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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Time Before Storage and Storage Temperature on Survival of Salmonella Inoculated on Fresh-Cut Melons

Authors
item Ukuku, Dike
item Sapers, Gerald

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 13, 2006
Publication Date: May 9, 2006
Citation: Ukuku, D.O., Sapers, G.M. 2006. EFFECT OF TIME BEFORE STORAGE AND STORAGE TEMPERATURE ON SURVIVAL OF SALMONELLA INOCULATED ON FRESH-CUT MELONS. Food Microbiology. 24:288-295.

Interpretive Summary: Prepared fresh-cut cantaloupes in the supermarket is popular in the U.S. due to the benefits of a nutritious diet and the convenience. However, there are many reports of disease due to consumption of fresh-cut cantaloupes that were contaminated with bacteria capable of causing human illness. At home, most fresh-cut melons are prepared and may be left at room temperature for a numbers of hours before consumption or even refrigeration of the leftovers after the initial consumption. In this study, we investigated the effect of waiting period and storage temperature on survival of Salmonella in the presence of native microflora of fresh-cut watermelon, cantaloupe and honeydew pieces. Populations of aerobic mesophilic bacteria, yeast and mold and Pseudomonas spp were higher on cantaloupe rind than watermelon and honeydew and the populations of these classes of organism transferred to fresh-cut cantaloupe and mixed fresh-cut pieces were also higher than in fresh-cut watermelon and honeydew. Populations of Salmonella, aerobic mesophilic bacteria, yeast and mold and Pseudomonas ssp in fresh-cut melons left at room temperature for up to 5 h before refrigeration were higher than populations in fresh-cut melons stored at 5C immediately after preparation. However, Salmonella populations in fresh-cut watermelon and honeydew pieces stored immediately at 5C for 12 days declined, while the populations in fresh-cut cantaloupe did not change. In fresh-cut melons stored at 10C for 12 days, the populations of Salmonella increased from 100 to 1000 CFU/g in watermelon and honeydew; 100 to 3900 CFU/g in cantaloupe pieces and 100 to 10,000 CFU/g in mixed fresh-cut melons suggesting that holding freshly prepared, contaminated fresh-cut melon pieces at 22C for 3 h prior to refrigerated storage would increase the chances of Salmonella proliferation, especially if the fresh-cut melons were subsequently stored at an abusive temperature.

Technical Abstract: The effects of a waiting period at room temperature (~22C) before refrigerating fresh-cut watermelon, cantaloupe and honeydew pieces contaminated with Salmonella on survival of the inoculated pathogen were investigated. Whole cantaloupes, honeydew melons and watermelons were washed with water, and fresh-cut pieces from individual melons were prepared and inoculated with a five strain cocktail of Salmonella 105 CFU/ml. Populations of aerobic mesophilic bacteria, yeast and mold and Pseudomonas spp were higher in fresh-cut cantaloupe than in fresh-cut watermelon and honeydew immediately after preparation. Populations of Salmonella, aerobic mesophilic bacteria, yeast and mold and Pseudomonas ssp in fresh-cut melons left at room temperature for up to 5 h before refrigeration were significantly (p<0.05) higher than populations in fresh-cut melons stored at 5C immediately after preparation. Populations of Salmonella recovered in fresh-cut melons after inoculation with the 105 CFU/ml Salmonella cocktail inoculum averaged 2 log10 CFU/g in all contaminated pieces. Populations in fresh-cut watermelon and honeydew pieces stored immediately at 5C for 12 days declined, while the populations in fresh-cut cantaloupe did not show significant (p>0.05) changes. Populations of Salmonella in fresh-cut melons stored at 10C for 12 days increased significantly (p<0.05) from 2 to 3 log10 CFU/g in watermelon, 1.9 to 3 log10 CFU/g in honeydew and 2 to 3.6 log10 CFU/g in cantaloupe pieces. Holding freshly prepared, contaminated fresh-cut melon pieces at 22C for 3 h or more prior to refrigerated storage would increase the chances of Salmonella proliferation, especially if the fresh-cut melons were subsequently stored at an abusive temperature.

Last Modified: 4/19/2014
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