Two decontamination methods were evaluated for inactivating a cocktail of Salmonella or Listeria monocytogenes inoculated onto model low moisture foods (LMFs; dried strawberry, dried apple, raisins, chocolate crumb, cornflakes, shell-on or deshelled pistachio nuts). One treatment was based on a peracetic acid-ethanol (PAA-ethanol) sanitizer combination with the other being an Advanced Oxidation Process (AOP) that simultaneously applied UV-C (254 nm), ozone and hydrogen peroxide. The low moisture food was spray inoculated then dried prior to treatment. With Salmonella it was found that a pre-incubation step in 1% w/v glycerol-tryptic soy broth for 1 h prior to plating, significantly increased recovery of the pathogen compared to TSB alone. However, no increased recovery of L. monocytogenes was observed using the TSB-glycerol pre-incubation step. No Salmonella was detected on cornflakes, chocolate crumb and strawberry using 1.25 parts per thousand (‰) PAA-ethanol. The inactivation of Salmonella on deshelled pistachio was significantly higher using 2.5‰ PAA-ethanol sanitizer compared to the AOP treatments tested. Only negligible reductions of Salmonella (<1 log cfu) were obtained with shell-on pistachio treated with PAA-ethanol sanitizer or AOP. Salmonella could be reduced on dried apple slices by >4 log CFU when 5.0‰ PAA-ethanol was applied. L. monocytogenes was more sensitive to PAA-ethanol compared to Salmonella and could be eliminated on all the LMFs apart from shell-on pistachio. An AOP treatment applied 10% v/v hydrogen peroxide, ozone and 54 mJ/cm2 UV-C could significantly reduce Salmonella on dried apple slices compared to when the individual elements (hydrogen peroxide, ozone or UV-C) were applied. Salmonella was also eliminated by AOP on the other LMFs (apart from shell-on pistachio) although the same level of inactivation was achieved by spraying with 10% v/v hydrogen peroxide alone. L. monocytogenes was sensitive to hydrogen peroxide and AOP being eliminated from all the LMFs. Although this may suggest that hydrogen peroxide spray was equivalent to AOP treatment it was noted that no residual H2O2 or changes in visual appearance was evident on samples treated with the latter process. The study has demonstrated that the two decontamination methods assessed can be applied to reduce Salmonella and L. monocytogenes on LMFs although efficacy is dependent on the pathogen and product type.
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This research was supported by the ILSI North America Food Microbiology Committee.