This indicator is determined by subtracting the fat content from the dry residue. The dry residue contains all chemical constituents of milk (fat, proteins, milk sugar, minerals, vitamins, enzymes, etc.). Depending on the stage of lactation, age, diet of feeding and other factors, it can fluctuate within significant limits - from 11 to 14%. SOMO is a more constant value. It is used to judge the naturalness of milk: if SNF 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, 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 their purity, the content of bacteria and somatic cells, the nature of the microflora, the presence of pathogens, chemical pollutants. The following milk safety indicators are regulated by the technical regulations for milk and dairy products:

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

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

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

Mycotoxins (aflatoxin MO;

Antibiotics (chloramphenicol, 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 the sanitary conditions for obtaining 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 basic sanitary and hygienic rules. Sources of contamination can be: udder, skin and hair of an animal, barnyard air, dairy dishes and equipment, feed, bedding, service personnel.

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

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

The content of bacteria in milk is determined on reductase sample. Bacteria in milk release enzymes, in particular reductase. In fresh, just milked milk, reductase is absent. Reductase decolours methylene blue or resazurin solutions added to milk. When methylene blue solution is added to milk, the mixture turns blue, when resazurin is added, it turns into a grayish-lilac color, and then becomes discolored under the action of reductase. The more reductase in the milk, the more rapidly the color is discolored. Having established the duration of discoloration of methylene blue or resazurin, the number of bacteria in it is determined using special tables.

The nature of microflora determined by a fermentation test. With the natural souring of milk, a clot forms. The nature of the clot depends on the predominance of a particular type of bacteria. According to the quality of the curd, milk belongs to one class or another.

Milk of cows with mastitis has a high bacterial contamination. The content of somatic cells in mastitis milk increases.

Somatic cells. They are represented mainly by leukocytes, the epithelium of the milk alveoli and the lactic duct and are common elements of normal milk. When animals become ill with mastitis, the migration of leukocytes to the inflammation center increases, which leads to an increase in the number of somatic cells in milk. Under production 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 skim 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. Technical conditions", GOST R 53503-2009" Skimmed milk - raw materials. Specifications "and GOST R 53435-2009" Raw cream. Technical conditions ".

Milk standardization and conformity assessment

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 in food raw milk obtained within 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 inhibiting, detergent, disinfecting and neutralizing substances, animal growth stimulants and medicines.

The mass fraction of dry fat-free substances (SNF) in cow's milk must be at least 8.2%. The density of cow's milk, the mass fraction of fat in which is 3.5%, must be at least 1027 kg / m3 at a temperature of 20 ° C or not less than the equivalent value for milk, the mass fraction of fat in which is different.

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

In 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 indicator must not be lower than the first group, the heat resistance indicator for the alcohol test - in accordance with the requirements of the national standard - not lower than the second group, KMAFanM must not exceed the level established for raw milk of the highest and first grades, the number of somatic cells - established for milk top grade.

Raw cow's milk intended for the production of sterilized milk, including concentrated milk or condensed milk, must correspond to the heat resistance 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 1х10 b unit / cm3; the number of spores of mesophilic anaerobic lactate-fermenting butyric acid 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 food diet food, QMAFAnM should not exceed 5 * 105 units / cm3, the number of somatic cells -5xYu5 in 1 cm3, the heat resistance index should not be lower than group 2.

GOST R 52054-2003 applies to natural cow milk - raw materials produced domestically and imported into the territory of Russia, intended for further processing. According to the standard, milk depending on microbiological, organoleptic and physical and chemical indicators subdivided into grades: superior, first, second and non-graded (Table 14.2).

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

If inhibiting substances are found in milk, it is classified as off-grade, 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 inhibiting substances.

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

The standard contains requirements for labeling, milk acceptance rules, control methods, transportation and storage conditions. The following frequency of quality indicators control when receiving milk has been established: organoleptic indicators, temperature, titratable acidity, fat mass fraction, 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 skim milk for 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 tint, fat mass fraction not more than 0.5%, protein mass fraction not less than 2.8%, acidity from 16 to 21 ° T, density not less than 1030 kg / m3.

