Colonization of tomatoes by Salmonella montevideo is affected by relative humidity and storage temperature

The influences of the relative humidity (RH) and storage temperature on the colonization of tomato surfaces by Salmonella Montevideo were studied. Red, ripe tomatoes (Lycopersicon esculentum) were spot inoculated in three separate trials with 100 pl (approximately 10(6) CFU) of Salmonella Montevideo and stored for 90 min at 22 degrees C under 97% RH to facilitate attachment of cells to the blossom end of tomato surfaces. Following this attachment step, tomatoes were washed to remove loosely adhered cells and then stored at 22 or 30 degrees C for up to 10 days under RH of 60, 75, 85, or 97%. At 0, 0.4, 1, 4, 7, and 10 days of storage, three tomatoes were individually hand massaged in 50 ml of 0.1% peptone water and the washes were separately analyzed to enumerate populations of Salmonella Montevideo. The number of Salmonella Montevideo cells attached after 90 min at 22 degrees C was 3.8 log CFU per tomato; this level was determined to be the initial colonizing population. After 10 days of storage at 30 degrees C, the Salmonella Montevideo population increased to 0.7, 1.0, 1.2, and 2.2 log CFU per tomato at 60, 75, 85, and 97% RH, respectively. A similar trend was observed at 22 degrees C, although populations were lower than at 30 degrees C. Scanning electron micrographs of tomato cuticles after storage revealed a well-defined biofilm containing bacteria. These findings reinforce the importance of maintaining stored tomatoes at temperatures that do not support growth of pathogenic bacteria and demonstrate the growth-promoting effects of high humidity.     

Survival of Salmonella on tomatoes stored at high relative humidity, in soil, and on tomatoes in contact with soil

Salmonellosis has been linked to the consumption of several types of raw fruits and vegetables, some of which may have been contaminated with Salmonella before harvesting. The objectives of this study were to investigate water and soil as reservoirs of Salmonella for the contamination of mature green tomato fruits. Salmonella survived for at least 45 days in inoculated moist soil. The population of Salmonella on tomatoes in contact with soil increased by 2.5 log10 CFU per tomato during storage for 4 days at 20 degrees C and remained constant for an additional 10 days. The number of cells inoculated on tomatoes decreased by approximately 4 log10 CFU per tomato during storage for 14 days at 20 degrees C and 70% relative humidity. Fruits in contact with inoculated soil for 1 day at 20 degrees C harbored Salmonella only near or on the skin surface. More Salmonella cells were observed in stem scar and subsurface areas of tomatoes as the time of storage increased. PCR fingerprinting revealed that among five Salmonella serotypes in the inoculum, Salmonella Montevideo was the most persistent on tomatoes in contact with inoculated soil and on spot-inoculated tomatoes, followed by Salmonella Poona and Salmonella Michigan. The results of this study demonstrate that an enhanced green fluorescent protein marker can be used to detect cells and monitor the growth of Salmonella in the presence of other microorganisms. Observations on the infiltration of Salmonella into tomato tissues support the contention that preharvest contact of produce with contaminated water or soil exacerbates problems associated with the postharvest removal of pathogens or their accessibility to treatment with sanitizers.     

Effect of inoculum size, relative humidity, storage temperature, and ripening stage on the attachment of Salmonella Montevideo to tomatoes and tomatillos

The influence of inoculum populations and environmental factors on attachment of Salmonella Montevideo to the surface of tomatoes and tomatillos was evaluated. To study the effect of inoculum size, red, ripe tomatoes were spot-inoculated with bacterial suspensions (10(5) and 10(8) CFU/fruit) and stored at 22 degrees C under 100% relative humidity. The effects of temperature (12, 22, and 30 degrees C) and relative humidity (75, 85, and 97%) on attachment of the pathogen (10(7) CFU/fruit) to tomatoes (red and green) and ripe tomatillos were also evaluated. Inoculated fruits were stored for 90 min at all combinations of temperature and relative humidity, and after rinsing with water, the number of cells attached to the surface was determined. Salmonella Montevideo attached to the surface of tomatoes within 90 min. A direct correlation between the number of attached cells and the population in the inoculum was observed. The percentage of cells that attached immediately after inoculation was approximately 0.3% for the three test products. After storage for 90 min at various temperature and relative humidity conditions, the number of adhering cells ranged from 4.0 to 5.4 log CFU/fruit (1.2% of inoculum). Both the type of product and the temperature/relative humidity combination had a significant (P < 0.05) effect on attachment of Salmonella Montevideo to the surfaces of tomatoes and tomatillos. Scanning electron micrographs of the cuticles of inoculated washed tomatoes and tomatillos revealed typical skin cell patterns, and only a few randomly dispersed Salmonella Montevideo were observed. Deposition of Salmonella Montevideo on the surface of tomatoes and tomatillos could result in attachment and subsequent colonization under suitable conditions.     

