The method is based on the separation of fat from milk under the action of concentrated sulfuric acid and isoamyl alcohol, followed by centrifugation and measurement of the volume of released fat in the graduated part of the butyrometer.

Equipment, materials and reagents

Butyrometers (butyrometers) glass versions 1-6, 1-7; rubber stoppers for butyrometers; pipettes with a capacity of 5.10, 10.77 cm 3; dispensers for measuring sulfuric acid and isoamyl alcohol with a capacity of 1 and 10 cm 3; centrifuge with a rotation frequency of less than 1000 s -1 and not more than 1100 s -1; water bath; butyrometers stand; mercury glass thermometers with a measurement range from 0 to 100 о С, with a division value of 1.0 о С; laboratory scales of the 4th accuracy class; general purpose hydrometer with a measurement range from 700 to 2000 kg / m 3; hourglass for 5 minutes according to normative and technical documentation or a stopwatch; sulfuric acid or technical sulfuric acid; isoamyl alcohol; distilled water.

Measurements

In two milk butyrometers, trying not to moisten the neck, pour 10 cm 3 of sulfuric acid with a dispenser (density from 1810 to 1820 kg / m 3) and carefully so that the liquids do not mix, add 10.77 cm 3 of milk with a pipette, attaching the tip of the pipette to the butyrometer neck at an angle. The milk level in the pipette is set at the lowest point of the meniscus.

Milk should flow slowly from the pipette. After emptying, the pipette is removed from the throat of the butyrometer no earlier than 3 seconds later. Blowing milk out of the pipette is not allowed. 1 cm 3 of isoamyl alcohol (density from 811 to 813 kg / m 3) is added to the butyrometer with a dispenser, trying not to wet the butyrometer neck. The level of the mixture in the butyrometer is set 1-2 mm below the base of the butyrometer neck, for which it is allowed to add a few drops of distilled water if necessary.

The butyrometers are closed with dry plugs, leading them slightly more than half into the butyrometers neck. It is recommended to apply chalk to the surface of the butyrometers stoppers to ensure measurements are taken. The butyrometers are shaken until the protein substances are completely dissolved, turning at least 5 times so that the liquids in them are completely mixed.

Install the butyrometers with the stopper down for 5 minutes in a water bath at a temperature of 65 ± 2 o C. After removing from the bath, insert the butyrometers into the centrifuge beakers with the graduated part towards the center. Butyrometers are arranged symmetrically, one against the other. With an odd number of butyrometers, a butyrometer filled with water instead of milk, sulfuric acid and isoamyl alcohol in the same ratio as for the analysis is placed in the centrifuge

Butyrometers are centrifuged for 5 minutes. Each butyrometer is taken out of the centrifuge and the fat column is adjusted by moving the rubber stopper so that it is in the graduated part of the butyrometer. Butyrometers are immersed with stoppers down for 5 minutes in a water bath at a temperature of 65 ± 2 ° C, while the water level in the bath should be slightly higher than the fat level in the butyrometer.

The butyrometers are taken out one at a time from the water bath and quickly read the fat. When reading, the butyrometer is held vertically, the border of fat should be at eye level. By moving the plug, the lower limit of the fat column is set at zero or a whole division of the butyrometer scale. The number of divisions is counted from it to the lower point of the meniscus of the column of fat with an accuracy of the smallest division of the butyrometer scale. The interface between the fat and the mixture in the butyrometer should be sharp and the fat column should be transparent.

If there is a "ring" (plug) of brownish or dark yellow color, various impurities in the fat column or a blurred lower boundary, the measurement is repeated.

In raw cow's milk, according to the Federal Law "Technical Regulations for Milk and Dairy Products", the mass fraction of fat should be in the range of 2.8-6.0%. The basic rate of fat mass fraction is 3.4%.

The mass fraction of fat in milk is determined after the destruction of the protective shells of the fat globules (Gerber acid method, Rose-Gottlieb extraction method) or without methods using semi-automatic and automatic devices.

The acidic method is considered the standard method and is still widely used in our country and in a number of other countries due to its accuracy, relative simplicity and availability.

Principle of the method: The method is based on the release and separation of fat from fat globules of a milk sample under the action of concentrated sulfuric acid and isoamyl alcohol, followed by its centrifugation.

The introduction of sulfuric acid into the butyrometer not only destroys the protein shells of the fat globules, but also acts on the main protein, calcium caseinate, which falls into flakes and dissolves in excess acid. The reaction is accompanied by an increase in the temperature of the mixture to 70-75 * C.

When isoamyl alcohol is added, it reacts with an acid to form isoamyl sulfuric ester, which spreads in excess of an acidic solution and lowers the surface tension at the interface between fat and milk plasma and promotes fat release.

Heating and subsequent centrifugation of the content of the butyrometer results in complete isolation and consolidation of fat into a continuous layer, the amount of which is measured on the butyrometer scale.

Instruments: devices for automatic metering of sulfuric acid and isoamyl alcohol for 10 and 1 ml, stand for butyrometers, butyrometer for milk with measuring ranges from 0 to 6% or from 0 to 7%, rubber stoppers for butyrometers, pipettes for 10.77 ml , water bath, centrifuge.

Materials for research and reagents: raw milk, sulfuric acid with a density of 1.81-1.82 g / cm 3, isoamyl alcohol 0.811-0.813 g / cm 3.

