Milk quality research. Study of the quality of drinking milk Results of the study of 5 types of milk

Evaluation of organoleptic quality indicators of drinking milk samples are given in table. 6 - 7 .

First, an external inspection of the packaging and labeling of samples was carried out in accordance with the requirements of GOST.

Table 6 - organoleptic evaluation of the quality of milk samples pasteurized with a fat content of 2.5%

After studying the labeling, it was noted that the products fully meet the requirements of regulatory documents, the manufacturer fully informs the buyer about the name and location of the manufacturer's enterprise, standard, composition, shelf life and storage time, nutritional and energy value, as well as storage conditions and production date.

Then an organoleptic evaluation of the quality of the product was made.

Such research samples as: Drinking milk pasteurized with a fat mass fraction of 2.5% "Merry Milkman" OJSC "Wimm-Bill-Dann"; Pasteurized drinking milk with a mass fraction of fat of 2.5% "Kubanskaya Burenka" OJSC "Wimm-Bill-Dann"; Drinking milk pasteurized with a mass fraction of fat 2.5% "Summer Day" OJSC "Company UNIMILK"; Drinking milk, pasteurized. Mass fraction of fat 2.5% "On the meadow" OJSC "Kagalnitsky Dairy Plant"; Drinking pasteurized milk. Mass fraction of fat 2.5% "Krasnodar" JSC "KALORIYA", fully meet the requirements for organoleptic indicators in accordance with the Technical Regulations and GOST R 52090-2003 "Drinking milk TU". All 5 samples in appearance are not transparent liquid. The consistency is liquid, homogeneous, not viscous, without mucus, protein flakes and impurities. The taste and smell are characteristic, pronounced, clean, fresh, without foreign tastes and odors, with a barely noticeable aftertaste of boiling. Milk under the trademarks "Summer Day" and "Krasnodar" had a sweetish aftertaste, which is not a deviation from the norm. The color of the samples is white, saturated, without extraneous shades, milk under the brand name "Krasnodar" had a bluish tint.

The scoring of each sample, taking into account the weight coefficient, is presented in table 7.

Table 7 - the quality of pasteurized milk with a fat content of 2.5%, taking into account the weight coefficient

According to Table 6, it can be seen that the highest score, taking into account the weight coefficient (4.9), was in sample No. the quality indicator was for sample No. 4 Drinking milk, pasteurized. Mass fraction of fat 2.5% "On the meadow" JSC "Kagalnitsky Dairy Plant"

In order to more thoroughly study the quality of selected samples of milk pasteurized with a fat content of 2.5%, acidity, density, mass fraction of fat, and protein content were determined. The results of the study of physical and chemical quality indicators of the studied cheese samples are presented in Table. 8.

Based on the physical and chemical studies carried out, it was found that all samples of drinking milk pasteurized with a fat content of 2.5%, sold in the Pyaterochka store, met the requirements of GOST R 52090-2003 “Drinking milk”. However, it should be noted that sample No. 5 has drinking pasteurized milk. The mass fraction of fat 2.5% "Krasnodar" OJSC "KALORIYA" was slightly higher titratable acidity in comparison with other samples and reduced density.

Table 8 - physical and chemical indicators of the quality of pasteurized milk with a fat content of 2.5%

In general, evaluating all the samples, we noted that the organoleptic and physico-chemical parameters of milk met the requirements of GOST R 52090-2003 “Drinking milk TU”, had good consumer properties and are recommended for sale to the consumer.

During the organoleptic evaluation of milk, the condition of the container, the appearance of the milk, its consistency, color, taste and smell are determined. :

When evaluating the appearance and consistency of milk, attention is paid to its uniformity, the presence of sediment, floating lumps and settled cream.

Color definition. Milk is poured into a transparent glass and examined for the presence of foreign shades.

Table 13 Sample No. 1 pasteurized drinking milk "Favorite" mass fraction of fat 2.5%

Conclusion on the organoleptic evaluation of sample No. 1 of pasteurized drinking milk “Lubimoe” with a mass fraction of fat of 2.5%, the package volume is 900 ml. complies with the requirements of GOST 31450-2013.

Table 14 Sample No. 2 pasteurized drinking milk "Luzinskaya Krynochka" with a mass fraction of fat of 2.5%

Conclusion on the organoleptic evaluation of sample No. 2 of pasteurized drinking milk "Luzinskaya Krynochka" with a mass fraction of fat of 2.5%, the package volume is 900 ml: meets the requirements of GOST 31450-2013.

Table 15 Sample No. 3 pasteurized drinking milk "Luzhaikino" with a mass fraction of fat of 2.5%

Conclusion on the organoleptic evaluation of sample No. 3 of Luzhaykino pasteurized drinking milk with a mass fraction of fat of 2.5%, the package volume is 900 ml. complies with the requirements of GOST 31450-2013.

Table 16 Sample No. 4 pasteurized drinking milk "VNIMI-Sibir" with a fat mass fraction of 2.5%

Conclusion on the organoleptic evaluation of sample No. 4 of pasteurized drinking milk "VNIMI-Sibir" with a mass fraction of fat of 2.5%, the package volume is 900 ml. complies with the requirements of GOST 31450-2013.

Conclusion on the organoleptic evaluation of sample No. 5 of pasteurized drinking milk “Live Milk” with a mass fraction of fat of 2.5%, the package volume is 900 ml. complies with the requirements of GOST 31450-2013.

Table 17 Sample No. 5 pasteurized drinking milk "Live Milk" with a mass fraction of fat of 2.5%

Organoleptic indicators - appearance, color, smell, texture, taste - are determined by the senses (sight, smell, touch). The assessment of smell and taste is carried out by specially trained and certified experts. The smell and taste of milk are determined both immediately after sampling and after their storage and transportation for no more than 4 hours at a temperature of 4±2°C. The analyzed samples of milk are compared with a sample of milk without odor and taste defects. The assessment of smell and taste is carried out on a five-point scale (Table 18).

Table 18

Comparative characteristics of samples of drinking cow's milk with a maximum fat content of 2.5% from different manufacturers. (Table 19).

