BEHAVIOR OF LISTERIA MONOCYTOGENES INOCULATED ON CANTALOUPE SURFACES AND EFFICACY OF WASHING TREATMENTS TO REDUCE TRANSFER FROM RIND TO FRESH-CUT PIECES

Authors: Ukuku, Dike; Fett, William

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2002
Publication Date: 6/1/2002
Citation: Ukuku, D.O., Fett, W.F. 2002. Behavior of listeria monocytogenes inoculated on cantaloupe surfaces and efficacy of washing treatments to reduce transfer from rind to fresh-cut pieces. Journal of Food Protection. 65(6):924-930.

Interpretive Summary: Many vegetables, including bean sprouts, cabbage, cucumber, potatoes, and radishes have been found to be contaminated with L. monocytogenes. A listeriosis outbreak attributed to the consumption of contaminated coleslaw and a multistate seed sprout recall due to potential contamination with L. monocytogenes have been reported. In this study we determined the effectiveness of chlorine and hydrogen peroxide for their ability to remov L. monocytogenes from the surface of cantaloupes inoculated in the laboratory. Also, the ability of the treatment to preclude the transfer of the pathogen from the rind to the inner flesh during slicing was investigated. Listeria monocytogenes inoculated on the cantaloupe rinds survived for up to 15 days during storage at 4oC and 20oC. Slicing through the rind with a knife was shown to transfer the pathogen to the fresh-cut pieces prepared from these cantaloupes. Washing with chlorine or hydrogen peroxide solutions reduced the L. monocytogenes on the melon surface by 99 to 99.9% and the fresh-cut pieces prepared from the sanitized melons were not contaminated with L. monocytogenes. Listeria monocytogenes directly inoculated onto fresh-cut pieces survived, but did not grow, during 15 days of storage at 4oC. Growth did occur during storage at higher temperatures. The results of this study indicate that sanitizing cantaloupe surfaces with chlorine or hydrogen peroxide can help to ensure the microbial safety of fresh-cut pieces of cantaloupe.

Technical Abstract: Attachment and survival of Listeria monocytogenes on external surfaces (rind) of inoculated cantaloupe, the resistance of the surviving bacteria to chlorine or hydrogen peroxide treatments, the potential for transfer of the pathogen from the rind to fresh-cut tissues during cutting and survival of L. monocytogenes on fresh-cut pieces were investigated. Surface treatment with 70% ethanol to reduce the native microflora on treated melon, followed by immersion in a four strain cocktail of L. monocytogenes (108 CFU/ml) for 10 min, deposited 4.2 log10 CFU/cm2 and 3.5 log10 CFU/cm2 treated and untreated cantaloupe rinds, respectively. L. monocytogenes survived on the treated or untreated cantaloupe rinds for up to 15 days during storage at 4oC and 20oC but populations declined by approximately 1 to 2 log10 CFU/cm2. Fresh-cut pieces prepared from inoculated whole cantaloupes stored at 4oC for 24 h post inoculation were positive for L. monocytogenes. Washing inoculated whole cantaloupes in solutions containing 1000 ppm chlorine or 5% hydrogen peroxide for 2 min at 1 to 15 days storage at 4oC post inoculation resulted in a 2.0 to 3.5 log reduction in L. monocytogenes on the melon surface and the fresh-cut pieces prepared from the sanitized melons were negative for L. monocytogenes. After direct inoculation onto fresh-cut pieces L. monocytogenes survived, but did not grow, during 15 days of storage at 4oC. It is concluded that the native microflora of cantaloupes appear to restrict the attachment of L. monocytogenes to the cantaloupe rind. Also, sanitizing with chlorine or hydrogen peroxide has the potential to reduce or eliminate the transfer of L. monocytogenes on melon surfaces to fresh-cut pieces during cutting.