Egg washing methods have greatly changed and improved in the last 60 years. Today the industry uses high-speed washing methods which have greatly improved control of wash water temperature, pH and proper use of detergents and sanitizers. However, there is a need to obtain further data on the effect of commercial processing on the bacterial load in shell eggs. Musgrove et al., 2005 (Journal of Food Protection 68:2367-2375) have recently studied the variation of microbiological populations on egg shell surfaces during commercial processing of shell eggs.
These researchers at the USDA Richard B. Russell Agricultural Research Center in Athens, Georgia surveyed three large in-line shell egg processing facilities in the Southeastern United States. Plants were designated as X, Y and Z. Eggs were collected at 12 processing points: the accumulator, prewash wetting, first washer, second washer, sanitizer spray, dryer, oiler, scales following check detection and candling, rewash belt entrance, rewash belt exit and packaging (two different packer belts). Aerobic bacteria, yeasts and molds, Enterobacteriaceae, Escherichia coli and Salmonella were monitored on the shell surface at each processing point.
All populations decreased throughout processing in all plants. Yeasts and molds in the shell rinse at the accumulator were not significantly different for any of the plants. When considering other populations, plant Y was found to have the lowest shell surface contamination at the accumulator. Shell rinse contamination for all populations was highest at the accumulator and the rewash belt.
Salmonella positive eggs were most prevalent at the accumulator, prewash rinse or rewash belts. Salmonella found ranged from 0 to 48% of pooled samples in three repetitions. Higher concentrations of Salmonella were observed from preprocessed than ready-to-pack eggs. Overall, their data indicated that commercial processing decreases microbial contamination including Salmonella on egg shell surfaces.
These authors observed that microbial contamination varied between plants. They noted that plant X was the oldest plant and the highest production capacity. Plant X also had the lowest wash water pH at 10.0; plants Y and Z had wash water pHs of 10.3 and 11.2, respectively. Earlier research has shown that wash water pH can affect the kill of microorganisms.
Other factors are also known to influence Salmonella survival such as wash water temperature, organic build up in the wash water and iron concentration. These authors postulated that contamination with organic matter and wash water temperature could also have been a factor affecting levels of contamination between plants.
This is an excellent study which should be of real value to our industry. We need to gain a better understanding of levels of microbial contamination on the egg shell. Any contamination on the shell can later penetrate the shell into the contents during storage. (Dr. Glenn W. Froning, Professor Emeritus, Department of Food Science and Technology, University of Nebraska, Lincoln, NE 68583-1919)