EFFECT OF HEATING MILK OF INDIAN COWS AND BUFFALOES BY
DIFFERENT PROCESSES
By C. P. ANANTAKRISHNAN, NOSHIR N. DASTUR and ZAL R. KOTHAVALLA, Imperial Dairy Research
Institute, Bangalore
(Received for publication on 13 April 1943)
HEATING milk before its consumption is uni-
versally practised in India. The method and
extent of heating no doubt varies from place to
place. The most common practice is to bring the
milk to the first boil and then keep it simmering
over extended periods. In some places milk is
stirred just before and during simmering to pre-
vent frothing. Sometimes a few drops of water
are added to break the froth and heating continued
further, the former being repeated twice or thrice.
Milk contains many constituents which are
highly sensitive to heat and these no doubt would
be affected by the milk being subjected to heat
under the various processes. No systematic
study has been carried out in this country to esti-
mate the loss that occurs during processing as
carried out under Indian household conditions.
Valuable data are available on the nutritive value of
raw vs. pasteurized milks [Stirling and Blackwood
1933; Milk Nutrition Committee, 1937], but on
account of low temperatures employed during
pasteurization these results are not applicable to
Indian conditions. Andross [1940] in Scotland
carried out some studies on the loss that occurs
on first boiling and mentions that 10 per cent of
the nourishment of milk is lost on boiling. The
greatest loss occurred in the case of albumin
(74.0 per cent), fat (23.5 per cent), proteins
(13.5 per cent) and calcium (13.7 per cent).
In all such studies in foreign countries the work
has only been confined to cow's milk whereas
cow's milk and buffalo's milk and mixed milk
are peculiar to India and no data are available for
them.
In the present investigation the changes that
occur in the chemical composition of milk when
subjected to heat during some of the common
methods of processing followed in this country
such as first boil, boiling followed by simmering
for 10 minutes and pasteurization have been
investigated.
EXPERIMENTAL
As stated above the studies have been carried
out with three types of milk, viz. cow's, buffalo's
and mixed. The mixed sample was prepared so
as to contain 60 per cent of buffalo's and 40 per
cent of cow's milk, this being the relative pro-
portion in which milk is produced from these two
classes of animals under rural conditions in India
in general. The milk used was obtained from
the Imperial Dairy Institute farm and was used
about four hours after production. In all
cases six samples of each type of milk were
examined, the untreated sample being always
tested for comparison.
(1) Methods of estimating the milk constituents
The milk samples were analysed for the follow-
ing :—
(a) Total solids (Golding, 1934).
(b) Fat (Gerber).
(c) Proteins (Kjeldhal, total N × 6.38).
(d) Chlorides (Davies, 1938).
(e) Lactose (titration with permanganate). (A.
O. A. C., 1940).
(f) Ash (A. O. A. C., 1940).
(g) Acidity. (A. O. A. C., 1940).
(h) Calcium was determined from the ash solu-
tion by titration with potassium permanganate.
(A. O. A. C., 1940).
(i) Phosphorous by titration with alkali and
magnesium gravimetrically. (A. O. A. C., 1940).
(j) pH was determined colorimetrically using
bromothymol blue as an indicator.
(k) Citric acid. This was estimated gravimetri-
cally as penta-broma-acetone [Lampitt and Rooke,
1936] from the clear filtrate obtained as follows:
50 ml. of milk were placed in a 200 ml. volumetric
flask and diluted with water. To this were added
10 ml. of (1:1) sulphuric acid, 5 ml. of 40 per cent
KBr and 20 ml. of 10 per cent sodium tungstate.
The mixture was made up to the mark, shaken and
filtered. 150 ml. of the filtrate were used for citric
acid estimation.
(l) Curd test. For this 50 ml. of milk were placed
in a 100 ml. beaker and brought to the required
temperature in a water-bath. To this was added
1 ml. of commercial rennet diluted 10 times. After
stirring for 10 seconds, the mixture was left undis-
turbed. From time to time the contents of the
beaker were gently tilted to observe the formation
of flakes on the sides. When this happened, the
time was noted and taken as the curdling time.
In the testing of boiled milk samples, the diluted
rennet solution took a very long time to curdle milk
and the accuracy of the test suffered. To over-
come this difficulty, 1 ml. of original rennet was
used.
All the determinations, except for citric acid,
were carried out in duplicates and the averages of
these taken.
(2) Methods used in the heat processing of milk
A. Heating milk to first boil. 500 ml. of milk were
placed in an aluminium vessel (7½ inches diameter;
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