Deana R. JONES,
Ph.D. Research Food Technologist
USDA Agricultural Research Service
Egg Safety and Quality Research Unit
According to estimated production values, 3.9 billion shell eggs were packaged for US retail in 2005 (American Egg Board, 2007). This was 60.4% of the total US egg production. These eggs are processed in one of three types of facilities: in-line, off-line or mixed operations. In-line processing facilities are becoming more common in the industry because they allow for the ease of having the laying hens on site. This removes the burden of transporting eggs to the processing facility and maintaining a nest run egg cooler. Furthermore, eggs are generally processed within 24 hours of lay preventing the need for on-farm refrigeration. There is extensive belting required for in-line complexes to deliver the eggs to the processing line. Feed, dirt/dust, feathers and broken eggs also travel on the belts and frequently enter the processing facility, falling below the egg line when there is a change in belts. Eggs from all flocks in the facility are generally combined on the collection belts and enter the processing facility together.
Off-line operations require eggs to be transported to the processing facility from remote farms. Eggs are generally transported on nest run egg carts or, occasionally, on pallets. These facilities must also maintain nest run egg coolers to store the eggs before processing. The nest run eggs must also move through the processing facility to the loader (located on the processing line). Off-line processing allows for batch processing of eggs from a single flock. This segregation can allow for targeted processing of eggs in order to meet customer quality needs. Mixed operations are in-line facilities which also have the capability of processing nest run eggs. This is generally utilized to meet customer orders in excess of facility laying capabilities and also for the processing of specialty eggs.
There can be drastic differences in structure and condition of egg processing facilities. Newer processing facilities often include environmental control, sealed surfaces and planned product flow. Older facilities can still be very effective in producing wholesome eggs of high microbiological quality, but are frequently more simplistic in their appearance. In summer, many of these facilities utilize cross-breeze and forced air to cool the processing environment. Many have low levels of building insulation. Furthermore, building surfaces are often worn with age and present challenges for facility cleaning and sanitation.
In a survey of shell egg processors conducted in 2003, half of the responses reported utilizing processing lines, which were 5 – 15 years old (Jones and Northcutt, 2005). As shell egg processing lines become worn they are often replaced with newer models. At this time, the line could be expanded to meet customer demand. Often, the new processing line is larger or in a slightly different configuration which can be cumbersome to retro-fit into an existing facility and can result in alteration of dry good storage and product flow in the facility.
Even the most effective production process can become contaminated from environmental sources. Understanding the microbiological status of a processing facility can aid in the development of more effective cleaning and sanitation programs. Furthermore, addressing the issues/factors contributing to equipment and facility microbial contamination allows for a more targeted approach in cleaning plan development. In our laboratories, we have conducted several studies focused on shell egg plant sanitation assessment. During this presentation, an overview of these results will be presented to assist participants in assessing their own cleaning and sanitation programs.
Survey of shell egg processing plant sanitation
A survey of microbiological levels present in shell egg processing plants was conducted in four south-eastern US states (Alabama, Georgia, North Carolina and South Carolina). A total of 9 processing lines were sampled in the joint project coordinated in our laboratory in conjunction with Auburn University, University of Georgia and North Carolina State University. Up to 30 sites were tested in each facility. The number of sites sampled was variable based on their presence in the facility (in-line, off-line, and mixed).
A 10 x 10 cm sterile gauze pad was moistened with 20 mL of sterile phosphate buffered saline in a sterile sample bag and utilized to sample predetermined locations within the processing facility. Mixed operations were they only facilities to have all 30 sites sampled. A negative control was prepared on site for each location to determine any potential background flora. Samples were taken immediately after the line was shut down at the end of the processing day (PRE) and again immediately prior to beginning processing the next day (POST). Samples were transported to our laboratory on ice and held at 4°C overnight before beginning laboratory procedures. All facilities reported conducting normal sanitation in procedures between samples times.
Samples were enumerated for total aerobic bacteria and Enterobacteriaceae. Total aerobic bacteria give an indication of general cleanliness. Enterobacteriaceae is the class of organisms which contains many human pathogens such as E. coli, Salmonella, and Enterobacter. Duplicate spread plates of plate count agar were utilized to enumerate total aerobic bacteria. Enterobacteriaceae were enumerated on duplicate pour plates of violet red bile glucose agar with overlay. The summary of results for contact, indirect contact and non-contact surfaces is found in Tables 1 – 3 (respectively).
There were no differences in bacterial counts on surfaces before and after sanitation for the processing lines sampled. Some of the highest levels of bacterial contamination were found on vacuum loader cups, recirculating water tanks, re-wash egg belts, processing room floor, and nest run carts. The levels of microbial contamination on the packer head brushes was also of concern since this is one of the last pieces of equipment the clean egg contacts before being placed in the egg carton.
