Efficacy of Gaseous Chlorine Dioxide in Killing Salmonella enterica on the Surface of Eggshells as Affected by Relative Humidity

Introduction: Chlorine dioxide (ClO₂) in aqueous and gaseous forms has been widely used to inactivate foodborne pathogens from foods and food-contact surfaces.  Compared to aqueous ClO₂, gaseous ClO₂ has been known to be more effective in killing foodborne pathogens and to leave less residue on food and food-contact surfaces after treatment.  Despite these advantages, the effectiveness of gaseous ClO₂ against Salmonella enterica on eggshells has rarely been reported.

Purpose: This study was done to evaluate the lethal activity of gaseous ClO₂ against S. enterica on the surface of eggshells and to determine the optimum relative humidity (RH) conditions for the treatment.

Methods: Eggshells were inoculated with S. enterica contaminated chicken feces, were placed in airtight containers (1.8 liters) in which RH had been adjusted to 23, 43, 68, 85, or 100%, and were exposed to gaseous ClO₂ (peak concentration: 141.7 ppm) for 0, 0.5, 1, 2, 4, and 6 h at 25°C.  After treating, the viable cell numbers of S. enterica on the eggshells were determined.

Results: The initial populations of S. enterica on eggshells were 5.9 log CFU/egg.  After treatments with gaseous ClO₂ at 23, 43, 68, 85, and 100% RH for 6 h, the populations of S. enterica on eggshells decreased by 0.8, 0.9, 3.1, 5.9, and 5.9 log CFU/egg, respectively.  At 85 and 100% RH, S. enterica on the surface of eggshells was completely inactivated within 4 h.

Significance: It was observed that gaseous ClO₂ was effective in inactivating S. enterica on the surface of eggshells and the lethality of gaseous ClO₂ against S. enterica on eggshells was maximized as the RHs were increased > 85%.