Purpose: Little is known about the degree to which bacteria can transfer from the surface of fresh produce items during peeling. This study quantified factors influencing the transfer of Salmonella from the surface of fresh cucumber to interior flesh and peeler during peeling.
Methods: Waxed and un-waxed Garden cucumbers (American slicing) were obtained from a supermarket and local grower, respectively. The effect of a 70% ethanol pre-treatment was also investigated. Wild type Salmonella Newport, and putative attachment mutants, JDB 279 (rpoS::Tn10:lac:kan) and JDB 287 (Tn10:lac:kan insertion in the agfD/agfB intergenic region) were used. Cucumbers were dip inoculated with the designated strain (~109 CFU/ml). Samples were dried for 12 or 24 h before peeling. Half of each inoculated cucumber was hand peeled using a sterilized peeler. The unpeeled half, the peeled half (flesh), the removed peel and the peeler were all enumerated for the presence of Salmonella. Percent transfer or log reductions were calculated as appropriate. Percent transfer was calculated by recipient surface/donor surface * 100.
Results: The majority (>50%) of Salmonella remained on the peel portion for all treatment groups. Relatively greater Salmonella transfer to flesh (0.13%) and peeler (0.20%) were observed during peeling of waxed cucumbers washed with 70% EtOH and dried for 24 h compared to other waxed cucumber groups. A significant difference between Salmonella Newport wild type and mutant strains (JDB 279 and JDB 287) transfer to the peel portion of waxed cucumbers was noted (P=0.0235). Significantly higher transfer of JDB 287 to flesh (P=0.0187) and peel (P=0.0222) was observed in un-waxed cucumbers prewashed with 70% EtOH.
Significance: This study shows the complex interactions occurring between Salmonella strains and cucumber surface characteristics during bacterial transfer during peeling.