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Kovalevska
A.,Chala K.
National University of Food Technologies, Kyiv,
Ukraine
Examination of milk
Milk is a white liquid produced by
the mammary glands of mammals.
Milk Processing
Most milk undergoes processing
before you buy it at the store. The three primary steps include:
pasteurization, homogenization and fortification.
Pasteurization heats the milk to
destroy harmful microorganisms and prolong shelf life. Normal pasteurization
keeps milk safer while maintaining its valuable nutrients. Ultra-high
temperature (UHT) milk is pasteurized at a much higher temperature to make it
sterile. UHT milk is then packed into special containers that keep it safe
without requiring refrigeration.
After pasteurization, milk
undergoes homogenization to prevent separation of the milk fat from the fluid
milk. Homogenization creates a smooth, uniform texture.
Examination of milk
Finally, milk is fortified to
increase its nutritional value or to replace nutrients lost during processing.
Vitamin D to facilitate the absorption
of calcium. Vitamin A is frequently added to reduced-fat, low-fat and fat-free
milks. Vitamin A promotes normal vision, particularly helping the eyes to
adjust to low-light settings.
There is a direct relation between
a milk-supply and the health of the people of a community. Milk may contain
disease germs when it is drawn from a diseased cow. Disease germs may be
introduced into it by unhealthy workmen or from unclean containers; and the
ordinary changes which milk undergoes may render it unwholesome. The
supervision of milk-supplies is one of the important duties of a health
officer.
Fresh milk is:
White (Calcium casinate)
Opaque Fluid
Faintly Sweetish (Lactose)
Cow’s Milk (Yellow, Lactochrome)
Salty Milk (End or Start of Lactation)
Composition.—Milk contains all the elements of a complete food in about the
following proportions: Protein 3.6%, Fat 3.8%, Sugar 4.7%, Ash 0.7%, Water
87.2%.
Adulteration.—A lowering of the
percentage of fats and solids in milk is caused principally by the removal of
cream or the addition of water. These processes constitute two forms of
falsification.
Specific Gravity.—Milk that has been
skimmed or watered may usually be detected by means of its specific gravity.
The specific gravity of milk that is above the minimum standard of composition
is between 1.030 and 1.034. Removing the cream increases the specific gravity,
since fat is lighter than whole milk. Adding water lowers the specific gravity,
since it reduces the percentage of solids which are dissolved in the liquid
part of milk. If the specific gravity of a sample of milk is below 1.030 or
above 1.034, the milk may be considered to be adulterated. It is possible to
remove the cream and to add a sufficient quantity of water to preserve a normal
specific gravity, but a sample of such milk would be so thin and blue as to be
suspicious.
Test for Fat
The test for fat is nearly
always made by the Babcock method, in which the casein is destroyed by
sulphuric acid and the fat is liberated and collected as clear oil. The
apparatus required are a graduated pipet, a centrifuge, and a special flask
with a neck holding 2 c.c.
The method is as follows:
Mix 17.5 c.c. of milk with 17.5 c.c. of sulphuric acid in the flask, and
centrifuge the mixture four minutes. Add boiling water until the contents begin
to rise into the neck and centrifuge two minutes. Add more boiling water until the
contents rise nearly to the top of the graduated part of the neck, and
centrifuge one minute. The melted fat will then have collected as clear yellow
oil, and its quantity may be read by means of the graduations on the flask. The
weight of 2 c.c. of butterfat is 10 per cent. of the weight of the 17.5 c.c. of
milk that was used. If the fat is measured by 0.4 of the graduations on the
neck of the flask, its quantity is 0.4 of 10 per cent., or 4 per cent. of milk.
The price of milk at dairies
and creameries is usually governed by its percentage of fat as determined by
the Babcock method.
Bacterial Examination—a
bacterial examination of milk is usually made to determine the number of
bacteria, regardless of their kind. The examination consists either in making
cultures from the milk and counting the colonies which develop; or in making a
smear of the undiluted milk and counting the individual bacteria.
Kinds of Bacteria in Milk
The bacteria that are
usually found in milk may be divided into four groups:
·
those
producing lactic acid
·
those
of fermentation and decay
·
those
of human diseases
·
those
that are inert
Literature:
1.
https://ru.scribd.com/doc/20325229/Physical-Examination-of-Milk
2.
http://www.healthguidance.org/entry/8969/1/Milk.html
3.
http://www.healthyeating.org/milk-dairy/dairy-facts/types-of-milk.aspx
4.
https://ru.scribd.com/document/251731555/Milk-Products