DETECTION OF ADULTERATION OF MILK WITH MILK POWDER
By K. N. SHAMA SASTRY and NOSHIR N. DASTUR, Imperial Dairy Research Institute, Bangalore
(Received for publication on 5 August 1946)
IN normal times cheap skim-milk powder is available and this is used freely in certain urban
centre to tone whole milk rich in. fat. If the milk powder solution is prepared carefully and tonning
so carried out that the final product conforms to the legal standard for fat percentage in milk, this
tonning cannot be detected by the routine methods normally used for testing milk. Nutritionally
such tonning is not objectionable but there is no doubt that the product cannot be regarded as genuine
milk. Further, such a practice has graver effects on the genuine liquid milk market than are
apparent at first sight and requires to be curbed by all available means.
The problem of adulteration of milk with milk powder is peculiar to the urban centres in India.
Studies have been, therefore, undertaken to find simple methods which will prove useful under house-
hold conditions and the laboratory. The results of these studies are given below.
Experimental
1. Milk powders used
Three brands of milk powders were used, viz., spray-dried skim-milk powder (New Zealand) ;
roller-dried skim milk powder (Benares) ; and roller-dried whole milk powder (Benares). Solutions
of different powders were prepared as follows :
(i) Spray-dried skim-milk powder. Skim-milk powder, 9.5 gm., was sprinkled over 90 ml. of
water (40ºC.), shaken for a minute and filtered through muslin. The fat percentage of this solution
was 0.1 per cent and the solids-not-fat content 8.4-8.5 per cent.
(ii) Roller-dried skim-milk powder. A quantity. 9.0 gm., of the powder were sprinkled over 90
ml. of water (60ºC.), shaken for one minute, cooled and filtered through muslin. The fat percentage
of the reconstituted skim-milk was 0.25 per cent and the S. N. F. varied from 8.4-8.5 per cent.
(iii) Roller-dried whole milk powder. Whole milk powder. 10.2 gm., was sprinkled over 90 ml.
of water (60ºC), shaken for a minute, cooled and filtered. The fat percentage of this solution varied
from 1.4-1.6 per cent and the S. N. F. from 8.4-8.5 per cent.
In all cases it was aimed to get S. N. F. of about 8.5 per cent and so the quantity of powder to
be used was varied accordingly.
2. Preparation of tonned milk
For preparing tonned milk, the fat percentage of fresh whole buffalo milk was brought to 4.0
per cent and that of fresh whole cow milk to 3.5 per cent by adding appropriate amount of
respective milk powder solutions.
3. Tests tried
(i) Stability to heat. Pure samples of milk, both raw and boiled can easily be distinguished
from similar samples of milk powder by their odour. However, such distinction could not be made
so easily with tonned samples. Hence trials were carried out by incubating the samples for different
lengths of time at 37ºC. This temperature was selected as facilities are usually available for main-
taining it in all public health laboratories.
In a series of experiments samples of milk and tonned milk, 50 ml. in glass stoppered bottles,
were kept at 37ºC. The flavour was compared at intervals of an hour over a period of eight hours.
It was found that under these conditions tonned milk samples developed a peculiar burnt flavour
which characterised them from other samples. This flavour became very pronounced after four
hours incubation and longer intervals did not seem to make much difference in the intensity of flavour.
This observation was made both with cow and buffalo tonned milks.
In the above experiments it was found that to distinguish tonned milk from pure milk, it was
necessary to have samples of raw milk for comparison. Due to the development of acidity during
incubation the burnt flavour in tonned milk became slightly masked. To overcome this, tests were
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