Effect of rapid cooling of shell eggs on microcrack development, penetration of Salmonella enteritidis, and eggshell strength

Eggs were subjected to cryogenic cooling treatments using liquid CO₂ or liquid N₂. In order to minimize the thermal stress in eggshells due to rapid cooling, a two-stage air-cooling method was also evaluated in this study. Eggs were cooled from an initial temperature of 25C to approximately 7C. It was found that cooling produced microcracks on eggshells. However, rapid cooling did not increase the penetration of Salmonella enterica serovar Enteritidis (Salmonella enteritidis) into egg contents. When egg contents alone were sampled for Salmonella enteritidis, extending the immersion time from 24 to 48 h significantly (P < 0.01) increased the penetration of Salmonella enteritidis from 5.0 to 25.0%. When egg contents together with eggshells were sampled, Salmonella enteritidis was detected in 100% of the egg samples at the above two time intervals. There were no significant differences (P > 0.05) in the eggshell strength between control (no cooling) and cooling treatments, indicating that cooling did not weaken eggshell strength.