Listeria monocytogenes survival in refrigerator dill pickles

Jin Kyung Kim*, Elaine M. D'Sa**, Mark A. Harrison*, Judy A. Harrison**, and Elizabeth L. Andress**

* Dept. of Food Science and Technology, University of Georgia, Athens
** Dept. of Foods and Nutrition, University of Georgia, Athens

Paper 33C-1. Presented at the Institute of Food Technologists Annual Meeting, Las Vegas, NV, July 14, 2004.

Note: This research study analyzed one particular pickling procedure that started with partially fermenting cucumbers at room temperature and then storing them in the refrigerator with no further treatment or processing. It does not represent findings or advice for any other type of refrigerator pickles.


Listeria monocytogenes can survive and grow in refrigerated foods with pH levels of approx. 4.0-5.0 and salt concentrations of 3-4%. Home-fermented refrigerator dill pickles fit this description. Contamination of this product with L. monocytogenes could cause serious problems since these items are not heated prior to consumption. This study determined L. monocytogenes survival and growth patterns in refrigerator dill pickles at three salt levels. Pickling cucumbers were inoculated with L. monocytogenes, brine mixtures were added and the cucumbers were held at room temperature for one week and then refrigerated for up to 3 months. The pH, percent NaCl, percent titratable acidity and total aerobic, psychrotrophic, lactic acid bacteria and Listeria populations were measured at the addition of brine, at 2, 4, and 7 days during storage at room temperature and then at weekly intervals during refrigerated storage. There was a rapid decrease in pickle pH after four days at room temperature (from 6.1-6.2 to 4.4-4.6) followed by a gradual decrease. The percent NaCl in the pickles rapidly increased up to 3 weeks at refrigeration temperatures, and the percent titratable acidity in the highest salt level was significantly lower (p<0.05). The initial Listeria population was 5.4-5.6 log cfu/cm² on the surface and 3.9-4.6 log cfu/g internally. There was approximately a 0.5-1 log increase during fermentation at room temperature followed by a population decline during refrigerator storage, with a greater decrease in the pickles with the highest NaCl content. Populations of total aerobes and lactic acid bacteria increased during room temperature storage and decreased gradually.



To determine the fate of L. monocytogenes on the surface and in the interior of cucumbers and in brines subjected to the different salt levels (1.3, 3.8, 7.6%)

Materials and Methods


Table 1. Population of L. monocytogenes on surface and in interior of cucumbers at three salt levels storage time

1/3    Number of tubes showing positive result /number of replicates

storage time

Fig. 1. Change patterns of microorganisms in the brines at three salt levels
A)Listeria    B) Total Aerobes    C) Lactic Acid Bacteria    D) Psychrotrophs

Table 2. Population of total aerobes on surface and in interior of cucumbers at three salt levels storage time

storage time

Fig. 2. The pH and percent titratable acidity at three salt levels - A) Cucumbers B) Brines

Table 3. Population of psychrotrophs on surface and in interior of cucumbers at three salt levels storage time


This material is based upon work supported by the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture, under Agreement No. 00-51110-9762.

Document Use:

Permission is granted to reproduce these materials in whole or in part for educational purposes only (not for profit beyond the cost of reproduction) provided the authors and the University of Georgia receive acknowledgment and this notice is included:

Reprinted with permission of the University of Georgia. Jin Kyung Kim, Elaine M. D'Sa, Mark A. Harrison, Judy A. Harrison and Elizabeth L. Andress. 2004. Listeria monocytogenes survival in refrigerator dill pickles. Athens, GA: The University of Georgia, Cooperative Extension Service.

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