Antimicrobial effect of electrolyzed water for inactivating Campylobacter jejuni during poultry washing

The effectiveness of electrolyzed (EO) water for killing Campylobacter jejuni on poultry was evaluated. Complete inactivation of C. jejuni in pure culture occurred within 10 s after exposure to EO or chlorinated water, both of which contained 50 mg/l of residual chlorine. A strong bactericidal activity was also observed on the diluted EO water (containing 25 mg/l of residual chlorine) and the mean population of C. jejuni was reduced to less than 10 CFU/ml (detected only by enrichment for 48 h) after 10-s treatment. The diluted chlorine water (25 mg/l residual chlorine) was less effective than the diluted EO water for inactivation of C. jejuni. EO water was further evaluated for its effectiveness in reducing C. jejuni on chicken during washing. EO water treatment was equally effective as chlorinated water and both achieved reduction of C. jejuni by about 3 log10 CFU/g on chicken, whereas deionized water (control) treatment resulted in only 1 log10 CFU/g reduction. No viable cells of C. jejuni were recovered in EO and chlorinated water after washing treatment, whereas high populations of C. jejuni (4 log10 CFU/ml) were recovered in the wash solution after the control treatment. Our study demonstrated that EO water was very effective not only in reducing the populations of C. jejuni on chicken, but also could prevent cross-contamination of processing environments.     

Efficacy of neutral electrolyzed water to inactivate Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, and Staphylococcus aureus on plastic and wooden kitchen cutting boards

This study evaluated the efficacy of neutral electrolyzed water (NEW; 64.1 mg/liter of active chlorine) to reduce populations of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes on plastic and wooden kitchen cutting boards. Its effectiveness was compared with that of a sodium hypochlorite solution (NaClO; 62.3 mg/liter of active chlorine). Inoculated portions of cutting boards were rinsed in either NEW or NaClO solutions, or deionized water (control). Plastic boards were rinsed for 1 min and wooden boards for 1 and 5 min. After each treatment, the surviving population of each strain was determined on the surface and in the soaking water. No significant difference (P > or = 0.05) was found between the final populations of each strain with regard to the treatment solutions (NEW or NaClO). However, a significant difference (P < or = 0.05) was revealed between surface materials after 1 min of washing. Whereas in plastic boards the initial bacterial populations were reduced by 5 log CFU/50 cm2, in wooden cutting boards they underwent a reduction of <3 log CFU/50 cm2. A 5-min exposure time yielded reductions of about 4 log CFU/50 cm2. The surviving populations of all bacteria in NEW and NaCIO washing solutions were <1 log CFU/ml after soaking both surfaces. This study revealed that NEW treatment is an effective method for reducing microbial contamination on plastic and wooden cutting boards. NEW efficacy was comparable to that of NaCIO, with the advantage of having a larger storage time.     

Effectiveness of sanitation with quaternary ammonium compound or chlorine on stainless steel and other domestic food-preparation surfaces.

The relative ability of various materials used for domestic and/or food-service sinks and countertops to be sanitized was determined. Both smooth (unused) and abraded surfaces were tested by exposure to 200 mg of quaternary ammonium compound per liter or 200 mg of sodium hypochlorite per liter. Surface materials tested included mechanically polished (type 304, #4 finish) and electropolished stainless steel, polycarbonate, and mineral resin. Surfaces were prepared for testing by allowing attachment of a Staphylococcus aureus culture for 4 h to achieve an initial attached population of 10(4) to 10(5) CFU/cm2. The test procedure involved immersion of the surface in sanitizer solution followed by wiping with a sanitizer-saturated cloth. Residual staphylococci were detected by overlaying agar directly on the treated surface. Results indicated that the stainless steels and the smooth polycarbonate, which had 0.5 log CFU/cm2 or fewer of residual staphylococci, were more readily sanitized by quaternary ammonium compound than were either the mineral resin surfaces, which had nearly 2.0 log CFU/cm2 of residual staphylococci, or the abraded polycarbonate which had nearly 1.0 log CFU/cm2 of residual staphylococci. Chlorine was most effective on the mechanically polished stainless steel, the unabraded electropolished stainless steel, and the polycarbonate surfaces, reducing cell populations to less than 1.0 log CFU/cm2. Chlorine was less effective on abraded electropolished stainless steel and mineral resin surfaces, where populations remained greater than 1.0 log CFU/cm2. Sanitation with quaternary ammonium compound or chlorine reduced S. aureus populations more than 1,000-fold on all surfaces except unabraded mineral resin.     

