THE VARIATIONS OF ACIDITY, ALCOHOL TEST AND PHOSPHATE
NUMBER IN SAMPLES OF FRESH BUFFALO MILK
By PANWAR GAJ-RAT SINGH, T. M. PAUL and C. P. ANANTAKRISHNAN, Indian Dairy Research
Institute, Bangalore
(Received for publication on 17 December 1946)
G ENERALLY milk can withstand high temperature without undergoing any unwelcome change
and this is a very important factor both from the manufacturers' as well as the consumers' points
of view. But, it is not very uncommon that sometimes certain samples of milk do not stand even
the ordinary boiling. To determine the hygienic .quality as well as to assess the suitability or other-
wise of the different lots of milk arriving on a factory platform for various methods of processing
different platform tests have been suggested from time to time. The boiling test, acidity determina-
tion, alcohol test and phosphate test are the chief among them. The boiling test when positive,
indicates that the milk has developed rather high acidity, which removes calcium from combination
with the protein, and therefore allows casein to settle. Boiling only accelerates the last phase of
this reaction. Acidity determination, as it is usually done, by titration against decinormal sodium
hydroxide, does not give a correct picture of the true acidity of a complex fluid like milk according
to Rogers et al. [1921]. Even the true acidity of milk as determined by pH value is not a criterion in
ascertaining the heat stability of milk according to the same authors. Again, acidity of milk from
individual animals, is subject to considerable variation and the value of acidity determination be-
comes very questionable. Thus the usefulness of the acidity test is limited to the detection of milk
that has developed considerable amount of acidity as a result of bacteriological action caused by
unhygienic ways of production. The alcohol test has been commonly used for weeding out milk
produced under unhygienic conditions, as well as those that are unstable to heat. According to
Sommer and Binny [1923] this test is subject to the influence of various factors, so much so, that its
usefulness is very restricted. The findings of Dahlberg and Garner [1921] do not guarantee that
this could always be used as a criterion of the heat stability of milk. The effects of acidity and the
concentration of salts are additive so far as the alcohol test is concerned, but Rogers and Deyshire
[1921] and Sommer and Hart [1926] suggest that the concentration of the mineral salts forms only
a minor factor in determining the heat stability of a milk. In fact no test which could predict the
heat stability of condensed milk with a reasonable amount of certainty was known till Ramsdell
et al. [1931] developed the phosphate test. The above authors have reported a phosphate number
ranging from 12 to 37 for single herd milk samples from Freisian and Channel Island breeds and
composite milk samples. According to their findings, milk samples with a phosphate number below
20 coagulated within four minutes during sterilization, while samples with a phosphate number above
20 had greater heat stability, but at the same time, they warn that a high pho phate number does
not always indicate a highly heat resistant milk sample.
Although there is no local or even seasonal surplus of milk in India for the manufacture of con-
densed milk, during the last war various isolated attempts were made in certain places to manufac-
ture condensed milk out of buffalo milk. Anantakrishnan and Kothavalla (unpublished work) have
reported that the alcohol test is more reliable than the phosphate test in predicting the suitability
of buffalo milk for condensing and sterilization, but this is just the contrary of the findings of Rams
dell et al. [1931]. Probably this difference might be due to certain peculiarities in the phosphate
number of buffalo milk as distinct from cow's milk which alone was investigated by the foreign
authors. Therefore a study of the seasonal and lactational variations in the phosphate number with
special reference to its relation to other platform tests like acidity and alcohol tests was undertaken
and the results of the investigation are presented in the following pages.
EXPERIMENTAL
Six Murrah buffaloes, all in the first month of lactation, were selected from the herd of the Indian
Dairy Research Institute. Milk samples were collected in the morning and tested for acidity, alcohol
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