Purpose: This study evaluated the minimum concentration of HOCl required to prevent cross-contamination of uninoculated tomatoes by Salmonella-inoculated tomatoes under clean and organic loading conditions.
Methods: Unwashed green round tomatoes inoculated with rifampicin (rif) resistant Salmonella (9 log CFU/tomato) were introduced into a recirculating waterbath along with uninoculated tomatoes. Tomatoes in the wash water were exposed to different HOCl (25, 50, 75, 100 ppm) and organic loading (0, 500 ppm Chemical Oxygen Demand [COD]) levels for 0, 30, 60, 120 s. At each time point, three inoculated and uninoculated tomatoes were placed in separate Stomacher® bags containing tryptic soy broth (TSB) and 0.1% Na2S2O3 for Salmonella enumeration. If levels were below the detection limit (< 2 log CFU/tomato), tomatoes were enriched in TSB (+rif) at 37°C for 48 h. Each experiment was performed in triplicate (n = 9).
Results: In the absence of HOCl, Salmonella was recovered in both the wash water (≥ 3.5 log CFU/ml) and uninoculated tomatoes (≥ 4.5 log CFU/tomato). Presence of HOCl in the wash water reduced Salmonella levels on uninoculated tomatoes to below the detection limit (< 2 log CFU/tomato). Enrichment revealed the presence of Salmonella on uninoculated tomatoes exposed to 25 and 50 ppm HOCl. However, the use of 75 or 100 ppm HOCl without organic loading, prevented Salmonella cross- contamination of uninoculated tomatoes, regardless of the contact time.
Significance: Results suggest that 75 ppm HOCl is sufficient to control Salmonella cross-contamination in a model flume system, in the absence of organic loading. The ability of packers to use less sanitizer could reduce associated chemical and disposal costs.