Title: Efficacy of integrated treatment of UV light and low dose gamma irradiation on Escherichia coli O157:H7 and Salmonella enterica on grape tomatoes Authors
Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 4, 2013
Publication Date: May 1, 2013
Citation: Mukhopadhyay, S., Ukuku, D.O., Fan, X., Juneja, V.K. 2013. Efficacy of integrated treatment of UV light and low dose gamma irradiation on Escherichia coli O157:H7 and Salmonella enterica on grape tomatoes. Journal of Food Science. DOI:10.1111/1750-3841.12154. Interpretive Summary: Fresh fruits and vegetables such as tomatoes are frequently consumed for their beneficial effect in human population. Unfortunately, with the increase in fresh produce consumption the number of outbreaks of foodborne illnesses also increased. Pathogens of primary concern appear to be E. coli O157:H7, Salmonella, L. monocytogenes, and Norwalk-like viruses. Many disinfectant agents and techniques have been applied to decontaminate produce; however, these single treatment methods did not meet the recommended guideline of 1.00E+05 number of pathogen colony inactivation as proposed by National Advisory Committee on Microbiological Criteria for Food. It is necessary to examine combined treatment strategy to prevent foodborne infections by these pathogens. This study was carried out to determine the effects of integrated treatment of UVC and low dose Gamma irradiation on inactivation of Escherichia coli O157:H7 and Salmonella enterica on whole Grape tomatoes. The results from this work indicate that combined low dose use of UVC light and Gamma irradiation treatment can adequately inactivate the inoculated pathogens of concern on tomato surface and can also significantly reduce the native spoilage microflora such as mold, yeast during storage. Therefore, the integrated treatment developed in this study may be used by the produce industry as an efficacious treatment strategy.
Technical Abstract: Efficacy of integrated treatment of UVC and low dose Gamma irradiation to inactivate mixed Strains of Escherichia coli O157:H7 and Salmonella enterica inoculated on whole Grape tomatoes was evaluated. A mixed bacterial cocktail composed of a three strain mixture of E. coli O157:H7 (C9490, E02128 and F00475) and a three serotype mixture of S. enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) was used based on their association with produce related outbreaks. Spot inoculation (50-100 microliter) of tomatoes surface was performed to achieve a population of approximately 1.00E+07 to 1.00E+08 CFU/tomato. Inoculated tomatoes were subjected to UVC (253.7 nm) dose of 0.6 KJ per square meter followed by four different low doses of gamma irradiations (0.1 kGy, 0.25 kGy, 0.5 kGy, 0.75 kGy). The fate of background microflora (mesophilic aerobic) including mold and yeast counts were also determined during storage at 5 degree C over 21 days. Integrated treatment significantly (p less than 0.05) reduced the population of the target pathogens. Results indicate about 3.4 + 0.27 and 3.0 +0.12 log CFU reduction of E. coli O157:H7, and S. enterica per tomato with UVC (0.6 KJ per square meter) and 0.25 kGy irradiation. Reduction in excess of 5 log CFU per fruit was accomplished by combined UVC treatment with 0.75 kGy irradiation, for all tested pathogens. The combined treatment significantly (p less than 0.05) reduced the native microflora compared to the control during storage. The data suggest efficacious treatment strategy for produce industry indicating 5 or higher log reduction which is consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods.