Search

In this study, smoked salmon fillets were artificially inoculated with Listeria monocytogenes (3.7 ± 0.2 log CFU g(-1)) and treated with X-ray irradiation generated by a RS 2400 X-ray machine (Rad Source Technologies Inc.) using doses of 0.0, 0.1, 0.5, 1.0, and 2.0 kGy. Unirradiated and irradiated samples were then stored at 5 °C for 35 days and tested for L. monocytogenes count after 0, 5, 10, 15, 20, 25, 30, and 35 days. Also, uninoculated-untreated and uninoculated-treated samples with the lowest and highest X-ray doses (0.1 and 2.0 kGy) were stored at 5 °C and examined for psychrotrophs and mesophiles counts after 0, 5, 10, 15, 20, 25, 30, and 35 days. The initial L. monocytogenes population (3.7 log CFU g(-1) ) was significantly (p < 0.05) reduced to an undetectable level (<1.0 log CFU g(-1)) by treatment with 1.0 kGy X-ray. Treatment with 0.1 kGy X-ray significantly reduced the initial psychrotrophs and mesophiles counts from 5.3 and 3.0 to 3.3 and 2.3, respectively. However, L. monocytogenes, psychrotrophs and mesophiles counts were gradually increased during storage. Treatment with 2.0 kGy X-ray kept the L. monocytogenes population under detectable level until 35 days. Treatment with 2.0 kGy X-ray kept the mesophiles and psychrotrophs counts within the acceptable level until 35 days. These results revealed that treatment with X-ray irradiation can significantly reduce the risk of listeriosis and extend the shelf life of smoked salmon during storage at 5 °C., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In the last two decades several foodborne disease outbreaks associated with produce were reported. Tomatoes, in particular, have been associated with several multi-state Salmonella outbreaks. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole Roma tomato surfaces by X-ray at 0.1, 0.5, 0.75, 1.0, and 1.5 kGy was studied. The main purpose of this study was to achieve a 5 log reduction in consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods. Moreover, the effect of X-ray on inherent microflora (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated Roma tomatoes, during storage at ambient temperature (22°C) for 20 days was also determined. Mixtures of three or two strains of each tested organism was spot inoculated (100 μl) onto the surface of Roma tomatoes (approximately 7-9 log per tomato), separately, and air-dried, followed by treatment with X-ray doses at 22°C and 55-60% relative humidity. Surviving bacterial populations on tomato surfaces were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). Treatment with X-ray significantly reduced the population of the tested pathogens on whole Roma tomato surfaces, compared with the control. Approximately 4.2, 2.3, 3.7 and 3.6 log CFU reduction of E. coli O157:H7, L. monocytogenes, S. enterica and S. flexneri per tomato were achieved by treatment with 0.75 kGy X-ray, respectively. More than a 5 log CFU reduction per tomato was achieved at 1.0 or 1.5 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the inherent microflora on Roma tomatoes. Inherent levels were significantly (p<0.05) lower than the control sample throughout storage for 20 days., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The main goal of this investigation was to study the efficacy of X-ray doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) on inoculated Escherichia coli O157: H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on shredded iceberg lettuce. The second goal was to study the effect of X-ray on the inherent microflora counts and visual color of shredded iceberg lettuce during storage at 4 degrees C for 30 days. Treatment with 1.0 kGy X-ray significantly reduced the population of E. coli O157: H7, L. monocytogenes, Salmonella enterica and S. flexneri on shredded iceberg lettuce by 4.4, 4.1, 4.8 and 4.4-log CFU 5 cm(-2), respectively. Furthermore, more than a 5 log CFU reduction of E. coli O157: H7, L. monocytogenes, S. enterica and S. flexneri was achieved with 2.0 kGy X-ray. Treatment with X-ray reduced the initial microflora on iceberg lettuce and kept them significantly (p < 0.05) lower than the control during storage at 4 degrees C and 90% RH for 30 days. Treatment with X-ray did not significantly (p > 0.05) change the green color of iceberg lettuce leaves. Treatment with X-ray significantly reduced selected pathogens and inherent microorganisms on shredded iceberg lettuce leaves, which could be a good alternative to other technologies for produce (lettuce) industry.

