Quantifying Condensation on Shell Eggs and its Effect on Salmonella Enteritidis Penetration into Egg Contents

Abstract

Salmonella Enteritidis (SE) prevalence in eggs is a major concern to the egg industry. Some research has shown that egg sweating, which can occur when refrigerated eggs are moved into a warmer ambient temperature with higher humidity from storage to loading docks or delivery trucks, has the potential to increase Salmonella penetration into egg contents. Objectives of this project were: 1) to compare three methods of quantifying condensate on sweated eggs, 2) to quantify moisture content on refrigerated shell eggs sweated at two temperatures (21 oC and 32 oC) and 3) to assess the effect of egg sweating on SE penetration into shell eggs over a six week period stored at 4 °C. The results of objective 1 showed there was no difference in quantifying egg sweat by either egg weight or weight of moisture absorbed on a paper towel (0.2% vs. 0.19% gain mL condensation/cm2) (P > 0.05). For objective 2, there was a significant difference found in the time it took for an egg to reach a maximum condensation amount (11 min at 32 °C, 60% RH, 17 min at 22 °C, 60% RH), as well as completely dry (25 min at 32 °C, 60% RH, 34 min at 22 °C, 60% RH) between the two temperatures (P < 0.05). To evaluate objective 3, a 2x2 factorial of SE inoculation and egg sweating was utilized. To evaluate contamination levels, shell rinse, shell emulsion, and egg contents were enumerated and assessed for prevalence of SE throughout 6 wks of 4 °C storage. Treatments included (SES) nalidixic acid-resistant SE inoculated and sweated, (SENS) NA-resistant SE inoculated and not sweated, (NSES) buffered peptone water (BPW) inoculated and sweated, and (NSENS) BPW inoculated and non-sweated. In week 1, the shell rinse SENS treatment had significantly higher SE counts (0.32 log10 CFU/mL) than the other three treatments, where no SE was detected (P < 0.05). After week 1, no SE counts were obtained from the egg shell rinse, shell emulsion or egg contents. The SENS treatment shell rinses had significantly higher SE prevalence than the sweated and inoculated treatment (SES) in wks 1 (100% vs. 34.3%), 2 (57.6% vs. 22.2%), and 3 (38.2% vs. 11.1%) (P < 0.05). During weeks 4, 5, and 6, there was no difference in SE prevalence between the SES and SENS treatment. Egg sweating did not increase SE penetration into the shell matrix across treatment or week (P < 0.05). The decreasing trend of SE prevalence on the shell rinse obtained over the six week period indicate that refrigeration is a very effective method to mitigate Salmonella growth. These results indicate that the normal occurrence of egg sweating is not harmful to egg safety.