Activated persulfate, a relatively new advanced oxidation process, has gained attention for its potential to ensure fresh produce safety. One of the major advantages is to avoid the formation of toxic chlorinated disinfection byproducts which are concerns for chlorine-based sanitizers. This study was aimed to investigate the efficacy of ferrous and alkaline activated persulfate in inactivating Escherichia coli O157:H7 and Listeria monocytogenes, with the primary focus on the effect of initial persulfate concentration, the effect of gradual addition of ferrous ion, and the stability of activated persulfate. The prepared 5-strain pathogen cocktails were treated by activated persulfate for 60 or 120 s. Sodium thiosulfate combined with phosphate buffer was used to quench the reaction. Both pathogens were plated onto non-selective agars for colony enumeration. The steady-state concentrations of sulfate and hydroxyl radicals were quantified in each activation conditions. The results showed higher initial persulfate concentration can lead to more pathogen reductions. About 8.50 log CFU/mL reduction was observed in 120 s after the initial persulfate concentration was increased to 80 mmol/L (ferrous activation on both pathogens) or 600 mmol/L (alkaline activation on L. monocytogenes). Gradual addition of ferrous ion into persulfate solution achieved more pathogen reductions than adding all ferrous ion at once. However, only the increases of reductions achieved by four sequential addition were significant (P < 0.05). In addition, the steady-state concentrations of both sulfate and hydroxyl radicals were found to be positively correlated with microbial reductions at all conditions. Furthermore, the pathogen inactivation efficacy of both ferrous and alkaline activated persulfate can be maintained for a relatively long period (up to 3 h).
Keywords: Advanced oxidation process; Escherichia coli O157:H7; Free radicals; Listeria monocytogenes; Sanitizer.
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