A Wash of Ethyl Acetoacetate Reduces Externally Added Salmonella enterica on Tomatoes

Abstract

The continuously high numbers of food-borne disease outbreaks document that current intervention techniques are not yet satisfactory. This study describes a novel wash for tomatoes that can be used as part of the food processing chain and is designed to prevent contamination with serovars of Salmonella enterica. The wash contains ethyl acetoacetate (EAA) at a concentration of 8% in H₂O. This wash reduced live bacterial counts (on Salmonella Shigella agar) of externally added S. Newport MDD14 by 2.3 log, counts of S. Typhimurium ATCC19585 by 1.5 log, and counts of S. Typhimurium FSL R6-0020 by 3.4 log. The naturally occurring background flora of the tomatoes was determined on plate count agar. The log reduction by EAA was 2.1. To mimic organic matter in the wash, we added 1% tomato homogenate to the 8% EAA solution. Prior to using the wash, the tomato homogenate was incubated with the EAA for 2 h. In the presence of the tomato homogenate, the log reductions were 2.4 log for S. Newport MDD14 and 3 log for S. Typhimurium FSL R6-0020. It seems like tomato homogenate did not reduce the efficacy of the EAA wash in the two S. enterica serovars tested. We propose the use of EAA as a wash for tomatoes to reduce bacterial counts of S. enterica well as naturally occurring background flora.

Keywords: Salmonella; food-antimicrobial; tomato; wash.

Figure 1

Concentration dependence of the survival of Salmonella after 5 min of incubation with EAA. Data are expressed in CFU/mL from three replicate experiments.

Figure 2

Effect of EAA on externally added S. enterica and naturally occurring background flora. Newport, S. Newport MDD14; ATCC, S. Typhimurium ATCC 19585; R6, S. Typhimurium FSL R6-0020. The log₁₀ CFU/g tomato data are plotted for each of the samples (grey bars, H₂O white bars, EAA). The S. enterica counts were taken from the SSA plates, the counts for naturally occurring background flora from the PBS tomatoes were taken from the PCA plates. The asterisks are indicative of the significance of the p-values from the t-test in ranked order (*** 0.0009, ** 0.0033, * 0.025, ns not significant).

Figure 3

Recovery of S. Typhimurium FSL R6-0020 from the tomatoes by means of silwet L-77. Log reductions were calculated between the 8% EAA wash and the H₂O wash. The log₁₀ CFU/g tomato data are plotted for each of the samples (grey bars, H₂O; white bars, EAA). The asterisks are indicative of the significance of the p-values from the t-tests (**** < 0.001, *** 0.0004, # not applicable as both groups yield identical data). WTWW, FSL R6-0020 with H₂O wash and H₂O recovery; ETWW, FSL R6-0020 with EAA wash and H₂O recovery; WTSW, FSL R6-0020 with H₂O wash and silwet L-77 recovery; ETSW, FSL R6-0020 with EAA wash and silwet L-77 recovery; PWTSW, PBS with H₂O wash and silwet L-77 recovery; PETSW, PBS with EAA wash and silwet L-77 recovery.

Figure 4

Effect of % tomato homogenate in the 8% EAA wash for the S. Newport MDD14 serovar. The log₁₀ CFU/g tomato data are plotted for each of the samples (grey bars, H₂O; white bars, EAA). The asterisks are indicative of the significance of the p-values from the t-test (* 0.039 and 0.021, ns not significant). TH, 1% tomato homogenate was added to the 8% EAA solution or H₂O.

Figure 5

Effect of 1% tomato homogenate in the 8% EAA wash for the and S. Typhimurium FSL R6-0020 serovar. The log₁₀ CFU/g tomato data are plotted for each of the samples (grey bars, H₂O; white bars, EAA). The asterisks are indicative of the significance of the p-values from the t-tests (* 0.0293, 0.0426, 0.0175, ns not significant). TH, 1% tomato homogenate was added to the 8% EAA solution or H₂O.