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Physico-chemical studies of milk Reductase test.The more microorganisms in milk, the faster the bleaching occurs, therefore, the rate of bleaching of methylene blue is an indirect indicator of the degree of contamination of milk.The reductase test results are indicative and cannot replace bacteriological analysis.

Physico-chemical studies of milk
Reductase test. When bacteria multiply in milk, the ruductase enzyme appears,
which is a product of their vital functions. Reductase has the ability to discolor some
dyes, such as methylene blue. The more microorganisms in milk, the faster the
bleaching occurs, therefore, the rate of bleaching of methylene blue is an indirect
indicator of the degree of contamination of milk. To do this, 2-3 drops of 1%
methylene blue after careful mixing are placed in a thermostat at a temperature of 37
° C, after pouring a small layer of liquid paraffin on top of the milk to stop air access.
With a large contamination of milk with microbes, bleaching occurs very
quickly: from several minutes to 1 hour. The reductase test results are indicative and
cannot replace bacteriological analysis.
Milk characteristic,
depending on the bleaching time of methylene blue
Bleaching
Duration
amount in 1 ml of
milk
Assessment
the class
More than 5,5 h
Less then 500 000. Good
1
from 2 to 5,5 h
from 500 000 to 4
mln
Satisfactory
2
from 20 min to 2 h from 4 mln to 20
mln
Bad
3
Less than 20 min
More than 20 mln Worse
4
The specific gravity of milk is determined by a special milk hydrometerlactodensimeter, which has two scales: the lower one to determine the specific
gravity, the upper one to determine the temperature of milk.
The specific gravity of milk can be expressed in g / cm3 or in conventional
values - degrees Keven. Each degree of Keven corresponds to a thousandth of a
gram. For example, with a specific gravity of milk 1,027, the density is 270 Kevena.
To determine the specific gravity, 150 ml of thoroughly mixed milk is poured
into a glass cylinder. The lactosensimeter is immersed in milk to the mark of 1.030 g
/ cm3 so that it does not touch the walls, and release it. The countdown is carried out
after 5 minutes on the scale of the device, determining the readings on the upper
border of the milk. At the same time, the temperature of milk on the upper scale is