Purpose: The purpose of this study was to assess the ability of hypochlorous acid to prevent cross contamination of Salmonella-inoculated tomatoes to uninoculated tomatoes in a model flume under clean and organic loading conditions.
Methods: Unprocessed, green, round tomatoes were inoculated with a 5-serovar cocktail of rifampicin (rif)-resistant Salmonella (9 log CFU/tomato), dried for 2 hr, and introduced alongside uninoculated tomatoes in a recirculating water bath containing water with simulated organic loads of 0, 500 and 4,000 ppm COD, and exposed to free chlorine levels of 0, 10 and 25 ppm. Three inoculated and three uninoculated tomatoes were removed at 0, 15, 60 and 120 s, placed into separate stomacher bags containing 100 ml buffered peptone water (BPW) + 0.1% Na2S2O3, and vigorously rubbed/shaken to recover any Salmonella. One ml samples were removed from the bags, serially diluted in BPW, and pour plated in tryptic soy agar (+ rif) to enumerate any Salmonella present. Each experiment was performed in triplicate (n = 9).
Results: Uninoculated tomatoes were cross contaminated to a level of ca. 5 log CFU/tomato when free chlorine was absent under all loading conditions. Under 500 ppm COD organic loading, no cross contamination (<2 log CFU/tomato) was observed when 10 or 25 ppm free chlorine was present. Under a 4,000 ppm COD organic load, 10 ppm free chlorine failed to prevent cross contamination; however, no cross contamination (<2 log CFU/tomato) was observed at 25 ppm free chlorine.
Significance: These data suggest that maintaining free chlorine as low as 25 ppm is adequate to prevent cross contamination of Salmonella in tomato packinghouse flumes or dump tanks as long as those levels are properly maintained.