Evaluation of gaseous chlorine dioxide as a sanitizer for killing Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, and yeasts and molds on fresh and fresh-cut produce

Gaseous chlorine dioxide (ClO2) was evaluated for effectiveness in killing Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on fresh-cut lettuce, cabbage, and carrot and Salmonella, yeasts, and molds on apples, peaches. tomatoes, and onions. Inoculum (100 microl, ca. 6.8 log CFU) containing five serotypes of Salmonella enterica, five strains of E. coli O157:H7, or five strains of L. monocytogenes was deposited on the skin and cut surfaces of fresh-cut vegetables, dried for 30 min at 22 degrees C, held for 20 h at 4 degrees C, and then incubated for 30 min at 22 degrees C before treatment. The skin surfaces of apples, peaches, tomatoes, and onions were inoculated with 100 microl of a cell suspension (ca. 8.0 log CFU) containing five serotypes of Salmonella, and inoculated produce was allowed to dry for 20 to 22 h at 22 degrees C before treatment. Treatment with ClO2 at 4.1 mg/liter significantly (alpha = 0.05) reduced the population of foodborne pathogens on all produce. Reductions resulting from this treatment were 3.13 to 4.42 log CFU/g for fresh-cut cabbage, 5.15 to 5.88 log CFU/g for fresh-cut carrots, 1.53 to 1.58 log CFU/g for fresh-cut lettuce, 4.21 log CFU per apple, 4.33 log CFU per tomato, 1.94 log CFU per onion, and 3.23 log CFU per peach. The highest reductions in yeast and mold populations resulting from the same treatment were 1.68 log CFU per apple and 2.65 log CFU per peach. Populations of yeasts and molds on tomatoes and onions were not significantly reduced by treatment with 4.1 mg/liter ClO2. Substantial reductions in populations of pathogens on apples, tomatoes, and onions but not peaches or fresh-cut cabbage, carrot, and lettuce were achieved by treatment with gaseous ClO2 without markedly adverse effects on sensory qualities.     

Persistence and growth of different Salmonella serovars on pre- and postharvest tomatoes

The interaction of a range of Salmonella serovars with pre- and postharvest tomatoes was evaluated. Serovars were selected on the basis of previous association in tomato-linked outbreaks of salmonellosis (Salmonella Javiana, Salmonella Montevideo, and Salmonella Newport) or those typically isolated from animal or clinical infections (Salmonella Dublin, Salmonella Enteritidis, Salmonella Hadar, Salmonella Infantis, Salmonella Typhimurium, and Salmonella Senftenberg). Salmonella serovars introduced onto the flowers of growing plants were recovered on and within the developing tomato fruit. Of all the Salmonella serovars tested, Montevideo appeared to be more adapted to survival within tomatoes and was recovered from 90% of the fruit screened. All of the Salmonella serovars could persist and grow when introduced onto unripened (green) tomato fruit. In general, growth (internal and external) was promoted at the high incubation temperature (25 degrees C) and high relative humidity (95%), although this was serovar dependent. The growth and persistence of Salmonella introduced on and into ripened (red) tomatoes was serovar dependent. Salmonella serovars Enteritidis, Typhimurium, and Dublin were less adapted to grow in or on intact red tomatoes than were serovars Hadar, Montevideo, or Newport. The results illustrated that a diverse range of Salmonella serovars can become established within and/or on preharvest tomatoes. The majority of Salmonella can grow and become established both on and within unripened tomatoes, but growth on ripened fruit was serovar dependent. The results provide a possible explanation why only a narrow range of Salmonella serovars are associated with foodborne illness outbreaks linked to tomatoes.     

