Microbiology of Pickled Vegetables

Pickling Cucumber Improvement Committee Meeting Abstract

Fred Breidt, Jr.

Department of Food Science, North Carolina State University

We have investigated the use of microbial interference (biocontrol) to prevent the growth of bacterial pathogens in non-acidified refrigerated pickles (NARPs). The use of a biocontrol culture may be needed to ensure safety of NARPs with an extended shelf life. Extended shelf life for NARPs was achieved by blanching fresh cucumbers and with the use of ingredients (garlic oil, irradiated spices) that have reduced microbial cell counts compared to typical ingredients. Using this procedure, the shelf life of NARPs was more than doubled.

A culture of Lactococcus lactis, previously isolated from sauerkraut, was tested to determine the ability of this microorganism to grow and become the predominant bacterial culture in NARPs during temperature abuse or spoilage. This culture produces a bacteriocin, which is an antimicrobial agent active against the human pathogen, Listeria monocytogenes. Growth rate measurements have shown that salt (NaCl) concentration is an important factor limiting the ability of the L. lactis culture to predominate over indigenous NARP microflora, including potential pathogenic cultures. We have isolated and characterized more than 80 lactic acid bacteria naturally present in NARPs, which may also serve as biocontrol agents for this product. We have also investigated how bacteriophage (viruses attacking bacteria) can affect lactic acid bacteria, such as the microorganisms used for biocontrol, as well as starter cultures for vegetable fermentations.

Understanding the microbial ecology of lactic acid bacteria in fermenting vegetables, including the effects of bacteriophage, may lead to safe, high quality, processed and fermented vegetable products.

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