Effects of electrolyzed oxidizing water on reducing Listeria monocytogenes contamination on seafood processing surfaces

The effects of electrolyzed oxidizing (EO) water on reducing Listeria monocytogenes contamination on seafood processing surfaces were studied. Chips (5 x 5 cm(2)) of stainless steel sheet (SS), ceramic tile (CT), and floor tile (FT) with and without crabmeat residue on the surface were inoculated with L. monocytogenes and soaked in tap or EO water for 5 min. Viable cells of L. monocytogenes were detected on all chip surfaces with or without crabmeat residue after being held at room temperature for 1 h. Soaking contaminated chips in tap water resulted in small-degree reductions of the organism (0.40-0.66 log cfu/chip on clean surfaces and 0.78-1.33 log cfu/chip on dirty surfaces). Treatments of EO water significantly (p<0.05) reduced L. monocytogenes on clean surfaces (3.73 log on SS, 4.24 log on CT, and 5.12 log on FT). Presence of crabmeat residue on chip surfaces reduced the effectiveness of EO water on inactivating Listeria cells. However, treatments of EO water also resulted in significant reductions of L. monocytogenes on dirty surfaces (2.33 log on SS and CT and 1.52 log on FT) when compared with tap water treatments. The antimicrobial activity of EO water was positively correlated with its chlorine content. High oxidation-reduction potential (ORP) of EO water also contributed significantly to its antimicrobial activity against L. monocytogenes. EO water was more effective than chlorine water on inactivating L. monocytogenes on surfaces and could be used as a chlorine alternative for sanitation purpose. Application of EO water following a thorough cleaning process could greatly reduce L. monocytogenes contamination in seafood processing environments.     

Method of applying sanitizers and sample preparation affects recovery of native microflora and Salmonella on whole cantaloupe surfaces

Standardized methods for applying sanitizer treatments to cantaloupes and for recovering surviving native microflora or Salmonella on inoculated cantaloupe after sanitizing are lacking. Accordingly, the objectives of this study were to compare four methods for applying sanitizers (dipping, dipping with rotation, dipping with agitation, and dipping with rubbing) using 200 ppm of chlorine or 5% H2O2, two recovery methods (homogenization of rind plugs in a stomacher or blender), and five selective recovery media for Salmonella. Whole cantaloupes were submerged in a cocktail of five strains of Salmonella (each at approximately 2 x 10(8) CFU/ml) for 10 min and allowed to dry for 1 h inside a biosafety cabinet and stored at 20 degrees C for approximately 23 h before sanitizing. The recovery of Salmonella from whole cantaloupe without sanitizing averaged 5.09 log CFU/cm2 by blending and 4.30 log CFU/cm2 by homogenization in a stomacher for the five selective agar media. Microbial populations (Salmonella or the indigenous aerobic mesophilic bacteria, gram-negative bacteria, lactic acid bacteria, Pseudomonas spp., and yeast and mold) were not significantly (P > 0.05) reduced by treating with water regardless of the treatment method used. Sanitizing with chlorine or H2O2 by dipping, with or without rotation for 2 min, also did not reduce microbial populations. However, populations of all classes of native microflora and Salmonella were significantly (P < 0.05) reduced by sanitizer treatments (2 min) applied with agitation or by rubbing. In general, sanitizer treatments applied by rubbing resulted in greater log reductions (by up to 1.7 log unit) than for treatments applied with agitation. Populations of native microflora and Salmonella recovered from cantaloupe were higher (by up to 1.8 log unit) by blending compared to homogenization in a stomacher. In most instances, selective media used did not differ significantly (P > 0.05) for recovery of Salmonella after washing treatments.     

Evaluation of peroxyacetic acid as a potential pre-grinding treatment for control of Escherichia coli O157:H7 and Salmonella Typhimurium on beef trimmings