Slade (2002) has suggested utilizing “zones” for sanitation procedures to increase their effectiveness. Utilizing the data from this study, sanitation programs could be revaluated for several areas to aid in more efficient sanitation. Improperly conducted sanitation practices can lead to increased microbial levels (Brake et al., 2003). Therefore, employee training and oversight is a key component to an effective cleaning program. Furthermore, cleaning compounds are often tested under laboratory conditions vs “real world” applications. Cleaning issues such as biological load, presence of protein and fat, and other issues may not be addressed during testing which could dramatically alter the effectiveness of the compounds (Powitz, 2002).
Further examination of vacuum loader cup microbiology
Vacuum loader cups were removed and rinsed at two shell egg processing facilities (a mixed and an off-line operation). Twenty cups were sampled at each of three visits per facility (total of 120 cups). Cups were randomly selected and placed in sterile sample bags with 50 mL of sterile saline. Each cup was rinsed for one minute before being aseptically removed and replaced on the processing line. Rinsates were transported to the laboratory on ice and immediately analyzed for the target bacterial populations.
Total aerobic counts and Enterobacteriaceae were enumerated as previously described. Campylobacter, Salmonella and Listeria were cultured via traditional pre-enrichment, enrichment and plating procedures as described by Jones et al. (2006).
Total aerobic bacteria and Enterobacteriaceae counts are summarized in Table 4. Aerobic levels were high (4.0 – 5.9 log cfu/mL) for all cups tested. Enterobacteriaceae levels ranged from 2.0 – 3.1 log cfu/mL. Enterobacteriaceae levels were higher for this study than the previously reported work (Jones et al., 2003). Differences in detected levels could be due in part to the whole cup rinse vs swabbing techniques utilized for the two studies.
Two (off-line facility) of the samples (1.6%) were positive for Campylobacter. Four (mixed operation) samples (3.3%) were positive for Salmonella. Two isolates each of Salmonella Anatum and Salmonella Heidelberg. Listeria was isolated from 86 of the samples (72%). The frequency of detection at the mixed operation was greater than the off-line facility (88% and 55%, respectively; P < 0.0001). After biochemical and motility testing, it was determined that one sample was Listeria monocytogenes and all other isolates were Listeria innocua.
The results of this study further substantiate the conclusions of previous research that more effective methods of cleaning and sanitation need to be developed for shell egg processing facilities (Davies and Breslin, 2003; Jones et al., 2003; Musgrove et al., 2004). While processors report that vacuum loader cups were replaced (due to wear) approximately every two weeks, levels of microbial contamination were higher than previously reported. With the identification of specific pathogens found on the surface of vacuum loader cups, more effective cleaning and disinfection programs can be developed to help eliminate growth niches.
While it appears more aggressive cleaning practices are warranted, it is also important to consider if the shell egg industry should be held to the same sanitation standards as the meat and poultry industries. During a study examining the effects of extended storage on the microbial quality of washed and unwashed eggs, it was determined that washed eggs maintained good microbial quality throughout 10 weeks of storage (Jones et al., 2004). Even though microbial quality remained high for washed shell eggs, emphasis should be placed on improving processing plant sanitation practices to enhance the wholesomeness of products from the facility.
American Egg Board. 2007. Industry facts. http://www.aeb.org/Industry/IndustryFacts.htm. Date accessed: January 26, 2007.
Brake, J., B. A. Lenfestey and S. Creech. 2003. The myths and realities of biosecurity and sanitation. 1. Teaching principles in the classroom. Poult. Sci. 82S:122.
Davies, R. H. and Breslin, M. 2003. Investigation of Salmonella contamination and disinfection in farm egg-packing plants. J. Appl. Microbiol. 94:191-196.
Jones, D. R., M. T. Musgrove, A. B. Caudill and P. A. Curtis. 2006. Frequency of Salmonella, Campylobacter, Listeria and Enterobacteriaceae detection in commercially cool water-washed shell eggs. J. Food Safety 26:264-274.
Jones, D. R, M. T. Musgrove and J. K. Northcutt. 2004. Variations in external and internal microbial populations in shell eggs during extended storage. J. Food Protect. 67:2657-2660.
Jones, D. R. and J. K. Northcutt. 2005. A survey of common practices in shell egg processing facilities and water use. Int. J. Poult. Sci. 4:734-736.
Jones, D. R., J. K. Northcutt, M. T. Musgrove, P. A. Curtis, K. E. Anderson, D. L. Fletcher and N. A. Cox. 2003. Survey of shell egg processing plant sanitation programs: Effect on egg contact surfaces. J. Food Protect. 66:1486-1489.
Musgrove, M. T., D. R. Jones, J. K. Northcutt, P. A. Curtis, K. E. Anderson, D. L. Fletcher and N. A. Cox. 2004. Survey of shell egg processing plant sanitation programs: Effects on non-egg contact surfaces. J. Food Protect. 67:2801-2804.
Powitz, R. W. 2002. A rational approach to using and selecting hard surface disinfectants and sanitizers. Food Safety Mag. 8:16-19, 51.
Slade, P. J. 2002. Verification of effective sanitation control strategies. Food Safety Mag. 8:24-29, 42-43.
From Proceedings of the “Midwest Poultry Federation Convention”, St. Paul, Minnesota, U.S.A.