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December 10, 2002
A: FROM MENTEE ROBIN B. IN CA
Ithink that non-pasteurized milk does not have bodily fluids
in it.
Pasteurization is when the milk is heated up to kill all the
bacteria etc in
it, so that it can have a longer shelf life. (That's why you
can sometimes
get milk that doesn't have to be refrigerated at all, because
it has been
extra-ultra-pasteurized.) So the milk has all the same stuff
in it before
being pasteurized as after being pasteurized, but some of
the living
organisms in the milk (germs) have been killed.
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December 10, 2002
A: FROM MENTOR SUZANNE FRANKS
IN KS
Naomi, pasteurization is a process in which milk is heated
to a specific
temperature for a specific length of time. For example, milk
might be heated to 63 degrees
Celsius for 30 minutes, or 72 degrees Celsius for 16 seconds.
(see http://www.foodsci.uoguelph.ca/dairyedu/pasteurization.html)
The heating process kills any organisms (bacteria) that might
be present in the milk that could cause spoilage. During the
heating
process, the milk is not allowed to be exposed to new sources
of contamination. So
pasteurization helps milk stay good longer, and also kills
any germs that might be hazardous to humans.
Since pasteurization is only a heating process, it does not
remove anything
from milk. The main difference between pasteurized and non-pasteurized
milk is
that potentially dangerous organisms, or organisms that might
speed up spoilage,
have been killed in pasteurized milk.
Milk is, itself, a bodily fluid, produced by the mammary glands
of cows, or
goats, or humans, or any mammals. Some things can get into
milk from the blood -
for example, if a human mother who is breast feeding is also
smoking, or drinking
alcohol, or taking drugs (prescription or illegal), these
substances might pass into the breast milk.
Likewise, sometimes cows can get into a field of grass where
there is a lot
of wild garlic chives, and then their milk can taste like
garlic.
In general, blood itself would not be present in milk. These
are two
separate fluid systems in the body. Substances present in
the blood - like alcohol, drugs, or
garlic - can pass from the blood into the milk. But the blood
system is generally separate
from the ducts where milk is made and stored.
Now, I am not a biologist, so maybe you will get a more detailed
answer on
this than I can give you as a biomedical engineer! But I hope
this helps.
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December 10, 2002
A: FROM MENTOR JOAN LUSK IN
RI
Milk is synthesized by the cells of the mammary gland. I'd
remembered hearing that the gland was "holocrine",
in which the
entire cell contents are secreted; but checking up on my memory
I
learned from http://classes.aces.uiuc.edu/AnSci308/intro.html
that the secretion
is "merocrine", in which the cells survive to make
more milk and
secret again. Blood is not secreted into the milk. In fact,
one
danger sign for breast cancer is finding a bloody discharge
from the
nipple - that wouldn't happen in a healthy woman. I suppose
that a
little secretion from sweat glands or sebaceous glands of
the skin
near the nipple could end up in milk by accident, but that's
surely a
very minor effect. Pasteurization simple heats the milk and
all it
contains - bacteria are killed, but nothing is physically
removed.
http://classes.aces.uiuc.edu/AnSci308/HumanLact.html
tells more about
human lactation.
Pasteurization is named for Louis Pasteur, an important founder
of
microbiology and its applications to curing and preventing
disease -
see
http://www.accessexcellence.org/AB/BC/Louis_Pasteur.html
for a
short bio. Oddly, Pasteur accomplished so much that the bio
here
doesn't even list the process named for him! The process of
pasteurization is described at
http://www.foodsci.uoguelph.ca/dairyedu/pasteurization.html
. A
major reason for pasteurizing milk is to kill the organism
that
causes tuberculosis, but the same heat treatment kills other
harmful
bacteria as well. The temperature and length of heating are
chosen
to sterilize the milk to the extent desired, while keeping
the nature
taste of milk as much as possible. See
http://www.foodsci.uoguelph.ca/dairyedu/TDT.html,
for example. In
the US, cheeses made from unpasteurized milk are generally
unavailable, but they are sold in Europe and are extra-flavorful.
Marketing unpasteurized milk products requires extra care
to be sure
the cows are free of diseases that pasteurization is designed
to
prevent be transmitted.
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