Microbiology
in
Dairy
Products
Milk
and
dairy
products
constitute
an
important
item
of
our
food.
These
products
are
very
suitable
for
microbial
growth.
It
thus
becomes
necessary
to
know
the
chemistry
of
milk,
its
spoilage,
method
of
preservation,
and
different
dairy
products
where
microbes
play
a
positive
rather
than
negative
role.
Milk
is
considered
as
a
complete
food
and
it
contains
proteins,
fat
,
carbohydrates,
minerals,
vitamins
and
water.
It
is
also
a
good
medium
for
the
growth
of
microorganisms.
It
is
therefore,
important
to
know
the
types
of
microorganisms
present
in
milk,
their
control
and
use
for
beneficial
purposes.
Milk
contains
relatively
few
bacteria
when
it
is
secreted
from
the
udder
of
an
healthy
animal.
However,
during
milking
operations
it
gets
contaminated
from
the
exterior
of
the
upper
and
the
adjacent
areas,
dairy
untensils,
milking
machines,
the
himds
of
the
milkers
from
the
soil
and
dust.
In
this
way
bacteria,
yeasts
and
molds
got
into
the
milk
and
constitute
the
normal
flora
of
milk.
The
number
of
contaminants
added
from
various
sources
depends
on
the
care
taken
to
avoid
contamination.
The
presence
of
these
nonpathogenic
organisms
in
milk
is
not
serious
but
if
these
organisms
multiply
quickly,
they
can
cause
spoilage
of
milk,
such
as
souring
or
putrefaction
and
develop
undesirable
odours.
Control
of
their
multiplication
in
milk
is
therefore,
very
essential.
Milk
may
also
contain
pathogenic
organisms,
derived
directly
from
the
animal
or
from
the
surroundings.
Microorganisms
that
are
harmful
and
found
in
milk
are
Streptococcus
cremoris,
Pseudomonas
sp.,
Mycobacterium
spp.
Serratia
marcescens,
enteric
bacteria
etc.
Normally,
milk
is
pasteurized
before
use.
However,
pasteurization
does
not
kill
all
the
bacteria;
the
survivors
(thermodurics),
depending
on
their
initial
number.
then
multiply
and
if
the
initial
number
is
high
they
cause
rapid
spoilage.
It
is
imporant,
therefore,
that
the
milk
be
refrigerated
at.
around
O°C
soon
after
pasteurization
to
prevent
the
growth
of
these
undersirable
microorganisms.
Pasteurization,
either
at
145°F
for
30
minutes
or
161°P
for
15"'30
seconds
eliminates
most
of
the
pathogenic
bacteria
particularly
Mycobacterium
tuberculosis.
Boiling
of
milk
destroys
all
microorganisms
except
spore
formers.
Sometimes,
on
cooling
or
under
improper
refrigeration,
spores
germinate
and
cause
spoilage
of
boiled
milk.
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