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Survival of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes on Inoculated Walnut Kernels during Storage

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Abstract:

The survival of single strains or cocktails of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes was evaluated on walnut kernels. Kernels were separately inoculated with an aqueous preparation of the pathogens at 3 to 10 log CFU/g, dried for 7 days, and then stored at 23°C for 3 weeks to more than 1 year. A rapid decrease of 1 to greater than 4 log CFU/g was observed as the inoculum dried. In some cases, the time of storage at 23°C did not influence bacterial levels, and in other cases the calculated rates of decline for Salmonella (0.05 to 0.35 log CFU/g per month) and E. coli O157:H7 (0.21 to 0.86 log CFU/g per month) overlapped and were both lower than the range of calculated declines for L. monocytogenes (1.1 to 1.3 log CFU/g per month). In a separate study, kernels were inoculated with Salmonella Enteritidis PT 30 at 4.2 log CFU/g, dried (final level, 1.9 log CFU/g), and stored at –20, 4, and 23°C for 1 year. Salmonella Enteritidis PT 30 declined at a rate of 0.10 log CFU/g per month at 23°C; storage time did not significantly affect levels on kernels stored at –20 or 4°C. These results indicate the long-term viability of Salmonella, E. coli O157:H7, and L. monocytogenes on walnut kernels and support inclusion of these organisms in hazard assessments.

Document Type: Research Article

DOI: https://doi.org/10.4315/0362-028X.JFP-11-278

Affiliations: 1: Department of Food Science and Technology, Department of Plant Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, USA 2: Department of Plant Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, USA 3: Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, California 95616, USA. ljharris@ucdavis.edu

Publication date: 2012-02-01

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