Purpose: This study evaluated the survival of Salmonella spp. and E. coli O157:H7 on the surface of raw peanuts inoculated at different levels and stored at various temperatures.
Methods: Raw peanuts were inoculated with three strains of Salmonella and three strains of E. coli O157:H7 which were associated with foodborne outbreaks. For each pathogen, the peanuts were inoculated at three levels (ca. 6, 4 and 2 log CFU/g) and stored under three temperature conditions (room temp, 23 ± 3°C; refrigerated, 4 ± 2°C; and frozen, -20 ± 2°C) for three months. Triplicate samples of 100 g each were pulled at three week intervals and analyzed using selective media (XLD for Salmonella and CTSMAC for E. coli O157:H7).
Results: Both Salmonella and E. coli O157:H7 levels declined rapidly in room temperature raw peanuts, but more slowly when the peanuts were refrigerated or frozen. The average reduction rates across three levels of Salmonella inoculum (± standard deviation) for room, refrigerated and frozen temperatures were -0.72 ± 0.20, -0.09 ± 0.07 and -0.10 ± 0.05 log CFU/month, respectively; while the averaged rates for three levels of E. coli O157:H7 inoculum for room, refrigerated and frozen temperatures were -0.63 ± 0.27, -0.16 ± 0.07, -0.12 ± 0.07 log CFU/month, respectively.
Significance: The information developed in this study can be used in risk assessment modeling to account for reductions which might occur during the production of peanuts products when stored at various temperatures, in distribution and after purchase by consumers.