Design a HACCP plan for shell egg processing.

Egg temperature as well as wash water pH and temperature play key roles in reducing microbial growth in shell eggs. These are important considerations for those developing a HACCP plan for shell egg processing lines. Researchers at North Carolina State University (Department of Food Science, Box 7624, Raleigh, NC 27695) have compiled data from published research related to the shell egg processing environment that could help companies developing a HACCP plan.

Shell eggs can acquire bacteria from every surface they contact. Egg temperature during processing is very important. USDA regulations require that wash water temperature be at 90 F or higher, or at least 20 F warmer than the highest egg temperature (whichever is greater). These temperatures must be maintained throughout the cleaning cycle. The temperature of incoming eggs will vary from season to season and from operation to operation. In off-line processing plants-where eggs are brought in from outside operations-initial internal egg temperatures of 62 F to 68 F are likely.

Although pre-processing coolers are held generally from 50 F to 60 F, egg temperatures decline only slightly. Egg temperatures at processing reflect initial internal temperatures. Regulations require that wash water be changed every 4 hr or more if needed to maintain sanitary conditions. When the difference between wash water temperatures is greater than 40 F, thermal checks and cracks increase, allowing surface microbes greater access to the interior of the egg.

Contact between wash water and eggs during processing causes the internal egg temperature to increase. Although blow drying the eggs after washing them causes a slight decrease, internal egg temperature rises generally throughout the process, and can continue to rise for up to 6 hr after the eggs are placed in a cooler.

The best approach for reducing microbial populations in wash water tanks and on eggs is to add detergents in amounts sufficient to maintain a pH of 11. Alkaline cleaning formulations produce an initial pH in the wash water near 11, and pH during operation continues in the 10 to 11 range, which is usually unfavorable for growth of most bacteria.

But many shell egg processors have no idea what the pH of their wash water is. Many monitor pH only at the start of a shift. The pH may be 10 or 11 at the beginning of the shift, but recycling wash water, overflow losses and replacement water help reduce pH levels. There is often little thought to maintaining a constant pH. When dual-tank systems are used, the pH in each tank can be different, depending on how the wash systems are connected.

The Food Production and Inspection Branch of Agriculture and Agri-Food Canada monitors egg-grading stations routinely in Canada, to ensure that egg washing guidelines are followed. The guidelines include: maintaining wash water at a temperature of 43.3 C; maintaining wash water at pH 10; maintaining and routinely cleaning washers and their parts; and completely changing wash water and cleaning holding tanks every 2 hr to 4 hr. These guidelines were developed to eliminate pathogens that may be present in the wash water and to minimize microbial contamination of the washed eggs.

Researchers also have found that the growth rate of S. enteritidis in eggs responds directly to the temperature at which the eggs were stored. Holding eggs at 40 F to 45 F reduced the heat resistance of S. enteritidis. It has been suggested that refrigeration reduces the level of microbial multiplication in shell eggs and lowers the temperature at which the organism is killed during cooking. This may be adequate justification to store eggs at 40 F to 45 F.

Further information. Patricia Curtis; phone: [phone]; fax: [phone]; email: [e-mail].