Raw cream according to GOST R 53435-2009, depending on the quality, is divided into 3 grades: the highest, the first and the second. Cream of the premium class must have a pronounced creamy, clean, sweetish taste and odor, homogeneous homogeneous consistency, heat resistance to alcohol test - the first group, titratable acidity not more than 17-13 ° T, depending on the mass fraction of fat. Cream of the 1st grade has a sweetish taste, the smell is creamy with a weak fodder flavor, in the cream of the 2nd grade - the smell is insufficiently pronounced creamy, insufficiently pure and / or with a fodder flavor, the consistency of cream of both varieties is uniform, homogeneous or with single lumps of fat, thermal stability 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 all types of cream is white, with a cream shade, uniform throughout the mass, the temperature is not higher than 10 ° C. Density of cream (at a temperature of 20 ° C) at mass fraction fat from 9 to 20% ranges from

Milk standardization and conformity assessment

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 cleaned from mechanical impurities. To purify milk on farms, filter strainers or milk separators are used. In accordance with the requirements of TR, milk must be cooled to a temperature of (4 ± 2) ° C within 2 hours after milking. At this temperature, it is allowed to store raw milk 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 skim milk, in the following cases: its acidity 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 indicated in the accompanying documentation.

Agricultural producers in the production of raw milk, raw skim 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 information for consumers. Raw milk, raw cream sold by legal entities or individuals for processing must be accompanied by shipping documents containing the following information: name and grade of the product, identification indicators (except for the mass fraction of milk solids), batch number, name and location of the manufacturer , volume (in liters) or weight (in kilograms), date and time (hours, minutes) of product shipment, temperature at 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 confirmation of conformity of milk
requirements of 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 State Control (Supervision) Body

conducts identification in order to establish the conformity 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.

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 are sick.

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 physiological norm... Milk before the end of lactation of cows has a low acidity.

When animals are sick, the acidity of milk usually 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 may have increased (up to 26 ° T) or decreased (less than 16 ° T) acidity, but nevertheless it cannot be considered substandard or falsified, since it is heat-resistant and withstands boiling or gives a negative reaction to the presence of soda, ammonia and admixture of inhibiting substances. The deviation of the natural (native) acidity of milk from the physiological norm in this case is associated with a violation of feeding rations. Such milk is accepted as varietal based on the testimony of the stall test, which confirms 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 a consequence of a serious violation of mineral metabolism in the animal body. It is usually caused by an insufficient amount of calcium salts in feed. Such cases occur when animals are fed large amounts of acidic feed (green mass of cereals, corn, corn silage, beet pulp, vinasse) poor in calcium salts. Fresh milk with increased natural acidity is suitable for production fermented milk products, cheese and butter.

The decrease in the acidity of milk is mainly due to the increased content of urea, which can be caused by excess consumption proteins with green fodder, the use of significant amounts of nitrogen supplements in animal diets or nitrogen fertilizers in pastures. It is not advisable to process milk with low acidity into cheeses - it curdles slowly 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 mol per liter.

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

Since in current GOSTs and technological instructions acidity is expressed in units of titratable acidity; in order to compare the pH readings for milk and basic fermented milk products with them, there are established averaged ratios. For example, for procured 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 can have high titratable acidity, but low active, and vice versa. With an increase in titratable acidity as a result of acid formation during the development of microorganisms, the pH does not change for some time due to the buffering properties of milk, characterized by the presence of proteins, phosphates, nitrites in it. If a certain amount of alkali is added to milk instead of acid, the pH value will not change, but the titratable acidity will change. Only when the acid and amide groups of amino acids of proteins are neutralized does a sharp change in active acidity occur.

The pH index is of great importance, since the stability of the polydispersed milk system, the conditions for the growth of microflora and its influence on the processes of cheese ripening, the rate of formation of components on which the taste and smell of dairy products depend, the thermal stability of milk proteins, and the activity of enzymes depend on it. The pH value is used to assess the quality of raw milk and dairy products.

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

Fresh natural milk obtained from healthy animals is characterized by certain physicochemical and organoleptic properties, which can differ sharply at the beginning and end of the lactation period, under the influence of animal diseases, certain types of feed, during storage of milk in an uncooled form and during its falsification. Therefore, according to the physicochemical and organoleptic properties of milk, it is possible to assess the naturalness and quality of the prepared raw materials, that is, its suitability for industrial processing.

