Growth of salmonella and other foodborne pathogens on inoculated inshell pistachios during simulated delays between hulling and drying

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Journal of Food Protection


During harvest, pistachios are hulled, separated in water into floater and sinker streams (in large part on the basis of nut density), and then dried before storage. Higher prevalence and levels of Salmonella were previously observed in floater pistachios, but contributing factors are unclear. To examine the behavior of pathogens on hulled pistachios during simulated drying delays, floater and sinker pistachios collected from commercial processors were inoculated at 1 or 3 log CFU/g with cocktails of Salmonella and in some cases Escherichia coli O157:H7 or Listeria monocytogenes and incubated for up to 30 h at 37°C and 90% relative humidity. Populations were measured by plating onto tryptic soy agar and appropriate selective agars. In most cases, no significant growth (P > 0.05) of Salmonella was observed in the first 3 h after inoculation in hulled floaters and sinkers. Growth of Salmonella was greater on floater pistachios than on corresponding sinkers and on floater pistachios with ≥25% hull adhering to the shell surface than on corresponding floaters with <25% adhering hull. Maximum Salmonella populations (2 to 7 log CFU/g) were ~2-log higher on floaters than on corresponding sinkers. The growth of E. coli O157:H7 and Salmonella on hulled pistachios was similar, but a longer lag time (approximately 11 h) and significantly lower maximum populations (4 versus 5 to 6 log CFU/g; P > 0.05) were predicted for L. monocytogenes. Significant growth of pathogens on hulled pistachios is possible when delays between hulling and drying are longer than 3 h, and pathogen growth is enhanced in the presence of adhering hull material. HIGHLIGHTS • Foodborne pathogens multiplied on undried inshell pistachios. • Pathogen growth was greater when hull material was present. • Drying delays of > 3 h led to significant increases in pathogen populations. • Managing drying delays will reduce the risk for growth of foodborne pathogens.

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