Storage method affects microbial stability of eggs

摘要

Outbreaks of human Salmonella Enteritidis infections have shown that shell eggs and egg products are the most common sources. Storage conditions prove to play an important role in the level of contamination of the egg content. Eggs are often blamedas being the cause of salmonella infection in humans. How these eggs have been infected is not clearly understood. It is assumed that transovarial transmission and especially shell penetration, play an important role in contamination of the egg content.In order to better understand this process, we designed a research project that was aimed to determine bacterial count on the eggshell, the moment of egg content contamination and sensorial changes of fresh hen's eggs in dependence of storage temperature. We obeyed the EU - directive that demands chilling after 21 days and a shelf life of 28 days. Freshly laid shell intact white eggs (weight S to XL) -clean respectively soiled- were stored with the air cell up uppermost for up to 55 days at different temperatures and relative humidities (see Table 1). For semi-quantitative detection of bacteria on the surface of the egg, shell eggs (n= 188) were directly rolled on blood agar (Nahragar I, Sifin TN 1164 with 5 percent blood of cattle) and the media wereincubated at 30 deg C for 48h. The bacterial count of the shell surface of 20 eggs each (clean and soiled) 4 days old were investigated by dipping the eggs in sterile peptone water and rubbing off the surface using sterile swabs. At intervals of 10 days(up to 30 days of storage time) and then later at 5 day-intervals, a defined number of eggs were disinfected, opened and the mixed egg content was plated directly (blood agar and brilliant green phenol red agar (Sifin TN 1111); 37 deg C 24h and 30 deg C24h) and enriched (1 ml in 50 ml nutrient bouillon (Sifin TN 1172) +0,5 percent glucose 30 deg C, 24h; plating on blood and brilliant green phenol red agar; incubation; 37 deg C 24h and 30 deg C 24h). Isolated bacteria were characterised. The eggs were also sensorily investigated for signs of freshness, e.g. separation and viscosity of albumen, curvature of yolk and smell.