Peroxyacetic acid was evaluated in four separate trials for ability to reduce populations of Escherichia coli O157:H7 and Salmonella serotype Typhimurium on fresh beef trim. Trial 1 examined the effectiveness of peroxyacetic acid on individual pieces of fresh beef trim. Trial 2 evaluated the efficacy of peroxyacetic acid at low levels of contamination on batches of fresh beef trim. Trial 3 studied a washing effect of water. Lastly, Trial 4 compared the effectiveness of peroxyacetic acid to lactic acid. At various inoculation levels, peroxyacetic acid reduced populations of both pathogens by approximately 1.0log(10)CFU/cm(2) on fresh beef trim. Trial 3 showed that approximately half of the reductions found in Trials 1 and 2 were due to a washing effect of the water dip. In addition, as shown in Trial 1, increases in concentrations (>200ppm) did not significantly increase log(10) reductions of both pathogens. Following a water dip in Trial 4, peroxyacetic acid caused a reduction of 0.7log(10)CFU/cm(2) in E. coli O157:H7 and 1.0log(10)CFU/cm(2) in Salmonella Typhimurium, whereas lactic acid caused a reduction of 1.3log(10)CFU/cm(2) in E. coli O157:H7 and 2.1log(10)CFU/cm(2) in S. Typhimurium following the water dip. These results show that peroxyacetic acid was not more effective than 2% l-lactic acid in reducing pathogens on fresh beef trim.     

Efficacy of ozonated and electrolyzed oxidative waters to decontaminate hides of cattle before slaughter

The hides of cattle are the primary source of pathogens such as Escherichia coli O157:H7 that contaminate preevisceration carcasses during commercial beef processing. A number of interventions that reduce hide contamination and subsequent carcass contamination are currently being developed. The objective of this study was to determine the efficacy of ozonated and electrolyzed oxidizing (EO) waters to decontaminate beef hides and to compare these treatments with similar washing in water without the active antimicrobial compounds. Cattle hides draped over barrels were used as the model system. Ozonated water (2 ppm) was applied at 4,800 kPa (700 lb in2) and 15 degrees C for 10 s. Alkaline EO water and acidic EO water were sequentially applied at 60 degrees C for 10 s at 4,800 and 1,700 kPa (250 lb in2), respectively. Treatment using ozonated water reduced hide aerobic plate counts by 2.1 log CFU/100 cm2 and reduced Enterobacteriaceae counts by 3.4 log CFU/100 cm2. EO water treatment reduced aerobic plate counts by 3.5 log CFU/100 cm2 and reduced Enterobacteriaceae counts by 4.3 log CFU/100 cm2. Water controls that matched the wash conditions of the ozonated and EO treatments reduced aerobic plate counts by only 0.5 and 1.0 log CFU/100 cm2, respectively, and each reduced Enterobacteriaceae counts by 0.9 log CFU/100 cm2. The prevalence of E. coli O157 on hides was reduced from 89 to 31% following treatment with ozonated water and from 82 to 35% following EO water treatment. Control wash treatments had no significant effect on the prevalence of E. coli O157:H7. These results demonstrate that ozonated and EO waters can be used to decontaminate hides during processing and may be viable treatments for significantly reducing pathogen loads on beef hides, thereby reducing pathogens on beef carcasses.     

Modeling of the effect of washing solution flow conditions on Escherichia coli O157:H7 population reduction on fruit surfaces

Washing produce with sanitizing solutions is an important step in reducing microbial populations during postharvest handling. Little information exists regarding the effects of washing solution flow conditions on the efficacy of pathogen reduction during washing. This study was undertaken to investigate the effects of washing conditions such as flow velocity, agitation rate, and contact time on the reduction of Escherichia coli O157:H7 populations from the surfaces of cantaloupe rind and cut apples. Top surfaces of cylindrical samples were spot inoculated with E. coli O157:H7 and treated with peroxyacetic acid (POAA; 80 mg/liter) solution under different flow velocities and agitation rates and with different washing modes. Test results indicate that the reduction rate of E. coli O157:H7 increased with the increase in flow velocity and agitation rate under the testing conditions. In a 3-min treatment in the flow-through chamber, the E. coli O157:H7 count reduction on cantaloupe rind and cup apples reached 2.5 and 2.3 log CFU/cm2, respectively, when the flow velocity increased from 0.0 to 0.8 m/min. Agitation conducted at the bottom of the treatment chamber reduced the E. coli O157:H7 population on cut apples by 1.2 log CFU/cm2 in 3 min, whereas in the treatment with the agitation over the top of the chamber, the survival count of E. coli O157:H7 was reduced by only 0.8 log CFU/cm2. The experimental data were used to fit four microbial reduction kinetic models. It was found that E. coli O157:H7 reduction from the fruit surfaces was best described by the Weibull model. These findings may be useful in designing produce wash systems for achieving enhanced pathogen reduction and improved produce quality and safety.     

