Correlation of eggshell strength and Salmonella enteritidis contamination of commercial shell eggs

Equivalency of peroxyacetic acid to chlorine as a shell egg sanitizing rinse

In the United States, all shell eggs processed under the USDA Agricultural Marketing Service voluntary grading standards must receive a shell sanitizing rinse of 100-200 ppm chlorine or its equivalent after leaving the washing process. A study was conducted to determine the concentration of peroxyacetic acid (PAA) which would be equivalent to 100-200 ppm chlorine (Cl) in reducing target organisms under the required washing conditions for shell eggs. Three isolates of Salmonella spp. (Enteritidis, Braenderup, and Typhimurium), as well as Enterobacter cloacae were used as inocula. Sanitizing treatments were negative control; deionized water; 100 and 200 ppm Cl; and 50-500 ppm PAA (7 concentrations). Considering all isolates tested, 100 and 200 ppm chlorine had 2.6 and 2.3 log cfu/mL cultural organisms remaining on shell surface; 50 and 100 ppm peracetic acid had 1.9 and 1.0 log cfu/mL cultural organisms remaining, respectively, compared with untreated control average of 3.8 log cfu/mL (P < 0.001). Salmonella Typhimurium was least resistant to shell sanitizer treatments. Peroxyacetic acid concentrations >250 ppm did not produce significant reductions in microbial populations as PAA concentration increased. Culturing for the prevalence of viable and injured organisms, 400-500 ppm PAA resulted in fewer eggs (P < 0.0001) being positive for Salmonella spp. E. cloacae was culturable via enrichment from 99.4% of inoculated eggs, regardless of sanitizer treatment. The results of this study indicate that 50-100 ppm PAA is equivalent to 100-200 ppm chlorine in reducing egg surface microorganisms. The use of 400-500 ppm PAA resulted in a lower incidence of viable, but not culturable, Salmonella spp. on the shell surface. E. cloacae resulted in almost 100% viable, but not culturable, organism recovery for all sanitizing treatments and should be considered as an indicator organism when studying processing facility sanitation procedures.

Analysis of Neutral Electrolyzed Water anti-bacterial activity on contaminated eggshells with Salmonella enterica or Escherichia coli

Neutral Electrolyzed Water (NEW) was tested in vitro and on artificially contaminated eggs against Salmonella enterica subsp. enterica or Escherichia coli. The antibacterial effect was measured 30 s after treatment. NEW microbicide activity results were compared against 2% citric acid and 0.9% saline solutions. NEW caused an in vitro decrease in Salmonella titers by ˃5.56 Log₁₀ CFU mL^-1 and in artificially contaminated eggs by ˃1.45 Log₁₀ CFU/egg. When it was tested against E. coli, it decreased in vitro bacterial titers by ˃3.28 Log₁₀ CFU mL^-1 and on artificially contaminated eggs by ˃6.39 Log₁₀ CFU/egg. The 2% citric acid solution caused an in vitro decrease of 0.4 Log₁₀ CFU mL^-1 of Salmonella and E. coli and on eggs artificially contaminated with E. coli or Salmonella there was a decrease of 0.06 and 0.62 Log₁₀ CFU/egg respectively. We evaluated egg cuticle integrity by scanning electron microscopy after treatments with evaluated solutions; the 2% citric acid solution caused damage to the cuticle and exposed eggshell pores and no interaction of NEW or NaCl with the cuticle was observed. NEW treatment showed a fast-bactericidal effect in vitro and table eggs.

Alternative Antimicrobial Commercial Egg Washing Procedures

Commercial table eggs are washed prior to packaging. Standard wash procedures use an alkaline pH and warm water. If a cool water method could be developed that would still provide a microbiologically safe egg, the industry may save energy costs associated with water heating. Four wash procedures were evaluated for Salmonella reduction: pH 11 at 48.9°C (industry standard), pH 11 at ambient temperature (∼20°C), pH 6 at 48.9°C, and pH 6 at ambient temperature. Alkaline washes contained potassium hydroxide-based detergent, while pH 6 washes contained approximately 200 ppm of chlorine and a proprietary chlorine stabilizer (T-128). When eggs were inoculated by immersion in a cell suspension of Salmonella Enteritidis and Salmonella Typhimurium, all treatments resulted in a slight and similar reduction of Salmonella numbers (approximately 0.77 log CFU/ml of shell emulsion reduction). When eggs were inoculated by droplet on the shell surface, Salmonella counts were reduced by approximately 5 log CFU when washed with chlorine plus the chlorine stabilizer at both temperatures and with the alkaline wash at the high temperature. The reductions in Salmonella by these treatments were not significantly (P > 0.05) different from each other but were significantly (P < 0.05) more than the reduction observed for the 20°C alkaline treatment and 20°C control water treatments. Ambient temperature acidic washes reduced Salmonella contamination to the same degree as the standard pH 11 warm water wash and may be a viable option to reduce cost, increase shelf life, and slow pathogen growth in and on shell eggs.

