Submitted to: International Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2014
Publication Date: 4/20/2015
Citation: Olanya, O.M., Annous, B.A., Taylor, J. 2015. Effects of Pseudomonas chlororaphis and gaseous chlorine dioxide on the survival of Salmonella enterica on tomatoes. International Journal of Food Science and Technology. 50:1102-1108.
Interpretive Summary: Produce contamination by Salmonella enterica is a major concern in food safety. To enhance food safety, we investigated the potential of using gas-phase antimicrobials and a competitive bacterium such as Pseudomonas chlororaphis for control of Salmonella on tomatoes. The tomatoes were spot-inoculated with the beneficial bacteria (non-pathogenic), with Salmonella serovars (Montevideo and Typhimurium), and then by applying the beneficial bacteria and Salmonella in sequence on tomatoes. Our results indicated that application of gaseous chlorine dioxide for 4 and 2 hrs (0.4 mg/L at 13 deg. C, 90 percentage of R.H.) showed a remarkable control of Salmonella as well as the beneficial bacteria on tomatoes. The populations of Salmonella on tomatoes were reduced to levels below detectable. The beneficial bacteria by itself showed low to moderate reductions of Salmonella when the both were applied on tomato. It appears that applying the two approaches for control of Salmonella may enhance food safety. More research is needed to ascertain if low level doses of chlorine dioxide and optimal beneficial bacteria may provide added advantage.
Technical Abstract: Produce contamination incited by Salmonella enterica serovars on tomatoes and various outbreaks of Salmonellisis have been reported periodically. Post-harvest intervention measures applied to limit produce contamination will improve food and consumer safety. The aim of this reserach was to evaluate the survival of Salmonella enterica serovars Montevideo and Typhimurium on spot-inoculated tomatoes when exposed to Pseudomonas chlororaphis and gaseous chlorine dioxide. Bacterial suspensions of Pseudomonas chlororaphis was applied onto stem-scars of tomatoes prior to inoculations with each serovar of S. Montevideo and S. Typhimurium. The replicated treatments were stored at 13 degrees C, prior to treatment with gaseous chlorine dioxide (ClO2) at 0.4 mg/L for 2 and 4 hrs, respectively. To evaluate the effect of P. chlororaphis on pathogen survival, tomatoes preemptively inoculated with P. chlororaphis and subsequently with S. Montevideo and S. Typhimurium were assessed. At 4 hrs of gaseous ClO2 treatment (146 ppm, 90% R.H., at 13 degrees C), the populations of S. Montevideo and S. Typhimurium that survived were 0.82 and 0 log CFU/g of produce, respectively. Whereas, the untreated controls of the same pathogens above had populations of 5.42 and 5.37 log CFU/g of produce. On the P. chlororaphis treated produce, 2.59 log CFU/g of bacteria were recorded relative to bacterial numbers of 5.83 log CFU/g in the untreated control. Bacterial survival at 2 hrs of ClO2 treatment was similar to that of 4 hrs. The survival of S. Montevideo and S. Typhimurium when co-inoculated with P. chlororaphis was reduced by 0.20 to 0.83 log CFU/g of produce. The post-harvest application of ClO2 and sequential protection by P. chlororaphis and other antagonistic microbes may enhance control of Salmonella on tomatoes. .