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Assessment of freshness of milk Table 1
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| Titrable acidity, °Т | Kipyatilny test | Spirit test | Characteristic Milk |
| Less than 16 16-20 | Changes | No | Milk is received from the patientanimal or it is diluted with water Fresh normal milk |
| 20-23 24-26 26-35 60 andmore | Changesno Can be curtailed Is curtailed Spontaneousfolding | Thin flakes It is a lot of flakes Large flakes Dense Clot | Milk stale and processing isn't subject Sour smack, it is impossible to use Sour on taste, it is impossible to use Folding at the room temperature |
Freshness of milk is expressed in degrees. The degree of freshness of - is the sum of value of titrable acidity and number of folding of milk.
The number of folding of - is the quantity of milliliters of 0,1 N of solution of sulfuric acid necessary for folding of 100 ml of milk. The degree of freshness of normal milk shouldn't be lower than 60. If in milk there were changes mainly under the influence of putrefactive bacteria, then folding of milk will require less acid. In such milk the degree of freshness will be lower, than in normal.
Falsification of milk is possible in places of his receiving or sending to the state enterprises of the dairy industry.
Milk is considered forged if foreign substances are added to it or a part of fat is removed from it.
At detection of falsification establish that it is added to milk (the nature of falsification) and in what quantity (extent of falsification). For definition of character and extent of falsification it is necessary to know physical and chemical indicators (a mass fraction (m) of solids, SOMO, fat and acidity) milk of the stall and studied tests. Most often milk is forged, adding water, skim milk or water with skim milk (double falsification). The forged milk sharply changes the structure and properties (tab. 2).
Change of structure and properties of milk at his falsification the Table 2
| Nature of falsification | ||||
| Indicator | Water | Fat-free milk (subremoval of cream) | Water + fat-free milk | |
| М.д.fat, % М.д. СОМО, % М.д.dry substances, % Density, г/см3 | 1. go down same -²- -²- | go down Doesn't change or slightlyraises Go down Raise | go down same -²- Almost not Changes |
Equipment, devices and technical means:
Flasks with a capacity of 150-200 ml, pipettes with a capacity of 1, 5 and 10 ml, burettes, test tubes, Petri's cups, areometer dairy, tile; 0,1 N solution of sulfuric acid, 0,1 N solution of a caustic natr, sulfuric acid with a density of 1,81-1,82 kg/m3; izoamilovy alcohol with a density of 0,810-0,813 kg/m3, 1% spirit solution of a fenolftalein, 68% solution of ethyl alcohol.
Work performance order
In a conic flask with a capacity of 150-200 ml measure 10 ml of milk by means of a pipette, add 20 ml distilled water and three drops of 1% - го spirit solution of a fenolftalein. Mix is carefully mixed and titrut 0,1 N solution of a caustic natr before emergence of the weak-pink coloring which isn't disappearing within one minute. Acidity of milk is equal in Turner's degrees to the quantity of milliliters of 0,1 N of solution of the caustic natr (heat) spent for neutralization of 10 ml of milk, increased on 10. Divergences between parallel definitions there have to be no more than 1 °Т.
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In mass analyses when a large amount of milk is subject to acceptance, define extreme acidity, i.e. acidity, is higher than which milk is considered sub-standard. In this case in a row the test tubes placed in a support are poured on 10 ml 0,1 N of the solution of alkali containing phenolphthalein and add 5 ml of the studied milk. Contents are mixed and watched coloring change. If solution has become colourless, so acidity of milk above norm.
When conducting heat test in a test tube pour 5 ml of milk and heat to boiling. Milk which titrable acidity higher than 24°T, at boiling is curtailed. Heating test allows to find also in fresh milk milk impurity with the increased acidity as the mixed milk at boiling also turns.
During spirit test in a test tube or Petri's cup pour 1 ml of the studied milk, add 1 ml of 68% ethyl alcohol, mix and monitor emergence of flakes of protein. As alcohol with a strength of 68% causes casein coagulation only at the acidity of milk exceeding 20°T spirit test gives the chance to reveal the extreme acidity of milk allowed by the standard and also to find sour milk in fresh. If acidity of milk is lower 20°T, then protein keeps the colloidal properties and milk doesn't turn. Lack of flakes curled up a squirrel testifies to freshness of milk. Formation of flakes, even hardly noticeable, indicates the lowered stability of proteins of milk.