Analysis progress: clean tested butyrometers are placed in a rack, and 10 ml of sulfuric acid is poured into one of them using an automatic pipette, taking care not to lubricate the neck of the butyrometer. Then, 10.77 ml of the test milk is measured with a pipette, by attaching the tip of the pipette to the inner wall of the butyrometer neck at an angle, let the milk slowly flow down the butyrometer wall so that it does not mix with sulfuric acid, and liquids are layered. The part of the milk remaining in the tip of the pipette should not be blown out, since the volume of the pipette is designed for the free flow of liquid. Then, 1 ml of isoamyl alcohol is poured into the butyrometer using an automatic pipette, avoiding wetting the neck of the butyrometer. Then the butyrometer is closed with a special rubber stopper and turned over 3-4 times to mix liquids, after placing the butyrometer in the cartridge and wrapping it with a napkin, then shake until the proteins are completely dissolved. The butyrometer is placed with a stopper down in a water bath with a temperature of 63-67 * C and kept for 5 minutes. Then they take it out, wipe it and put it in the centrifuge cartridge, the butyrometers are set in a seven-digit and even number, if an odd number, the butyrometer is set with water. The centrifuge is closed with a lid and turned on for 5 minutes. Then the butyrometer is taken out of the centrifuge and placed with the stopper down in a water bath at a temperature of 63-67 * C for 5 minutes. The water level in the water bath must be higher than the liquid in the butyrometer. The butyrometer is removed from the bath, wiped off and quickly read off the scale. To do this, holding the butyrometer vertically at eye level, by moving the plug up and down, set the lower border of the fat column on any whole division and count the number of divisions to the lower point of the meniscus of the fat column. If the fat column does not abruptly separate from the rest of the liquid, the butyrometer must be shaken, placed in a bath with a temperature of 63-67 * C for 5 minutes. Centrifuge and put in the bath again, read the fat content.

Acid method for determining ppm has significant disadvantages: the duration of the definition. The use of expensive reagents, an increased danger for maintenance personnel, the inability to control the fat content of the product in the flow, etc.

The semi-automatic and automatic butyrometers developed in recent years are free from these disadvantages. Their action is based on measuring the degree of light scattering by fat globules or the intensity of their fluorescence, as well as measuring the speed of propagation of ultrasound in milk, the degree of absorption of infrared radiation by milk components, etc.

10 ml of sulfuric acid (density 1.81-1.82) is poured into a pure milk butyrometer, without wetting the neck, and carefully so that the liquids do not mix, add 10.77 ml of milk with a pipette, attaching its tip to the wall of the neck of the butyrometer at an angle ( the milk level in the pipette is set at the lower meniscus level). Blowing out the mast from the pipette is not allowed. Then, 1 ml of isoamyl alcohol (density 0.810-0.813) is added to the butyrometer.

The butyrometer is closed with a dry rubber stopper, inserting it slightly more than

in half, in the neck, turn over 4-5 times until the protein substances are completely dissolved and uniform mixing, after which they are placed with a stopper down for 5 minutes in a water bath with a temperature of 65 + -2 degrees C. Having taken out from the bath, the butyrometers are inserted into the cartridges (glasses) of the centrifuge with the working part towards the center, placing them symmetrically against each other. With an odd number of butyrometers, a butyrometer filled with water is placed in the centrifuge. After closing the centrifuge lid, the butyrometers are centrifuged for 5 minutes at a speed of at least 1000 rpm. Then each butyrometer is removed from the centrifuge and rubber-

howling plugs adjust the fat column in the butyrometer so that it is in the tube with a scale. Then the butyrometers are re-immersed with their plugs down in a water bath at a temperature of 65+ - 2 ° C. After 5 minutes, the butyrometers are removed from the water bath and the fat is quickly counted. For this, the butyrometer is held vertically with the fat border at eye level. By moving the plug up and down, set the lower limit of the fat column on the whole division of the butyrometer scale and from it the number of divisions is counted to the lower level of the meniscus of the fat column. The interface between fat and acid should be sharp, and the fat column should be transparent.

If there is a ring (plug) of brownish or dark yellow color, as well as various impurities in the fat column, the analysis is repeated.

The butyrometer reading corresponds to the percentage of fat in the milk.

The volume of 10 small scale divisions on the milk butyrometer corresponds to 1% fat in the product. The fat count is carried out with an accuracy of one small division of the butyrometer. The discrepancy between parallel determinations should not exceed 0.1% fat.

The arithmetic mean of two parallel determinations is taken as the final result.

Determination of protein content in milk

10 ml of milk, 10-12 drops of a 1% alcoholic solution of phenolphthalein are poured into a flask, and 0.1 N HCI is added dropwise. sodium hydroxide solution until a pale pink color appears, which does not disappear when shaken. Then add 2 ml of neutral (phenolphthalein) formalin and titrate with 0.1 N. sodium hydroxide solution until a pale pink color appears, which does not disappear within a minute. The amount of alkali used for titration after the addition of formalin is multiplied by a factor of 1.92 and the total protein content in milk is obtained, and by multiplying by a factor of 1.51, the casein content (in%) is determined.

Determination of bacterial contamination of milk

(reductase test)

Bacteriological examination of milk. For bacteriological research

using an accelerated test for reductase, take 10 ml of milk, heat it in a water bath to 38-40 ° C and add 1 ml of a working solution of methylene blue. The tubes are closed with sterile rubber stoppers, mixed thoroughly and placed again in a water bath at a temperature of 38-40 ° C (the water level in the bath must be higher than the level of the contents of the tube).

At the time of the onset of milk discoloration, the bacterial

contamination and class of milk according to the table.

For control, put the same sample of milk in a test tube, but without adding

methylene blue, which is viewed 10 minutes and 1 hour after sample setting.

_______________________________________________________________________________

Discoloration rate Bacteria count Milk grade and grade

in 1 ml of milk

____________________________________________________________________

Less than 10 minutes More than 20 million IV, very poor

From 10 minutes to 1 hour Up to 20 million III, poor

1 hour to 3 hours Up to 4 million II, satisfactory

More than 3 hours Up to 500 thousand I, good

Note. To prepare a saturated alcoholic solution of methylene blue, take 10 g and mix with 100 ml of 96% ethyl alcohol.

The solution is placed in a thermostat at 37 0 C for 24 hours, then filtered.

To prepare a working solution of methylene blue, take 5 ml of saturated

an alcoholic solution of methylene blue + 195 ml of distilled water, and then this solution is diluted 10 times, i.e. 1 ml of a 2.5% solution + 9 ml of distilled water. The solution must be prepared prior to sampling.

Milk test for brucellosis

In the study of milk with a ring test for brucellosis, 1 ml of milk and 1 drop of colored brucellosis antigen (a suspension of brucellosis stained with hematoxylin) are poured into a test tube with a diameter of 5 - 8 mm and placed in a thermostat at 37 degrees. C for 40 - 45 minutes. A positive reaction is characterized by the appearance of a blue ring in the upper layer of the liquid, with a dubious reaction, a weakly colored bluish ring, and with a negative one, no changes occur.

