Purpose: To evaluate the effect of the material of food containers in combination with the type of the food residues on; (i) the recovery of Salmonella sp. from surfaces and (ii) the growth rate and the lag time of Salmonella detached from surfaces and subsequently exposed to mild pH and NaCl conditions.
Methods: A 5-strain Salmonella composite was inoculated (6 log CFU/ml) in 5 food homogenates (FH; 1:10 with water); ground beef (GB), lettuce (L), mayonnaise (M), GB+L, GB+L+M, with or without 1% of a commercial detergent, while MRD served as control. Following incubation at 25 °C for 24h, plastic or metallic coupons (n=6) were spot-inoculated and stored under the same conditions. Cells were detached from each surface with a cotton swab. Growth kinetic parameters were determined in TSB with pH 5.5 and 2% NaCl in a Bioscreen C, by correlating serial dilutions with time to detection (TTD).
Results: Salmonella populations reached 7.9-8.5 log CFU/ml during storage in all FH with or without detergent, except for M where the low pH (3.93-4.08) caused slight reductions (0.3-1.7 log CFU/ml). The presence of the detergent resulted in lower recovery (0.3-2.5 log CFU/g) of the pathogen, regardless of the FH type or the material of the coupon. The growth rate of Salmonella (0.04 – 0.08 h-1) was not significantly (P > 0.05) affected by the stresses encountered during storage on the coupons. In contrast, the lag time decreased (P < 0.05) by 2.7 hours and increased (P < 0.05) by 5.2 hours, following inoculation in V and M+V without detergent and remaining on metallic surface, respectively.
Significance: Results may assist to identify sources of contamination where risk is higher, and contribute with data on bacterial transfer for QMRA.