Reduction of bacteria on spinach, lettuce, and surfaces in food service areas using neutral electrolyzed oxidizing water

Food safety issues and increases in food borne illnesses have promulgated the development of new sanitation methods to eliminate pathogenic organisms on foods and surfaces in food service areas. Electrolyzed oxidizing water (EO water) shows promise as an environmentally friendly broad spectrum microbial decontamination agent. EO water is generated by the passage of a dilute salt solution ( approximately 1% NaCl) through an electrochemical cell. This electrolytic process converts chloride ions and water molecules into chlorine oxidants (Cl(2), HOCl/ClO(-)). At a near-neutral pH (pH 6.3-6.5), the predominant chemical species is the highly biocidal hypochlorous acid species (HOCl) with the oxidation reduction potential (ORP) of the solution ranging from 800 to 900mV. The biocidal activity of near-neutral EO water was evaluated at 25 degrees C using pure cultures of Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis. Treatment of these organisms, in pure culture, with EO water at concentrations of 20, 50, 100, and 120ppm total residual chlorine (TRC) and 10min of contact time resulted in 100% inactivation of all five organisms (reduction of 6.1-6.7log(10)CFU/mL). Spray treatment of surfaces in food service areas with EO water containing 278-310ppm TRC (pH 6.38) resulted in a 79-100% reduction of microbial growth. Dip (10min) treatment of spinach at 100 and 120ppm TRC resulted in a 4.0-5.0log(10)CFU/mL reduction of bacterial counts for all organisms tested. Dipping (10min) of lettuce at 100 and 120ppm TRC reduced bacterial counts of E. coli by 0.24-0.25log(10)CFU/mL and reduced all other organisms by 2.43-3.81log(10)CFU/mL.     

Efficacy of electrolyzed oxidizing water in inactivating Salmonella on alfalfa seeds and sprouts

Studies have demonstrated that electrolyzed oxidizing (EO) water is effective in reducing foodborne pathogens on fresh produce. This study was undertaken to determine the efficacy of EO water and two different forms of chlorinated water (chlorine water from Cl2 and Ca(OCl)2 as sources of chlorine) in inactivating Salmonella on alfalfa seeds and sprouts. Tengram sets of alfalfa seeds inoculated with a five-strain cocktail of Salmonella (6.3 x 10(4) CFU/g) were subjected to 90 ml of deionized water (control), EO water (84 mg/liter of active chlorine), chlorine water (84 mg/liter of active chlorine), and Ca(OCl)2 solutions at 90 and 20,000 mg/liter of active chlorine for 10 min at 24 +/- 2 degrees C. The application of EO water, chlorinated water, and 90 mg/liter of Ca(OCl)2 to alfalfa seeds for 10 min reduced initial populations of Salmonella by at least 1.5 log10 CFU/g. For seed sprouting, alfalfa seeds were soaked in the different treatment solutions described above for 3 h. Ca(OCl)2 (20,000 mg/liter of active chlorine) was the most effective treatment in reducing the populations of Salmonella and non-Salmonella microflora (4.6 and 7.0 log10 CFU/g, respectively). However, the use of high concentrations of chlorine generates worker safety concerns. Also, the Ca(OCl)2 treatment significantly reduced seed germination rates (70% versus 90 to 96%). For alfalfa sprouts, higher bacterial populations were recovered from treated sprouts containing seed coats than from sprouts with seed coats removed. The effectiveness of EO water improved when soaking treatments were applied to sprouts in conjunction with sonication and seed coat removal. The combined treatment achieved 2.3- and 1.5-log10 CFU/g greater reductions than EO water alone in populations of Salmonella and non-Salmonella microflora, respectively. This combination treatment resulted in a 3.3-log10 CFU/g greater reduction in Salmonella populations than the control (deionized water) treatment.     

Stability of electrolyzed oxidizing water and its efficacy against cell suspensions of Salmonella typhimurium and Listeria monocytogenes

