Purpose: To compare the effects of inoculation method and physiological state of cells (planktonic or biofilm) on the recoverability and stability of Salmonella enterica ser. Tennessee on whole black peppercorn.
Methods: Whole black peppercorns were inoculated with S. Tennessee cells using a wet inoculation method where planktonic cells grown for 24h in TSB were applied directly to peppercorns. Alternately, biofilms were formed on peppercorns over a 24h period of static incubation in TSB. Peppercorns were dried to aw = 0.3, and held for 28 days. Peppercorns (n = 3) were sampled after drying (time 0), and after 1, 14, 21, and 28 days of storage. Cells were enumerated by serial dilution and plated onto XLT-4 and TSA.
Results: In general, recovery of Salmonella was high after 28d storage, with averages of 4.31 log CFU/g and 5.15 log CFU/g recovered for planktonic and biofilm cells, respectively. Plate counts from peppercorns inoculated using the two methods were comparable throughout the study, with the exception of the 14 day sample, in which the biofilm counts (5.89 log CFU/g) were statistically greater (P = 0.0186) than the planktonic counts (4.90 log CFU/g). The log reduction from initial inoculation levels after 28 days was significantly larger (P = 0.0176) for planktonic cells (1.73 log reduction) than the biofilm cells (0.03 log reduction).
Significance: The inoculation method influenced the recoverability of Salmonella from whole peppercorns after drying. Identifying a standardized strategy for inoculation of whole peppercorns is an imperative step toward developing a standardized protocol for validation testing of commercial spice processing methods.