The microflora of raw milk and the impact of milk on their survival at low pH : a thesis presented in partial fulfilment of the requirements for the degree of Doctorate of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
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Date
2015
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
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The Author
Abstract
Milk
is
an
excellent
food
source
as
it
contains
a
plentiful
supply
of
nutrients
and
minerals.
Although
normally
consumed
after
pasteurisation,
there
is
growing
evidence
that
raw
milk
provides
health
benefits
beyond
nutrition
alone.
Epidemiological
studies
of
children
have
shown
that
those
who
regularly
consume
raw
milk
appear
to
have
a
lower
incidence
of
asthma
and
non--specific
allergy
than
those
who
consume
processed
commercial
milk.
The
gastrointestinal
tract
is
a
key
location
for
immune
development
as
interaction
with
microflora
can
occur
at
the
mucosal
surface.
Milk
may
have
a
role
to
play
in
the
early
stages
of
this
process
either
due
to
the
microbes
it
harbours
or
to
the
physical
and
chemical
properties
of
milk
itself.
The
aim
of
this
study
was
to
identify
bacterial
isolates
unique
to
raw
milk,
that
would
not
survive
pasteurisation;
and
to
determine
whether
milk
allowed
for
a
greater
survival
of
these
bacteria
during
ingestion.
Bacterial
isolates
were
cultured
from
either
raw
or
pasteurised
milk
and
tested
for
their
ability
to
survive
pasteurisation.
A
subset
of
thermosensitive
isolates
were
identified
for
further
analysis
representing
those
species
likely
to
be
present
in
raw
milk
but
not
processed.
This
thermosensitive
subset
was
challenged
for
their
ability
to
tolerate
acid
conditions
(pH
2.5)
both
in
the
presence
and
absence
of
milk
to
determine
the
likelihood
of
their
survival
during
ingestion.
A
high
throughput
acid
tolerance
test
was
developed
to
screen
raw
milk
bacteria
for
acid
tolerance.
Data
supports
the
hypothesis
that
milk
significantly
increased
the
survival
of
raw
milk
bacteria
exposed
to
pH
2.5
and
that
specific
components
found
specifically
in
milk
were,
at
least
in
part
responsible
for
this
effect.
In
conclusion,
a
unique
subset
of
bacteria
found
only
in
raw
bovine
milk,
and
not
in
processed
milk,
has
been
identified
that
when
ingested
with
milk
are
able
to
come
through
an
acid
challenge
not
dissimilar
to
that
of
the
stomach
and
survive.
This
opens
the
possibility
that
these
bacteria
present
in
raw
milk
are
able
to
enter
the
lower
GI
tract
and
interact
with
the
immune
system
via
Peyers
patches.
Description
Keywords
Raw milk, Microbiology, Health aspects, Gastrointestinal system, Low pH, Acid tolerance