Electrolyzed oxidizing (EO) water has proved to be effective against foodborne pathogens attached to cutting boards and poultry surfaces and against spoilage organisms on vegetables; however, its levels of effectiveness against Listeria monocytogenes and Salmonella Typhimurium in cell suspensions have not been compared with those of other treatments. In this study, the oxidation reduction potentials (ORPs), chlorine concentrations, and pHs of acidic and basic EO water were monitored for 3 days at 4 and 25 degrees C after generation. There were no differences between the pHs or ORPs of acidic and basic EO waters stored at 4 or 25 degrees C. However, the free chlorine concentration in acidic EO water stored at 4 degrees C increased after 24 h. In contrast, the free chlorine concentration in acidic EO water stored at 25 degrees C decreased after one day. Cell suspensions of Salmonella Typhimurium and L. monocytogenes were treated with distilled water, chlorinated water (20 ppm), acidified chlorinated water (20 ppm, 4.5 pH), acidic EO water (EOA), basic EO water (EOB), or acidic EO water that was "aged" at 4 degrees C for 24 h (AEOA) for up to 15 min at either 4 or 25 degrees C. The largest reductions observed were those following treatments carried out at 25 degrees C. EOA and AEOA treatments at both temperatures significantly reduced Salmonella Typhimurium populations by > 8 log10 CFU/ml. EOA and AEOA treatments effectively reduced L. monocytogenes populations by > 8 log10 CFU/ml at 25degrees C. These results demonstrate the stability of EO water under different conditions and that EO water effectively reduced Salmonella Typhimurium and L. monocytogenes populations in cell suspensions.     

An in vitro system for the comparison of excision and wet-dry swabbing for microbiological sampling of beef carcasses

An in vitro system for the comparison of wet-dry swabbing and surface tissue excision was developed to ascertain whether the commonly accepted statement of the advantage (in terms of bacterial recovery) of the tissue excision method is also legitimate when different kinds of bacteria are used. A total of 1,770 sections (2.5 by 10 cm) of bovine skin were individually inoculated on the subcutaneous fat side by spreading various suspensions of marker organisms (nalidixic acid-resistant Escherichia coli, vancomycin-resistant Enterococcus faecalis, and methicillin-resistant Staphylococcus aureus) at different concentrations and sampled by two standard methods: cotton wet-dry swabbing and excision. Most counts from cuts sampled by excision were significantly (P < 0.05) higher than the wet-dry swabs; however, no differences were observed between the control and the sampling method when sections were inoculated with bacterial solutions at a concentration of 10(3) CFU/ml and sampled by excision. For sections inoculated with bacterial solutions at a concentration of 10(3) CFU/ml, counts given as log CFU/25 cm2 ranged from 1.97 (S. aureus sampled by wet-dry swab) to 3.06 (S. aureus sampled by excision). For sections inoculated at a concentration of 10(4), counts given as log CFU/25 cm(2) ranged from 2.15 (E. faecalis sampled by wet-dry swab) to 3.19 (S. aureus sampled by excision). For sections inoculated at 10(5), counts given as log CFU/25 cm(2) ranged from 2.94 (E. faecalis, wet-dry swab) to 3.98 (S. aureus, excision), and for sections inoculated at 106, counts given as log CFU/25 cm(2) ranged from 3.53 (E. coli, wet-dry swab) to 4.69 (S. aureus, excision). The proposed system, which enabled a considerable amount of samples to be analyzed under controlled experimental conditions and a large number of data to be generated in a short time, demonstrated among the tested microorganisms that whereas the excision method recovered the highest number of bacteria, control means were always (with the exception of an inoculum of 10(3)/ml) significantly higher than means from either of the sampling methods. Our results indicate that particular attention should be paid to the diverse microflora that can contaminate carcasses in a given slaughterhouse and that it is not appropriate to generalize by saying that the destructive method is the reference technique for the bacteriological sampling of carcasses in slaughterhouses, especially when the contamination is higher than 10(3) CFU/25 cm(2).     

Reduction of Salmonella enterica on alfalfa seeds with acidic electrolyzed oxidizing water and enhanced uptake of acidic electrolyzed oxidizing water into seeds by gas exchange

Alfalfa sprouts have been implicated in several salmonellosis outbreaks in recent years. The disinfectant effects of acidic electrolyzed oxidizing (EO) water against Salmonella enterica both in an aqueous system and on artificially contaminated alfalfa seeds were determined. The optimum ratio of seeds to EO water was determined in order to maximize the antimicrobial effect of EO water. Seeds were combined with EO water at ratios (wt/vol) of 1:4, 1:10, 1:20, 1:40, and 1:100, and the characteristics of EO water (pH, oxidation reduction potential [ORP], and free chlorine concentration) were determined. When the ratio of seeds to EO water was increased from 1:4 to 1:100, the pH decreased from 3.82 to 2.63, while the ORP increased from +455 to +1,073 mV. EO water (with a pH of 2.54 to 2.38 and an ORP of +1,083 to +1,092 mV) exhibited strong potential for the inactivation of S. enterica in an aqueous system (producing a reduction of at least 6.6 log CFU/ml). Treatment of artificially contaminated alfalfa seeds with EO water at a seed-to-EO water ratio of 1:100 for 15 and 60 min significantly reduced Salmonella populations by 2.04 and 1.96 log CFU/g, respectively (P < 0.05), while a Butterfield's buffer wash decreased Salmonella populations by 0.18 and 0.23 log CFU/g, respectively. After treatment, EO water was Salmonella negative by enrichment with or without neutralization. Germination of seeds was not significantly affected (P > 0.05) by treatment for up to 60 min in electrolyzed water. The uptake of liquid into the seeds was influenced by the internal gas composition (air, N2, or O2) of seeds before the liquid was added.     

Influence of inoculation method, spot inoculation site, and inoculation size on the efficacy of acidic electrolyzed water against pathogens on lettuce

The influence of bacterial inoculation methods on the efficacy of sanitizers against pathogens was examined. Dip and spot inoculation methods were employed in this study to evaluate the effectiveness of acidic electrolyzed water (AcEW) and chlorinated water (200 ppm free available chlorine) against Escherichia coli O157:H7 and Salmonella spp. Ten pieces of lettuce leaf (5 by 5 cm) were inoculated by each method then immersed in 1.5 liters of AcEW, chlorinated water, or sterile distilled water for 1 min with agitation (150 rpm) at room temperature. The outer (abaxial) and inner (adaxial) surfaces of the lettuce leaf were distinguished in the spot inoculation. Initial inoculated pathogen population was in the range 7.3 to 7.8 log CFU/g. Treatment with AcEW and chlorinated water resulted in a 1 log CFU/g or less reduction of E. coli O157:H7 and Salmonella populations inoculated with the dip method. Spot inoculation of the inner surface of the lettuce leaf with AcEW and chlorinated water reduced the number of E. coli O157:H7 and Salmonella by approximately 2.7 and 2.5 log CFU/g, respectively. Spot inoculation of the outer surface of the lettuce leaf with both sanitizers resulted in approximately 4.6 and 4.4 log CFU/g reductions of E. coli O157:H7 and Salmonella, respectively. The influence of inoculation population size was also examined. Each sanitizer could not completely eliminate the pathogens when E. coli O157:H7 and Salmonella cells inoculated on the lettuce were of low population size (10(3) to 10(4) CFU/g), regardless of the inoculation technique.     

Direct microscopic observation of lettuce leaf decontamination with a prototype fruit and vegetable washing solution and 1% NaCl-NaHCO3

Efficacy of a prototype, food-grade alkaline surfactant washing solution and 1% NaCl-NaHCO3 (pH 10.0) against Escherichia coli O157:H7 cells on lettuce leaves was evaluated. Lettuce was inoculated with 10(9) CFU/ml of E. coli O157:H7 for 24 +/- 1 h at 4 degrees C. Samples were rinsed and treated with the prototype washing solution containing lauryl sodium sulfate or NaCl-NaHCO3 for 3 min at 22 degrees C. Viability of E. coli O157:H7 cells was examined by plate counts at the surface and cut edge, and by confocal scanning microscopic (CSLM) observation of samples stained with Sytox green and Alexa 594 conjugated antibody against E. coli O157:H7 at intact leaf surface, stomata, and damaged tissue (0 to 10, 30 to 40, and 0 to 40 microm from the cut surface). Although both treatments caused significant log reductions in CFU at the surface and cut edge, log reductions were greater for the prototype washing solution (0.7 to 1.1 log CFU/cm2) than for NaCl-NaHCO3 (0.2 to 0.4 log CFU/cm2) (P < 0.05). Percentage of viability determined by CSLM for prototype washing solution was significantly greater at 30 to 40 microm from cut surfaces than at 0 to 10 and 0 to 40 microm from cut surfaces and intact surfaces (P < 0.05). Stomata provided moderate protection. NaCl-NaHCO3 was less effective than the prototype washing solution, and high percentages of E. coli O157:H7 cells remained viable at all sites except at the surface. The percent viabilities determined by CSLM were not significantly different from those determined by plate counts for NaCl-NaHCO3 treatment (P > 0.05). However, CSLM indicated significantly greater percent viability than plate counts for lettuce treated with the prototype washing solution (P < 0.05). Surfactant-containing washing solutions warrant additional testing for decontamination of fresh produce.     