MILK FALSIFICATION AND METHODS OF ITS DETECTION

Control of milk pasteurization

Peroxidase test:

5 ml of pasteurized milk is poured into a test tube, 5 drops of starch solution KCl and 5 drops of 0.5% solution of hydrogen peroxide are added. The contents are mixed. If the color of the contents of the tube has not changed, then the milk is pasteurized correctly. A blue staining of the contents of the test tube indicates that the milk is not pasteurized or raw milk has been added to the correctly pasteurized milk.

Lactoalbumin test:

Used to establish pasteurization at temperatures above 80 ° C.

In a flask, mix 5 ml of pasteurized milk and 20 ml of water, add 3 ml of 0.1 N solution of sulfuric acid to precipitate casein and filter. 5 ml of filtrate is added to a test tube and boiled. If milk is pasteurized at 80 ° C, then when it is boiled, albumin flakes are not formed, and when the filtrate is cooled, there will be no sediment.

(approved by the Decree of the USSR State Committee on Product Quality Management and Standards dated July 26, 1990 N 2293)

Edition of 07.26.1990 - Effective from 01.07.1991

INTERSTATE STANDARD

MILK AND DAIRY PRODUCTS

METHODS FOR DETERMINING FAT

Milk and dairy products.

Method of determination of fat

GOST 5867-90

ISS 67.100.10

Group H19

Introduction date 1991-07-01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the All-Union Scientific Research and Design Institute of the Dairy Industry (VNIKMI), the Scientific and Production Association of the Butter and Cheese Industry "Uglich" (NPO Uglich), the Union Scientific Research Institute of Instrument Engineering (SNIIP)

DEVELOPERS

Ya.I. Kostin, Cand. tech. sciences; O. A. Geraimovich, I. R. Davydova, Cand. chem. sciences; YY Sviridenko, Cand. tech. sciences; Yu.P. Andrianov, Cand. tech. sciences; N.V. Smurygina; A.Yu.Ber, Cand. tech. sciences; L.A. Dyachenko, Cand. tech. sciences

2. APPROVED AND PUT INTO EFFECT by the Decree of the USSR State Committee for Product Quality Management and Standards dated July 26, 1990 N 2293

3. The standard corresponds to ST SEV 3838-82 in terms of determining the mass fraction of fat in cheese

4. REPLACE GOST 5867-69, GOST 6822-67 in part of clause 2.2

5. REFERENCE REGULATORY AND TECHNICAL DOCUMENTS

6. The limitation of the period of validity has been removed according to protocol N 4-93 of the Interstate Council for Standardization, Metrology and Certification (IUS 4-94)

7. REDISSION

This standard applies to milk, milk drink, dairy and milk-containing products, fermented milk products, cheese and cheese products, butter and butter paste, butter-vegetable spread and butter-vegetable ghee, ice cream and establishes methods for determining the mass fraction of fat: acidic in milk and dairy products, turbidimetric in raw milk and extraction in rennet and processed cheeses.

The standard does not apply to casein, canned dairy products and dry dairy products.

1. METHODS OF SAMPLING

Sampling of milk and dairy products and their preparation for analysis - in accordance with GOST 13928, GOST 3622 and GOST 26809.

2. ACID METHOD

The method is based on the separation of fat from milk, milk drink, dairy and milk-containing products, fermented milk products, cheese and cheese products, butter and butter paste, butter-vegetable spread and butter-vegetable ghee, ice cream under the action of concentrated sulfuric acid and isoamyl alcohol with subsequent centrifugation and measurement of the volume of released fat in the graduated part of the butyrometer.

2.1 Apparatus, materials and reagents

Butyrometers (butyrometers) glass versions 1-6, 1-7, 1-40, 2-0.5, 2-1.0 in accordance with GOST 23094 or TU 25-2024.019.

Rubber plugs for butyrometers according to TU 38-105-1058.

Pipettes 2-1-5, 3-1-5, 6-1-10, 7-1-10 and 2-1-10, 77 according to GOST 29169.

The pear is rubber.

Instruments (dispensers) for measuring isoamyl alcohol and sulfuric acid with a capacity of 1 and 10 cm3, respectively, in accordance with GOST 6859.

Centrifuge for measuring the mass fraction of fat in milk and dairy products according to the normative and technical documentation with a rotation frequency of no less and no more.

Baths are water, ensuring the maintenance of temperature (65 ± 2) ° С and (73 ± 3) ° С.

Stand for butyrometers.

Mercury glass thermometers with a measuring range from 0 to 100 ° C, with a graduation of 0.5 and 1.0 ° C in accordance with GOST 28498.

Laboratory scales of the 4th accuracy class with the maximum weighing limit of 200 g according to GOST 24104<*>.

<*> On July 1, 2002, GOST 24104-2001 was put into effect (hereinafter).

Cylinder 1-50, 1-100 in accordance with GOST 1770.

General purpose hydrometer with a measurement range from 700 to 2000 kg / m3 in accordance with GOST 18481.

Sandglass clock for 5 minutes or stopwatch according to normative and technical documentation.

Sulfuric acid according to GOST 4204 or technical sulfuric acid according to GOST 2184 (vitriol oil of contact and concentration systems).

Isoamyl alcohol according to GOST 5830 or technical isoamyl alcohol, grade A.

2.2. Measurements

2.2.1. Milk (raw, pasteurized of various types, except skim, sterilized, for baby food and milk drink)

2.2.1.1. In two milk butyrometers (types 1 - 6 or 1 - 7), trying not to moisten the throat, pour 10 cm3 of sulfuric acid with a dispenser (density from 1810 to 1820 kg / m3) and carefully so that the liquids do not mix, add 10 with a pipette, 77 cm3 of milk by attaching the tip of the pipette to the throat of the butyrometer at an angle. The milk level in the pipette is set at the lowest point of the meniscus.

Milk should flow slowly from the pipette. After emptying, the pipette is removed from the butyrometer neck no earlier than 3 seconds later. Blowing milk out of the pipette is not allowed. 1 cm3 of isoamyl alcohol is added to the butyrometers with a dispenser.

