Purpose: In order to develop prevalence and level information for raw runner peanuts used for the production of peanut butter a total of 10,162 samples (350 g) spanning three crop years (2009 – 2011) were analyzed for Salmonella and enterohemorrhagic Escherichia coli (EHEC).
Methods: Double-blinded study samples (1,500 g) were obtained from backup 22-kg samples representing lots of runner peanuts (all grades) where a primary sample had tested negative for aflatoxin. The 350 g portions were analyzed using a PCR multiplex assay targeting specific DNA markers unique to Salmonella, E. coli O157 and enterohemorrhagic E. coli. Positive samples were culturally confirmed, and pathogenic organism levels determined using a most probable number (MPN) dilution series.
Results: Salmonella was detected in 68 samples, with the highest prevalence rates observed for the crop year 2009 and among market grades for “splits”. Only 3 samples were positive for EHEC. For most samples only the original enrichment was positive, yielding an MPN result of 0.74 CFU/350 g. For 11 samples MPN values ranged from 1.7 to 5.3 CFU/350 g.
Significance: It is generally acknowledged that Salmonella in raw peanuts can be significantly reduced by heat treatment applied by dry- or oil-roasting, as it is routinely done prior to the production of peanut butter. The information from the this study can be used to develop quantitative microbial risk assessments which would assist manufacturers in understanding what level of microbial intervention should be provided by the roasting process to protect public health.