Report on performance of a task
On the basis of the received results to make the conclusion about the general freshness of samples of milk and its suitability to further processing.On the basis of the received results to draw a conclusion on naturalness of milk, to define if necessary character and extent of falsification.
Control questions:
1. What requirements are imposed to milk as raw materials for production of dairy products?
2. For what purpose control heat stability of milk? In what ways?
3. State a technique of conducting alcoholic test.
Laboratory work №2
Definition of percentage of fat, the dry fat-free rest (SOMO) and density in tests of milk by means of the analyzer of quality of Laktan milk.
Work purpose: to get acquainted with a technique of definition of physical and chemical indicators in tests of milk by means of the analyzer of quality of Laktan 1-4 milk.
Task:
1. Will get acquainted with the principle of operation of the ultrasonic device "Laktan 1-4".
2. To determine percentage of fat, protein, the dry fat-free rest (SOMO) and density in tests of milk by the analyzer of quality of Laktan 1-4 milk.
3. On the basis of the received results to make the conclusion.
Short theoretical data
Analyzer "laktan 1-4" provide measurement in milk and cream mass fraction of fat, SNF and density. The principle of operation of devices based on the dependence of the propagation velocity of ultrasonic vibrations in milk, from its composition. Vosstaknovlenny milk, tinned test of milk, low fat milk and cream of different fat content can be an object of a research besides integral. Range of measurements of a massokvy share of fat makes from 0 to 20% (for cream fat content higher than 15% before the analysis prepare cultivation), SOMO — from 6 to 12%, density — from 1000 to 1040 kg/m3. As preservative for tests of milk it is possible to use a potassium bichromate.
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The Laktan 1-4 analyzer which appearance is shown in fig. 2 is placed in the plastic case consisting of two demountable parts: top and lower.
Fig. 2 Ultrasonic analyzer of Laktan 1-4 milk
In the top part of a raspolokzhena all main details of the analyzer, in the lower part there is a power supply. The lower part also serves as a support, obeskpechivayushchy stability of the analyzer in working situation. The upper and lower parts are connected in this position the guides, which also serve as contacts for electrical connection of the analyzer with the power supply. On the forward panel are located: the digital indicator, a holder for fixing of a the sample taker, the button for the choice of an operating mode of the analyzer, I will corrode for connection of the accumulator.
4 models of the Laktan-Super analyzer are created. Analyzers of models 150 and 200 with a productivity up to 30 tests in an hour of a calculated for application at the dairy plants of a small and average power, in farms. Devices of models 500 and 550 a performance to 200 tests an hour can be used at the large dairy enterprises, in the selection centers, regional laboratories
Equipment, devices and technical means:
drinking milk, flask, thermometer, water bath, OUSE device "Laktan 1-4".
Work performance order
The principle of measurement of a speed of distribution of ultrasound which is function of a mass fraction of fat, SOMO, density and temperature of milk (cream) is the basis for operation of the analyzer.
The analyzer consists of system of reception of milk (cream), the block of heating and a termostatirovaniye, the device of measurement and calculation on the basis of the microcomputer. In the measurement mode test is consistently warmed up to two set temperatures.
Before work the device is given into position. In the Laktan 1-4 analyzer after installation of a glass about breakdown of milk turn on the Start-up button in situation "Measurement", and on knot of control of the piston micropump the signal arrives. There is a fence of test of milk in a measuring cell in which within 1,5 min. she heats up and termostatirutsya at a temperature of 41 ° C. Then during 5 with at this temperature measure the geknerator frequency which is proportional to the speed of distribution of an ultrasound. After that test heats up to temperature of 65 °C, generator frequency is measured again. On values of the found frequencies of the microcomputer calculates mass fractions of fat and SOMO, values, which are displayed on indicators (everyone 5 c). After define of mass fractions milk merges in a glass about breakdown.
Preparation of the analyzer for use
1.1 Requirements to the measured samples:
1) The fresh, tinned, pasteurized, normalized, restored, skim milk and milk of long storage is allowed to the analysis.
2) Sampling is made in accordance with GOST 13928 and GOST 26809 (for milk and cream), in accordance with GOST 3622 (for powdered milk, the concentrated milk and ice cream) and according to indications of a technique of performance of measurements (further MVI).
3) Preparation of tests to be made according to requirements of MVI.
4) The working volume of the analyzed milk test – 25 mm3.
5) Acidity of the analyzed milk no more than 20 T °.
6) Temperature of the analyzed milk from 15 °C to 35 °C.
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