Table 19. Comparative characteristics of drinking cow's milk samples with a maximum fat content of 2.5% from different manufacturers

milk organoleptic competitiveness

Conclusion: Samples No. 1, No. 2, No. 3, No. 4 and No. 5 after the organoleptic evaluation are evaluated as excellent. The organoleptic evaluation of the quality of milk and dairy drinks showed that pasteurized drinking milk "Lubimoe", "Luzinskaya Krynochka", "Luzhaikino", "VNIMI-Siberia and "Live Milk" meet the requirements of GOST 31450-2013.

Khachatryan A.Yu. 1

Smirnova D.V. 1

1 OGBPOU "Kostroma Regional Medical College named after S. A. Bogomolov"

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Introduction

The life of any person is unthinkable without milk. Our survey (150 people, questionnaire Appendix 1) showed that they often buy it as a component of a healthy diet, but most people do not know why milk is really useful.

Milk is considered to be a universal food product. It is difficult to enumerate the number and categories of food products in the preparation of which this valuable and wonderful product is used. The importance of milk in children's and dietary nutrition is undeniable. In addition to the main components - proteins, carbohydrates and fats, milk contains about 200 useful substances. In terms of nutritional value, that is, meeting the physiological needs of the body in basic trace elements, milk is a unique product and can replace any product, but not a single product can replace milk.

Of course, in order for milk to become an assistant in maintaining health, timeliness and regularity of intake are necessary, however, as well as the quality of the consumed product. It is very important to eat high-quality milk, in which the chemical composition and nutritional value are as balanced as possible.

Currently on the shelves of Kostroma stores there is a large selection of milk from various producers in our region and other regions of our country. Interest in the quality of milk and dairy products among the population is always constant.

Hypothesis: if you analyze milk and find out which manufacturer produces the highest quality and healthiest product, then you can recommend this brand for regular consumption.

Goal of the work: study of the quality of milk of various brands sold at retailers in Kostroma.

Tasks:

conduct a survey of consumer preferences for milk of students and teachers.

to study the literature in order to establish the factors that determine the quality and value of a given product;

to master the methods for determining the organoleptic and physico-chemical parameters of milk from various manufacturers sold in the retail food chain of the city of Kostroma;

Subject of study: organoleptic and physico-chemical parameters of milk.

Object of study: milk of various brands sold in Kostroma.

Research methods:

Theoretical methods. Experimental: the method of organoleptic evaluation of smell and taste, the method for determining the density of milk by the areometric method, the gravimetric method for determining the dry matter, the indicator method for determining acidity, the acid method for determining fat, the method for determining protein according to Kjeldahl,

Research methodology.

Method for determining organoleptic indicators.

Organoleptic indicators must comply with the following parameters:

Method for determining physico-chemical parameters.

Method for determining the density of milk.

To determine the density of milk, we used the hydrometric method based on determining the volume of the displaced liquid and the mass of the hydrometer floating in it.

Determination of the density of raw, drinking, skimmed cow's milk is carried out at a temperature of (20 ± 5) °C. 250 or 500 cm3 samples for analysis are thoroughly mixed and carefully, to avoid foaming, pour along the wall into a dry cylinder, which should be kept in a slightly inclined position.

The cylinder with the analyzed sample is installed on a flat horizontal surface and the temperature of the sample (t 1) is measured. The reading of temperature readings is carried out no earlier than 2-4 minutes after lowering the thermometer into the sample.

A dry and clean hydrometer is slowly lowered into the analyzed sample, immersing it until 3-4 mm remains to the expected mark of the hydrometer scale. Then leave it in a free floating state. In this case, the hydrometer should not touch the walls of the cylinder.

The first reading of the density readings (p 1 ,) is carried out on the hydrometer scale 3 minutes after it is established in a stationary position. After that, the hydrometer is carefully raised to the height of the ballast level in it and lowered again, leaving it in a free floating state. After establishing it in a stationary state, a second reading of the density readings (p 2) is carried out. The operator's eyes should be at the level of the meniscus when reading the density reading. The readings are taken along the upper edge of the meniscus.

Reading of indications on hydrometers of type AON-1 or AON-2 reading of indications is carried out to the price of the smallest division. Then repeat the measurement of the sample temperature (t 2).

The arithmetic mean of the results of two temperature measurements t 1 and t 2 rounded to the first decimal place is taken as the result of measuring the temperature of the analyzed sample of the product (G).

For the result of measurements of the density of the analyzed sample of the product (p cf) at the temperature t of the analyzed sample, the arithmetic mean of the results of two hydrometer readings p 1 and p 2, rounded to the first decimal place, is taken.

Dry matter determination method

A glass bottle with 20-30 g of well-washed and calcined sand and a glass rod that does not protrude beyond the edges of the bottle is placed in an oven (Appendix 2, Fig. 3) and kept at 102 ± 2 "C for 30-40 minutes. After that the vial is removed from the oven, covered with a lid, cooled in a desiccator for 40 minutes and weighed with an error of not more than 0.001 g. 10 ml of milk is added to the same vial with a pipette, closed with a lid and immediately weighed. Then the opened bottle and the lid are placed in an oven with a temperature of (102 ± 2) C. After 2 hours, the bottle is removed from the oven, covered with a lid, cooled in a desiccator for 40 minutes and weighed.

Subsequent weighings are carried out after drying for 1 hour until the difference between two successive weighings is equal to or less than 0.001 g. If an increase in weight is found during one of the weighings after drying, the results of the previous weighing are taken for calculations.

The mass fraction of dry matter C,%, is calculated by the formula:

where m 0 is the mass of the bottle with sand and a glass rod, p

m is the weight of the weighing bottle with sand, glass rod and a sample of the test product before drying. G;

m 1 is the mass of the weighing bottle with sand, a glass rod and a sample of the test product after drying, g.

Method for determining acidity.

We used an indicator method to determine the acidity. The method is based on the neutralization of free acids, acid salts and free acid groups contained in the product with sodium hydroxide solution in the presence of the phenolphthalein indicator.

Place (1.000 ± 0.005) g of phenolphthalein into a 100 ml volumetric flask, add 73 ml of ethanol, stopper and mix gently. The volume of the solution was brought up to the mark with distilled water.

Milk is measured into a conical flask with a capacity of 100 or 250 ml, distilled water is added in volumes of 10 ml of milk and 20 ml of water and 1 ml of cobalt sulfate solution. The mixture is thoroughly mixed.

