Adulterants

The ease with which milk can be adulterated has always attracted unscrupulous persons to adulterate the same with numerous compounds. The most common of them include starch or cereal products, cane sugar, glucose, urea and ammonium sulphate. Tests for their detection are now available which can easily detect these compounds. Some of these compounds are highly injurious to the health of individuals.Laws are now available which can lead to the punishment for adding these prohibited substances. These compounds are primarily added to raise the density of milk.

i. Starch or cereal flour (atta)

Starch is a tasteless, odourless and cheap adulterant which is readily available. It is often added as an adulterant because it is not sweet like sugar. It is difficult to be detected organoleptically in small quantities. Starch can be easily detected as blue coloured starch iodide complex on heating and cooling with 1% iodine solution.

The demand for liquid milk is far greater than the availability of milk. This forces the adulteration with a view to make quick profits. A large volume of milk issupplied to the consumer directly by the producers through vendors at the door step without any sort of processing, packaging or quality control. The milk supplied to the consumers is most prone to adulteration, as they do not bother about such adulteration and are under the impression that they are getting pure milk. However,such milks are often maximum adulterated. Compared to vendors the milk supplied in the organized sector is tested for the adulterants by random analysis of procured samples. The easiest way is to adulterate the milk with water and keep the fat within the PFA limit. The addition of water, however, decreases the SNF content and is compensated by adulterating milk with cheaper solid ingredients like sugar,starch, urea etc.

Starch is detected by a very simple and quick test using 10% iodine solution. In the presence of starch a voilet blue colour of starch iodine complex is obtained on boiling.

•  Take 5 ml milk in a test tube. Boil the milk over a flame. Cool the milk.
•  Add 1 to 2 drops of iodine solution.
•  Formation of voilet blue colour indicates the presence of starch or cereal flour.

ii. Cane Sugar

Cane sugar is added to raise the total solids content in milk. This adulterant is readily available and is cheaper than milk solids. When added in large quantity it is detected by sweet taste imparted to milk. It can also be detected by resorcinol reagent, which gives redish brown colour in the presence of sucrose.

•  Take 5 ml sample in a clean test tube
•  Add 5 ml resorcinol reagent and mix well
•  Place the tube in a boiling water bath for five minutes or heat directly on the flame to boiling
•  Development of red colour with or without the separation of brown red precipitate indicates the presence of cane sugar in milk.

iii. Glucose

Glucose is added to milk to increase its density. It is odorless, colourless and is not as sweet as cane sugar. It is detected by modified Barfoed’s reagent either directly from milk or clean filtrate of milk. In the presence of glucose Barfoed’s reagent gives a deep blue colour. To detect glucose in milk.

•  Take 1 ml milk sample in a test tube.
•  Add 1 ml Barfoed’s reagent. Heat for 3 minutes in a boiling water and then cool.
•  Now add 1 ml phosphomolybdic acid reagent and mix.
•  A deep blue colour shows the presence of glucose. Pure milk only gives a faint blue colour.

iv. Urea

Urea is available readily as chemical fertilizer with farmers. It is often used as an adulterant to boost total solids after dilution with water or skim milk. Urea is detected in serum part of milk after removing casein from the filtrate in alkaline medium. In alkaline medium in the presence of phenol a bluish green colour indicates the presence of urea.

•  Take 5 ml milk in a 50 ml conical flask and add 1 ml acetic acid or TCA 24% solution and heat for 3 minutes in boiling water both. Filter the precipitate. Collect the filtrate
•  Take 1 ml filtrate, add 1 ml NaOH solution, followed by 0.5 ml sodium hypochlorite solution mix and finally add 0.5 ml phenol solution.
• A bluish green colour is formed with phenol in the presence of urea.

v. Ammonium Sulphate

Ammonium sulphate is also a fertilizer, it addition boosts the solids content of milk.Detection of ammonium sulphate is carried out on casein free filtrate prepared as per urea detection.