Several recent foodborne disease outbreaks associated with leafy green vegetables, including spinach, have been reported. X-ray is a non-thermal technology that has shown promise for reducing pathogenic and spoilage bacteria on spinach leaves. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves using X-ray at different doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) was studied. The effect of X-ray on color quality and microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated spinach was also determined. A mixture of three strains of each tested organism was spot inoculated (100 microl) onto the surface of spinach leaves (approximately 8-9 log ml(-1)), separately, and air-dried, followed by treatment with X-ray at 22 degrees C and 55-60% relative humidity. Surviving bacterial populations on spinach leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction/leaf was achieved with 2.0 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on spinach leaves and inherent levels were significantly (p < 0.05) lower than the control sample throughout refrigerated storage for 30 days. Treatment with X-ray did not significantly affect the color of spinach leaves, even when the maximum dose (2.0 kGy) was used.

This study was conducted to evaluate the inactivation effect of X-ray treatments on Escherichia coli O157: H7, Salmonella enteric (S. enterica), Shigella flexneri (S. flexneri) and Vibrio parahaemolyticus (V. parahaemolyticus) artificially inoculated in ready-to-eat (RTE) shrimp. A mixed culture of three strains of each tested pathogen was used to inoculate RTE shrimp. The shrimp samples were inoculated individually with selected pathogenic bacteria then aseptically placed in sterile plastic cups and air-dried at 22 degrees C for 30 min (to allow bacterial attachment) in the biosafety cabinet prior to X-ray treatments. The inoculated shrimp samples were then placed in sterilized bags and treated with 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 2.0, 3.0 and 4.0 kGy X-ray at ambient temperature (22 degrees C and 60% relative humidity). Surviving bacterial populations were evaluated using a non-selective medium (TSA) with the appropriate selective medium overlay for each bacterium; CT-SMAC agar for E. coli O157: H7, XLD for S. enterica and S. flexneri and TCBS for V. parahaemolyticus. More than a 6 log CFU reduction of E. coli O157: H7, S. enterica, S. flexneri and V. parahaemolyticus was achieved with 2.0, 4.0, 3.0 and 3.0 kGy X-ray, respectively. Furthermore, treatment with 0.75 kGy X-ray significantly reduced the initial microflora on RTE shrimp samples from 3.8 +/- 0.2 log CFU g(-1) to less than detectable limit (<1.0 log CFU g(-1)).

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica on strawberries by chlorine dioxide gas at different concentrations (0.5, 1, 1.5, 3 and 5 mgl(-1)) for 10 min were studied. A cocktail of three strains of each targeted organism (100 microl) was spotted onto the surface of the strawberries (approximately 8-9 log ml(-1)) separately followed by air drying, and then treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity. Approximately a 4.3-4.7 logCFU reduction per strawberry of all examined bacteria was achieved by treatment with 5 mgl(-1) ClO(2) for 10 min. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. enterica were determined using first-order kinetic models to establish D-values and z-values. The D-values of E. coli, L. monocytogenes and S. enterica were 2.6+/-0.2, 2.3+/-0.2 and 2.7+/-0.7 min, respectively, at 5 mgl(-1) ClO(2). The z-values of E. coli, L. monocytogenes and S. enterica were 16.8+/-3.5, 15.8+/-3.5 and 23.3+/-3.3 mgl(-1), respectively. Furthermore, treatment with ClO(2) gas significantly (p < or = 0.05) reduced the initial microflora (mesophilic, psychrotrophic bacteria, yeasts and molds) on strawberries. Treatment with ClO(2) gas did not affect the color of strawberries and extended the shelf-life to 16 days compared to 8 days for the untreated control.