title: Survival of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes on inoculated walnut kernels during storage.
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.
authors.affiliation: Department of Food Science and Technology, Department of Plant Sciences, University of California, Davis, Davis, CA 95616, USA.
authors.forename: Tyann
authors.initials: T
authors.lastname: Blessington
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Mitcham
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Harris
mesh_terms: D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000254:growth & development*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D031324:Juglans / Q000382:microbiology*; D008089:Listeria monocytogenes / Q000254:growth & development*; D019779:Salmonella enterica / Q000254:growth & development*; D013696:Temperature; D013997:Time Factors