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Characterization of efficacy and flow in a commercial scale forced air ozone reactor for decontamination of apples

Arévalo Camargo, J., Murray, K., Warriner, K., Lubitz, W.
Lebensmittel-Wissenschaft + [i.e. und] Technologie 2019 v.113 pp. 108325
Lactobacillus, Listeria monocytogenes, air, air flow, apples, bacteria, decontamination, ozone, porosity
Air flow characteristics and decontamination efficacy are investigated within a forced-air ozone reactor designed to control Listeria monocytogenes on apple fruit. The commercial reactor introduced an air-ozone mix through a column of apples (540 kg contained within two bins; dimensions 1.21 m × 1.21 m × 0.72 m) for a defined air velocity and time period. The apple bed had high porosity (ɛ = 0.533) with a corresponding low pressure differential (10 Pa/m). Incoming air flowed through the ozone generator with low air velocities (0.022 m/s) introducing 39 ppm of the antimicrobial gas into the chamber. As the air flow was increased to 0.147 m/s, the corresponding ozone concentration at the entry point into the chamber dropped to 4 ppm through dilution. At the lowest air velocity the log reduction of Lactobacillus (surrogate bacteria for Listeria) inoculated onto applies varied between 0.5 and 2.5 log CFU across the bed, compared to 1.6 to 2.5 log CFU reductions that were observed at air velocities greater than 0.088 m/s. It was found the homogeneity in decontamination efficacy across the bed was primarily dependent on the applied air velocity with ozone concentration (4–39 ppm) and treatment time (5–40 min) being less influential.