Trip Answers

Question answered:16/06/08

Using our usual sources of information, namely the NLH Library and the TRIP and Medline databases we found relatively little information to answer this question.

 

However, the British Egg Information Service website offers detailed information on the nutritional analysis and constituents of the egg. In relation to fats, it states:

 

“Fat
11.2% of the egg content is fat. The fat of an egg is found almost entirely in the yolk; there is less than 0.05% in the albumen.
Approximately 17% of an egg’s fatty acids are polyunsaturated, 44% monounsaturated and only 32% saturated.” [1]

 

Concerning the risk of salmonella, we found two rather old references in the Medline databases, dating from 1994 and 1991 respectively and both are by the same author. The abstracts of these articles read:

 

“Salmonella enteritidis can contaminate the contents of clean, intact shell eggs as a result of infections of the reproductive tissue of laying hens. The principal site of infection would appear to be the upper oviduct. In egg contents the most important sites of contamination are either the outside of the vitelline membrane or the albumen surrounding it. In fresh eggs, only few salmonellas are present and as albumen is an iron-restricted environment, growth will only occur once storage-related changes to vitelline membrane permeability, which allow salmonellas to invade yolk contents, have taken place. When this happens high populations are achieved in both yolk contents and albumen. Some eggs from naturally infected hens have been found to contain large numbers of S. enteritidis. The rate of change in membrane permeability is temperature-dependent. In eggs stored at 20 degrees C, yolk invasion is uncommon until eggs have been stored for 3 weeks. In stimulated kitchen conditions where temperatures reached 30 degrees C, salmonellas could grow rapidly after a few days.” [2]

 

“Over 5700 hens eggs from 15 flocks naturally infected with Salmonella enteritidis were examined individually for the presence of the organism in either egg contents or on shells. Thirty-two eggs (0.6%) were positive in the contents. In the majority, levels of contamination were low. Three eggs, however, were found to contain many thousands of cells. In eggs where it was possible to identify the site of contamination, the albumen was more frequently positive than the yolk. Storage at room temperature had no significant effect on the prevalence of salmonella-positive eggs but those held for more than 21 days were more likely (P less than 0.01) to be heavily contaminated. In batches of eggs where both shells and contents were examined, 1.1% were positive on the former site and 0.9% in the latter.” [3]

 

Given the comparative lack of information to answer this question, we would recommend contacting the British Egg Information Service for further assistance:

 

The British Egg Information Service,
52A Cromwell Road,
London SW7 5BE
Tel: 0207 052 8899

 

References
1. British Egg Information Service. Nutritional values of the egg. (http://www.nutritionandeggs.co.uk/eggs_nutrition/nutrition1.html)
2. Humphrey TJ. Int J Food Microbiol. 1994 Jan;21(1-2):31-40. Contamination of egg shell and contents with Salmonella enteritidis: a review. (http://www.hubmed.org/display.cgi?uids=8155476)
3. Humphrey TJ, Whitehead A, Gawler AH et al. Numbers of Salmonella enteritidis in the contents of naturally contaminated hens' eggs. Epidemiol Infect. 1991 Jun;106(3):489-96. (http://www.hubmed.org/display.cgi?uids=2050203)

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