The level of the mixture in the butyrometer is set 1 - 2 mm below the base of the butyrometer neck, for which it is allowed to add a few drops of distilled water.

It is recommended to use weighing when dosing the sample to improve the measurement accuracy, especially for low density milk. In this case, 11.00 g of milk is first weighed with a count of 0.005 g, then sulfuric acid and isoamyl alcohol are added.

2.2.1.2. The butyrometers are closed with dry stoppers, injecting them slightly more than half into the butyrometers neck. The butyrometers are shaken until the protein substances are completely dissolved, turning at least 5 times so that the liquids in them are completely mixed.

2.2.1.3. Place the butyrometers with the plug facing down for 5 min in a water bath at a temperature of (65 ± 2) ° C.

2.2.1.4. Having taken out from the bath, the butyrometers are inserted into the centrifuge beakers with the graduated part towards the center. Butyrometers are arranged symmetrically, one against the other. With an odd number of butyrometers, a butyrometer filled with water instead of milk, sulfuric acid and isoamyl alcohol in the same ratio as for the analysis is placed in the centrifuge.

Butyrometers are centrifuged for 5 minutes. Each butyrometer is taken out of the centrifuge and the fat column is adjusted by moving the rubber stopper so that it is in the graduated part of the butyrometer.

2.2.1.5. Butyrometers are immersed with stoppers down for 5 minutes in a water bath at a temperature of (65 ± 2) ° С, while the water level in the bath should be slightly higher than the fat level in the butyrometer.

2.2.1.6. The butyrometers are taken out one at a time from the water bath and quickly read the fat. When reading, the butyrometer is held vertically, the border of fat should be at eye level. By moving the plug, the lower limit of the fat column is set at zero or a whole division of the butyrometer scale. The number of divisions is counted from it to the lower point of the meniscus of the column of fat with an accuracy of the smallest division of the butyrometer scale.

The interface between fat and acid should be sharp, and the fat column should be transparent. If there is a "ring" (plug) of brownish or dark yellow color, various impurities in the fat column or a blurred lower boundary, the measurement is repeated.

2.2.1.7. When analyzing homogenized or reconstituted milk, the determination of the mass fraction of fat in it is carried out in accordance with the above requirements, but three times centrifugation and heating are carried out between each centrifugation in a water bath at a temperature of 65 ± 2 ° C for 5 min.

When using a centrifuge with heated butyrometers, one centrifugation is allowed for 15 minutes, followed by holding in a water bath at a temperature of (65 ± 2) ° С for 5 minutes.

2.2.2. Fermented milk products (kefir, yogurt, fermented baked milk, acidophilus, sour cream, cottage cheese, curd products, etc., including fermented milk products for baby food), cream, ice cream.

Determination of fat is carried out in accordance with clauses 2.2.1.1 - 2.2.1.7, the requirements specified in Table 1, and the following additional conditions:

sequence of operations when filling the butyrometer - weighing the product into the butyrometer counting down to 0.005 g, adding water (if necessary), sulfuric acid and isoamyl alcohol;

sulfuric acid is added to the butyrometer with water carefully, slightly tilting the butyrometer;

when determining fat in cream, sour cream, cottage cheese, curd products and ice cream, heating the butyrometers with the test mixture before centrifugation is carried out in a water bath with frequent shaking until the protein is completely dissolved;

when determining fat in cream, sour cream and milk ice cream, the level of the mixture in the butyrometer is set at 4 - 5 mm below the base of the butyrometer neck, when determining fat in cream ice cream and ice cream - by 6 - 10 mm.

Table 1

2.2.3. Cheese (rennet and processed) and cheese products

2.2.3.1. The measurement conditions correspond to the requirements of Table 1.

1.50 g of cheese is weighed into two butyrometers, counting down to 0.005 g, then 10 cm3 of sulfuric acid is poured in with a dispenser, and (9 ± 1) cm3 is added so that the liquid level is 4 to 6 mm below the base of the butyrometer neck. 1 cm3 of isoamyl alcohol is added to the butyrometers with a dispenser. Butyrometers are closed with stoppers and placed in a water bath at a temperature of (65 ± 2) ° C. Butyrometers are kept in a water bath with frequent shaking until the protein is completely dissolved within (60 ± 10) min.

In the case of incomplete dissolution of the protein within the specified time, it is allowed to set the temperature of the water bath (73 ± 3) ° C upon repeated determination. The reading of the butyrometer readings is carried out after a five-minute exposure of the butyrometer in a water bath at a temperature of (65 ± 2) ° C.

2.2.4. Butter

2.2.4.1. Non-filler oil

The mass fraction of fat in oil is found by calculation (see clause 2.3.5).

2.2.4.2. Filled Oil and Filled Oil Paste

The measurement conditions correspond to the requirements of Table 1.

In two butyrometers, 2.50 g of oil are weighed, counting down to 0.005 g, 10 cm3 of sulfuric acid is poured in with a dispenser, and (6 ± 1) cm3 of sulfuric acid is added so that the liquid level is 4 to 6 mm below the base of the butyrometer neck.

1 cm3 of isoamyl alcohol is added to the butyrometers with a dispenser. Close the butyrometers with stoppers and place them in a water bath at a temperature of (65 ± 2) ° C. Butyromeres are kept in a water bath with frequent shaking until the protein is completely dissolved. Further measurements are carried out in accordance with clauses 2.2.1.5 - 2.2.1.6.

2.2.5. Skim milk, buttermilk

2.2.5.1. The measurement conditions correspond to the requirements of Table 1.

2.2.5.2. Sulfuric acid is measured into two butyrometers, the necks of which are closed with stoppers on the side of the graduated part, carefully, trying not to wet the neck. Then the test product is measured into each butyrometer using a pipette with a capacity of 10.77 cm3 (2 times), carefully pouring it along the wall of the butyrometer.

2.2.5.3. 2 cm3 of isoamyl alcohol is added to the butyrometers with a dispenser.

2.2.5.4. The butyrometers are closed with large plugs and shaken until the protein substances are completely dissolved, turning over from time to time.