Inactivation of salmonella on tomato stem scars by edible chitosan and organic Acid coatings

This study was conducted to investigate the efficacy of antimicrobial coatings for inactivation of Salmonella on the surface of tomato stem scars. Scars were inoculated with a four-strain cocktail of Salmonella (serovars Montevideo, Newport, Saintpaul, and Typhimurium) and coated with acid-chitosan solutions. The chitosan coating with three acids (3A plus chitosan), the chitosan coating with one acid, and the three-acid solution without chitosan reduced the populations of Salmonella by 6.0, 3.6, and 5.3 log CFU per stem scar, respectively. Addition of allyl isothiocyanate (10 μl/ml) to the 3A plus chitosan coating did not significantly increase (P > 0.05) the antimicrobial efficacy. Although the populations of Salmonella in the controls (ca. 7.5 log CFU per stem scar) did not change significantly throughout the 14-day storage period at 10° C, Salmonella cells were reduced to undetectable levels (< 0.7 log CFU per stem scar) in the samples treated with 3A plus chitosan coating after two days of storage, and no growth was observed for the remaining storage period. Results from this study demonstrate that coatings of acid plus chitosan provide an alternative antimicrobial intervention for decontamination of tomatoes.     

Bactericidal activity of isothiocyanate against pathogens on fresh produce

The bactericidal activity of allyl and methyl isothiocyanate (AITC and MITC) was tested with a rifampicin-resistant strain of Salmonella Montevideo and streptomycin-resistant strains of Escherichia coil O157:H7 and Listeria monocytogenes Scott A. Iceberg lettuce inoculated with high (10(7) to 10(8) CFU/g) and low (10(3) to 10(4) CFU/g) concentrations of bacterial pathogens was treated with AITC and MITC in sealed containers at 4 degrees C for 4 days. AITC showed stronger bactericidal activity than MITC against E. coli O157:H7 and Salmonella Montevideo, whereas MITC showed stronger activity against L. monocytogenes than E. coli O157:H7 and Salmonella Montevideo. Up to 8-log reduction occurred with E. coli O157:H7 and Salmonella Montevideo on lettuce following treatment with vapor generated from 400 microl of AITC for 2 and 4 days, respectively. AITC was used to treat tomatoes inoculated with Salmonella Montevideo on stem scars and skin and apples inoculated with E. coli O157:H7 on stem scars. The bactericidal effect of AITC varied with bacteria species and exposure time. Salmonella Montevideo inoculated on tomato skin was more sensitive to AITC than that on stem scars. Treatment with vapor generated from 500 microl of AITC caused an 8-log reduction in bacteria on tomato skin but only a 5-log reduction on tomato stem scars. The bactericidal activity of AITC was weaker for E. coli O157:H7 on apple stem scars; only a 3-log reduction in bacteria occurred when 600 microl of AITC was used.     

The effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on whole Roma tomatoes

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.     

Microbiological profile of greenhouses in a farm producing hydroponic tomatoes

Produce, including tomatoes, has been implicated in several outbreaks of foodborne illness. A number of the sources of contamination for produce grown in open fields are known. However, as an alternative agricultural system, hydroponic greenhouses are reasonably expected to reduce some of these sources. The objective of the present study was to determine the microbiological profile of tomatoes grown in greenhouses at a Mexican hydroponic farm with a high technological level and sanitary agricultural practices (SAPs) in place. Tomatoes and other materials associated with the farm were analyzed for the presence of Salmonella enterica and populations of Escherichia coli, coliforms, and Enterobacteriaceae. Tomatoes showed median levels of 0.8 log CFU per tomato for Enterobacteriaceae, < 0.5 log CFU per tomato for coliforms, and 0.5 most probable number per tomato for E. coli. Despite the physical barriers that the facilities provide and the implemented SAPs, we found that 2.8% of tomatoes were contaminated with Salmonella and 0.7% with E. coli. Other Salmonella-positive materials were puddles, soil, cleaning cloths, and sponges. Samples from the nursery and greenhouses were positive for E. coli, whereas Salmonella was found only in the latter. Although hydroponic greenhouses provide physical barriers against some sources of enteric bacterial contamination, these results show that sporadic evidence of fecal contamination and the presence of Salmonella can occur at the studied greenhouse farm.     

