It's
important for all egg farmers – large and small - to produce eggs
that present the lowest health risks for consumers. Production of
visibly clean eggs, free from dirt and faecal contamination, is the
primary concern in the supply of table eggs and it's not hard as long
as the farm has good flock management practices.For the shelf life of
an egg and from a food safety perspective, it is important to lower
the level of bacterial contamination on eggs. If there is an increase
in the number of bacteria present on the egg shell surface, the
chances rise of eggshell penetration and contamination of the egg
internally. Washing and sanitising are common practices on some farms
but studies on the quality of stored eggs has frequently shown that
washing increases the probability of spoilage.The cleaning of eggs by
washing has been widely condemned.
The
egg emerges from the cloaca moist and at a temperature of 41°C and
organic matter adheres to the moist shell and as it cools bacteria
can be drawn into the pores of the shell (Sexton, 2014). The
outermost layer of the shell is the cuticle. This is a non-calcified
proteinacious layer added to the shell just before it leaves the
uterus. The cuticle is responsible for the smooth, glossy appearance
of a freshly laid egg and the cuticle protects the egg from invasion
with microorganisms. On the surface of the cuticle are pores that
extend through the calcified layer to the egg membrane. These pores
are responsible for the exchange of gases (oxygen into the egg and
CO2 out) and loss of water vapour from the egg interior. A typical
hen’s egg contains 6,500 pores, with the greatest concentration of
pores at the blunt end of the shell over the air cell. The shell is
not considered to be a significant obstacle to bacterial penetration
although the underlying shell membranes are a more effective barrier
. It is a vulnerable package and may crack. Egg shell integrity
declines with increasing bird age.
At
oviposition, 90% of eggs are germ free. The eggshell can be
contaminated by any surface with which the egg comes in contact.
Faeces, water, caging material, nesting material, insects, hands,
broken eggs, dust on the egg belt, blood and soil are the most common
sources of eggshell contamination Eggs
become contaminated internally by two primary means, transovarian or
trans-shell contamination
-
Freshly laid eggs may be contaminated through the oviduct and the presence of certain bacterial species can indicative of an infected bird. This is called vertical transmission, i.e., transovarian transmission of Salmonella spp., especially S. Enteritidis, which is dependent upon the presence of infected ovaries and the migration of bacteria across the vitelline membrane into the substance of the yolk during egg formation. Vertical transmission occurs as a result of Salmonella infection of the reproductive organs i.e. ovaries or oviduct and the egg yolk membrane or albumen surrounding is directly contaminated. Salmonella enteritidis is not endemic in Australian laying flocks.
-
Horizontal transmission, which can occur both before and after shell formation. Infection of the inner egg can occur from the moment of ovulation onwards until consumption. Trans-shell contamination involves the initial contamination of the egg surface, followed by the subsequent penetration by the microorganisms into the albumen or in some cases directly into the yolk. Trans-shell movement of bacteria can occur under the appropriate conditions of temperature, humidity etc in spite of the number of defence mechanisms to limit the effects of such an event
Washing
of eggs is rarely applied within the European Union, except by a few
packers in Sweden and one in the Netherlands however it is common in
the USA, Japan and here
inAustralia.
The practice of washing of eggs in Europe has been developed to clean
dirty eggs (grade B) however it seems
that in some countries where washing is practised it is seen as a
means of improving microbial quality and of reducing the risks of
infection of the internal egg.
.
In Australia the vast majority of eggs are washed prior to packing to
remove dirt and faecal material and in
an effort to
reduce the microbial contamination of the egg shell. However,
if the washing process is not carefully controlled, it c an actually
increaxse the level of contamination.
The
EU is concerned about egg washing and the possibility of
deterioration of the cuticle, which protects the egg against
dehydration and offers a natural barrier to common microorganisms,
and occasional pathogenic microorganisms, present in the flora that
colonise the surface of the egg. There is also concern in the EU and
in Australia that
washing is
used to cover up poor husbandry and hygiene standards on farms and in
packing centres.
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