Chlorine dioxide dose, water quality and temperature affect the oxidative status of tomato processing water and its ability to inactivate Salmonella

Abstract

Water disinfection is a vital control-point to minimize transmission of diverse pathogens from water sources or produce within and among lots at harvest, during initial postharvest handling, and within subsequent postharvest re-packing and processing. The use of ClO2 as an alternative to NaClO for water disinfection is being adopted by the fresh tomato postharvest handling industry. Lack of data to define performance for this specific water sanitizer under commercial conditions is a barrier to setting meaningful standards and audit criteria for water sanitation and associated food safety goals. The current work aims to establish a correlative capacity of the Oxidation Reduction Potential (ORP) to ClO2 dose, under different conditions of water turbidity and temperature, and their potential to reflect the efficacy in inactivation of Salmonella enterica in tomato process wash water during primary packing. ORP was monitored at delivered doses of 1, 3 and 5 mg/L ClO2, 10, 25 and 40 °C water temperature, and varying turbidity (0, 40 and 160 NTU). As main results, inverse correlations between water turbidity, temperature and ORP were observed. An increase in turbidity significantly reduced the final ORP and increased the contact time required for a 5-log inactivation of S. enterica at any assayed temperature. An increase in temperature and ClO2 concentration reduced the contact time and achieved a 6-log reduction of S. enterica within a 2 min of contact time. Additionally, differences in the required contact time were determined for inactivation of seven different S. enterica serovars. ClO2 was effective in achieving a 6-log reduction, or greater, of S. enterica under a range of water quality and temperature. However, water composition strongly affects the dynamic ORP status which can limit total inactivation of S. enterica. Data acquired demonstrated the impacts of water quality and temperature to maintain an effective ORP toward inactivation of S. enterica. The outcomes of these studies will likely be useful in reassessing the current definition of adequate water quality and safety standards where ClO2 is used.