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

摘要

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℃ 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℃ 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 O151 :W (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℃ for 1 year. Salmonella Enteritidis FT 30 declined at a rate of 0.10 log CFU/g per month at 23℃; storage time did not significantly affect levels on kernels stored at - 20 or 4℃. 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.