2.2.5.5. Butyrometers are installed with a large plug down for 5 min in a water bath at a temperature of (65 ± 2) ° C.

2.2.5.6. Having taken out from the bath, the butyrometers are installed in the centrifuge with the graduated part towards the center. Centrifuge three times for 5 minutes or twice for 10 minutes. Between centrifugation, the butyrometers are thermostated for 5 min in a water bath at a temperature of (65 ± 2) ° C.

2.2.5.7. After the first centrifugation, to facilitate the regulation of the fat level in the butyrometer, the small plug is slightly opened without removing it completely. Using a large plug, set the upper liquid level in the graduated part of the butyrometer. The smaller hole is then closed tightly.

Usually, no noticeable fat separation is observed after the first centrifugation.

After a second centrifugation and incubation in a water bath, check the position of the liquid level.

2.2.5.8. After the third centrifugation, remove the small plugs from the butyrometers, place them for 5 min in a water bath at a temperature of (65 ± 2) ° С and make sure that the liquid level does not rise above the scale divisions.

2.2.5.9. Taking the butyrometer out of the bath and adjusting the large stopper, set the lower limit of fat at zero or the nearest whole scale division and quickly read the fat.

2.2.6. Serum

2.2.6.1. To purify whey from protein particles, the sample is heated to (35 ± 5) ° С and filtered through a cotton filter or through at least three layers of gauze.

2.2.6.2. In serum after separation, the measurement of the mass fraction of fat is carried out in the same way as the measurement of the mass fraction of fat in low-fat milk in accordance with the requirements of clause 2.2.5 and Table 1.

2.3. Processing of results

2.3.1. For the measurement result, the arithmetic mean of the results of two parallel observations is taken, the discrepancy between which (convergence) does not exceed the values \u200b\u200bindicated in Table 1.

2.3.2. Butyrometer readings for measurements in milk, incl. low-fat; fermented milk products, incl. sour cream, cottage cheese; cream (with a mass fraction of fat not more than 40%), ice cream, ice cream, buttermilk and whey correspond to the mass fraction of fat in these products in percent.

2.3.3. The mass fraction of fat X,%, in milk ice cream and cheese is calculated by the formula

in cream with a fat mass fraction of more than 40% and in butter with fillers according to the formula

where Р is the result of measurements according to clause 2.3.1,%;

M is the weight of the sample, g;

11 and 5 are the weights of the weighed portions of the products that are used to calibrate butyrometers (11 - for butyrometers 1 - 6; 1 - 7; 5 - for butyrometers 1-40), g

2.3.4. The mass fraction of fat in cheese and cheese product in terms of dry matter,%, is calculated by the formula

where B is the mass fraction of moisture in cheese and cheese product, determined in accordance with GOST 3626,%;

2.3.5. Mass fraction of fat in oil without fillers and,%, is calculated by the formulas:

where is the mass fraction of fat in oil and butter paste without fillers of all types, except salted,%;

B - mass fraction of moisture in oil, determined in accordance with Section 6 of GOST 3626 (production method),%;

Mass fraction of fat in salted oil,%;

С - mass fraction of defatted dry matter in oil, determined according to GOST 3626,%;

Mass fraction of salt in oil, determined in accordance with Section 6 of GOST 3627 (production method),%;

100 - conversion factor of the mass fraction of fat per 100 g of the product.

2.3.6. The limits of the permissible error of the measurement results at a confidence level of 0.90 correspond to the data in Table 2.

table 2

3. OPTICAL (TURBIDIMETRIC) METHOD FOR DETERMINING THE MASS FAT IN MILK AND MILK DRINK

The method is based on photometric measurement of the degree of attenuation of the radiant flux of light scattering by a layer of fat globules of milk, milk drink.

3.1. Equipment, materials and reagents

A device for determining the mass fraction of fat TsZhM-1 according to TU 10-11-299.

Laboratory scales of the 4th class of accuracy with the highest weighing limit of 200 g according to GOST 24104.

Flask 1-1000-2, 2-1000-2, 1-2000-2, 2-2000-2 in accordance with GOST 1770.

Funnel V-75-140 XC, V-100-150 in accordance with GOST 25336.

Cylinder 1-100 in accordance with GOST 1770.

Flask KN-1-3000-34 / 35TS in accordance with GOST 25336.

Pipettes 2-2-2, 3-2-2, 2-2-5, 3-2-5 in accordance with GOST 29169.

Mercury glass thermometers with a measurement range from 0 to 100 ° C, with a graduation of 1 ° C in accordance with GOST 28498.

Bath water.

Heating device for a water bath.

A glass of SV in accordance with GOST 25336.

A bottle with a capacity of 10 dm3 according to OST 6-09-108.

Plastic cups with lids.

Universal indicator paper for measuring pH in the range of 9 - 10, according to regulatory and technical documentation.

Trilon B according to GOST 10652 or according to the normative and technical documentation, analytical grade

Sodium hydroxide in accordance with GOST 4328 or according to the technical and standard documentation of chemically pure grade. or ch.d.

Auxiliary substance OP-7 in accordance with GOST 8433 or emulsifier sintanol DS-6 in accordance with regulatory and technical documentation.

Potassium dichromate according to GOST 4220, chemically pure grade

Antifoam AS-60 or antifoam propynol B-400 according to the technical specifications.

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.

3.2. Test preparation

3.2.1. Solvent preparation

3.2.1.1. Weighed portions - 45 g of Trilon B and 7.6 g of sodium hydroxide are weighed counting down to 0.1 g.

Weighed portions or 45 g of Trilon B and 7.6 g of sodium hydroxide from the consumer container are completely transferred into the flask, dissolved in 3 dm3 of distilled water, boiled for 15 minutes and cooled to a temperature of (20 ± 2) ° C. The solution in the flask is thoroughly mixed until the reagents are completely dissolved and poured into a bottle with a capacity of 10 dm3, which is pre-graduated using a volumetric flask and a mark is made for a volume of water of 10 dm3 at a temperature of (20 ± 2) ° С.