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

The acidity of the analyzed product, T (in Turner degrees), is calculated by multiplying the volume of sodium hydroxide solution, in cubic centimeters, used to neutralize the acids contained in a certain volume of the analyzed product, by 10. The final result of the analysis is taken as the arithmetic mean of the results of two parallel determinations, rounded to the first decimal place.

Fat determination method.

We determined fat by the acid method. 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 fat released in the graduated part of the butyrometer.

Trying not to wet the throat, pour 10 ml of sulfuric acid into two milk butyrometers with a dispenser and, carefully so that the liquids do not mix, add 10.77 ml of milk with a pipette, placing the tailbone of the pipette to the throat at an angle. The level of milk in the pipette is set at the lowest point of the meniscus. The milk should flow out of the pipette slowly. After emptying, the pipette is removed from the neck of the butyrometer not earlier than after 3 s. Blowing milk out of a pipette is not allowed. Add 1 ml of isoamyl alcohol 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.

Butyrometers are closed with dry plugs, introducing them a little more than halfway into the neck of the butyrometers. Butyrometers are shaken until the protein substances are completely dissolved, 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. (65 ± 2) degrees. After removing from the bath, the butyrometers are inserted into the centrifuge glasses 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 analysis is placed in the centrifuge.

Butyrometers are centrifuged for 5 minutes (Appendix 2, Fig. 1). Each butyrometer is removed from the centrifuge and the column of fat is adjusted by moving the rubber stopper so that it is on 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. In this case, the water level in the bath should be slightly higher than the level of fat in the butyrometer.

Butyrometers are taken out one at a time from the water bath and a quick reading of fat is carried out. When counting, the butyrometer is held vertically, the border of fat should be at eye level (Appendix 2, Fig. 4 and 5). By moving the cork, the lower limit of the fat column is set to the zero or whole division of the butyrometer scale. The number of divisions is counted from it to the lower point of the meniscus of the fat column with an accuracy of the smallest division of the butyrometer scale.

The interface between fat and acid should be sharp, and the column of fat should be transparent. In the presence of a “ring” (cork) of a brownish or dark yellow color and. various impurities in the column of fat or a blurred lower limit, the measurement is repeated.

After the first centrifugation, in order to facilitate the adjustment of the fat level in the butyrometer, the small stopper is slightly opened without removing it completely. Using a large stopper, set the upper level of the liquid from the graduated part of the butyrometer. Then the smaller hole is tightly hidden. Usually, no noticeable separation of fat is observed after the first centrifugation.

After the second centrifugation and water bath, the position of the liquid level is checked.

The result of intentions is taken as the arithmetic mean of the results of two parallel observations.

Method for determining the mass fraction of protein according to Kjeldahl.

The Kjeldahl method is based on the mineralization of a milk sample with concentrated sulfuric acid in the presence of an oxidizing agent, an inert salt of potassium sulfate and a catalyst - copper sulfate. In this case, the amino groups of the protein are converted into ammonium sulfate dissolved in sulfuric acid.

The mass fraction of nitrogen in this solution is measured chemically by alkalizing the solution, distilling ammonia with steam, absorbing it with a solution of boric acid and titrating the latter with a solution of hydrochloric acid, indicating the equivalence point by changing the color of the indicator.

Measure 1 ml of product into a weighing beaker. 10 ml of sulfuric acid and 10 ml of hydrogen peroxide are added to the Kjeldahl flask (Appendix 2, Fig. 7) or test tube. The Kjeldahl flask or test tube is placed in the aluminum block socket on the electric stove. Set the heating regulator of the tile to the front position.

After the rapid boiling of the contents of the flask or test tube has ceased, approximately 10 minutes after the start of heating, set the heating regulator of the tile to the position corresponding to the maximum. Heating is continued until the liquid becomes clear, colorless or slightly bluish. The Kjeldahl flask with the obtained mineralizate is cooled in air to room temperature.

Add 20 ml of distilled water to the Kjeldahl flask with mineralizate and mix thoroughly in a circular motion until the precipitate dissolves. Assemble the distillation apparatus (see appendix fig. 2). Turn on the electric stove under the steam generator flask, open the clamp on the steam outlet line and the sewer, and close the clamp on the steam supply line to the Kjeldahl flask. Heat the flask and the converting flask to a boil. The Kjeldahl flask or test tube is attached to the distillation apparatus.

In a conical flask with a capacity of 250 ml, 20 ml of a mixture of boric acid with an indicator solution is measured with a graduated cylinder. Position the conical flask so that the end of the condenser tube is below the top level of the mixture in the flask.

Measure with a graduated cylinder 50 ml of sodium hydroxide solution and carefully, avoiding emissions, pour it through a separating funnel into a Kjeldahl flask. The faucet of the funnel is immediately closed. Close the clamp on the steam outlet line and open the clamp on the steam supply line from the steam generator flask and the Kjeldahl flask or test tube.

The distillation is carried out until the volume of the condensate reaches 90-120 ml (distillation time 5 min). The contents of the conical flask with a solution of the indicator, boric acid and condensate are titrated with a solution of hydrochloric acid with a concentration of 0.2 mol / dm 3 until the color changes to green (Appendix 2, Fig. 6)

The volume of acid used to titrate the contents of the flask is counted.

The mass fraction of total nitrogen X in% with the chemical method of measurement is calculated by the formula:

Where V 1 is the volume of acid used for titration, cm 3;

V 2 - the volume of acids spent on titration during the control measurement,

c - concentration of hydrochloric acid

m is the mass of the sample of the product, g:

1.4 is the conversion factor for the volume a of acid to the mass fraction of total nitrogen.

The mass fraction of protein Y, % is determined by the formula

Y \u003d 6.38 X where 6.38 is the mass of milk protein, equivalent to a unit mass of total nitrogen.

Main part.

Research results.

Organoleptic indicators.

Physical and chemical indicators. Indicators of the mass fraction of protein in milk

Indicators of the mass fraction of fat in milk

Density indicators

Acidity indicators

Dry matter content

Conclusion

As a result of the survey, the majority of respondents buy milk in a supermarket or store for themselves and family members in a carton. They prefer milk of trade marks Karavaevo and Vologda with pasteurized fat content of 2.5%. It turned out that the respondents did not understand the difference in the degree of processing of milk and could not explain why it is useful. In their choice, they are guided primarily by the date of manufacture and shelf life, least of all they pay attention to the price, fat content and manufacturer.

