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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE Title: Inactivation of Salmonella spp. on tomatoes by plant molecules

Authors
item Mattson, Tyler -
item Johny, Anup -
item Amalaradjou, Mary Anne -
item More, Karen -
item Schreiber, David -
item Patel, Jitu
item Venkitanarayanan, Kumar -

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 2010
Publication Date: January 1, 2011
Repository URL: http://hdl.handle.net/10113/49052
Citation: Mattson, T., Johny, A., Amalaradjou, M., More, K., Schreiber, D., Patel, J.R., Venkitanarayanan, K. 2011. Inactivation of Salmonella spp. on tomatoes by plant molecules. International Journal of Food Microbiology. 44(3):464-468.

Interpretive Summary: Natural antimicrobials derived from plants were evaluated for reducing Salmonella on tomatoes. Plum tomatoes were inoculated with a cocktail of Salmonella (108 CFU) and washed in sterile deionized water (control), chlorine (100 ppm), carvacrol (CAR- 0.25 and 0.75%), trans-cinnamaldehyde (TC- 0.5 and 0.75%), eugenol (EUG- 0.25 and 0.75%) and ß-resorcylic acid (BR- 0.7 and 1%), for 15 sec, 1 min, and 3 min. Immediately after washing, surviving populations of Salmonella were determined by plate count. The plant molecules significantly reduced Salmonella on tomatoes compared to washing in water and chlorine. Both concentrations of CAR and TC, and 0.75% EUG decreased Salmonella counts on tomatoes by ~ 6.0 log CFU/ml at 1 min. Both concentrations of BR decreased the pathogen on tomatoes to undetectable levels at 3 min of exposure. No Salmonella was detected in the wash water containing the plant molecules or chlorine, whereas a substantial population of the pathogen survived in the control wash water. Moreover, none of the dipping treatments had any effect on the red color of tomatoes (P > 0.05). The results of this study will be useful to growers and processors in developing inovative strategies for disinfection of produce.

Technical Abstract: The efficacy of carvacrol (CAR), trans-cinnamaldehyde (TC), eugenol (EUG) and ß-resorcylic acid (BR) as a wash treatment for reducing Salmonella spp. on tomatoes was investigated. Plum tomatoes inoculated with a six-serotype mixture of Salmonella (108 CFU) were subjected to washing in sterile deionized water (control) or deionized water containing chlorine (100 ppm), CAR (0.25 and 0.75%), TC (0.5 and 0.75%), EUG (0.25 and 0.75%), or BR (0.7 and 1.0%) for 15 sec, 1 min, and 3 min. Immediately after washing, tomatoes were transferred to separate sampling bags containing 50 ml of Dey-Engley neutralizing broth and hand rubbed for 1 min. One ml of wash suspension from 10 each bag was serially diluted (1:10) with 9 ml of sterile PBS, and 0.1-ml portions from 11 appropriate dilutions were spread plated on duplicate tryptic soy agar and xylose lysine desoxycholate agar plates. The plates were incubated at 37°C for 24 h before counting the colonies. The plant molecules were more effective (P < 0.05) in reducing Salmonella on tomatoes compared to washing in water and chlorine. Both concentrations of CAR and TC, and 0.75% EUG decreased Salmonella counts on tomatoes by ~ 6.0 log CFU/ml at 1 min. Both concentrations of BR decreased the pathogen on tomatoes to undetectable levels at 3 min of exposure. Washing of tomatoes in deionized water and chlorine for 3 min reduced Salmonella by ca. 2.0 and 4.0.log CFU/ml, respectively. No Salmonella was detected in the wash water containing the plant molecules or chlorine, whereas a substantial population of the pathogen survived in the control wash water. Moreover, none of the dipping treatments had any effect on the red color of tomatoes (P > 0.05). Results indicate that CAR, TC, EUG and BR could effectively be used to kill Salmonella on tomatoes, but additional studies on sensory and quality characteristics of tomatoes treated with plant molecules are warranted.

Last Modified: 8/29/2014
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