MVSc

Pooled milk samples were collected from cow and
buffaloes maintained at the University Livestock Farm at weekly
intervals. Three chemical preservatives viz., formalin (0.4
per cent), potassium dichromate (0.4 per cent) and bronopol (0.1
per cent) were studied for their efficiency of preservation.
Calculated levels of preservatives were added and the
samples were stored at room temperature in dark place. Major milk
constituents like fat, total solids and solids not fat were estimated
in control and preserved samples. Physical properties of milk such
as pH, titratable acidity, clot on boiling test, lactometer reading as
well as efficiency of preservation were studied in control and
preserved milk samples ..
Milk samples treated with formalin could be stored up
to 90 days without any spoilage changes. A cream plug formed
after 24 hours of storage and a white sedimentation at the bottom
appeared after one month of storage.
Potassium dichromate treated samples could be stored
for 30 days. There after the samples curdled and became green in
colour towards the end of the storage period.

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Bronopol preserved cow and buffalo milk samples
could be stored for 24 and 16 days respectively and samples became
mild pink in colour as the storage period advanced.
There was a significant increase in titratable acidity in
cow and buffalo milk samples preserved with all the three chemical
preservatives. The increase in acidity was steady and progressive
in formalin and bronopol preserved samples. But an abrupt
increase in acidity was noticed in potassium dichromate preserved
samples immediately after the addition of preservative and there
after a successive decrease was noticed.
The pH values showed a significant decline during
storage in preserved milk samples. Decline in pH was abrupt in
potassium dichromate treated samples whereas it was gradual in
samples treated with the other two preservatives.
Formalin heated milk samples remained COB negative
throughout the storage period of 90 days, whereas potassium
dichromate and bronopol treated samples became COB positive
after 15 and eight days of storage respectively.
No significant variation was noticed in fat percentage
of preserved milk samples estimated by Gerber method. But a
slight decrease in fat per cent was observed in formalin and

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potassium dichromate treated samples. The concentration of Sulphuric
acid used was increased to 94 per cent for estimating fat percentage in
formalin preserved milk samples.
Formalin preserved samples showed inconsistent changes
in fat percentage estimated by Milko- Tester. So this method cannot be
recommended for formalin preserved milk samples. Bronopol treated
milk samples showed lesser variation in milk fat percentage estimated
by Milko-Tester when compared to potassium dichromate and formalin.
There was a non-significant increase in total solids and
solids not fat content in potassium dichromate preserved samples.
Potassium dichromate preserved samples showed
significant increase in lactometer reading, where as formalin and
bronopol treated samples did not show any significant changes in
lactometer reading.
Formalin appears to be ideal for the existing standard
methods of estimating milk solids. With the popularization of
instrumental methods for fast and accurate analysis of milk
constituents, formalin will not be suitable as a milk sample preservative
in future. Further, formalin and potassium dichromate have deleterious
effects on human health and environment. Even though bronopol is
little expensive, it is best suited for instrumental analysis of milk
constituents and safe for handlers. So, bronopol is recommended as a
preservative for the near future.