Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona on whole cantaloupe by chlorine dioxide gas

The objectives of this study were to examine inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona inoculated onto whole cantaloupe and treated with ClO2 gas at different concentrations (0.5, 1.0, 1.5, 3.0 and 5.0 mg l−1) for different times (0, 2.0, 4.0, 6.0, 8.0 and 10.0 min). The effect of ClO2 gas on the quality and shelf life of whole cantaloupe was also evaluated during storage at 22 °C for 12 days. A 100 μl inoculation of each targeted organism was spotted onto the surface (5 cm2) of cantaloupe rind (approximately 8–9 log CFU 5 cm−2) separately, air dried (60 min), and then treated with ClO2 gas at 22 °C and 90–95% relative humidity for 10 min. Surviving bacterial populations on cantaloupe surfaces were determined using a membrane transferring method with a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. Poona were determined using nonlinear kinetics (Weibull model). A 3 log CFU reduction of E. coli O157:H7, L. monocytogenes and S. Poona were achieved with 5.0 mg l−1 ClO2 gas for 5.5, 4.2 and 1.5 min, respectively. A 5 log CFU reduction of S. Poona was achieved with 5.0 and 3.0 mg l−1 ClO2 gas for 6 and 8 min, respectively. A 4.6 and 4.3 log reduction was achieved after treatment with 5.0 mg l−1 ClO2 gas at 10 min for E. coli O157:H7 and L. monocytogenes, respectively. Treatment with 5.0 mg l−1 ClO2 gas significantly (p<0.05) reduced the initial microflora (mesophilic bacteria, psychrotrophic bacteria, and yeasts and molds) on cantaloupe by more than 2 log CFU cm−2 and kept them significantly (p<0.05) lower than the untreated control during storage at 22 °C for 12 days. Treatment with ClO2 gas did not significantly (p>0.05) affect the color of whole cantaloupe and extended the shelf life to 9 days compared to 3 days for the untreated control, when stored at ambient temperature (22 °C).