ARS | Publication request: Transfer of Listeria monocytogenes serovars from cantaloupe rind surfaces to fresh cut pieces during preparation: effect of native microflora waiting period and storage temperature on the population of pathogens

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2012
Publication Date: N/A

Interpretive Summary: At home, most fresh-cut melons are prepared and may be left at room temperature for a numbers of hours before consumption or leftovers maybe refrigerated for a later use. The recent outbreak of listerosis linked to consumption of fresh-cut cantaloupes suggests the need to investigate ways of reducing transfer of this bacterium to fresh-cut pieces. Whole cantaloupes rind surface inoculated with L. monocytogenes bacteria, air dried in a biosafety cabinet for 1 h and then washed with water and water containing 2.5 % hydrogen peroxide were used for fresh-cut preparation. Microbial populations of these fresh-cut pieces were determined immediately by the plate count or enrichment method after preparation and storage at 5, 10 and 20 deg C. Aerobic mesophilic bacteria, and yeast and mold including the inoculated populations of L. monocytogenes were transferred to the interior flesh during fresh-cut preparation. Populations of this class of organisms transferred to fresh-cut cantaloupes prepared from whole melon washed with water containing 2.5% hydrogen peroxide were very low and L. monocytogenes populations were below detection (< 2 CFU/g). Storage temperatures at 10 and 20 deg C encouraged recovery, survival and growth of L. monocytogenes on fresh-cut pieces prepared from untreated whole cantaloupes while this population remained below detection at 5 deg C for 72 h. Therefore washing whole cantaloupe rind surfaces with 2.5% hydrogen peroxide will inactivate L. monocytogenes populations’ present, reduced transfer of this pathogen during fresh-cut preparation and enhanced the microbial safety of the fresh-cut cantaloupes stored at 5 deg C.

Technical Abstract: The most recent outbreak of listerosis linked to consumption of fresh-cut cantaloupes suggests the need to investigate the behavior of Listeria monocytogenes in the presence of native microflora of cantaloupe pieces during storage. Whole cantaloupes were inoculated with L. monocytogenes (8.3 CFU/ml suspension) for 10 min and air dried in a biosafety cabinet for 1 h and then were treated (unwashed, water washed, and 2.5 % hydrogen peroxide washed). Fresh-cut pieces (~3 cm) prepared from these melons were left at 5 deg C and 10 deg C for 72 h and room temperature (20 deg C) for 48h. Some fresh-cut pieces were left at 20 deg C for 2 h and 4 h and then refrigerated at 5 deg C. Microbial populations of fresh-cut pieces were determined immediately by the plate count or enrichment method immediately after preparation. Aerobic mesophilic bacteria and yeast and mold of whole melon and inoculated populations of L. monocytogenes on cantaloupes rind surfaces averaged 6.4 log CFU/cm2, 3.3 log CFU/cm and 4.6 log CFU/cm, respectively. Only H2O2 (2.5%) treatment reduced the aerobic mesophilic bacteria, yeast and mold and L. monocytogenes populations to 3.8, 0.9 and 1.8 log CFU/cm2, respectively. The populations of L. monocytogenes transferred from melon rinds to fresh-cut pieces were below detection (< 2 CFU/g). Increased storage temperatures enhanced the lag phases and growth of L. monocytogenes. These results suggest that indigenous microflora of cantaloupes transferred to fresh-cut pieces were unable to inhibit the survival and growth of L. monocytogenes.