Decontamination Efficacy of Combined Chlorine Dioxide with Ultrasonication on Apples and Lettuce

The bacterial reduction of Salmonella and Escherichia coli O157:H7-inoculated apples and lettuce by ClO2 at 0, 5, 10, 20, and 40 ppm with and without 170-kHz ultrasonic treatments for 3, 6, and 10 min, respectively, have been studied. The treatments of ClO2 at 20 and 40 ppm for 3, 6, and 10 min or at 5 and 10 ppm for 6 and 10 min with 170-kHz ultrasonication caused 3.115 to 4.253 log reductions in Salmonella and 2.235 to 3.865 log reduction in E. coli O157:H7 on inoculated apples. Using combined ClO2 and ultrasonication to treat 4.48 × 104 CFU/g Salmonella and 1.07 × 105 CFU/g E. coli O157:H7-inoculated lettuce, the bacterial reductions were 2.257 to 2.972 and 1.357 to 2.264 log, respectively. The residual ClO2 decreased with increasing treatment times, over 80% of ClO2 was detected after the 3-min treatment, and more than 70% remained after the 10-min treatment time. No bacteria were recovered from the posttreatment solutions of ClO2 or ClO2 combined with ultrasonication. The temperature of the ClO2 treatment was 20.1 °C, and it increased to 40.1, 44.9, and 50.3 °C, with 170-kHz ultrasonic treatments for 3, 6, and 10 min, respectively, on apples.

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