Title: Effects of UV-C treatment on inactivation of Salmonella and Escherichia coli O157:H7 on tomato surface and steam scars, native microbial loads, and quality of grape tomatoes Authors
Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 18, 2014
Publication Date: March 29, 2014
Citation: Mukhopadhyay, S., Ukuku, D.O., Juneja, V.K., Fan, X. 2014. Effects of UV-C treatment on inactivation of Salmonella and Escherichia coli O157:H7 on tomato surface and steam scars, native microbial loads, and quality of grape tomatoes. Food Control. http://dx.doi.org/10.1016/j.foodcont.2014.03.027. Interpretive Summary: A diet rich in fruits and vegetables can provide protective role against the development and progression of cardiovascular and degenerative disease. Unfortunately tomatoes, like other fresh produce, are often contaminated with human pathogens. The purpose of present study was to evaluate the effectiveness of UV-C dose treatment to inactivate foodborne pathogens including Salmonella enterica and E. coli O157:H7 located both on the surface and stem scar sites of tomato and to examine the treatment efficacy on growth of native microflora which is responsible for spoilage and the treatment effect on the quality during storage. Results indicate that pathogens located on the stem scar are resistant to UV-C inactivation compared to the population on the surface.
Technical Abstract: This study investigated the effectiveness of ultraviolet-C (UV-C) light inactivation as affected by the location of pathogens on the smooth surface and at stem scars of Grape tomatoes. A bacterial cocktail containing three strains of E. coli O157:H7 (C9490, E02128 and F00475) and a three serotypes of S. enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) were used. Tomatoes were spot inoculated using approximately 100 microliters of inoculums to achieve a population of about 10 7-8 CFU/tomato. Additionally, the effects of treatment on color, texture, lycopene content, and background microbial loads during post-UVC storage at 4C for 21 days were determined. Results showed that UV-C doses of 0.60-6.0 kJ/m2 resulted in 2.3-3.5 log CFU per fruit reduction of E. coli O157:H7 compared to 2.15-3.1 log CFU per fruit reduction for Salmonella on the surfaces. Under same condition, log reductions achieved at stem scar were 1.7-3.2 logs CFU for E. coli O157:H7 and 1.9-2.8 logs CFU for Salmonella. The total aerobic mesophilic organisms (PCA) and anaerobic lactic acid bacteria (LAB) counts of treated tomatoes were significantly (p less than0.05) lower during storage compared to control group and the yeast and mold populations were reduced significantly below the detection limit during the same time. Firmness and color of treated tomato was not affected during storage. UV-C radiation could potentially be used for sanitizing fresh tomatoes and extending shelf-life. This study indicates that the specific location of pathogens on the produce influences the effectiveness of UV-C treatment, which should be taken into consideration for the design of UV-C systems for produce sanitization.