45G-13 |
Inhibition of Listeria monocytogenes by native microflora of whole Cantaloupe |
D. O. UKUKU and W. F. Fett. Food Safety Intervention Technologies Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598 Cantaloupe melon has never been associated with outbreaks of listeriosis due to contamination with L. monocytogenes. In these studies we tested the hypothesis that the naturally occurring microflora on the cantaloupe surface is antagonistic to pathogen survival. Whole cantaloupe melons were washed with 70% ethanol, 200 ppm chlorine or water to reduce the native microflora or were left untreated (controls). Melons were then inoculated with a four strain cocktail of L. monocytogenes, allowed to dry for 2 h and stored at 5, 10 and 20 C for 15 days. Samples for microbial analyses were taken every three days. In addition, fresh-cut pieces were prepared from the treated or untreated melons, inoculated with L. monocytogenes (3.48 log CFU/g), stored and sampled as above. Finally, growth in vitro of L. monocytogenes in sterile or non-sterile homogenates prepared from cantaloupe rind and fresh-cut pieces was compared. Initial populations of L. monocytogenes recovered from unwashed and water washed melon rind immediately after inoculation and drying were highest for the treatments (EtOH and chlorine) that led to the greatest reduction of the native microflora (APC, yeast and mold). During storage of the whole melons, populations of L. monocytogenes declined most rapidly on melons that were washed with water or untreated. For inoculated fresh-cut pieces, more rapid declines in pathogen populations occurred on pieces that were prepared from water washed or untreated whole melons. Listeria grew in sterile rind and fresh-cut homogenates at 5 and 20 C, but not in non-sterile homogenates. Increasing starting populations of the pathogen allowed for growth in the non-sterile homogenates. The results of these studies indicate that the native microflora of whole cantaloupe rind is inhibitory to initial attachment, growth and survival of L. monocytogenes.
Session 45G, Fruit & Vegetable Products: Vegetables (Fresh)
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