Vapor Phase Hydroxyl- or Chlorine-radical Treatment for Inactivating Listeria monocytogenes on Mushrooms (Agaricus bisporus) Without Negatively Affecting Quality or Shelf-life.

Processes based on generating vapor phase hydroxyl-radicals or chlorine-radicals were developed for inactivating Listeria monocytogenes on mushrooms without negatively affecting quality. Antimicrobial radicals were generated from the UV-C degradation of hydrogen peroxide or hypochlorite and ozone gas. Response Surface Modelling (RMS) was used to identify the interaction between the operating parameters for the hydroxyl-radical process; UV-C 254nm intensity, hydrogen peroxide concentration and ozone delivered. There was an inverse relationship between hydrogen peroxide concentration and UV-C intensity in terms of the log reduction of L. monocytogenes . The independent parameters for the chlorine-radical process were hypochlorite concentration, pH, and UV-C intensity. From predictive models, the optimal hydroxyl-radical treatment was found to be 5% v/v H 2 O 2 , 2.86 mW/cm 2 UV-C intensity (total UV-C dose 144 mJ/cm 2 ) and 16.5 mg ozone. The chlorine-radical optimal process parameters were 10 ppm hypochlorite (pH 3.0), ozone 11.0 mg and 4.60 mW/cm 2 UV-C intensity. When inoculated mushrooms were treated with the optimal hydroxyl-radical and chlorine-radical process the log CFU reduction of L. monocytogenes was found to be 2.42±0.42 and 2.61±0.30 log CFU respectively without any negative effects on mushroom quality (weight loss and Browning Index during 14 days storage at 4°C). The levels of L. monocytogenes inactivation were significantly greater compared to when the individual elements of the radical processes were applied and control using a 90 s dip in 1% v/v hydrogen peroxide. The study has demonstrated that both hydroxyl-radical and chlorine-radical vapor-phase treatments are both equally effective at inactivating L. monocytogenes on mushrooms and can be considered as a preventative control step.