15D-4 |
Inactivation of Listeria monocytogenes on lettuce by gaseous and aqueous chlorine dioxide gas and chlorinated water |
C. B. D'LIMA and R. H. Linton. Dept. of Food Science, Purdue Univ., 1160 Food Scince Bldg., West Lafayette, IN 47907-1160 There have been numerous cases of food borne disease outbreaks associated with consumption of fresh fruits and vegetables. Chlorine dioxide gas has been used successfully to treat selected produce and the objective of this study was to evaluate its effectiveness on lettuce. The purpose was to obtain a maximum logarithmic reduction of inoculated L. monocytogenes on lettuce while maintaining quality of leaves using gaseous and aqueous chlorine dioxide and chlorinated water. Lettuce leaves were spot inoculated with L. monocytogenes. The leaves were stored for 24 hours at 4°C and then treated with 0.2- 9.0 mg/L chlorine dioxide gas at 22°C. To determine the microbial counts on leaves before and after the treatments, a membrane-transferring-plating method with tryptic soy agar and Modified Oxford agar was used. Chlorine dioxide water and chlorine water were also used to treat inoculated leaves. The combinations of chlorine dioxide gas followed by either chlorine dioxide water or chlorinated water were also studied. A logarithmic reduction of 1.7±0.9 log cfu/25g leaves was obtained using chlorine dioxide gas at a concentration of 0.2 mg/L for 1 hour. It was not possible to use concentrations above 0.2 mg/L due to discoloration of leaves. Using chlorine dioxide water at a concentration of 18ppm gave a logarithmic reduction of 2.1±0.60 log cfu/25g leaves. Chlorine water at a concentration of 180ppm gave a reduction of 2.3±0.21 log cfu/25g leaves. The maximum logarithmic reduction with combination treatments was 2.4±0.38 log cfu/25g leaves. To maintain good quality of lettuce leaves, chlorine dioxide gas treatments showed similar effectiveness in reducing L. monocytogenes compared with chlorine dioxide water and chlorinated water. It suggests that the disinfection of lettuce is limited to approximately a 2 log reduction using this technology.
Session 15D, Food Microbiology: Fruits and vegetables
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