Survival of Shigella sonnei on smooth tomato surfaces, in potato salad and in raw ground beef

This study investigated the survival of a five-strain Shigella sonnei cocktail on smooth tomato surfaces, in potato salad and in raw ground beef. All inocula were resistant to the antibiotic rifampicin to allow simple detection of the target culture among the indigenous microflora of the food samples. Inoculated tomatoes were stored at 13 degrees C/85% relative humidity, the standard holding conditions for mature, green tomatoes. Inoculated potato salad and ground beef samples were stored at 2.5 degrees C and 8.0 degrees C to study the effects of varied refrigerated temperatures. Surviving populations were estimated using a three-tube most probable number (MPN) method. Tryptic soy broth tubes supplemented with 100 ppm rifampicin were inoculated with appropriate dilutions of the recovered inocula and scored for growth after overnight enrichment. S. sonnei populations declined rapidly to undetectable levels (2 days) when dried on smooth surfaces of tomatoes. S. sonnei populations did not decrease in potato salad and ground beef stored at 2.5 degrees C and 8.0 degrees C over the shelf-life of the products.     

Preliminary evaluation of flow-through immunocapture followed by real-time PCR for the detection of Salmonella serovars on tomato surfaces within 8 hours

This study reports a preliminary evaluation of flow-through immunocapture (FTI) followed by real-time PCR (FTI-PCR) for the detection of Salmonella serovars on tomato surfaces within 8 h. The FTI-PCR method was compared with real-time PCR, direct plating of FTI beads on xylose lysine desoxycholate (XLD), and the conventional culture method for Salmonella found in the U.S. Food and Drug Administration's (FDA) Bacteriological Analytical Manual (BAM). Unwaxed green tomatoes were spot inoculated with a five-serovar Salmonella cocktail on smooth surfaces at levels of 10(0) to 10(4) CFU per tomato and washed in lactose broth (LB) using a shake-rub method. The resulting LB rinse was incubated at 37 degrees C for 4 h prior to analysis by FTI-XLD, real-time PCR, or FTI-PCR and for 24 h as the first step in the BAM Salmonella culture method. For FTI-XLD, the observed lowest detection level (LDL) was 4.6 x 10(1) CFU per tomato. There was no significant difference in performance between the FTI-XLD method and the BAM Salmonella culture method (P > 0.05); however, the FTI-XLD method reduced the overall assay time by 48 h. For real-time PCR and FTI-PCR, the observed LDLs were 4.6 x 10(1) and 9.2 x 10(0) CFU per tomato, respectively. The FTI-PCR method was superior to the BAM Salmonella culture method (P < 0.05) for the detection of Salmonella serovars on tomato surfaces and was completed within 8 h.     

Dispersal of Salmonella Typhimurium by rain splash onto tomato plants

Outbreaks of Salmonella enterica have increasingly been associated with tomatoes and traced back to production areas, but the spread of Salmonella from a point source onto plants has not been described. Splash dispersal by rain could be one means of dissemination. Green fluorescent protein-labeled, kanamycin-resistant Salmonella enterica sv. Typhimurium dispensed on the surface of plastic mulch, organic mulch, or soil at 10? CFU/cm2 was used as the point source in the center of a rain simulator. Tomato plants in soil with and without plastic or organic mulch were placed around the point source, and rain intensities of 60 and 110 mm/h were applied for 5, 10, 20, and 30 min. Dispersal of Salmonella followed a negative exponential model with a half distance of 3 cm at 110 mm/h. Dispersed Salmonella survived for 3 days on tomato leaflets, with a total decline of 5 log and an initial decimal reduction time of 10 h. Recovery of dispersed Salmonella from plants at the maximum observed distance ranged from 3 CFU/g of leaflet after a rain episode of 110 mm/h for 10 min on soil to 117 CFU/g of leaflet on plastic mulch. Dispersal of Salmonella on plants with and without mulch was significantly enhanced by increasing rain duration from 0 to 10 min, but dispersal was reduced when rainfall duration increased from 10 to 30 min. Salmonella may be dispersed by rain to contaminate tomato plants in the field, especially during rain events of 10 min and when plastic mulch is used.     