All components of milk have different effects on physicochemical properties his. For example, the viscosity and surface tension of milk largely depend on the mass fraction of protein, dispersity and hydration properties of proteins, but the values ​​of electrical conductivity and osmotic pressure are almost independent. Almost all components of milk affect its density and acidity, milk minerals significantly affect its acidity, electrical conductivity, osmotic pressure and freezing point, but do not affect viscosity, etc.

Acidity - titratable (total) and active.

Total (titratable) acidity is expressed in Turner degrees and is determined by titrating 100 ml of milk with 0.1 N alkali solution in the presence of phenolphthalein indicator until neutral. Acidity is a criterion for assessing the quality of harvested milk in accordance with GOST 13264-88 "Cow's milk" procurement requirements.

The acidity of freshly milked milk is 16-18oT. It is conditioned acidic salts- dehydrogenated phosphates and dehydrocitrates (about 9-13oT), proteins - casein and whey proteins (4-6oT), carbon dioxide, acids (lactic, citric, ascorbic, free fatty and other components of milk (1-3oT).

When raw milk is stored, the titratable acidity increases as microorganisms develop in it, which ferment milk sugar to form lactic acid. An increase in acidity causes undesirable changes in the properties of milk, for example, a decrease in the resistance of proteins to heat. Therefore, milk with an acidity of 21oT is accepted as off-grade, and milk with an acidity above 22oT is not subject to delivery to dairy factories.

The acidity of milk depends on the breed of animals, on food rations, age, physiological state, etc. The acidity changes especially strongly during the lactation period and during animal diseases.

In the first days after calving, acidity is increased due to the high content of proteins, salts, after 40-60 days it reaches the physiological norm. And before the end of lactation, cows have low acidity.

The deviation of the natural acidity of milk from the physiological norm affects the technological properties of milk. So, milk with low acidity is impractical to process into cheeses, since it is slowly coagulated by rennet, and the resulting clot is poorly processed.

pH (active acidity) is the concentration of hydrogen ions. It is expressed by the negative logarithm of the concentration of hydrogen ions, denoted by pH. The higher the concentration of H2 ions, the lower the pH value. For normal fresh milk, the pH is 6.47-6.67. This acidity is favorable for the stability of the colloidal system of milk and the development of bacteria. At increased activity acidity, the development of the microorganism slows down, and with a significant decrease in pH, it stops.

TU 6-09-2540-72

TU 6-09-5360-87

TU 25-2024.019-88

TU 27-32-26-77-86

State Pharmacopoeia of the USSR X

5. REDISSION


Amendment published in IMS N 8, 2009

Corrected by the manufacturer of the database

This standard applies to milk and milk and milk-containing products and establishes the following titrimetric methods acidity determination: potentiometric, using phenolphthalein indicator; method for determining the limiting acidity of milk.

The standard does not apply to casein and canned milk.

1. SAMPLING METHODS

1. SAMPLING METHODS

Methods for sampling milk and milk and milk-containing products and preparing them for analysis in accordance with GOST 13928 and GOST 26809.

2. POTENTIOMETRIC METHOD

The method is used when disagreements arise.

The method is based on neutralizing the acids contained in the product with a sodium hydroxide solution to a predetermined pH = 8.9 using an automatic titration unit and indicating the equivalence point using a potentiometric analyzer.

2.1. Equipment, materials and reagents

Potentiometric analyzer with a measuring range of 4-10 units. pH with a scale division of 0.05 units. NS.

Automatic titration unit, hardware-compatible with a potentiometric titrator and having a solution dispenser (burette) with a capacity of at least 5 ml with a graduation value of not more than 0.05 ml.

GOST 24104 *.
_______________
* Since July 1, GOST 24104-2001 has been put into effect (hereinafter).

Glasses V-1-50 TS, V-2-50 TS, V-1-100 TS, V-2-100 TS in accordance with GOST 25336.

Flasks 1-1000-2, 2-1000-2 in accordance with GOST 1770.

Pipettes 2-2-10, 2-2-20 in accordance with GOST 29169.

Cylinders 1-50-1, 1-50-2, 3-50-1, 3-50-2 in accordance with GOST 1770.

GOST 9147.

Sodium hydroxide, standard titer according to TU 6-09-2540, solution with a molar concentration of 0.1 mol / dm3.

Distilled water in accordance with GOST 6709.

It is allowed to use other measuring instruments with metrological characteristics and equipment with technical characteristics not worse, as well as reagents in quality not lower than the above.

