Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2015
Publication Date: 2/12/2015
Citation: Carter, M.Q., Chapman, M.H., Gabler, F., Brandl, M. 2015. Effect of sulfur dioxide fumigation on survival of foodborne pathogens on table grapes under standard storage temperature. Food Microbiology. 49:189-196. doi: 10.1016/j.fm.2015.02.002.
Interpretive Summary: We determined the survival of three common foodborne pathogens, Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica Thompson inoculated on freshly harvested California table grapes under standard cold storage condition. We also determined the survival and persistence of these three pathogens on grapes following sulfur dioxide fumigation, a traditional treatment used to control post-harvest fungal decay on table grapes. We found that L. monocytogenes was highly sensitive to cold storage alone and also highly susceptible to SO2 fumigation. A single standard fumigation (200 ppm-hr) was sufficient to inactivate L. monocytogenes on grapes under the conditions examined. S. enterica Thompson displayed similar survival fitness as L. monocytogenes on table grapes during cold storage and was much more sensitive to cold alone compared with E. coli O157:H7. E. coli O157:H7 had the highest tolerance to sulfur dioxide fumigation, whereas the susceptibility of S. enterica Thompson to sulfur dioxide was dependent on the amount of bacteria contaminated on the table grapes. Our study suggests that standard cold storage temperature with sulfur dioxide fumigation was effective in reducing and eliminating L. monocytogenes, S. enterica Thompson and E. coli O157:H7 inoculated 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.
Technical Abstract: We examined the persistence 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 (104 cells/grape) and high (106 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.