Effect of nisin in combination with EDTA, sodium lactate, and potassium sorbate for reducing Salmonella on whole and fresh-cut cantaloupet

Nisin (50 microg/ml), EDTA (0.02 M, disodium salt), sodium lactate (NaL, 2%), and potassium sorbate (KS, 0.02%) were tested individually and in various combinations as sanitizer treatments for reducing Salmonella on whole and fresh-cut cantaloupe. Whole cantaloupe and fresh-cut pieces were inoculated with a five-strain cocktail of Salmonella to give 4.76 +/- 0.23 log CFU/cm2 and 3.42 +/- 0.13 log CFU/g, respectively. Inoculated whole melons and fresh-cut pieces were stored at 5 degrees C for 7 days. Washing treatments were applied to inoculated whole melons at days 0, 3, and 7 of storage, and surviving bacterial populations were determined. The effect of the washing treatments on transfer of Salmonella to fresh-cut pieces prepared immediately after treatment was also determined. Directly inoculated fresh-cut pieces were treated at day 0, and surviving bacteria were enumerated at days 0, 3, and 7 of storage. The combination treatments of nisin-EDTA, nisin-NaL, nisin-KS, NaL-KS, and nisin-NaL-KS all resulted in reductions of approximately 3 log CFU/cm2 at day 0 for whole melons. When tested alone, all compounds, along with water washes, were ineffective. After 3 and 7 days of storage, the five combination washing treatments were less effective, resulting in reductions of approximately 2 log CFU/cm2. None of the combination treatments completely eliminated transfer of pathogen survivors to fresh-cut pieces. The combination treatments nisin-NaL, nisin-KS, NaL-KS, and nisin-NaL-KS, but not nisin-EDTA, gave significant (P < 0.05) reductions of Salmonella directly inoculated onto fresh-cut pieces. Washing with nisin-NaL-KS was significantly (P < 0.05) more effective than the other three combination treatments, resulting in a reduction of 1.4 CFU/g. Inhibition by the four effective treatments carried over from day 0 through day 7 of storage, with no increase in the population of Salmonella on the stored fresh-cut pieces. Sensory evaluations indicated that treatment of fresh-cut pieces with nisin-NaL and NaL-KS, but not nisin-KS or nisin-NaL-KS, were acceptable in terms of appearance, odor, and overall acceptability. After the required regulatory approval, treatment of whole cantaloupe with nisin in combination with EDTA, NaL, KS, or NaL and KS and of fresh-cut pieces with nisin-NaL or NaL-KS could help ensure the microbiological safety of fresh-cut cantaloupe.     

Antimicrobial effect of electrolyzed oxidizing water against Escherichia coli O157:H7 and Listeria monocytogenes on fresh strawberries (Fragaria x ananassa)

ABSTRACT:  Antibacterial activity of electrolyzed oxidizing (EO) water prepared from 0.05% or 0.10% (w/v) sodium chloride (NaCl) solutions against indigenous bacteria associated with fresh strawberries ( Fragaria × ananassa ) was evaluated. The efficacy of EO water and sodium hypochlorite (NaOCl) solution in eliminating and controlling the growth of Listeria monocytogenes and Escherichia coli O157:H7 inoculated onto strawberries stored at 4 ± 1 °C up to 15 d was investigated at exposure time of 1, 5, or 10 min. Posttreatment neutralization of fruit surfaces was also determined. More than 2 log₁₀ CFU/g reductions of aerobic mesophiles were obtained in fruits washed for 10 or 15 min in EO water prepared from 0.10% (w/v) NaCl solution. Bactericidal activity of the disinfectants against L. monocytogenes and E. coli O157:H7 was not affected by posttreatment neutralization, and increasing exposure time did not significantly increase the antibacterial efficacy against both pathogens. While washing fruit surfaces with distilled water resulted in 1.90 and 1.27 log₁₀ CFU/mL of rinse fluid reduction of L. monocytogenes and E. coli O157:H7, respectively, ≥ 2.60 log₁₀ CFU/mL of rinse fluid reduction of L. monocytogenes and up to 2.35 and 3.12 log₁₀ CFU/mL of rinse fluid reduction of E. coli O157:H7 were observed on fruit surfaces washed with EO water and NaOCl solution, respectively. Listeria monocytogenes and E. coli O157:H7 populations decreased over storage regardless of prior treatment. However, EO water and aqueous NaOCl did not show higher antimicrobial potential than water treatment during refrigeration storage.     