2.2. Preparing for measurements

2.2.1. Instrument preparation

Connect the automatic titration unit to the analyzer according to the instructions supplied with the unit. Then connect the unit and the analyzer to the network and warm them up for 10 minutes.

Fill the dispenser of the automatic titration unit with sodium hydroxide solution.

According to the instructions attached to the potentiometric analyzer, adjust it to a pH measurement range that would include pH = 8.9.

According to the instructions supplied with the automatic titration unit, adjust it to the equivalence point equal to 8.9 units. pH, and the unit is set to pH = 4.0, starting from which the sodium hydroxide should be fed dropwise.

Set the holding time after the end of the titration, equal to 30 s.

2.3. Taking measurements

2.3.1. Milk, milk-containing product, dairy compound product, cream, yogurt, acidophilus, kefir, kumis and other fermented milk products

2.3.1.1. In a glass with a capacity of 50 ml, measure 20 ml of distilled water and 10 ml of the analyzed product. The mixture is thoroughly mixed.

When analyzing cream and fermented milk products, transfer the remains of the product from a pipette into a glass by rinsing the pipette with the resulting mixture 3-4 times.

2.3.1.2. A rod of a magnetic stirrer is placed in the beaker and the beaker is placed on the magnetic stirrer. The agitator motor is switched on and the electrodes of the potentiometric analyzer and the dispenser drain tube of the automatic titration unit are immersed into the glass with the product. The "Start" button of the automatic titration unit is turned on, and after 2-3 s, the "Exposure" button is turned on. At the same time, the sodium hydroxide solution begins to flow from the block dispenser into the glass with the product, neutralizing the latter. Upon reaching the equivalence point (pH = 8.9) and expiration of the holding time (30 s), the neutralization process automatically stops, and the "End" signal lights up on the panel of the automatic titration unit. After that, all buttons are turned off. The amount of sodium hydroxide solution consumed for neutralization is counted.

2.3.2. Ice cream, sour cream

5 g of the product is weighed into a glass. Mix the product thoroughly with a glass rod, gradually add 30 cm of water to it and mix. Measurements are carried out in accordance with clause 2.3.1.2.

2.3.3. Curd and curd products

5 g of the product is added to a porcelain mortar. Mix thoroughly and grind the product with a pestle. Then quantitatively transfer the product into a glass with a capacity of 100 ml, washing it off with small portions of water heated to 35-40 ° C. The total volume of water is 50 ml. Then the mixture is stirred and measurements are carried out in accordance with clause 2.3.1.2.

2.4. Processing of results

2.4.1. The acidity in Turner's degrees is found by multiplying the volume, cm3, of the sodium hydroxide solution consumed to neutralize a certain volume of the product, by the following factors:

10 - for milk, milk compound product, cream, yogurt, acidophilic milk, kefir, koumiss and other fermented milk products;

2.4.2. The maximum permissible error of the measurement result at the accepted confidence level = 0.95 is, ° T:

± 0.8 - for milk, dairy compound product, cream, ice cream;

± 1.2 - for yogurt, acidophilic milk, kefir, koumiss and other fermented milk products;

± 2.3 - for sour cream;

± 3.2 - for cottage cheese and curd products.

The discrepancy between two parallel measurements should not exceed, ° T:

1.2 - for milk, dairy compound product, cream, ice cream;

1.7 - for yogurt, acidophilic milk, kefir, koumiss and other fermented milk products;

3.2 - for sour cream;

4.3 - for cottage cheese and curd products.

The arithmetic mean of the results of two parallel determinations is taken as the final measurement result, rounding the result to the second decimal place.

If the discrepancy is greater, the test is repeated with four parallel determinations. In this case, the discrepancy between the arithmetic mean of the results of the four determinations and any value of the four results of the determination should not exceed, ° T:

0.8 - for milk, dairy compound product, cream, ice cream;

1,2 - for curdled milk, acidophilic milk, kefir, koumiss and other fermented milk products;

2.3 - for sour cream;

3.2 - for cottage cheese and curd products.

If the discrepancy is greater, all reagents are prepared anew, state verification of the instruments used is carried out and the test is repeated with four parallel determinations. In this case, if there is a discrepancy greater than the above values, the performance of this work is entrusted to an operator of higher qualifications.

