Purpose: Determine the minimum effective concentration of peracetic acid (PAA) to inactivate Salmonella enterica and Listeria monocytogenes in imazalil solutions.
Methods: Imazalil (300 ppm) was prepared with citrus packinghouse water and combined with 0, 10, 15, and 20 ppm PAA. Salmonella enterica or L. monocytogenes cocktails were separately inoculated (5.5 log CFU/ml) into imazalil preparations and held at 16 or 40°C for up to 5 minutes. At each time point, samples (n=6) were neutralized in Dey-Engley broth and plated onto appropriate agar; remaining samples were enriched at 37°C for 48 hours to confirm the presence of pathogens.
Results: At 16°C, ≥ five log reductions of Salmonella were achieved in ≥ five, three, or two minutes at 10, 15, or 20 ppm PAA, respectively in the packinghouse water (control). In the presence of imazalil, PAA efficacy was improved: ≥ five-log reductions were achieved in ≥ three minutes at 10 ppm, or ≥ two minutes at 15 or 20 ppm PAA. Salmonella could not be detected by enrichment after three minutes of exposure to ≥10 ppm PAA in the presence of imazalil. A five-log reduction of L. monocytogenes was not observed in the packinghouse water, even at 20 ppm PAA. However, in the presence of imazalil ≥ five-log reductions of L. monocytogenes were observed in ≥ three minutes at 15 or 20 ppm PAA; L. monocytogenes could not be detected by enrichment after exposure to 15 or 20 ppm PAA for five or three minutes, respectively. The efficacy of PAA was improved at 40°C; times to achieve ≥ five-log reduction in both pathogens was observed within one minute at 20 ppm PAA.
Significance: PAA has the potential to prevent cross contamination of fruit in imazalil applications used in citrus packinghouses.