Antimicrobial activity of ClO₂ gas against Salmonella Enteritidis on almonds

Nuts, including almonds, are occasionally contaminated with Salmonella spp. In this study, we used chlorine dioxide (ClO₂) gas to inactivate S. enterica subsp. Enterica serovar Enteritidis on almonds. Almonds inoculated with a single strain of S. Enteritidis (8.95 log cfu/mL) were exposed to ClO₂ gas generated from 1.0 or 1.5 mL ClO₂ solution in a sealed container at 50 or 60 °C (43% relative humidity) for up to 10 h. The concentration of ClO₂ gas peaked at 354-510 and 750-786 ppm within 0.5 h upon deposition of 1.0 and 1.5 mL of aqueous ClO₂, respectively, and gradually decreased thereafter. Population of S. Enteritidis on almonds treated at 50 °C decreased to 1.70-2.32 log cfu/sample within 1 h of exposure to ClO₂ gas and decreased to below the detection limit (1.7 log cfu/sample) at all ClO₂ concentrations after 8 h. At 60 °C, the microbial population fell below the detection limit within 1 h, regardless of the volume of ClO₂ solution supplied. Microbial survival on almonds treated with ClO₂ gas and stored at 12 or 25 °C was observed for up to 8 weeks and the organism was not recovered from the almonds treated for 10 h and stored at 12 °C for 2-8 weeks. The lightness (L value) and redness (a value) of almonds treated for 10 h were not changed by ClO₂ gas treatment, but yellowness (b value) increased. Results showed that Salmonella on almonds was successfully inactivated by ClO₂ gas treatment and the microbial survival did not occur during storage.