3. METHOD WITH APPLICATION OF PHENOLPHTHALEIN INDICATOR

The method is based on the neutralization of the acids contained in the product with sodium hydroxide solution in the presence of phenolphthalein indicator.

3.1. Equipment, materials and reagents

Laboratory scales of the 4th accuracy class with the maximum weighing limit of 200 g in accordance with GOST 24104.

Centrifuge according to TU 27-32-26-77.

Drying cabinet with thermostat allowing to maintain temperature (50 ± 5) ° С.

Bath water.

Mercury glass thermometer with a measurement range of 0-100 ° C and a graduation of 0.1 ° C in accordance with GOST 28498.

Flasks 1-100-2, 2-100-2, 1-1000-2, 2-1000-2 in accordance with GOST 1770.

Flasks P-2-50-34 TS, P-2-100-34 TS, P-2-250-34 TS, P-2-250-50 in accordance with GOST 25336.

Glasses V-1-100 TS, V-1-250 TS in accordance with GOST 25336.

Funnels V-36-80 XC in accordance with GOST 25336.

Glass butyrometers 1-40; 2-0.5 in accordance with GOST 23094 or TU 25-2024.019.

Pipettes 1-2-1, 2-2-1, 4-2-1, 2-2-5, 2-2-10, 2-2-20 in accordance with GOST 29169.

Cylinder 1-1-100 in accordance with GOST 1770.

Burettes 6-1-10-0.02, 6-2-10-0.02, 7-1-10-0.02, 7-2-10-0.02 according to GOST 29251.

Porcelain mortar with pestle in accordance with GOST 9147.

Glass sticks.

The tripod is laboratory.

Stoppers for butyrometers.

Filter paper in accordance with GOST 12026.

Sodium hydroxide standard-titer according to TU 6-09-2540 solution of molar concentration 0.1 mol / dm3.

Phenolphthalein according to TU 6-09-5360, 70% alcohol solution mass concentration of phenolphthalein 10 g / dm 3.

Cobalt sulfate, solution of mass concentration of cobalt sulfate 25 g / dm 3 according to GOST 4462.

Diethyl ether for anesthesia according to the State Pharmacopoeia of the USSR X.

Distilled water in accordance with GOST 6709.

Rectified ethyl alcohol according to GOST 5962 * or technical ethyl alcohol (hydrolysis) according to GOST 17299, or technical rectified ethyl alcohol according to GOST 18300.
_______________
* On the territory of the Russian Federation, GOST R 51652-2000 is in force.

It is allowed to use other measuring instruments with metrological characteristics and equipment with technical characteristics not worse, as well as reagents of quality not lower than the above.

3.2. Preparation for analysis

3.2.1. Preparation of reference color standards for milk and cream

In a flask with a capacity of 100 or 250 ml, measure milk or cream and distilled water in the volumes indicated in Table 1, and 1 ml of a solution of cobalt sulfate. The mixture is thoroughly mixed.

Table 1

The shelf life of the standard is no more than 8 hours at room temperature.

3.2.2. Preparation of control color standards for a mixture of ethyl alcohol and diethyl ether

To 10 cm of alcohol add 10 cm of diethyl ether and 1 cm of a solution of cobalt sulfate. The mixture is thoroughly mixed.

3.2.3. Preparation of control color standards for butter and butter paste, their fat phase

To 5 g of oil, melted as indicated in clause 3.2.6, add 20 ml of a neutralized mixture of alcohol and ether and 1 ml of a solution of cobalt sulfate. The mixture is stirred.

3.2.4. Preparation of color control standards for butter plasma and butter paste

To 10 ml of plasma prepared as described in clause 3.2.7, add 20 ml of water. The resulting mixture is washed 3-4 times with a pipette and 1 ml of a solution of cobalt sulfate is added. The mixture is stirred.

3.2.5. Preparation of a mixture of ethyl alcohol and diethyl ether

A mixture of ethyl alcohol and diethyl ether is prepared immediately before measuring the acidity of butter and butter paste or its fat phase as follows.

In a flask with a capacity of 50 ml, add 10 ml of alcohol and ether, 3 drops of phenolphthalein and neutralize the mixture with an alkali solution until a faint pink color appears, which does not disappear within 1 min and corresponds to the control standard of color according to clause 3.2.2.

