Effect of sulfur dioxide fumigation on survival of foodborne pathogens on table grapes under standard storage temperature.

We examined the fate of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica Thompson inoculated on freshly-harvested table grapes under standard cold storage with initial and weekly sulfur dioxide (SO2) fumigation. L. monocytogenes and S. enterica Thompson were much more sensitive to cold temperature than E. coli O157:H7. Furthermore, L. monocytogenes was highly susceptible to SO2. Initial fumigation with 100 or 200 ppm-hr was sufficient to eliminate this pathogen on grapes with low (10(4) cells/grape) and high (10(6) cells/grape) inocula, respectively. Initial fumigation with 300 ppm-hr reduced S. enterica Thompson population about 300- and 10-fold on grapes with low and high inocula, respectively. Initial fumigation with 300 ppm-hr reduced E. coli O157:H7 population to less than 10-fold, regardless of inoculum density. When grapes were inoculated with the high inoculum and fumigated on days 0 and 7 with 200 or 300 ppm-hr SO2, S. enterica Thompson and E. coli O157:H7 were completely inactivated between days 8 and 14 of cold storage. Standard cold storage combined with SO2 fumigation was effective in reducing and eliminating all three pathogens on table grapes, however, depending on the dose, two or three fumigations were needed for elimination of S. enterica Thompson and E. coli O157:H7.