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.

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.