Detection of salmonella by flow-through immunocapture real-time PCR in selected foods within 8 hours

This study investigated flow-through immunocapture (FTI), using the Pathatrix device, followed by plating on xylose lysine desoxycholate (XLD) agar (FTI-XLD) or analysis by real-time PCR (FTI-PCR) for the detection of Salmonella on smooth tomato surfaces and in potato salad and ground beef within 8 h. Food samples were inoculated with an appropriate dilution of a five-serovar Salmonella cocktail and enriched for 5 h. Following enrichment, samples were analyzed by the FTI-XLD and FTI-PCR methods. Food samples were also analyzed by a modified U.S. Food and Drug Administration Bacteriological Analytical Manual (BAM) Salmonella culture method for comparison. Salmonella inoculated at 10(0) CFU per tomato or 10(0) CFU/25 g was detected by the FTI-XLD method in 6, 8, and 4 of 10 samples for tomatoes, potato salad, and ground beef, respectively. Salmonella inoculated at 10(0) CFU per tomato or 10(0) CFU/25 g was detected by the FTI-PCR method in 8, 9, and 9 of 10 samples for tomatoes, potato salad, and ground beef, respectively. The FTI-PCR method achieved significantly higher (P < 0.05) detection of Salmonella on tomatoes, whereas the FTI-XLD method achieved significantly lower (P < 0.05) detection of Salmonella in ground beef when compared with the modified BAM Salmonella culture method; however, all other comparisons to the modified BAM method were not significantly different. The FTI-XLD method demonstrated the ability to isolate presumptive Salmonella colonies up to 48 hfaster than did the modified BAM Salmonella culture method.     

Inactivation of Salmonella during drying and storage of Roma tomatoes exposed to predrying treatments including peeling, blanching, and dipping in organic acid solutions

The objective of this study was to evaluate the influence of predrying treatments, i.e., peeling, blanching prior to inoculation, and dipping in organic acid solutions, on inactivation of Salmonella during drying (60 degrees C for 14 h) and aerobic storage (25 degrees C for 28 days) of inoculated (five-strain composite, 7.1 to 7.4 log CFU/g) Roma tomato halves. Four predrying treatments groups were established. One group received no treatment (C). In the other three groups, unpeeled-unblanched, unpeeled-blanched (steam blanched at 88 degrees C for 3 min), peeled-unblanched, and peeled-blanched tomato halves were immersed for 10 min in water (W), ascorbic acid solution (AA; 3.40%, pH 2.48), or citric acid solution (CA; 0.21%, pH 2.51). Appropriate dilutions of homogenized tomato samples were spread plated on tryptic soy agar with 0.1% pyruvate and XLT4 agar for bacterial enumeration during drying and storage. Ten minutes of immersion in W, AA, or CA reduced bacterial populations by 0.7 to 1.6 log CFU/g. After 14 h of dehydration, total log reductions in the populations of bacteria were 3.2 to 4.5 (C), 3.7 to 4.9 (W), > 5.6 to > 6.1 (AA), and 4.5 to 5.5 (CA) log CFU/g, depending on type of agar used and condition of tomato samples. During drying and storage, the order of pathogen inactivation for predrying dipping treatments was AA > CA > W > C, with AA and CA rendering bacterial populations below detectable levels ( < 1.3 log CFU/g) prior to storage and between 7 and 14 days of storage, respectively. The results also indicated that peeling and blanching of tomatoes prior to inoculation may not necessarily affect destruction of Salmonella during the drying process. Use of predrying acid dipping treatments of tomatoes, especially in AA, may improve destruction of Salmonella during the dehydration process.     

Development of a proposed standard method for assessing the efficacy of fresh produce sanitizers

A series of studies was done for the purpose of developing a proposed standard method to evaluate point-of-use home sanitizers for fresh produce. Preliminary experiments were done to determine the survival of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes after inoculation onto the surface of ripe tomatoes and drying for up to 24 h at 22 +/- 2 degrees C. Within 2 h, the initial population (6.88 log10 CFU/tomato) of E. coli O157:H7 was reduced by approximately 3 log10, while reductions in similar initial populations of Salmonella and L. monocytogenes were approximately 1 and 0.6 log10 CFU/tomato, respectively, after 40 min and 3 h. A pilot study evaluated treatment with 200 ppm free chlorine and a prototype Fit produce wash (Fit) for their efficacy in killing a five-serotype mixture of Salmonella or L. monocytogenes spot inoculated on tomatoes using the proposed inoculation and recovery procedures. Inoculated tomatoes were sprayed with chlorinated water, Fit, or sterile distilled water (control) and hand rubbed for 30 s. Each tomato was then placed in a plastic bag and rinsed with 200 ml of sterile water by vigorously agitating for 30 s to simulate a procedure consumers might use for sanitizing and rinsing produce in a home setting. Each tomato was transferred to a second bag, and 20 ml of sterile 0.1% peptone was added; tomatoes were rubbed by hand for 40 s. Populations of Salmonella or L. monocytogenes in the rinse water and the 0.1% peptone wash solution were determined. Treatment with 200 ppm chlorine and Fit resulted in > or = 3.07 and > 6.83 log10 reductions, respectively, in Salmonella. Treatment with 200 ppm chlorine and Fit reduced the number of L. monocytogenes by > or = 3.33 and > or = 4.96 log10 CFU/tomato, respectively. The proposed standard method for testing the efficacy of point-of-use produce sanitizers needs to be evaluated for reproducibility of results through a larger scale series of experiments.     

