Utilization of ClO2 Gas for Non-Thermal Sanitation

Chlorine dioxide (ClO₂), an oxidizing agent, is gaining interest in the food industry due to its broad antimicrobial effects. A promising application for ClO₂ is in vapor-phase decontamination, either as fumigation gas in the production line or as headspace antimicrobial gas in food packaging systems. When ClO₂ is absorbed into fresh produce the gas may react with organic matter and with microorganisms residing on the produce, yielding chlorite (ClO₂^-) as a major by-product, along with other compounds in trace amounts. This study explored the ClO₂-absorption behavior of Romaine lettuce and cherry tomatoes as well as factors affecting the inactivation efficacy of ClO₂ gas in vapor-phase decontamination. Inoculated and uninoculated Romaine lettuce and cherry tomatoes were exposed to an atmosphere 3.0 and 6.0 mg/L of ClO₂ gas for 7.5 to 90 min. The treated samples were then analyzed for residual ClO₂ and ClO₂^- using amperometric titration. Inactivation efficacies of ClO₂ were determined against E. coli O157:H7 in lettuce and Salmonella spp. in cherry tomatoes. The results showed that ClO₂ absorption increased as ClO₂ concentration and/or exposure time increased. Also, cutting of the lettuce, which introduced cut edges and bruises, increased ClO₂ absorption by 10 times After treatment with 3.0 mg/L ClO₂ gas for 30 min, 9.37 ± 1.71 and 0.92 ± 0.40 mg ClO₂^-/kg of lettuce were recovered from fresh-cut and whole leaf lettuce samples, respectively. Washing, which added additional moisture to the sample (around 7% wt/wt), did not significantly affect the absorption behavior. Decreasing the processing temperature also reduced the amount of ClO₂ absorbed. For cherry tomatoes, the amount of ClO₂ recovered was at least 10 times lower than that from fresh-cut lettuce, regardless of the treatment conditions. In general, reductions in pathogen populations increased as ClO₂ concentration and/or treatment time increased. The correlation between antimicrobial efficacy of ClO₂ and its absorption is being determined.