As a result of the analysis of the organoleptic and physico-chemical properties of milk of 8 brands sold in the retail network of Kostroma, we did not find deviations from GOST.

Bibliography

1. GOST 31450-2013 Drinking milk. Specifications.

2. Skurikhin N. M., Nechaev A. P. Everything about food from the point of view of a chemist. - M.: Higher school, l99l.

3. Workshop on the basics of agriculture. — M.: Enlightenment, 1991

4. GOST 23327-98. Milk and dairy products. Method for measuring the mass fraction of total nitrogen according to Kjeldahl and determining the mass fraction of protein.

5. GOST R 54758-2011. Milk and milk processing products. Density determination methods.

6. Zhvanko Yu. N., Pankratova GV, Mamedova 3. I. Analytical chemistry and technological control in public catering. - M .: Higher School, 1989.

7. GOST 28283-89 Cow's milk. Method of organoleptic evaluation of smell and taste

8. Zlotnikov E. G., Estrin Z. R. Features of the organization of experimental work // Chemistry at school. - 1997. - No. 4. - S. 66-68.

9. GOST 23327-98. Milk and dairy products. Method for measuring the mass fraction of total nitrogen according to Kjeldahl and determining the mass fraction of protein.

10. GOST 5867-90 Milk and dairy products. Methods for determining fat

11. GOST R 54758-2011. Milk and milk processing products. Density determination methods.

12. GOST R 54669-2011. Milk and milk processing products. Methods for determining acidity.

13. GOST 3626-73. Milk and dairy products. Methods for determining moisture and dry matter.

Annex 1

Questionnaire for the survey of milk consumers

Your gender: M F Age:

1. What kind of milk do you buy more often:

A) natural; b) with a fat norm of 2.5%; c) with a fat norm of 3.2%;

d) with a fat norm of 1.5%; e) Melted; e) does not matter;

2. How often do you buy milk:

a) every day b) once a week c) twice a week; d) once a month

3. How much do you usually buy when going to the store:

a) less than a liter; b) liter; c) 1.5-2 liters; d) more than 2 liters.

4. Specify the place of purchase:

a) a supermarket b) Shop; c) Stall (outside the market); d) the market;

e) a specialized dairy shop;

5. Which brand of milk do you prefer:

aSavushkin product; Prostokvashino; Karavaevo, Levashovo, Minsk, Vologda, House in the village, Zdravushka; Lianozovskoe; Brest Litovsk, Borovikovo, Other___________________

6. What do you pay attention to when choosing milk:

Price; Manufacturer; Taste qualities; brand popularity; Quality; % fat; storage period; date of manufacture; presence of quality marks; type of processing; package

7. Preferred form of packaging:

a) Cardboard; b) Plastic bottle; c) glass bottle; d) plastic bag; e) in bottling

8. Do you always pay attention to the expiration date: and sometimes; b) always; c) never; d) if there is time.

9. Why do you buy milk: a) Component of a healthy diet; b) Daily diet; c) for cooking; d) delicious; Other________________

10. At what price do you buy milk (for 1 liter) _______________(write in rubles)

11. Do you know why milk is good for: Specifically why I do not know; No; Yes, because _________________________________________________________

12. Who do you buy milk for: for myself; for adult family members; for children; for friends and acquaintances; for animals.

13. What type of milk processing do you prefer: pasteurized; sterilized; ultra pasteurized; fresh (on tap); melted; Hard to say.

Annex 2

Rice. 1. Centrifuge

Rice. 2. Device for distillation of ammonia. Rice. 3. Drying cabinet

Rice. 4 and 5. Determination of fat content. Butyrometers (Butyrometers)

Rice. 6. Determination of protein. Titration. Rice. 7. Kjeldahl flask

Laboratory stages of sanitary examination of milk: determination of organoleptic properties, physicochemical and bacteriological examination.

Criteria for assessing the quality of milk:

compliance with the milk quality standard;

freshness of milk;

falsification of milk (primary and secondary);

the presence of foreign impurities of biogenic and anthropogenic nature.

The most common ways falsifications milk is diluted with water, degreasing and reducing the acidity of stale milk. Signs of dilution of milk with water are a liquidish consistency, a bluish tint, a decrease in the specific gravity, fat content and dry residue of milk, as well as the presence of nitrates in milk. Possible secondary falsification milk in order to hide dilution with water - the addition of an aqueous solution of starch, which normalizes the consistency and specific gravity of milk, but does not compensate for the nutritional and biological value and does not exclude the harmful effects of impurities contained in water. Signs of skimmed milk can be a bluish tint, an increase in specific gravity against the background of a significant decrease in the fat content of milk. Signs of an artificial decrease in the acidity of milk are normal (16-22 0 T) or abnormally reduced (less than 16 0 T) acidity, the presence of soda.

1. Organoleptic examination of milk

Appearance and the color of the milk is assessed when viewed in a transparent cylinder (milk volume 50-60 ml). Homogeneity, the presence of sediment and impurities are noted. Natural whole milk should have a white color with a yellowish tint. A blue tint can be found in skimmed or diluted milk. The pink tint can be determined by an admixture of blood, colored bacteria, or depend on the animal's food (beets, carrots, rhubarb).

Consistency milk is determined by the trace remaining on the walls of a transparent vessel after shaking. At normal consistency, a white trace should remain. If milk is diluted with water, no trace remains. If the milk has a viscous consistency (in the case of multiplication of mucous bacteria in the milk or the presence of starch), then the trace is slimy and viscous.

Smell determined after shaking the milk in a conical flask closed with a watch glass. Natural fresh milk has a pleasant milky smell; a sour smell indicates sour milk; the smell of ammonia or hydrogen sulfide - about the development of putrefactive bacteria. Other odors (oil, kerosene, fish, perfume) may appear in milk if storage rules are violated.

Taste milk is determined by rinsing the mouth with a small amount of milk (5-10 ml). The taste of whole high-quality milk is pleasant, sweetish. The taste of salty, bitter, astringent may indicate an illness in the animal. The composition of a dairy animal's diet (eg, wormwood) can also change the taste of the milk.

