Saturday, May 16, 2015

There is no need for eggs to be washed - even though it is common practice

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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