Survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on Raw Peanut and Pecan Kernels Storedat -24, 4, and 22°C

Abstract

Cocktails of lawn-collected cells were used to determine the survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on the surface of raw peanut and pecan kernels. Kernels were inoculated with mixtures of four to five strains at 3 or 6 log CFU/g, dried at room temperature, and then stored at -24 ± 1, 4 ± 2, and 22 ± 1°C for 28 or 365 days. In most cases, rates of decline of the pathogens did not differ significantly between the two inoculum concentrations in the 28-day study. At 6 log CFU/g, populations of all pathogens were reduced by 0.5 to 1.6 log CFU/g during an initial 3-day drying period on both peanuts and pecans. The moisture content of peanuts and pecans remained stable at -24 ± 1 and 22 ± 1°C; at 4 ± 2°C, the moisture content increased from 3.8 to 5.6% on peanuts and from 2.6 to 3% on pecans over 365 days. Pathogen populations were stable on pecans stored under frozen and refrigerated conditions, except for L. monocytogenes, which declined at a rate of 0.03 log CFU/g/30 days at 4 ± 2°C. Salmonella populations were stable on peanuts stored at -24 ± 1 and 4 ± 2°C, but E. coli O157:H7 and L. monocytogenes declined at rates of 0.03 to 0.12 log CFU/g/30 days. At 22 ± 1°C, Salmonella, E. coli O157:H7, and L. monocytogenes declined at a rate of 0.22, 0.37, and 0.59 log CFU/g/30 days, respectively, on peanuts, and at 0.15, 0.34, and 1.17 log CFU/g/30 days, respectively, on pecans. Salmonella counts were above the limit of detection (0.30 log CFU/g) throughout the study. In most cases during storage, counts obtained from pecans were higher than from peanuts.

Modeling and Statistical Issues Related to Salmonella in Low Water Activity Foods

“…There was no significant decline of Salmonella on raw peanuts at freezing or refrigeration temperatures (Brar et al, 2015). The average decline over 365 days was 0.3-log 10 CFU at −24°C and 0.4-log 10 CFU at 4°C.…”

“…The average decline over 365 days was 0.3-log 10 CFU at −24°C and 0.4-log 10 CFU at 4°C. Salmonella populations had higher declines on raw peanuts at 22°C, with an average log reduction of 2.0-log 10 CFU over 365 days (Brar et al, 2015). Salmonella survival is character ized by an initial decline during the first seven days of storage, which does not seem to be influenced by temperature (Figure 10.1).…”

“…In the following subsections, using the data collected by Brar et al (2015) on Salmonella survival on raw peanuts at three different temperatures (−24, 4, and 22°C), a case study on how to develop a primary and secondary predictive model for survival of Salmonella is shown This approach could be used for survival data on any pathogen in any food, and is explored here for survival of Salmonella in low water activity foods.…”

“…In Figure 10.1, Salmonella survival on raw peanuts at three different (Brar et al (2015), reprinted with permission of the authors).…”

“…temperatures (−24 , 4, and 22°C), as collected by Brar et al (2015), is plotted against 365 days. There was no significant decline of Salmonella on raw peanuts at freezing or refrigeration temperatures (Brar et al, 2015).…”