15D-6 |
Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on strawberries by chlorine dioxide gas |
Y. HAN, R. H. Linton, and P. E. NELSON. Dept. of Food Science, Purdue Univ., 1160 Food Science Bldg., West Lafayette, IN 47907 Concerns have been raised about the microbial safety of strawberries. Non-thermal disinfection using chlorine dioxide (ClO2) gas could potentially be an effective method to reduce pathogens on strawberries. Our objective was to determine the ClO2 gas treatments to achieve a 5 log reduction of E. coli O157:H7 or L. monocytogenes on strawberries. Strawberries were spot-inoculated with 7-8 log cfu/strawberry of each pathogen and stored for 24 hours at 4 oC. The strawberries were treated with 0.2-4 mg/L ClO2 gas for 30 min at 21oC and 90-95% relative humidity, then washed with neutralizing buffer (NB). Membrane filtration was used to concentrate low bacterial populations (<2 log cfu/ml). Microbial populations were determined using a direct surface-plating (SP) method with a selective medium or a membrane-transferring-plating (MTP) method with tryptic soy agar and sorbital MacConkey agar (E. coli O157:H7) or modified oxford agar (L. monocytogenes). After 24 hour storage, the difference between cell populations on the SP and the MTP was 0.52±0.36 log cfu/sample for E. coli O157:H7 (P>0.05) and 1.62±0.43 log cfu/sample for L. monocytogenes (P<0.05), respectively. The significant differences (P<0.05) between the inoculated populations of L. monocytogenes and recovered by the SP or the MTP was 3-4 log and 2-3 log, respectively. With the increase of ClO2 gas concentration from 0.2 mg/l to 3 mg/l, the log reductions of E. coli O157:H7 or L. monocytogenes increased from 2.15 to 5.46 or from 1.22 to 4.15, respectively, based on the MTP method. More than 5 log reductions of E. coli O157:H7 could be achieved by 4 mg/l or more ClO2 gas treatments. E. coli O157:H7 showed higher resistance to ClO2 gas than L. monocytogenes on strawberries. ClO2 gas treatment is a promising disinfection technique for reducing E. coli O157:H7 and L. monocytogenes on strawberries.
Session 15D, Food Microbiology: Fruits and vegetables
|