3.2.1.2. The auxiliary substance OP-7 is heated in a water bath at a temperature of 35 to 40 ° C to a liquid consistency. Using a pipette, 5 cm3 of the auxiliary substance is transferred into a flask with a capacity of 3 dm3 and dissolved in 2 dm3 of distilled water, boiled for 15 minutes and cooled to a temperature of (20 ± 2) ° C. The solution is poured into a glass bottle with a capacity of 10 dm3, in which Trilon B and sodium hydroxide are dissolved.

3.2.1.3. 2 cm3 of antifoam AS-60 is dissolved in 2 dm3 of distilled water heated to a temperature of 70 - 80 ° C, containing an auxiliary substance OP-7, and the solution is poured into the same glass bottle with a capacity of 10 dm3.

3.2.1.4. In the absence of components for the preparation of the solution according to clauses 3.2.1.2 - 3.2.1.3, it is prepared as follows: 3.6 g of a mixture of the emulsifier sintanol DS-6 and antifoam agent propinol B-400 from consumer containers (sintanol DS-6 3 g, propynol B -400 0.6 g) is placed in a glass with a volume of distilled water from 25 to 30 cm3, boiled for 15 minutes and cooled to a temperature of (6 ± 2) ° C. For complete dissolution of the reagents, the mixture is thoroughly mixed. The solution from the glass is completely transferred into a flask with a capacity of 3 dm3 and 2 dm3 of distilled water, boiled for 15 minutes and cooled to a temperature of (6 ± 2) ° C, is added. The solution is stirred until the components are completely dissolved and poured into a bottle with a capacity of 10 dm3, in which Trilon B and sodium hydroxide are dissolved.

3.2.1.5. The volume of the solution in the bottle is brought to 10 dm3, cooled to a temperature of (20 ± 2) ° С, boiled for 15 min with distilled water. Using a universal indicator paper, check the pH of the solution, which should be in the range of 9.5 - 10.0. If the pH of the solution is not within the specified limits, then a mistake was made in the preparation of the solution and a new solution should be prepared.

The solution should be used no earlier than 24 hours after preparation. The solution is stored in a dark place in a tightly closed bottle for no more than 4 weeks at a temperature not exceeding 25 ° C.

3.2.2. Requirements for verification and control of the metrological characteristics of the device during operation

3.2.2.1. After installation and repair, the device is subject to mandatory verification.

3.2.2.2. Periodic verification of the device to confirm the correctness of the readings of the mass fraction of fat on the device is carried out at least once a quarter.

3.2.2.3. The device must be checked by the gravimetric method in accordance with GOST 22760 or by the acid method specified in this standard.

3.2.2.4. The device is subject to mandatory daily control during operation. In case of replacement of reagents, detection and correction of malfunctions in operation, the device is also subject to mandatory control.

3.2.3. Instrument calibration

3.2.3.1. To calibrate the device, prepare milk and milk drink samples in the range of fat mass fraction values \u200b\u200bfrom 0 to 6.5%. Samples are prepared from one batch of bulk milk, milk drink. To do this, fresh milk, milk drink is cooled to a temperature not higher than 6 ° C and kept for 7-10 hours to settle the cream. A sample of milk, a milk drink with a low mass fraction of fat, is obtained by sampling milk, a milk drink from the bottom of the vessel, and with a high one from the upper layer. By mixing these two samples of milk, milk drink in certain proportions, samples with a mass fraction of fat in the entire determined range are obtained.

In each sample, two parallel determinations are carried out in accordance with GOST 22760 or four parallel determinations, if the acid method specified in this standard is used as a control. The difference between parallel determinations should not be more than 0.03% when measuring fat by the method according to GOST 22760 or 0.1% when measuring fat by the acid method specified in this standard. The arithmetic mean of the parallel determinations is calculated.

3.2.3.2. To calibrate the device, prepare at least five samples of milk, milk drink with different mass fraction of fat corresponding to the measurement range. In each sample, the mass fraction of fat is determined by control methods in accordance with clause 3.2.3.1 and on the device. The instrument is adjusted according to the results of measuring these samples. The samples are heated in a water bath to a temperature of (40 ± 2) ° С, mixed thoroughly, avoiding the formation of bubbles. Then determine the mass fraction of fat in the sample on the device in five replicates. It is necessary to determine the mass fraction of fat in calibration samples in order of gradual increase in fat content. The result of the first measurement is discarded, and the arithmetic mean is determined from the remaining four measurements.

The device can be calibrated by samples of fresh or canned milk, milk drink.

3.2.4. Checking the device

3.2.4.1. For periodic verification of the operation of the device, samples are prepared in accordance with clause 3.2.3.1 and the mass fraction of fat is determined according to clause 3.2.3.2.

3.2.4.2. The difference between the measurements of the mass fraction of fat in the samples analyzed on the device and the control method according to GOST 22760 should be no more than ± 0.06%, and the control acid method specified in this standard should be no more than ± 0.11%. If, during verification, the difference between the average values \u200b\u200bof the mass fraction of fat in the samples measured on the device and by control methods is more than indicated, then the device is adjusted. Then, repeated determinations of the mass fraction of fat are carried out on the device in those samples of milk, milk drink, in which the mass fraction of fat was determined before adjusting the device.

3.2.5. Daily control of the calibration of the device

3.2.5.1. For daily control of the calibration of the device, prepare two samples of fresh natural bulk milk, a milk drink with a low and high mass fraction of fat and determine the mass fraction of fat on the device and the control method according to GOST 22760 or the acid method specified in this standard, in accordance with clause 3.2. .3.1. The samples are preserved with potassium dichromate, adding it in such an amount that its mass concentration is 1 g / dm3.

3.2.5.2. Each sample of canned milk, milk drink (at least 30 cm3) is poured into weighing cups or plastic cups with lids, or bottles with corks of 50 or 100 cm3 capacity. Samples of milk, milk drink, tightly closed, are stored for three days.

3.2.6. Instrument control

3.2.6.1. Every day before work, they check the correct operation of the device. Heat in a water bath to a temperature of (40 ± 2) ° С for one bottle of milk, milk drink with a low and high mass fraction of fat. Mix the samples thoroughly to avoid the formation of bubbles. Then determine the mass fraction of fat in the sample on the device in four replicates.

