Objectives:
To detect the adulteration in milk by qualitative and quantitative tests.
Relevant information:
Milk is commonly adulterated with water to increase the volume so as to derive extra profit. Additional separated milk or partial removal of fat are the other forms of adulteration of milk. Further milk is also adulterated with water soluble solid substance to adjust lactometer reading. The mixing of buffalo milk with cow milk/ goat milk and then selling as buffalo milk is also taken as a part of adulteration of milk.
Precaution:
Control tests of pure milk is essential while deciding the purity of milk.
Detection of water by Cryoscopic method:
Freezing point of milk is the only reliable test for detecting adulteration of water in milk. The freezing point of any solution is proportional to its osmotic pressure of the concentration of dissolve particles. The freezing point of milk is dependent on the slats and lactose present in it and is remarkably constant. Additional water will lower the osmotic pressure and is proptional to the amount of water added. Thus by determining the depressing of freezing point of milk sample, the quantity of added water may be determined.
Material required:
Milk adulterated and pure milk,
Ice,
Conc. Sulphuric acid,
Diethyl either, ethyl alcohol and fresh distilled water.
Sucrose solution A: 7 gm of pure sucrose dissolved in distilled water the volume is made upto 100 ml at 20 0 C.
Apparatus:
Hortvet Cryoscope
Control thermometer with scale range from 20-30 0 C with scale graduation accuracy of 0.1 0 C standard thermometer with a scale range from 1 0 C to 2 0 C & with scale graduation of 0.1 0 C ( This is differential thermometer of Backman type specially designed for milk testing).
Procedure:
Make three freezing point determinations as directed under (B) on each of the following:
1. Recently boiled distilled water
2. Sucrose solution
3. Sucrose solution
Tabulate the results in following form.
Express the results as degrees of freezing point depression below the average of observed freezing points obtained on the sample of the pure water (-w) which mean above (+) or (-) the 0 mark on the scale.
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Freezing point “7 gm sucrose Soliction A” 10 gm sucrose sol. B
Observation ——————————————— —————————————–
Pure Observed Freezing Observed Freezing
Water freezing Point freezing Point
(-w) Points (-s) depression Point (-s) depression
(S-w) (S-w)
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Average:
Obtain each freezing point depression of the sucrose solution by the algebraic subtraction of the average of the freezing point reading of pure water (+w) from each observed freezing point (omit results which are in market disagreement) Apply the average of the freezing point depression obtained on the standard sucrose solution for the purpose of correcting the thermometer reading obtained on sample of milk in the manner illustrated in the table.