3.2.6. Preparation of the fat phase of butter and butter paste

About 150 g of the test oil is weighed into a dry, clean glass with a capacity of 250 ml. The glass is placed in water bath or an oven at a temperature of (50 ± 5) ° С and incubated until complete melting and separation of the oil into fat and plasma. The glass is removed from the water bath (drying cabinet) and carefully drained upper layer fat, filtering it through a paper filter into a flask with a capacity of 250 ml.

3.2.7. Plasma preparation of butter and butter paste

The remaining plasma in the glass is transferred to the butyrometer 2-0.5. The butyrometer is tightly closed with a stopper, placed in a centrifuge and centrifuged for 5 minutes at a speed of 1000 minutes. Then the butyrometer is placed in a glass with cold water graduated part upwards and incubated until milk fat solidifies, separated from the plasma during centrifugation. The fat-free plasma is carefully poured into a dry, clean 100 ml glass and mixed thoroughly with a glass rod.

3.3. Analysis

3.3.1. Milk, milk-containing product, dairy compound product, cream, yogurt, acidophilus, kefir, kumis and other fermented milk products

3.3.1.1. Distilled water and the analyzed product in the volumes indicated in Table 1 and three drops of phenolphthalein are measured into a flask with a capacity of 100 to 250 ml. When analyzing cream and fermented milk products, transfer the remains of the product from the pipette into the flask by rinsing the pipette with the resulting mixture 3-4 times.

The mixture is thoroughly mixed and titrated with a sodium hydroxide solution until a slightly furrowed coloration appears, for milk and cream, corresponding to the control standard of color according to clause 3.2.1, which does not disappear within 1 min.

For a dairy compound product, for a more accurate determination of the end of titration, a control flask with 10 cm of the same milk sample and 40 cm of distilled water is placed next to the sample to be titrated.

3.3.2. Ice cream, sour cream

3.3.2.1. In uncolored ice cream and sour cream, acidity is determined as follows: 5 g of the product is weighed in a flask with a capacity of 100 or 250 ml, 30 ml of water and three drops of phenolphthalein are added. The mixture is thoroughly mixed and titrated with sodium hydroxide solution until a faint pink color appears, which does not disappear within 1 min.

3.3.2.2. The acidity of colored ice cream is determined as follows: 5 g of ice cream is weighed in a flask with a capacity of 250 cm3, 80 cm3 of water and three drops of phenolphthalein are added. The mixture is thoroughly mixed and titrated with an alkali solution until a faint pink color appears, which does not disappear within 1 min.

To determine the end of the titration of colored ice cream, place the flask with the titrated mixture on White list paper and a flask with a mixture of 5 g of this ice cream sample and 80 cm of water is placed next to it.

3.3.3. Curd and curd products

5 g of the product is added to a porcelain mortar. Mix thoroughly and grind the product with a pestle. Then add in small portions 50 cm of water heated to a temperature of 35-40 ° C and three drops of phenolphthalein. The mixture is stirred and titrated with an alkali solution until a faint pink color appears, which does not disappear within 1 min.

3.3.4. Butter and butter paste, their fat phase, plasma

3.3.4.1. Determination of acidity of butter and butter paste

In a flask with a capacity of 50 and 100 ml, 5 g of butter and butter paste are weighed, the flask is heated in a water bath or an oven at a temperature of (50 ± 5) ° С until the oil melts, add 20 ml of a neutralized mixture of alcohol with ether, three drops of phenolphthalein and titrate with an alkali solution with constant stirring until a slightly pink color appears, which does not disappear within 1 min and corresponds to the control standard of color according to clause 3.2.3.

3.3.4.2. Determination of the acidity of the fat phase of butter and butter paste

In a flask with a capacity of 50 or 100 ml, 5 g of the fat prepared according to clause 3.2.6 is weighed. Then the analysis is carried out as indicated in clause 3.3.4.1.

3.3.4.3. Determination of plasma acidity of butter and butter paste

In a flat-bottomed flask with a capacity of 100 ml, add 10 ml of plasma prepared according to clause 3.2.7, 20 ml of distilled water. The resulting mixture is washed 3-4 times with a pipette, then 3 drops of phenolphthalein are added and titrated with constant stirring with an alkali solution until a faint pink color appears, which does not disappear within 1 min and corresponds to the control standard of color according to paragraph 3.2.4.

