LABEC M-MIA-LA User Manual
Page 64
Ultrasonic milkanalyser
Operation manual
04.11.09
62/107
The difference between tow consecutive measurements of one and the same
sample could not be more than 0,2 g for 100 g product.
4. Determination of casein content in the milk.
4.1. General
The methods are based on the Volker's method.
For making the analyses are used pure reactive for analyses (p.r.а.) and
distilled water or water with equal purity.
4.2. Sampling
According corresponding Appendices.
4.3. Basic principles.
Added to the milk formalin liberates acidic residuum from the protein's end
groups, which are titrated with soda caustic solution. The soda caustic
quantity is proportional to the casein in the milk content.
4.4. Necessary devices and reagents
- Glass 250 сm
3
.
- Pipettes Foll - 25,5 сm
3
.
- Pipettes Mor from 1 сm
3
, with division 0,1 сm
3
.
- Soda caustic p.r.а. - 0,143 n solution.
- Formalin 40% p.r.a - freshly neutralized.
- Phenolphthalein - 2 % solution in 70 % ethyl alcohol.
- Potassium oxalate p.r.а. 28 % water solution.
- Cobalt sulphate p.r.а. 5 % water solution.
4.5. Making the determination:
For cow milk
Reference sample preparation.
20 cm
3
from the measured milk are poured in a glass vessel together with 1
cm
3
3 % water solution of cobalt sulphate. The sample is shaken and a slight
rose color of the solution is received, which serves as a standard in the
research.
4.6. Making the measurement
20 cm
3
from the milk are measured in a glass and a titrated with 0,1 N soda
caustic, using phenolphthalein as an indicator, till the color of the standard
sample is reached. The volume of the used soda caustic is not taking into
consideration.
4 cm
3
38-40 % formalin are added towards the neutralized sample and the
rose color disappears as a result of the liberated carboxylic groups. It is well