Concerning marketing standards of eggs, Regulation no. 2295/2003, defines 2 grades of eggs (A and B) according to different physical characteristics as follows: (i) Grade A eggs (“fresh eggs” or “table eggs* ”) should have a “normal, clean and undamaged” shell and cuticle; they will not be washed or cleaned before or after grading, and will be not chilled or treated for preservation.”; (ii) Grade B eggs, i.e. eggs “which do not meet requirements applicable to eggs in grade A”, may only be used by the food or non-food industries.
It is important to produce eggs that present the lowest health risks for the consumer. A major challenge is that shell eggs are considered a primary source of human salmonellosis in Europe. Egg-associated infections are mainly caused by S. Enteritidis.
The shell serves as a competent barrier to bacterial ingress with an array of antimicrobial properties for the egg. But it is a vulnerable package and its physical structures encourage the propagation of crack sites and so its handling following oviposition requires the minimum of trauma. Also, egg shell integrity declines with increasing bird age.
There are basically two routes by which the egg and its contents can become infected with bacteria:
1) 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.
2) Horizontal transmission, which can occur both before (internal) and after (external) shell formation. Infection of the egg contents can occur from the moment of ovulation onwards until consumption. Trans-shell movement of bacteria can occur under the appropriate conditions of temperature, humidity etc. in spite of a number of defence mechanisms to limit the effects of such an event.
The practice of washing of eggs has been mainly developed to clean dirty eggs (grade B). Nevertheless, another reason for washing eggs is to improve the hygienic quality of eggs by decreasing the bacterial load on the surface (“sanitizing”) and thereby preventing the infection of eggs by horizontal transmission of bacteria.
This opinion identifies and evaluates advantages and disadvantages, from a safety point of view, of using washing systems to sanitize table eggs (grade A).
Modern in-line egg washing procedures can normally be divided into three stages. The pre-washing or wetting stage is usually done using a gentle spray of warm water. The washing process typically involves rubbing the eggs with brushes and/or spraying them with jets of potable water containing chemicals. The final stage of the process, rinsing, aims to remove any loose debris that the egg has picked up during the main wash and also to remove the residues of any chemicals or other dissolved matter. These stages are followed by what may be referred to as post-washing treatments, such as drying and possibly oiling and/or cooling.
The major advantage of using washing systems for table (Grade A) eggs is the reduction of microbial load on the surface of “clean” eggs (sanitized eggs). Data regarding current egg washing practices indicates a bacterial reduction of 1 to 6 log10 units. However, sanitizing eggs will not prevent egg related diseases caused by microorganisms, such as S. Enteritidis, that are already present inside the egg. Table eggs sanitised by these means will contribute to a general hygienic improvement and a decrease in the potential for cross-contamination during food preparation.
The major disadvantage of egg washing is the potential damage to the physical barriers, such as the cuticle, which can occur during or after washing, for instance from incorrect operations, in particular washing eggs in cold water. Such damage may favour trans-shell contamination with bacteria and moisture loss and thereby increase the risk to consumers particularly if subsequent drying and storage conditions are sub-optimal. Whilst any shell damage should be seen as a disadvantage of washing, it should be balanced against the fact that washed eggs normally have considerably lower microbiological populations on the shell. Nonetheless,the aim must be to avoid, or at least minimise any such damage. No epidemiological data on the public health effect of egg washing is available.
There are also other options that can reduce the risks to consumers associated with washing of eggs. These include:
1. Preventing Salmonella spp. infection, especially S. Enteritidis, in primary layer production will reduce the occurrence of Salmonella spp. in eggs, especially on the surface of the eggs, and thereby reducing the risks associated with egg washing. If Salmonella spp. is not present, any risks associated with potential damage to the cuticle from washing, will be much lower compared with a situation where the birds may be infected with Salmonella spp.
2. The risks associated with egg washing can be reduced by the adoption of defined best washing practice procedures at all times. In countries where the washing of Class A eggs is permitted, the process is carried out using on-line systems whereby all eggs destined for Class A are treated. The process is undertaken immediately prior to grading and packing.
3. Prompt and thorough drying of eggs after washing and before packing is important to avoid mould growth and bacterial trans-shell penetration.
4. Oiling the cuticular surface of the egg which seals the shell pores can help to maintain the internal quality of eggs during storage and can thereby reduce the risk associated with washing.
5. Storage of eggs below 8°C could be an option to prevent growth of pathogenic bacteria such as Salmonella spp. present in the egg. However, after eggs have been refrigerated, they need to be kept in that state, mainly because a cold egg left out at room temperature can lead to condensation facilitating the growth of bacteria on the shell and probably ingress into the egg especially if the shell is damaged.
6. The use of UV-light either alone or in connection with washing can reduce bacterial load further. However, the reduction depends on the dose of UV used and on the protection of microorganism as a result of shadow as is the case in dirty eggs.
According to the information provided by Sweden, washed eggs had lower microbial counts on the shell surface than unwashed eggs and no movement of microbes from the shell to the content was reported following washing process. However, no data were provided regarding whether the particular Swedish washing process caused any damage to the shell cuticle. Moreover, specification of the maximum holding time for eggs prior to washing and of the maximum iron content for the water was not given. In Sweden, consumer preference is weighted in favour of washed eggs and the Swedish authorities point out that to ensure egg safety, the process must be conducted under the strictest rules with regard to operation of apparatus. "
The evaluation of advantages and disadvantages of egg washing need to be related to a particular system of washing. If well done, there are clear advantages to egg washing because of the reduced microbial load, but poor practices increase the risk. The greatest risk in relation to egg washing is penetration of the egg by Salmonella spp. Thus, in countries where the Salmonella prevalence in layers is very low, the risk of egg washing will also be lower. Taking into account the very low prevalence of Salmonella spp. in Swedish egg production, the risk associated with egg washing using the current system under strict rules is considered to be outweighed by the advantages of egg washing.