Efficacy of detergents in removing Salmonella and Shigella spp. from the surface of fresh produce

Fresh produce has been implicated in several foodborne disease outbreaks. Produce surfaces can be primary sites of contamination during production and handling. One approach to reduce contamination is to treat fresh produce with rinsing agents. In this study, different detergent agents were used at 22 and 40 degrees C to determine their efficacy in removing Salmonella and Shigella spp. from the surfaces of strawberries, tomatoes, and green-leaf lettuce. Produce was inoculated at 22 degrees C with a cocktail of nalidixic acid-resistant organisms (6 to 6.5 log CFU/ml). After air drying for 1 h, samples were rinsed with either 0.1% Tween 80, 0.1% sodium lauryl sulfate (SLS), or water (control) at 22 or 40 degrees C. Rinse solutions were spiral plated onto tryptic soy agar supplemented with 50 mg of nalidixic acid per liter. In trials involving strawberries and lettuce, Salmonella and Shigella were removed at levels of 4 and 3 log CFU/ml, respectively, except from Salmonella-inoculated strawberries rinsed with SLS, for which minimal removal rates were 1.5 log CFU/ml at 22 degrees C and < 1 log CFU/ml at 40 degrees C. When whole strawberries were analyzed after rinsing with SLS, few organisms were recovered. This result suggests that SLS may have a lethal or sublethal effect on Salmonella, especially when a 40 degrees C solution is used. Salmonella and Shigella removal rates for tomatoes were 1 and 1.5 log CFU/ml lower, respectively, than those for strawberries or lettuce. Overall, detergents were no more effective in removing organisms from produce than water was. The detergents examined would not constitute effective overall produce rinse treatments.     

Calcinated calcium killing of Escherichia coli O157:H7, Salmonella,and Listeria monocytogenes on the surface of tomatoes

This study was conducted to evaluate the efficacy of calcinated calcium, 200 ppm chlorine water (1% active chlorine), and sterile distilled water in killing Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on the surfaces of spot-inoculated tomatoes. Inoculated tomatoes were sprayed with calcinated calcium, chlorinated water, or sterile distilled water (control) and hand rubbed for 30 s. Populations of E coli O157:H7, Salmonella, and L. monocytogenes in the rinse water and in the residual (0.1% peptone) wash solution were determined. Treatment with 200 ppm chlorine and calcinated calcium resulted in 3.40- and 7.85-log10 reductions of E. coli O157:H7, respectively, and 2.07- and 7.36-log10 reductions of Salmonella, respectively. Treatment with 200 ppm chlorine and calcinated calcium reduced L monocytogenes numbers by 2.27 and 7.59 log10 CFU per tomato, respectively. The findings of this study suggest that calcinated calcium could be useful in controlling pathogenic microorganisms in fresh produce.     

Effectiveness of Individual or Combined Sanitizer Treatments for Inactivating Salmonella spp. on Smooth Surface, Stem Scar, and Wounds of Tomatoes

