52
Bacteriological Examination of Milk
This conclusively proves that there is no
justification for taking the colour fringe of
ghee as characteristic of ghee. This test has
the same utility and limitations in its applica-
tion as the refractive index taken by itself.
Refractive indices and colour fringes of ghee
from animals fed on oil cakes
It is well known that the nature of the fat
included in the ration has a great influence on
the chemical composition of the milk secreted
fat [Hilditch and Thompson, 1936]. The wide
variation observed in fat from different species
of animals, collected in different seasons and
from different parts of the country, can in the
main be ascribed to this cause. In the present
studies some experiments have been carried out
on the effect of feeding varying amounts of same
cake to cows and buffaloes. The amount of
cake included in the diet varied from 2 lb. to
10 lb. per animal per day. Each feeding trial
covered a period of two weeks.
A typical series of data are given in Table
VII below.
TABLE VII
Refractive indices and colour fringes of butter fat
secreted by animals fed on sesame cake
Sample
No.
1
2
3
4
5
6
Quantity
of
Sesame
cake fed
in lb.
—
2
4
6
8
10
Cow butterfat
Refrac-
tive
index
at 40°C.
43.0
43.2
44.4
45.5
46.8
46.4
Colour
of the
fringe
Pink
Pink
Violet
Violet
Blue
Blue
Buffalo butterfat
Refrac-
tive
index
at 40°C.
4.18
43.7
42.8
44.5
45.0
45.0
Colour
of the
fringe
Red
Pink
Pink
Violet
Violet
Violet
These results once more emphasize the fact
that the colour fringes change rapidly with the
feed given to animals and hence cannot be
taken as an inherent characteristic of butterfat.
Detection of adulteration using refractive indices
and colour of the fringes
Some experiments on the detection of adul-
teration in ghee by noting the refractive index
and colour of the fringes were carried out. It
was found that unless the characteristics of the
original ghee sample were known, it was ordi-
narily not possible to classify samples adul-
terated with 25 per cent of foreign fats even as
suspicious.
SUMMARY
(i) Ghee samples from different parts of India
show wide range in their refractive indices
(39.0 to 45.2) and colour of the fringes. The
nature of the fringe colour may be of some value
in a small district where only one type of ghee
is produced, but the information obtained re-
garding the quality of the ghee by this method
cannot be any better than that given by the
refractive index.
(ii) Owing to the great variation in the colour
bands given by ghee from different parts of
India, adulteration upto anything less than 25
per cent cannot even be suspected.
(iii) There is evidence to show that the colour
of the fringe can be artificially manipulated,
e.g. by varying the temperature at which the
reading is taken or by adjusting the refractive
index of a mixture of fats which need not con-
tain ghee.
(iv) A close relationship exists between the
colour of the fringes and the refractive indices.
(v) The colour of the fringe and the refrac-
tive index are affected by the nature of the
food fed to milch animals.
REFERENCES
Athavale, V. T. and Jatkar, S. K. K. (1938). J. Ind
Inst. Sci., 21A, 15
Godbole, N. N. (1936). Current Science 4, 578
—
and Sadgopal (1938). Butterfat, 78
Hawley, H. (1935-36) Current Science 4, 815
Hilditch, T. P. and Thompson H. M. (1936). Bioch
mical Journal 30, 677
COMPARATIVE STUDY OF MILK AGAR AND MODIFIED MILK AGAR
FOR THE BACTERIOLOGICAL EXAMINATION OF MILK
By H. LAXMINARAYANA and E. V. SESHACHARYULU, Imperial Dairy Research Institute, Bangalore
(Received for publication on 14 July 1943)
MILK agar recommended by the Ministry of
Agriculture [1934] is generally used to determine
the number of bacteria in milk by the plate
method. As the prices of the constituents of the
medium, namely peptone and lemco, have greatly
increased due to war, Barkworth and Davis [1942]