15D-7 |
Inactivation of Listeria monocytogenes inoculated on different apple surfaces using chlorine dioxide gas |
J. DU, Y. Han, and R. H. Linton. Dept. of Food Science, Purdue Univ., 1160 Food Science Bldg., West Lafayette, IN 47907-1160 An increase in outbreaks caused by foodborne pathogens has been associated with apple products. Chlorine dioxide (ClO2) gas has been found to be highly effective in reducing pathogens, including Listeria monocytogenes, on selected produce. However, inactivation of L. monocytogenes on apples by ClO2 has not been studied. Our objective was to determine the conditions of ClO2 gas treatments to achieve a 3 or more log reduction of L. monocytogenes on the calyx, stem cavity and pulp surface of apples. Apples were spotted with 5-8 log cfu/spot site of a mixture of L. monocytogenes on the calyx, stem cavities and pulp surfaces. The apples were dried for 2-3 h at 21oC in a bio-safety cabinet, then treated with 1.0- 8.0 mg/L ClO2 gas at 21oC and 90% relative humidity. Microbial log reductions were determined using a membrane-transferring-plating method with tryptic soy agar and Modified Oxford agar, a 3-tube MPN method, or an end-point method. 4.29±0.20 and 4.33±1.07 log reductions were achieved on the calyx and stem cavities, respectively, by 4.0 mg/L ClO2 gas treatment for 30 min. Using the end point method, an 8.0 mg/L ClO2 treatment for 30 min resulted in complete inactivation of 3.64-5.30 log cfu/spotted site on the calyx cavity and a 3.50 - 4.96 log cfu/spotted site on stem cavity. On the pulp surfaces, a 5.52±0.95 log cfu/spotted site reduction was observed after a 4.0 mg/L ClO2 treatment for 10 min. Log cfu/spotted site reductions ranging from 3.91±0.04 to 6.53±0.07 were observed after 4.0 mg/L ClO2 gas treatment for 30 min. ClO2 gas treatments could achieve more than a 5 log reduction of L. monocytogenes on apple pulp surfaces and more than a 3 log reduction was observed for the calyx and stem areas. ClO2 gas treatment is a promising non-thermal technique for microbial reduction on apples.
Session 15D, Food Microbiology: Fruits and vegetables
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