2. Physical and chemical study of milk

1). Reductase test . A positive reductase test is an indirect method for detecting microbial contamination. A reductase test is carried out using an aqueous solution of the redox indicator methylene blue (the color of the oxidized form is blue, the reduced form is colorless) at a temperature of 37 ° C (in a thermostat). The initial solution of methylene blue has a blue color. In the presence of reductase in milk, its discoloration occurs.

20 ml of test milk and 2-3 drops of 1% aqueous solution of methylene blue are placed in a sterile test tube (flask), thoroughly mixed, 0.5 ml of sterile vaseline oil is layered over the mixture and placed in a thermostat. The rate of discoloration of methylene blue indicates the degree of microbial contamination of milk (Table 16). On this basis, the quality of milk is evaluated with an indication of the quality class.

Table 16. Sanitary assessment of the degree of microbial contamination of milk, depending on the time of decolorization of methylene blue reductase

2). Determination of the specific gravity of milk using a lactodensimeter . Milk (150 ml) is poured into a large glass cylinder, the lactodensimeter is carefully lowered into it to the 1.030 mark on the lower scale so that it does not touch the walls and bottom of the cylinder, and left for 5 minutes. According to the readings on the lower scale, the specific gravity is measured, and on the upper scale, the temperature. The specific gravity of milk (d) can be expressed in absolute units (g / cm 2) or conventional units (Keven degrees). Each degree of Kevin is equal to one thousandth of a g / cm 2, for example, d \u003d 1.027 g / cm 3 \u003d 27K.

Since the specific gravity of milk depends on temperature, for the adequacy of comparison with the norm (at 20С), the scale readings should be “brought” to 20С. At T>20С, a correction equal to 0.2Keven for each degree of temperature difference should be added to the value established by the lactodensimeter; at N<20С - следует вычесть эту поправку.

Example. Milk has specific gravity d 10 =1.028 g/cm 2 , temperature t=+10С. Then the density of milk, expressed in Kevin degrees and “reduced” to 20С, is equal to: d 20 \u003d 28 - (0.2 x 10) \u003d 26 K, which is lower than the normal specific gravity of whole milk ( 1.028-1.034 g/cm 2 =28-34  Keven) by 2Keven.

3a). Determination of the fat content of milk Gerber way . The essence of the method consists in isolating the fat phase from milk using sulfuric acid and isoamyl alcohol and measuring the volume of fat in a Gerber 14 butyrometer after centrifugation in a milk centrifuge for 5 minutes. When centrifuging a mixture of milk, sulfuric acid and isoamyl alcohol, phase separation occurs, fat is collected in the narrowed upper end of the vessel, along the length of which divisions from 0 to 6 are applied, each division corresponds to 1% fat (measurement accuracy 0.1%).

3b) Determination of the fat content of milk by an acid-free method . 5 ml of a 10% soda solution, 10 ml of test milk, 3-3.5 ml of an alcohol mixture (amyl alcohol: ethanol = 1:6) and 2-5 drops of a working solution of phenolphthalein are poured into the Gerber butyrometer. The butyrometer is stoppered, shaken until a homogeneous liquid is formed, placed with the stopper down in a water bath (65-70°C) for 5 minutes, after which it is centrifuged in a milk centrifuge. After it stops, the butyrometer is carefully transferred to a water bath and kept there for 3-4 minutes, after which the fat content is determined on a scale. The marked result is compared with the norm of fat content of whole milk (fat content not less than 3.2%).

4). Dry residue calculation . The dry matter of milk consists of proteins, fats, carbohydrates and mineral salts. The dry residue can be determined by weight, or use the calculation according to the Farington formula: C \u003d [(4.8  W + d 4 20) / 4] + 0.5, where W is fat content (%); d 4 20 - density (degrees Kevin); 4.8; 4 and 0.5 are empirical coefficients.

5). Determination of the acidity of milk by titration 15 . The acidity of milk is measured in Turner degrees (0 T): 1 0 T corresponds to the volume (ml) of 0.1 N sodium hydroxide solution used to neutralize acids in 100 ml of milk. To determine the acidity of milk, 10 ml of milk, 20 ml of distilled water, 3-4 drops of a 1% solution of phenolphthalein are poured into a conical flask. The mixture is titrated with a 0.1 N alkali solution until a stable, slightly pink color appears. The volume of alkali solution used for titration is multiplied by 10 (for conversion to 100 ml of milk). Assess the acidity of milk should be based on the fact that the acidity of fresh milk = 16-19 T, enough fresh - 20-22 T, stale milk has more than 23 T.

6). Tests for adulteration of milk

6a). Definition soda in milk. Baking soda can be added to milk to hide its high acidity. Neutralizing lactic acid, soda does not delay the development of microorganisms in milk, which increases the epidemic risk, and contributes to the destruction of vitamin C, which reduces the nutritional value of the product. Milk with soda added is classified as adulterated and unfit for human consumption. Rosolic acid serves as an indicator to detect soda in milk.

Pour 5 ml of milk into a test tube and add 4-5 drops of a 0.2% alcoholic solution of rosolic acid. In the presence of soda, the milk turns crimson; in the absence of soda, a yellow-brown color appears. The measurement limit is 0.1% soda in milk.

6b). Definition starch in milk. Starch is added to milk for the purpose of falsification to give it a thicker consistency after dilution with water. Lugol's solution (KI, I 2) serves as an indicator for the presence of starch. Starch-added milk is classified as adulterated and unfit for human consumption.

10-15 ml of test milk and 1 ml of Lugol's solution are poured into a conical flask. In the presence of starch, milk turns blue; without starch, it turns brown.

6c) Test for nitrates , which can appear in milk as a result of dilution of milk with water containing nitrates. 10 ml of milk and 0.3 ml of 20% CaCO 3 solution are poured into the flask. The mixture is boiled until the milk curdles, cooled and filtered. 1-2 crystals of diphenylamine are placed in a porcelain cup and 1 ml of concentrated sulfuric acid is poured. A few drops of filtrate are carefully layered along the edge of the cup. The appearance of a blue color indicates the presence of nitrites and nitrates.