ABSTRACT: Unwaxed, green tomatoes ('Florida 47' cultivar) were contaminated with Salmonella and then treated with aqueous solutions of sodium hypochlorite (HOCl; 200 ppm), acidified sodium chlorite (ASC; 1200 ppm), peroxyacetic acid (PAA; 87 ppm), or chlorine dioxide gas (ClO₂; total 100 mg). Additionally, a combined treatment of immersion in HOCl, followed by immersion in ASC and then exposure to ClO₂ gas was investigated. Tomatoes were spot inoculated with a 5-strain Salmonella cocktail on smooth surfaces, stem scar tissue, or puncture wounds. A 3 replicate set of each of the sample groups was stored at 20 °C and 95% relative humidity (RH) and retested after 5 d. Greater than 4.0-log unit reductions of Salmonella spp. inoculated on the smooth surface of the tomatoes were seen for all aqueous sanitizer treatments, with Salmonella populations below the detection limit after 5 d of storage. All aqueous treatment groups showed > 1.0-log unit reductions in Salmonella at the stem scar and >2.0-log unit reduction at puncture wounds. The ClO₂ gas treatment reduced Salmonella to undetectable levels at the stem scar, but had no apparent effect on populations inoculated in puncture wounds. The combined treatment resulted in a 3.0-log unit reduction of inoculated Salmonella at puncture wounds. In all cases except for treatment with chlorine, surviving Salmonella populations did not increase after the 5 d of storage. Results of this study suggest the combined treatment was most effective for minimizing the risk of Salmonella contaminated on tomatoes.     

Efficacy of slightly acidic electrolyzed water in killing or reducing Escherichia coli O157:H7 on iceberg lettuce and tomatoes under simulated food service operation conditions

Abstract: The objective of this study was to evaluate the efficacy of slightly acidic electrolyzed (SAEO) water in killing or removing Escherichia coli O157:H7 on iceberg lettuce and tomatoes by washing and chilling treatment simulating protocols used in food service kitchens. Whole lettuce leaves and tomatoes were spot‐inoculated with 100 μL of a mixture of 5 strains of E. coli O157:H7. Washing lettuce with SAEO water for 15 s reduced the pathogen by 1.4 to 1.6 log CFU/leaf, but the treatments did not completely inactivate the pathogen in the wash solution. Increasing the washing time to 30 s increased the reductions to 1.7 to 2.3 log CFU/leaf. Sequential washing in SAEO water for 15 s and then chilling in SAEO water for 15 min also increased the reductions to 2.0 to 2.4 log CFU/leaf, and no cell survived in chilling solution after treatment. Washing tomatoes with SAEO water for 8 s reduced E. coli O157:H7 by 5.4 to 6.3 log CFU/tomato. The reductions were increased to 6.6 to 7.6 log CFU/tomato by increasing the washing time to 15 s. Results suggested that application of SAEO water to wash and chill lettuce and tomatoes in food service kitchens could minimize cross‐contamination and reduce the risk of E. coli O157:H7 present on the produce. Practical Application: SAEO water is equally or slightly better than acidic electrolyzed (AEO) water for inactivation of bacteria on lettuce and tomato surfaces. In addition, SAEO water may have the advantages over AEO water on its stability, no chlorine smell, and low corrosiveness. Therefore, SAEO water may have potential for produce wash to enhance food safety.     

Survival and growth of Salmonella and Listeria in the chicken breast patties subjected to time and temperature abuse under varying conditions

Chicken breast patties were inoculated with a mixture of Salmonella Senftenberg, Salmonella Typhimurium, Salmonella Heidelberg, Salmonella Mission, Salmonella Montevideo, Salmonella California, and Listeria innocua. The initial inoculation of bacteria was approximately 10(7) log10 CFU/g. The inoculated patties were processed in a pilot-scale air convection oven at an air temperature of 177 degrees C, an air velocity of 9.9 m3/min, and a low (a wet bulb temperature of 48 degrees C) or high (a wet bulb temperature of 93 degrees C) humidity condition. The patties were processed to a final center temperature of 65 to 75 degrees C. The survivors of Salmonella and Listeria in the processed patties were evaluated. Processing humidity affected the survivors of bacteria. More survivors of Salmonella and Listeria (>2 logs) were obtained for the patties cooked at low humidity than at high humidity. After thermal processing, the patties were stored under air, vacuum, or CO2 at refrigerated (4 degrees C) or thermally abused (8 to 15 degrees C) temperatures. Storage temperature, time, and gas environment affected the bacteria growth. Higher storage temperature and longer storage time correlated to an increased growth of bacteria in the cooked chicken patties. Less Salmonella (2 logs) and Listeria (0.5 to 1 log) cells were obtained in the patties stored under vacuum than in air. Storing the patties in 30% CO2 reduced the growth of Salmonella more than 2 log10 CFU/g. At a CO2 level of 15%, 1 log10 CFU/g of reduction was obtained for Listeria in cooked chicken patties.