Salmonella contamination in shell eggs exposed to modified-pressure imaging for microcrack detection

Microcracks in egg shells are a food safety risk and are difficult for professional human graders to detect. Modified-pressure imaging technology with 99.6% accuracy has been developed to detect microcracks. This study was conducted to determine whether the microcrack detection system would increase penetration of Salmonella into egg contents or lead to cross-contamination within the system. Thirty dozen grade A large white retail eggs were used for each of 3 replicates. Cracked eggs were removed and 72 eggs/replicate were dip inoculated in buffered peptone water containing 10(5) cfu/mL of nalidixic acid-resistant Salmonella Typhimurium (ST), whereas 144 eggs were dipped in sterile buffered peptone water. All eggs were incubated overnight at 25°C before imaging. Forty-five eggs of each treatment were imaged in the following order: control, inoculated, control. Imaged and nonimaged eggs from each treatment were used for cultural analysis of a shell rinse, shell emulsion, and contents sample for each egg. The ST levels were monitored on brilliant green sulfa agar with 200 mg/L of nalidixic acid. Egg contents were also enriched to determine the prevalence of ST in low levels. Salmonella Typhimurium was not detected on or in any of the control eggs, including the eggs imaged after the inoculated eggs. The highest level of ST was detected in inoculated shell emulsions (4.79 log cfu/mL). No differences in ST levels were found for any sample location between imaged and nonimaged inoculated eggs. Therefore, the modified-pressure imaging system for microcrack detection did not result in microbial cross-contamination or increase the level of microbial penetration in inoculated eggs. The imaging system can be used to assess eggs for cracks without negative food safety implications.

Modified pressure imaging for egg crack detection and resulting egg quality

Cracks in the shell surface compromise the primary barrier for external microbial contamination of the egg. Microcracks are very small cracks in the shell surface that are difficult to detect by human graders. New technology has been developed that uses modified pressure and imaging to detect microcracks in eggs. Research has shown the system to have an accuracy of 99.6% in detecting both cracked and intact eggs. A study was undertaken to determine if quality differences existed between modified pressure imaged and control eggs during extended cold storage. Three replicates were conducted with eggs stored at 4 degrees C for 5 wk with weekly quality testing. The physical quality factors monitored were Haugh units, albumen height, egg weight, shell strength, vitelline membrane strength and elasticity, and whole egg total solids. All measurements were conducted on individual eggs (12/treatments per replicate) each week with the exception of whole egg solids, which were determined from 3 pools (4 eggs each)/treatment per replicate each week. Percentage of whole egg total solids was the only significant difference (P < 0.05) between treatments (23.65% modified pressure imaged and 23.47% control). There was a significant difference (P < 0.05) for egg weight between replicates (60.82, 58.02, and 60.58 g for replicates 1, 2, and 3, respectively). Therefore, imaging eggs in the modified pressure system for microcrack detection did not alter egg quality during extended cold storage. Utilizing the modified pressure crack detection technology would result in fewer cracked eggs reaching the consumer, consequently enhancing food safety without affecting product quality.

Eggshell penetration of various types of hens' eggs by Salmonella enterica serovar Enteritidis

Egg weight, shell thickness, number of pores, cuticle deposition, eggshell strength (dynamic stiffness and damping ratio), and the ability of Salmonella enterica serovar Enteritidis (SE) to penetrate the eggshell were determined. Penetration was assessed by filling the eggs with a selective medium that allowed viewing of Salmonella growth on the inside of the shell and membrane complex. After inoculation of each shell with on average 2.71 log CFU, the eggs were stored for up to 14 days at 20 degrees C and 60% relative humidity. Commercially available eggs were used. At 14 days of storage, only 6.0% of the eggs from free-range hens and 16.0% of the generic (i.e., eggs from hens in conventional battery cages that were given standard feed) white eggs were penetrated. The generic brown, organic, and omega-3-enriched eggs were penetrated at a frequency of 30 to 34%. In a second experiment it was shown that the layer strains of the hen (ISA-Brown Warren versus Bovans Goldline), which were kept in furnished cages, did not affect eggshell penetration by SE. For Bovans Goldline hens, the housing system (furnished cage versus aviary) did not affect penetration, while a trend was visible toward a higher fraction of penetrated eggshells when hens were fed corncob mix rather than standard feed. Eggshell penetration was observed more frequently in the absence of cuticle spots and for eggs having lower dynamic stiffness values. Shell contamination at the end of storage was highly correlated with SE penetration.