Based on the results of the examination, they give a conclusion on the good quality, freshness and integrity of the milk. At the same time, they are guided by the norms for whole, fresh and high-quality milk.

Serova Tamara

research of different brands of milk, sour cream, cottage cheese

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Municipal budgetary educational institution

"Primoksha Secondary School"

Kovylkinsky municipal district

Republic of Mordovia

Research work:

"Research on Milk and Dairy Products"

MBOU "Primokshanskaya secondary school"

Head: Kanunnikova L.N. -

Biology teacher

p. Primokshansky

2016

Page

1. Introduction.

1.1. Statement of the problem ………………………………………………………………2

1.2. Goals and objectives ……………………………………………………………………..2

2 A bit of history …………………………………………………………………….3-6

3. Materials and methods

3.1. Place and timing of the study …………………………………………7

3.2. Experimental methodology ……………………………………………8-9

4 . Research results

4.1 Examination of milk samples…………………………………………………9-11

4.2 Study of sour cream samples…………………………………………………..11

12

5. Conclusions ……………………………………………………………………………..13

6. List of used literature…………………………………………………..14

7. Appendix ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

1. Introduction

1.1 Statement of the problem.

Today, milk is an indispensable product of mankind. It is a must for baby food. In terms of chemical composition and biological properties, it occupies an exceptional place among products of animal origin. Nowadays, scientists, knowing the chemical composition of milk and its physiological significance, pay much attention to the milk diet of children and the elderly.But not all people are happy to drink milk and eat dairy products. Now more and more milk is bought in the store. And low-quality dairy products often appear on the market. It is no secret that during pasteurization and sterilization of milk used to destroy unwanted microflora, as well as to increase the shelf life, some changes in its components occur.I also buy milk in the store and therefore decided to conduct a study to find out whether the quality of store milk is good and what is being sold to us today under the guise of milk and dairy products.Object of study: Milk and dairy products from different manufacturers: "House in the village" fat content 3.8%, "33 cows" 3.2% fat and homemade milk bought on the market, as well as dairy products: sour cream "Meadow Village" and "Summer Day" "both 20% fat, cottage cheese "Full cat" 9% fat and "Prostokvashino 5% fat.Subject of study: The degree of dilution with water and the presence of impurities in milk and dairy products and their compliance with the composition indicated on the package.Research hypothesisrelated to the suggestion that milk and dairy products sold in stores would contain impurities and not match the composition on the packaging.Purpose of the study: to investigate the quality of milk and dairy products: sour cream and cottage cheese, coming to stores for sale. Tasks : 1. To study the method for the degree of dilution of milk and the presence of impurities contained in milk.2. Select objects for research.3. Conduct an experiment.4. Determine the methods of milk falsification;5. Compare milk from different manufacturersFor this you need:1. study the literature on the topic; 2. study methods for determining milk quality indicators; 3. do experiments to determine the quality of milk; 4. analyze the results; 5. draw conclusions.

Milk. A bit of history.Milk is the first food that humans, like other mammals, receive immediately after birth. But adult mammals - with rare exceptions - do not digest milk. In contrast, many people continue to drink milk throughout their lives. Studies show that adults' addiction to this children's food is associated with the development of animal husbandry and the spread of a specific gene mutation, thanks to which adults digest milk.

In historical terms, people have been eating meat for millions of years, and drinking milk for no more than a few thousand - since the domestication of domestic animals. The appearance of milk in the diet of an adult is a specific cultural achievement of an already civilized person.

Digesting whole milk as an adult is a challenge. Because our body is genetically programmed to digest milk in childhood. It must be said that in ancient times children were fed for quite a long time. The child was already talking and running calmly, but as a reward he could join the mother's breast. For this milk sugar, maltose, a special enzyme must be produced that decomposes this sugar. Either the presence or absence of this enzyme affects whether we digest whole fresh milk or not. Immediately make a reservation that all this applies only to whole fresh milk. And I must say that really many people do not tolerate this milk. It is believed that this is a very useful product, but in fact, for many it causes sharp pains in the stomach that will soon come.

If a child refuses milk, this means that he, in principle, cannot consume it. This can be genetically determined - and therefore, in this sense, parents need to be more attentive to their child. Apparently, at some point, a mutation arose in humans that allowed them to digest milk as adults. And when domestic animals appeared, this mutation began to spread, because its carriers received certain advantages. And therefore, by analyzing the frequency of occurrence, the presence of this necessary enzyme in the adult population, we can find those groups that are most likely in the past for a long time and stably consume unfermented milk. It is possible to determine the history of the people by genetics, how long ago they used or used fresh milk in the past. At least we can interpret these facts in this way. So - the easiest way to digest whole milk is the population of Northern Europe. Animal husbandry appeared very early there and for many millennia people could consume milk. The northern climate is not conducive to rapid fermentation, and therefore it is quite possible that this is why whole milk is in use among northern Europeans.

All dairy products are to a greater or lesser extent fermented, that is, treated with bacteria. And everyone uses them, because maltose is already decomposed by bacteria. Therefore, those who, in fact, built their diet on milk are, of course, nomads. Nomads were closely associated with herds of animals and, naturally, fed on milk. They learned to collect milk in large quantities, process and store it a very long time ago. The most famous traditional drinks and dishes from milk are koumiss, first of all, this is fermented mare's milk. Kumis, by the way, is a low-alcohol drink, which was consumed in large quantities, as historical sources testify, by the nomads of the early Iron Age, primarily by the Scythians. As Herodotus writes, the Scythians needed slaves primarily in order to constantly produce a huge amount of koumiss. It needs to be shaken all the time. And the Scythians were called warriors of mares. Similarly, cheese, such a rather specific cheese, which is not at all like the soft and fragrant cheese that is sold in stores today, this cheese of nomads, which is made in the usual way - milk is fermented and then strongly heated. And now this more solid mass is put under the press, it becomes dense, then it is heavily salted, and in fact this cheese becomes incredible hardness and is stored for an unlimited amount of time. It can be soaked, added in pieces to tea, somewhere else. Cheese, along with koumiss, is also a very ancient product. And probably, we can say that his age is also about five thousand years. These northern European cheeses that we know today are a much later phenomenon. And early cheeses are cheeses of nomads.

