Eggshell Sterilization Methods

Introduction: Countless microbes are found on egg shells, and these microbes often signify health risks for any organisms that produce faecal matter, including human beings.  In order to destroy these bacteria, the industry has discovered numerous eggshell sterilization methods, including UV light treatment, “cold fog,” ozone, and washing. Ozone sterilization has drawbacks: small capacity and questions of safety regarding the environment and workers. Washing, on the other hand, removes the egg's layer of natural defense against bacteria.

Purpose: Thus the studies reported here represent a comparison of the two most widespread treatment technologies: UV light treatment and "cold fog” technology.

Methods: Freshly laid eggs were artificially inoculated separately with fresh cultures of either Listeria monocytogenes, Salmonella Enteritidis or Escherichia coli and incubated for 24 hours to produce on the egg surface a viable cell count of approximately 10⁸-10⁹CFU/ml. Then attempts were made to model both UV light and “cold fog” treatments in the way they are applied industrially.

Results: One result of the trials was that the time period of UV light as applied by the industry was insufficient in every case of bacteria we examined. Five minutes of treatment failed to approach the 10⁵-10⁶ order of magnitude viable cell count reduction that was expected.  The “cold fog” process brought the microbe count within the level of observability. Using this treatment, eggshells were sterilized according to current and frequently used parameters, besides which the shells contained no traces of preservatives.

Significance: It may be said, in summary, that as far as possible, it is advisable to choose eggs whose shells have been sterilized with “cold fog” process disinfectant material. Further, production plants where UV light sterilization is in use would be advised to change their technology such that the longest possible treatment time is applied.