Prewashing with acidified sodium chlorite reduces pathogenic bacteria in lightly fermented Chinese cabbage

Efficacy of prewashing with acidified sodium chlorite (ASC) for the sanitation of lightly fermented Chinese cabbage was evaluated. The population of the natural microflora on the cabbage leaves was reduced about 2.0 log CFU/g just after washing with ASC, a significant reduction compared with the control distilled water wash (P < or = 0.05). In the control experiment, viable aerobic bacteria increased gradually when incubated at 10 degrees C; however, ASC-washed cabbage maintained a lower microbial concentration. The treatment of Chinese cabbage with ASC reduced the population of artificially inoculated Escherichia coli O157:H7, Salmonella Enteritidis, Staphylococcus aureus, and Listeria monocytogenes by 2.4 log CFU/g. The sanitation efficacy of ASC was 1.6 log CFU/g higher than that of distilled water washing. The viable cell counts of all pathogenic bacteria tested remained constant during 8 days of storage at 10 degrees C for both washing treatments, with the exception of L. monocytogenes, whose viable cell counts increased gradually with time for both treatments. No significant differences in color, odor, taste, and texture in raw leaves were observed after the ASC wash compared with after the distilled water wash. These results indicate that prewashing with ASC could control bacterial growth in lightly fermented Chinese cabbage without changing the product quality.     

Efficiency of electrolyzed oxidizing water on reducing Listeria monocytogenes contamination on seafood processing gloves

Food processing gloves are typically used to prevent cross-contamination during food preparation. However, gloves can be contaminated with microorganisms and become a source of contamination. This study investigated the survival of Listeria monocytogenes on gloves and determined the efficacy of electrolyzed oxidizing (EO) water for reducing L. monocytogenes contamination on seafood processing gloves. Three types of reusable gloves (natural rubber latex, natural latex, and nitrile) and two types of disposable gloves (latex and nitrile) were cut into small pieces (4 x 4 cm(2)) and inoculated with 5-strain L. monocytogenes cocktail (5.1 x 10(7) CFU/cm(2)) with and without shrimp meat residue attached to surfaces. L. monocytogenes did not survive well on clean reusable gloves and its populations decreased rapidly to non-detectable levels within 30 min at room temperature. However, high levels of Listeria cells were recovered from clean disposable gloves after 30 min of inoculation. Presence of shrimp meat residue on gloves enhanced the survival of L. monocytogenes. Cells of L. monocytogenes were detected on both reusable and disposal gloves even after 2 h at room temperature. Soaking inoculated gloves in EO water at room temperature for 5 min completely eliminated L. monocytogenes on clean gloves (>4.46 log CFU/cm(2) reductions) and significantly (p<0.05) reduced the contamination on soil-containing gloves when compared with tap water treatment. EO water could be used as a sanitizer to reduce L. monocytogenes contamination on gloves and reduce the possibility of transferring L. monocytogenes from gloves to RTE seafoods.     

Spread of bacterial pathogens during preparation of freshly squeezed orange juice

To study the potential of three bacterial pathogens to cross-contaminate orange juice during extraction, normal operation conditions during juice preparation at food service establishments were simulated. The spread of Salmonella enterica serovar Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes from inoculated oranges to work surfaces and to the final product was determined. The transference of these three bacterial pathogens to orange juice made from uninoculated oranges with the use of contaminated utensils was also studied. Fresh oranges were inoculated with a marker strain of rifampicin-resistant Salmonella Typhimurium, E. coli O157:H7, or L. monocytogenes. Final pathogen levels in juice were compared as a function of the use of electric or mechanical juice extractors to squeeze orange juice from inoculated oranges. Pathogen populations on different contact surfaces during orange juice extraction were determined on sulfite-phenol red-rifampicin plates for Salmonella Typhimurium and E. coli O157:H7 and on tryptic soy agar supplemented with 0.1 g of rifampicin per liter for L. monocytogenes. After inoculation, the average pathogen counts for the orange rind surface were 2.3 log10 CFU/cm2 for Salmonella Typhimurium, 3.6 log10 CFU/cm2 for E. coli O157:H7, and 4.4 log10 CFU/cm2 for L. monocytogenes. This contamination was spread over all utensils used in orange juice squeezing. Mean pathogen counts for the cutting board, the knife, and the extractor ranged from -0.3 to 2.1 log10 CFU/cm2, and the juice contained 1.0 log10 CFU of Salmonella Typhimurium per ml, 2.3 log10 CFU of E. coli O157:H7 per ml, and 2.7 log10 CFU of L. monocytogenes per ml. Contact with contaminated surfaces resulted in the presence of all pathogens in orange juice made from uninoculated oranges. These results give emphasis to the importance of fresh oranges as a source of pathogens in orange juice.