What else can we say about milk, how did its history develop?
Several thousand years ago, milk entered the food arsenal of early pastoral societies, and since then all pastoralists have been very closely associated with milk and dairy products. Again, if we turn to the East, to Japan, to China, of course, Central and South China, there the traditions of dairy food are very weak. Just as they eat little meat, they drink little milk. Apparently they can't drink because they don't have the gene responsible for producing the enzyme that breaks down maltose. Accordingly, they do not have a tradition of dairy culture, it has not developed for them. And therefore, if we take huge China, then only in the north, only where there are nomads, traditional ancient nomads, cheese is already appearing there, a variety of other dairy products are appearing. But in the central and southern regions it is not common. The attitude towards milk in India is interesting. Sacred cows and therefore, naturally, milk is a sacred product. And according to some interpretations, the divine drink of immortality, there are very different views on what it is. Someone says that it is a narcotic drink, someone says that it is honey, but someone says that milk should also be part of the divine drink of immortality. In fact, in cultures where humans are closely related to domestic ungulates, milk will certainly always be present, and in a variety of forms. If in Eurasia all nomads use sour milk, then, for example, in Africa, pastoralists drink whole milk. There they have a very peculiar tradition of food communication with animals. Incisions are made on the neck of the cow, and a small amount of blood is poured into the cup, then this wound is necessarily smeared with clay, and a small amount of fresh milk is added there. And this mixture, as you understand, is very nutritious, the same blood with milk, in our opinion, will not be very appetizing. But they practice a diet that provides a complete fortified food without any problems.
Today we are practically unable to drink milk. What is the value, one of the greatest values ​​of milk? Because it is a natural product that is very rich in immune bodies. Why is breast milk so beneficial for babies? Because it is not only their feeding, but their protection from a variety of infections. Now milk is a powder dissolved in water, that is, devoid of all the most important properties of milk. Therefore, I think it is wrong to call milk what we consume today - it is some other, secondary product that is useful, there are many available forms of calcium, proteins, easily digestible fats, all this is understandable. But it is the dairy specificity of a useful product that is largely lost in today's standard milk production.

3.Material and technique

3.1. Location dates for the study. The amount of collected material.

The study was conducted in March-April 2016. The study was carried out in three stages.

• At the first stage, the methodology for the experiment was chosen. The objects of the study were three brands of milk:

1. Milk is homemade, bought at the market. The fat content of milk is from 3.2. This milk cost 40 rubles per liter. 2. Milk pasteurized "House in the village". The fat content of milk is from 3.2% to 4% (3.8%), this milk cost 62 rubles per liter. 3. .Ultra pasteurized milk "33 cows". The fat content of milk is 3.2%. This milk cost 75 rubles per liter.

Two brands of sour cream: 1. "Summer Day" 20% fat - 39.50 rubles per 200g. 2. "Meadow Village" 20% fat - 70 rubles per 500g. (28 rubles for 200g.).

Two brands of cottage cheese: 1. "Full cat" 9% fat - 30 rubles per 200g. 2. "Prostokvashino" 5% fat - 102 rubles for 220g.

• At the second stage, experimental work was carried out to identify the presence of impurities and starch in milk and dairy products, as well as their degree of compliance with the composition indicated on the package.
• At the third stage, the obtained results were processed and systematized.

3.2. Experiment Method

1) Milk quality

The degree of dilution of milk with water

a) Pour 1 part of milk and 2 parts of ethyl alcohol into a test tube. The resulting mixture is shaken for 30 seconds, after which it is poured into a Petri dish, placed in a dark place, after 5-7 seconds flakes appear in the liquid.

Milk diluted by 20% - flakes appear after 30 seconds.

Milk diluted by 40% - flakes appear after 30 minutes.

Milk diluted by 50% - flakes appear after 40 minutes.

b) Pour milk into saucers and sprinkle it with paints that spread over the entire surface. Then a dishwashing detergent is taken and dripped onto the milk: if the paint spreads quickly around the edges, then the milk is fatty, if slowly, then the milk is diluted with water. Thus, the fatter the milk, the stronger the reaction.

2. Determination of foreign impurities in milk.

a) Take different samples of milk, sour cream, cottage cheese.

Drop a strip of litmus paper.

If there are no impurities, the litmus paper will not change,

If the paper turns red, there is an acid (for example, boric or salicylic acid).

If the paper turns blue - there is soda (so that the milk does not sour longer).

b) We drop a drop of iodine into different samples of milk, sour cream and cottage cheese. If the milk turns purple, then it contains starch.

c) add a few drops of acetic acid to different samples of milk, if abundant foam is released, then chalk has been added to the milk.

d) We dip a glass rod into different samples of milk and sour cream and draw some kind of drawing on a clean piece of paper. Then the leaf is held over the fire of a candle. If there is palm oil in the milk, then a greasy trace will appear, and if not, a brown pattern will appear.

e) determine the density of milk according to the formula: density = mass / volume. Normal density of milk is 1030 kg/m3 or 1.03 g/cm3.

f) Give the cat different samples of milk, sour cream and cottage cheese to eat: if it eats, then milk is free of impurities.

4. Research results

4.1 Examination of milk samples:

1. We poured one volume part of milk and two parts of pure ethyl alcohol into a test tube, and the resulting mixture was shaken for 30 seconds, after which it was quickly poured onto a transparent glass saucer placed against a dark background.

Having done practical work, we concluded that homemade milk purchased from private traders was not diluted with water, since flakes appeared after 6 seconds. “33 cows” is diluted with water by 20%, since the flakes appeared after 3 minutes, and the “House in the Village” milk sample did not show any result at all, we made several attempts with it, but we did not receive flakes either after an hour or 12 hours . From this we conclude that milk powder has been added to this sample.