3.2.6.2. The arithmetic mean of the mass fraction of fat is determined from the last two measurements.

The difference in the analysis results between the control and instrumental methods must comply with clause 3.2.4.2. In case of non-compliance with the requirements of clause 3.2.4.2, the device is adjusted using adjusting devices.

3.2.6.3. It is allowed to use devices to attenuate the radiant flux during testing.

3.3. Testing

3.3.1. Before starting the test, the device is connected to the network 1 hour before operation.

3.3.2. After the solvent has been sucked in, the readings from 0 to 0.05% are set on the reading device of the device.

3.3.3. The correctness of the readings of the device is checked in accordance with clause 3.2.5.

3.3.4. Then the device is checked for the convergence of the results by fourfold measurement of the mass fraction of fat in milk samples, milk drink with low and high fat content. The discrepancy between the last three measurements for one sample should not exceed ± 0.05% fat.

3.3.5. Prepared for testing, heated to (40 ± 2) ° C, a sample of milk, milk drink enters the mixer, where it is mixed with the solvent. Then the mixture is homogenized and fed into a photometric cuvette. The radiation transmitted through the mixture layer is photometric. The fat mass fraction is counted on the scale of the device.

3.4. Processing of results

3.4.1. Readout of readings is carried out on a scale or digital indicator with a readout resolution of not more than 0.01% of the mass fraction of fat.

3.4.2. It is necessary to carry out two measurements of the mass fraction of fat in the same sample of milk, milk drink. If the readings differ by no more than 0.05%, then the arithmetic mean of the two measurements, rounded to 0.01%, is taken as the final result. If the discrepancy between the readings is more than 0.05%, a third measurement is taken. The final result is the arithmetic mean of two measurements that differ by no more than 0.05%. The limit of the admissible value of the systematic component of the error (the difference in the average values \u200b\u200bof the measurement results) of the turbidimetric method is ± 0.1% at \u003d 0.95 in comparison with the method specified in GOST 22760 for combined natural milk, milk drink. The limit of the permissible value of the standard deviation of the random component of the error of the method when measuring the same sample of combined natural milk, milk drink is 0.02% (based on the results of single measurements).

The systematic component of the device error is not more than:

in the range (0.10 - 0.99)% ± 0.06%;

in the range (1.00 - 6.50)% ± 0.10%.

The root-mean-square deviation of the random component of the error of the device is not more than:

in the range (0.10 - 0.99)% - 0.03%;

in the range (1.00 - 6.50)% - 0.05%.

The root-mean-square deviation of the random component of the error of the device when measuring the same sample of combined natural milk, milk drink with a mass fraction of fat in the range (0.10 - 6.50)% is not more than 0.02%.

4. EXTRACTION METHOD FOR DETERMINING THE MASS FAT PART OF FAT IN ROUGH AND MELTED CHEESE AND CHEESE PRODUCTS

The method is used when disagreements arise in assessing the quality of the product.

The essence of the method consists in processing the cheese with hydrochloric acid, adding alcohol and then extracting the fat from the acid-alcohol mixture with diethyl and petroleum ethers, evaporating the solvents and weighing the residue (the Schmidt-Bonzinski-Ratzlav principle).

4.1. Equipment, materials and reagents

Lever laboratory scales of the 2nd class of accuracy with the maximum weighing limit of 200 g in accordance with GOST 24104.

Mercury glass thermometers with a measurement range from 0 to 100 ° C with a graduation of 1 ° C in accordance with GOST 28498.

Centrifuge according to the normative and technical documentation, providing centrifugal acceleration from 700 to 900 m / s2.

A laboratory drying cabinet, providing temperature control (102 ± 2) ° С, well ventilated, or a vacuum drying cabinet, providing temperature control from 70 to 75 ° С and a pressure of 6650 Pa.

Desiccator according to GOST 25336.

Bath water.

Extraction flask equipped with a glass ground stopper.

It is allowed to use cork plugs in accordance with GOST 5541, treated first with diethyl, then with petroleum ether, kept for at least 20 minutes in water at a temperature of (60 ± 2) ° С and cooled in water to saturate before use.

Electric tiles in accordance with GOST 14919.

Laboratory glass flat-bottomed flasks with a capacity of 150 to 250 cm2 in accordance with GOST 1770.

Glass balls or pieces of porcelain, or pieces of carborundum, or other material that improves the boiling effect, fat-free, non-porous, not crumbling during use.

A glass for weighing in accordance with GOST 25336 or watch glass.

Porcelain mortar.

Cellulose film, unvarnished and soluble in hydrochloric acid, which does not affect the test results, thickness (0.004 ± 0.001) cm, width (5.0 ± 0.1) cm, length (7.5 ± 0.1) cm.

Hydrochloric acid, analytical grade, density 1.125 g / cm3 in accordance with GOST 3118.

Rectified technical ethyl alcohol according to GOST 18300.

Diethyl ether according to GF IX, without peroxides.

Petroleum ether according to the normative and technical documentation, with a boiling point from 30 to 60 ° C.

Drinking water in accordance with GOST 2874<*>.

<*> GOST R 51232-98 is in force on the territory of the Russian Federation.

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.

4.2. Test preparation

4.2.1. The selected cheese sample is crushed, placed in a porcelain mortar and mixed thoroughly.

4.2.2. Dry the flask in an oven (or vacuum drying) for (45 ± 15) min, after placing a small amount of glass beads or pieces of porcelain or pieces of carborundum in it. The flask is then cooled in a desiccator and weighed to 0.0001 g.

4.2.3. Immediately before use, prepare a mixed solvent from equal volumes of diethyl and petroleum ethers.

4.3. Testing

4.3.1. About 2 g of the crushed cheese sample is placed in a weighing bottle or on a watch glass, weighed up to 0.0001 g and transferred to a dry flat-bottomed flask or extraction flask.

A sample of cheese for testing is allowed to be weighed on cellulose film, which is then folded up and placed in a flask together with the sample of cheese.

4.3.2. Pour (9 ± 1) cm3 of hydrochloric acid into the flask with the test sample and keep it in a boiling water bath with constant shaking until the cheese is completely dissolved. After that, the flask is kept in a boiling water bath for 20 min and cooled to a temperature of (20 ± 2) ° С in cold tap water.

