Salmonella contamination of shell eggs and subsequent recalls in 2010 resulted in economic losses to the egg industry and increased consumer concerns about the safety of eggs, according to Drs Craig D. Coufal and Christine Z. Alvarado of Texas A&M University. In addition, they continue, HACCP regulations for egg processing are probable in the near future.

Treatment of eggs with chlorine or quaternary ammonium (QAC) sprays as a final disinfection step following washing has been the standard for egg processing in the US for decades. The use of ultraviolet light (UV) as a final disinfection step for shell egg processing has been approved by the USDA but has not gained widespread use in the US egg industry.

Previous research has indicated that all the egg sanitistion processes listed above do not completely disinfect the surface of shell eggs during processing. As a result, more effective eggshell sanitisation technologies are needed to help assure the safety of shell eggs and egg products.

The overall goal of this project, sponsored by the US Poultry and Egg Association (USPoultry), was to develop and evaluate improved egg sanitization processes for shell eggs to enhance food safety.

The specific objectives were to:

1. survey egg processors across the US to determine current practices and costs of shell egg sanitisation
2. conduct a microbial survey of egg processing facilities to evaluate current sanitisation of shell eggs
3. evaluate the effectiveness of pre-wash egg disinfection procedures
4. determine efficacy and quality parameters of current methods of egg sanitization compared to alternative technologies and
5. conduct an economic analysis to compare current and alternative methods for the sanitization of shell eggs.

The survey of egg processors across the US indicated that egg sanitisation practices are quite standardised across the industry. This is not surprising since 77 per cent of respondents indicated they were processing eggs under inspection (presumably USDA) and must, therefore, follow set guidelines.

Eighty-three percent of egg processors are using a chlorine solution rinse in the final disinfection step.

Results also indicate that few processors apply a sanitisation process prior to egg washing or conduct microbiological monitoring. Eggs sampled from six egg packing plants in Texas verified that currently used egg sanitisation methods significantly reduce the microbial load on eggshells but usually leave a low level of bacteria remaining on the eggshell surface (2.1 log10 cfu per egg).

Four trials were conducted to evaluate the use of hydrogen peroxide (H₂O₂) in combination with ultra violet (UV) light to treat eggs prior to washing. Results indicated that treatment prior to washing resulted in fewer dirty eggs following washing, and visibly clean eggs after washing had lower microbial counts if they were treated prior to washing.

Several experiments were conducted to compare the effectiveness of eggshell disinfectants currently used in the egg industry to alternative methods of peracetic acid (PAA), PAA in combination with UV light, and hydrogen peroxide in combination with UV light.

Peracetic acid was found to be more effective than chlorine but less effective than QAC.

Hydrogen peroxide with UV light was the most effective sanitiser, resulting in zero microbial counts on most eggshells.

Sensory panel evaluation indicated that eggs treated with hydrogen peroxide and UV light were perceived by consumers to be equal to untreated eggs and eggs treated with QAC but eggs treated with chlorine received the highest scores for taste and texture.

While hydrogen peroxide with UV light was found to be a superior eggshell disinfectant to methods currently used in the egg industry, the cost is higher, according to Coufar and Alvarado.

In addition, experiments conducted to evaluate the effectiveness of various disinfectants to reduce Salmonella inoculated on eggshells found that all the disinfectants, including those currently used in the egg industry, reduce Salmonella on eggshell surfaces to levels below detection by rinse and plate sampling technique.

January 2014