2. When adding liquid dishwashing detergent to milk, in sample No. 2 (“House in the village”) the paints spread, but with a pause of 1-2 seconds, in sample No. 3 (“33 cows”) the reaction occurred instantly, and in sample No. 1 (homemade milk) showed the lowest fat content: the paints spread quite a bit, only in the center, therefore it was heavily diluted with water. But, when we left milk samples in glasses to find out how quickly it turned sour, a decent layer of cream settled in homemade milk: 5 mm per 50 g. Therefore, experiments with paints and detergents are not suitable for determining the fat content of homemade milk. Then we decided to check the density of milk and found out the following: sample No. 1 (homemade milk) density = 1.04 g/cm 3 , sample No. 2 ("House in the village") density = 0.95 g / cm 3 , sample No. 3 ("33 cows") density = 0.99 g/cm 3 . So, we concluded that homemade milk has a high density, slightly higher than the norm (1.03 g / cm 3 ) and fat content. Sample No. 3 "33 cows" corresponds to the declared fat content on the package, and sample No. 2 "House in the village" is diluted with water and does not correspond to the fat content declared on the package from 3.2 to 4%, although on the bottle cap, under the date of manufacture and expiration date the exact figure was 3.8%.

3. Then we lowered the universal litmus paper into all milk samples in order to find impurities: no foreign impurities were found in all milk samples, since the litmus paper strips did not change their color. Also, as mentioned above, we left all milk samples at room temperature in order to find out how long it would go sour. Homemade milk turned sour after 10 hours, “House in the Village” milk (pasteurized, shelf life 7 days) after 24 hours, and ultra-pasteurized milk “33 cows” (shelf life 6 months) turned sour only on the third day. This suggests that beneficial lactic acid bacteria are present in homemade milk, they ferment milk, and they are killed in pasteurized and ultra-pasteurized milk, thereby increasing the shelf life of the product. But homemade milk may contain pathogens that cause poisoning in the human body, which cannot be detected at home, laboratory tests are needed.

4. When iodine was dropped to detect starch in all samples, it did not change its color, therefore, this substance is not present in milk.

5. Then we took a blank sheet of paper and with a glass rod drew a pattern with milk from each sample, in order to detect palm oil. When the drawings dried up (after 1 hour), we each held them over a burning candle, all the drawings appeared without leaving greasy marks on the leaf, therefore there is no palm oil in any milk sample.

6. Some manufacturers may add chalk to milk. To this end, we added vinegar to the samples. If we found foaming, then chalk is present. But in our case, no foam was found in any of the samples, therefore, there is no chalk in the milk.

7. And finally, we decided to involve the best expert in the field of milk - the cat Musya, in order to find out which of the samples is the best. Cats are known to love to lap up milk. Of all the samples, the cat preferred milk from a private trader. Sample No. 2 sniffed and moved away, sample No. 3 tried a little, but did not eat.

4.2 Study of sour cream samples:

1. We applied strips of universal litmus paper to each sample, they did not change color, which means there are no acid-base impurities.

2. We decided to check the sour cream for palm oil content, for this we drew drawings with a glass rod on a clean sheet of paper, dipping them in sour cream samples, when they dried (after 1.5 hours), held them over a candle fire. In sample No. 1 (“Summer Day”), the pattern showed up well, but oily stains were still visible at the edges, which means that palm oil is present in this sample, and in sample No. 2 “Meadow Village”, the pattern did not want to appear for a long time, but fatty stains appeared to a greater extent than in the first sample. As a result, the picture did not appear all and was more pale. Therefore, palm oil was present in both samples of sour cream, but in the sample "Meadow Village" it contained more. The packaging did not list the content of palm oil in the composition of the product.

3. We checked samples of sour cream for starch content, for this we added a few drops of iodine. There was no reaction, therefore there is no starch in these samples.

4. They offered to try sour cream for the cat Musa. The cat did not eat any of the samples. Therefore, some impurities are still present.

Study of curd samples.

1. We attached strips of indicator paper to each curd sample. The color has not changed, therefore there are no acid-base impurities.

2. We checked the cottage cheese samples for starch content, for this we added a few drops of iodine. In sample No. 2 "Prostokvashino" there was no reaction, therefore there is no starch in this sample. But in sample No. 1 “Fed Cat”, the reaction to starch turned out to be positive, therefore, this sample contains starch, although it is not indicated on the package as part of the product.

3. They offered these samples to the cat Musa, who, with great appetite, tried the cottage cheese of the Prostokvashino brand, and only tried the cottage cheese of the Satisfied Cat brand, but did not eat it.

5. Conclusions

In the course of our research, we studied methods for determining the quality of milk. As objects, 3 brands of milk were selected, which we checked for the presence of impurities and the degree of dilution with water.All the milk that we took as objects for research turned out to be good, without impurities. These brands of milk can be eaten. But milk sample No. 3 "33 cows" was diluted with water, and milk powder was added to sample No. 2 "House in the village". 2 samples of sour cream "Summer Day" and "Meadow Village" 20% fat were tested. These samples did not contain starch, but did contain palm oil. In the study of the cottage cheese of two samples "Full cat" 9% fat and "Prostokvashino" 5% fat, it turned out that starch is present in the sample "Full cat". The foreign substances found by us in milk and dairy products: palm oil in sour cream, starch in cottage cheese and milk powder in milk were not indicated on the packaging as part of the products. Homemade milk is in all respects suitable for human consumption, but it may contain pathogens that the cow suffers from and which are almost impossible to detect at home. Therefore, such milk must be boiled.

Thus, our hypothesis was partially confirmed. There is a legend about two frogs that got into a bowl of milk. One went to the bottom and drowned, and the other, in order not to drown, began to flounder and beat with her paws. After some time, a piece of butter was churned out of the milk, on which the frog climbed and got out of the bowl. But it seems that modern frogs are very unlucky in this respect: there is neither density nor fat content in milk. And it happens that there is no milk in milk.

6. List of used literature:

1. Valeology: Proc. allowance / Under the editorship of Solomin V.P., Varlamov Yu.L. - St. Petersburg, 1995.

2. Kovalko V.I. Health-saving technologies., Moscow, VAKO, 2007

3. Horse I.Ya., Baturin A.K. (ed.). Baby food. Moscow: Resurrection, 1994.

4. Zaitseva V. Nutrition ideal and real.//Health of children.-2007.- №6.

5. Weiner E.N. Fundamentals of rational nutrition. - Lipetsk, 1999.

6. Health: Teaching aid for teachers of grades 1-11 / Ed.

7. Mirskaya N. How to feed children//Health of children.-2004.-№1-p.32-34.

Internet resources:

3.http://www.elinahealthandbeauty.com/All_about_milk.htm

4.http://ru.wikipedia.org

5.http://www.medlinks.ru