4.3.3. If the processing of cheese with hydrochloric acid is carried out in an extraction flask, then 10 cm3 of ethyl alcohol is poured into it and carefully mixed.

If the processing of cheese with hydrochloric acid was carried out in a flat-bottomed flask, then the sample treated with hydrochloric acid is transferred to an extraction flask, rinsing the original container successively with 10 cm3 of ethyl alcohol, 25 cm3 of diethyl ether and 25 cm3 of petroleum ether, collecting the washing liquid in the extraction flask.

After adding 25 cm3 of diethyl ether, the extraction flask is closed with a ground stopper, shaken vigorously with constant inversion for 1 min. Then carefully remove the stopper and add 25 cm3 of petroleum ether to the flask, using the first 5-10 cm3 to rinse the stopper and the inside of the neck of the flask. Then close the flask with a ground stopper and shake with constant inversion for 30 s.

4.3.4. Leave the flask alone until the upper liquid layer is clean and clearly separated from the lower layer. If a clear separation of the layers is not achieved, the liquid is centrifuged using an extraction flask.

4.3.5. Remove the stopper, rinse it and the inner surface of the neck of the flask with 5-10 cm3 of mixed solvent so that it flows into the flask. Thereafter, the top layer is carefully transferred by decantation or by means of a siphon tube into a flat-bottomed flask prepared in 4.2.2.

If the top layer is transferred by decantation, a small amount of water can be added to improve the separation of the layers.

Rinse the outer and inner surfaces of the neck of the flask or the tip and bottom of the siphon tube with 5-10 cm3 of mixed solvent, while the solvent from the outside of the neck of the extraction flask should drain into the flat-bottomed flask, and from the inside into the extraction flask.

4.3.6. A second extraction is carried out by repeating the operations described above and while adding 15 cm3 of diethyl and petroleum ethers.

4.3.7. The third extraction is performed in the same way as the second, only without rinsing the flask. The maximum amount of solvents is carefully evaporated or gradually distilled off from the flat-bottom flask, as the diethyl and petroleum ethers are removed, increasing the temperature of the water bath from (30 ± 2) to (60 ± 2) ° C.

4.3.8. After the disappearance of the odors of solvents, the flask is heated by placing it for 1 hour in an oven (or vacuum drying). Then cool in a desiccator to a temperature of (20 ± 2) ° С and weigh up to 0.0001 g.

Subsequent weighing of the flask is carried out after drying for 30 - 60 minutes until the difference in mass between successive weighings is not more than 0.001 g. In the case of an increase in the mass of the flask with its contents after repeated drying, the result of the previous weighing is taken for calculation.

4.3.9. To check the completeness of the dissolution of the extracted fraction, (20 ± 5) ml of petroleum ether is added to the flask, while the flask is gradually heated to a temperature not exceeding 60 ° C with constant stirring of the contents of the flask in a circular motion until the fat is completely dissolved.

If the extracted fraction does not completely dissolve in petroleum ether, then the content of insoluble sediment is determined after removing the fat with warm petroleum ether. The ether treatment is repeated at least three times. Before each decantation, the insoluble residue is allowed to settle to the bottom. After complete removal of fat, the flask with the insoluble residue is heated in a water bath, gradually increasing its temperature from 30 to 60 ° C in order to completely remove petroleum ether. After the smell of petroleum ether disappears, the flask with the undissolved residue is dried in an oven (or vacuum drying) for 1 h, cooled to a temperature of (20 ± 2) ° С and weighed with a countdown to 0.0001 g.

4.3.10. Simultaneously with the determination of the mass fraction of fat, a control experiment is carried out with 10 cm3 of distilled water.

If the mass of the dry residue in the flask after drying exceeds 0.0005 g, then the reagents should be checked for purity or replaced.

4.4. Processing of results

4.4.1. The mass fraction of fat,%, in rennet or processed cheese and cheese product is calculated by the formula

where is the mass of the flask with the fat of the last weighing, g;

Weight of empty flask or with dry insoluble residue, g;

The mass of the flask after the last weighing in the control experiment, g;

Weight of empty flask or with dry insoluble residue in the control experiment, g;

Test sample weight, g.

The arithmetic mean of the results of two parallel determinations is taken as the final test result, the discrepancy between which should not exceed 0.2%.

4.4.2. The margin of error of the method at a confidence level of 0.95 is 0.2%.

Method for determining the mass fraction of fat. (GOST 5867-90)

In a clean milk butyrometer, trying not to moisten the neck, pour 10 sulfuric acid (density 1.81 - 1.82) and carefully so that the liquids do not mix, add 10.77 milk with a pipette, attaching the pipette tip at an angle to the wall of the neck of the butyrometer (level milk in a pipette is set at the lower point of the meniscus); milk from the pipette should flow slowly; after emptying, the pipette is removed from the neck of the butyrometer no earlier than 3 seconds later. Blowing milk out of the pipette is not allowed. Then 1 isoamyl alcohol is added to the butyrometer. The butyrometer is closed with a dry stopper, lowering the stopper down for 5 minutes in a water bath with a temperature of 652. After removing from the bath, the butyrometers are installed in the centrifuge cartridges (glasses) with the working part towards the center, placing them symmetrically, one against the other. If the number of butyrometers is odd, a butyrometer filled with water is placed in the centrifuge. After closing the centrifuge lid, the butyrometers are centrifuged for 5 min at a speed of at least 1000. Then the butyrometer is taken out of the centrifuge and by moving the rubber stopper the fat column in the butyrometer is adjusted so that it is in the tube with the scale. Butyrometers are immersed with stoppers down in a water bath. The water level should be slightly above the level in the butyrometer. The temperature of the water in the bath should be 652. After 5 minutes, the butyrometers are removed from the water bath and the fat is quickly counted. When reading the butyrometer, hold it vertically, the fat boundary should be at the gas level. By moving the plug up and down, the lower limit of the fat column is set on the whole division of the butyrometer scale and the number of divisions is counted from it to the lower point of the meniscus of the fat column. The fat interface should be sharp and the fat column should be transparent. If there is a ring (plug) of brownish or dark yellow color, as well as various impurities in the fat column, the analysis is repeated.