Back After 5 years. Did lot of research on Problems in Mumbai and Andheri (East).
Now I have a test series right from the Diary board to detect Milk adulteration.
There are many methods known for detection of adulteration in milk but the
methods discussed below are simple but rapid and sensitive methods to detect
adulteration.
I. Detection of Neutralizers in milk
1) Rosalic acid test (Soda Test)
In milk neutralizers like hydrated lime, sodium hydroxide, sodium carbonate
or sodium bicarbonate are added which are generally prohibited.
How to detect?
Take 5 ml of milk in a test tube and add 5 ml alcohol followed by 4-5 drops
of rosalic acid. If the colour of milk changes to pinkish red, then it is
inferred that the milk is adulterated with sodium carbonate / sodium bicarbonate
and hence unfit for human consumption.
This test will be effective only if the neutralizers are present in milk. If
the added neutralizers are nullified by the developed acidity, then this test
will be negative. In that case, the alkaline condition of the milk for the
presence of soda ash has to be estimated.
How to proceed?
2) Take 20 ml of milk in a silica crucible and then the water is evaporated
and the contents are burnt in a muffle furnace. The ash is dispersed in 10 ml
distilled water and it is titrated against decinormal (N/10) hydrochloric acid
using phenolphthalein as an indicator. If the titre value exceeds 1.2 ml, then
it is construed that the milk is adulterated with neutralizers.
II. Test for detection of hydrogen peroxide
Take 5 ml milk in a test tube and then add 5 drops of paraphenylene diamine
and shake it well. Change of the colour of milk to blue confirms that the milk
is added with hydrogen peroxide.
III. Test for detection of formalin
Formalin (40%) is poisonous though it can preserve milk for a long
time.
How to detect?
Take 10 ml of milk in test tube and 5 ml of conc. sulphuric acid is added on
the sides of the test tube with out shaking. If a violet or blue ring appears at
the intersection of the two layers, then it shows the presence of formalin.
IV. Test for detection of sugar in milk
Generally sugar is mixed in the milk to increase the solids not fat content
of milk i.e. to increase the lactometer reading of milk, which was already
diluted with water.
How to detect?
Take 10 ml of milk in a test tube and add 5 ml of hydrochloric acid along
with 0.1 g of resorcinol. Then shake the test tube well and place the test tube
in a boiling water bath for 5 min. Appearance of red colour indicates the
presence of added sugar in milk.
V. Test for detection of starch
Addition of starch also increases the SNF content of milk. Apart from the
starch, wheat flour, arrowroot, rice flour are also added.
How to detect?
Take 3 ml milk in a test tube and boil it thoroughly. Then milk is cooled to
room temperature and added with 2 to 3 drops of 1% iodine solution. Change of
colour to blue indicates that the milk is adulterated with starch.
VI. Test for detection of glucose
Usually poor quality glucose is added to milk to increase the lactometer
reading. There are two tests available to detect the adulteration of milk with
glucose.
How to proceed?
1. Phosphomolybdic or Barford Test
Take 3 ml of milk in a test tube and add 3 ml Barford’s reagent and mix it
thoroughly. Then keep it in a boiling water bath for 3 min and then cool it for
2 min by immersing in tap water with out disturbance. Then add 1 ml of
phosphomolybdic acid and shake. If blue colour is visible, then glucose is
present in the milk sample.
2. Diacetic test
Take a strip of diacetic strip and dip it in the milk for 30 sec to 1 min. If
the strip changes colour, then it shows that the sample of milk contains
glucose. If there is no change in the colour of the strip, then glucose is
absent. In this method the presence of glucose in milk can be quantified by
comparing the colour developed with the chart strip.
VII. Test for detection of urea
1. Urea is generally added in the preparation of synthetic milk to raise the
SNF value.
Five ml of milk is mixed well with 5 ml paradimethyl amino benzaldehyde
(16%). If the solution turns yellow in colour, then the given sample of milk is
added with urea.
2. Take 5 ml of milk in a test tube and add 0.2 ml of urease (20 mg / ml).
Shake well at room temperature and then add 0.1 ml of bromothymol blue solution
(0.5%). Appearance of blue colour after 10-15 min indicates the adulteration
milk with urea.