Bactericidal activity of isothiocyanate against pathogens on fresh produce

The bactericidal activity of allyl and methyl isothiocyanate (AITC and MITC ) was tested with a rifampicin-resistant strain of Salmonella Montevideo an d streptomycin-resistant strains of Escherichia coli O157:H7 and Listeria m onocytogenes Scott A. Iceberg lettuce inoculated with high (10(7) to 10(8) CFU/g) and low (10(3) to 10(4) CFU/g) concentrations of bacterial pathogens was treated with AITC and MITC in sealed containers at 4 degrees C for 4 d ays. AITC showed stronger bactericidal activity than MITC against E. coli O 157:H7 and Salmonella Montevideo, whereas MITC showed stronger activity aga inst L. monocytogenes than E. coli O157:H7 and Salmonella Montevideo. Up to 8-log reduction occurred with E. coli O157:H7 and Salmonella Montevideo on lettuce following treatment with vapor generated from 400 mu l of AITC for 2 and 4 days, respectively. AITC was used to treat tomatoes inoculated wit h Salmonella Montevideo on stem scars and skin and apples inoculated with E . coli O157:H7 on stem scars. The bactericidal effect of AITC varied with b acteria species and exposure time. Salmonella Montevideo inoculated on toma to skin was more sensitive to AITC than that on stem scars. Treatment with vapor generated from 500 mu l of AITC caused an 8-log reduction in bacteria on tomato skin but only a 5-log reduction on tomato stem scars. The bacter icidal activity of AITC was weaker for E. coil O157:H7 on apple stem scars; only a 3-log reduction in bacteria occurred when 600 mu l of AITC was used .