•  Take 1 ml filtrate, add 0.5 ml NaOH, 0.5 ml sodium hypochlorite solution and mix. Now add 0.5 ml phenol and heat for 20 seconds in boiling water bath.
•  Formation of a bluish colour which changes to dark blue shows the presence of ammonium sulphate. The colour is stable for over 12 hours.

Note: In pure milk only salmon pink colour is formed, which gradually changes to bluish in course of about 2 hours.

vi. Partial Removal of Fat by Skimming

An indication of the removal of excess fat from milk give the following changes to milk:

•  Lowering of fat percentage in milk
•  Higher density of milk sample at 27 0 C
•  Higher ratio of solids-not-fat to fat in milk

vii. Addition of Skim Milk

Addition of separated milk or skimmed milk results in following changes in the milk:

•  Addition of skim milk results in lowering of fat in milk
•  Higher density of toned milk sample at 27 O C
•  Higher percentage of solids-not-fat
•  Higher ratio of solids-not-fat to fat.

viii. Dilution of milk by addition of water

Milk is commonly adulterated by adding water as it is highly profitable. It causes following effects:

•  Fat percentage is lowered
•  Density of milk is lowered at 27 O C
•  Lowering of solids-not-fat content of milk
•  Lowering of freezing point depression of milk

i)Determination of Specific Gravity of Milk by Lactometer

In routine analysis of milk the density in determined with the help of a lactometer.The lactometer is graduated at a temperature of either 15.5 0 C or 27 0 C. Lactometer consists of a long, slender glass stem of uniform diameter connected to a larger glass chamber that facilitate lactometer to float. Lower end of the lactometer is filled with synthetic material which makes the lactometer to float and also keeps it in upright position.

•  Warm the milk to 40 0 C for 5 minutes
•  Cool the milk near the temperature of 27 0 C, the temperature of lactometer graduation.
•  Pour gently the milk in a 250 ml cylinder avoiding air bubbles and place the lactometer so that it floats freely.
•  Take the lactometer reading and note the temperature Take the average of two readings
•  Correct the lactometer reading from the table.

Lactometer reading for genuine cow milk is between 26-30 and 28-32 for buffalo milk. These readings are converted to specific gravity by prefixing 1.0 for lactometer readings e.g. a reading of 28 will give a specific gravity of 1.028.
 

Calculation

% TS =(C . L . R/4) + 1.2 F + 0.14

% S.N.F. = + 0.2 F + 0.14

Where TS = Total solids in milk sample

S.N.F. = solids-not-fat in milk sample

F = Fat Percentage in sample

C.L.R.= corrected lactometer reading at 15.5 0 C

Note: If the temperature is above 15.5 0 C then to each 1 0 C rise in temperature add 0.2 to each lactometer reading. On the other hand if the temperature in below 15.5 0 C then to each 1 0 C lowering of temperature subtract 0.2 from the lactometer reading. For example, if the temperature is 16.5 and reading is 30 then the C.L.R reading will be 30.2 (30+0.0.2). On the other hand if the temperature is 14.5 0 C and the lactometer reading in 29 then the C.L.R. will be 28.8 (29.0-0.2).

ii)Fat Determination

a) Gerber Method: For routine fat analysis of milk Gerber method is commonly followed for fat estimation. It is a rapid method and results are available in short time. Gerber method is volumetric method for fat analysis.

b) Roese-Gottlieb method: In this method fat is extracted from milk with the help of fat extraction reagent i.e. solvent ether. Ammonia and alcohol are added to facilitate fat extraction. Ammonia dissolves the fat globule membrane and alcohol helps in the passage of the fat globules in the aqueous phase. This is a gravimetric method of fat estimation.

iii) Freezing Point (FP)

Milk contains upto 85 percent water and varies widely in composition. Thus a constant parameter of milk is difficult to assign for milk. As such freezing point is a fairly constant property with a freezing point value between 0.530 to 0.555 0 C.Freezing point is a colligative property which depends upon the number of solute particles present in the system or solution. The solvent is water and its freezing point is always constant. On addition of water in milk the solute particles in the solvent are diluted which affect the freezing point of milk. This results in an increase in freezing point depression of milk. With cryoscopy the percent water added is calculated as percent-added water