3.4. Processing of results

3.4.1. Acidity, in Turner degrees (° T), is found by multiplying the volume, cm, of sodium hydroxide solution spent on neutralizing the acids contained in a certain volume of the product by the following factors:

10 - for milk, dairy compound product, cream, curdled milk, acidophilic milk, kefir, koumiss, other fermented milk products, as well as plasma of butter and butter paste;

20 - for ice cream, sour cream, cottage cheese and curd products.

3.4.2. The acidity of butter and butter paste and their fat phase in Kettstopher degrees (° K) is found by multiplying by two the volume of sodium hydroxide solution used to neutralize the acids contained in 5 g of the product.

3.4.3. The permissible error of the analysis result at the accepted confidence level = 0.95 is:

± 1.9 ° T - for milk, dairy compound product, cream, yogurt, acidophilic milk, kefir, kumis, other fermented milk products and ice cream;

± 2.3 ° T - for sour cream;

± 3.6 ° T - for cottage cheese and curd products;

±

± 0.5 ° T - for butter plasma and butter paste.

The discrepancy between two parallel definitions should not exceed:

2.6 ° T - for milk, dairy compound product, cream, yogurt, acidophilic milk, kefir, kumis, other fermented milk products and ice cream;

3.2 ° T - for sour cream;

5.0 ° T - for cottage cheese and curd products;

0.1 ° K - for butter and butter paste and their fatty phase;

0.6 ° T - for butter plasma and butter paste.

The arithmetic mean of the results of two parallel determinations is taken as the final analysis result, rounding the result to the second decimal place.

If the discrepancy is greater, the test is repeated with four parallel determinations. In this case, the discrepancy between the arithmetic mean of the results of the four determinations and any value of the four results of the determination should not exceed:

1.8 ° T - for milk, dairy compound product, cream, yogurt, acidophilic milk, kefir, koumiss, other fermented milk products and ice cream;

2.3 ° T - for sour cream;

3.6 ° T - for cottage cheese and curd products;

0.1 ° K - for butter and butter paste and their fatty phase;

0.5 ° T - for butter plasma and butter paste.

If the discrepancy is greater, all reagents are prepared anew, state verification of the instruments used is carried out and the test is repeated with four parallel determinations. In this case, if there is a discrepancy greater than the above values, the performance of this work is entrusted to an operator of higher qualifications.

4. METHOD FOR DETERMINING THE LIMITING ACIDITY OF MILK

The method is used when carrying out preliminary sorting of milk, dairy and milk-containing products.

The method is based on neutralizing the acids contained in the product with an excess amount of sodium hydroxide in the presence of the phenolphthalein indicator. In this case, the excess of sodium hydroxide and the intensity of the color in the resulting mixture are inversely proportional to the acidity of the milk.

4.1 Apparatus, materials and reagents

Flasks 1-1000-2, 2-1000-2 in accordance with GOST 1770.
Phenolphthalein according to TU 6-09-5360, 70% solution of phenolphthalein mass concentration 10 g / dm 3.

4.2. Preparation for analysis

To determine the limiting acidity, working solutions are prepared that determine the corresponding degree of acidity.

In a volumetric flask, measure the required volume of sodium hydroxide solution in accordance with the requirements of Table 2, add 10 ml of phenolphthalein and distilled water to the mark.

table 2

4.3. Analysis

In a number of test tubes add 10 ml of sodium hydroxide solution prepared to determine the corresponding degree of acidity.

5 cm of the product is poured into each tube with the solution and the contents of the tube are mixed by inversion.

If the contents of the test tube become discolored, then the acidity of this sample of the product will be higher than the degree corresponding to this solution.

APPENDIX (reference)

APPLICATION
Reference

Turner degrees (° T) mean the volume, cm3, of an aqueous solution of sodium hydroxide with a molar concentration of 0.1 mol / dm3, required to neutralize 100 g (cm) of the test product.

Kettstopher degrees (° C) mean the volume, cm, of an aqueous solution of sodium hydroxide with a molar concentration of 0.1 mol / dm3, required to neutralize 5 g of butter and butter paste or their fat phase, multiplied by 2.

Electronic text of the document
prepared by JSC "Kodeks" and verified by:
official publication
Milk and dairy products.
General methods of analysis: Sat. GOSTs. -
Moscow: IPK Standards Publishing House, 2004

Document revision taking into account
changes and additions prepared
JSC "Codex"