APPLICATION OF CHLORINE TO REDUCE POPULATIONS OF ESCHERICHIA COLI ON BEEF

The effects of chlorine against 2 strains of E. coli attached to the surface of beef carcass tissue (BCT) were examined using a model carcass washer. Lean and adipose BCT with approximately 5 log ₁₀ CFU/cm ² E. coli bacteria were spray-treated with water and sodium hypochlorite (NaOCl) to give chlorine concentrations of 50, 100, 250, 500, or 800ppm, incubated for 24 h, 4C, and E. coli populations enumerated. Spray treatments with water did significantly (P < 0.05) reduce the bacterial populations of either organism attached to lean or adipose BCT, as compared to populations of controls; however, reductions were less than 0.60 log ₁₀ CFU/cm ². Treatments with 500 and 800 ppm chlorine against E. coli ATCC 25922 attached to BCT resulted in the greatest reductions of 1.22 and 1.28 log ₁₀ CFU/cm ², respectively. At 800 ppm chlorine , E. coli O157:H7 ATCC 43895 attached to BCT was reduced by 1.04 log ₁₀ CFU/cm ², whereas spray treatments with 50, 100, 250, and 500 ppm chlorine resulted in reductions of < 1 log ₁₀ CFU/cm ². Spray treatments with chlorine from sodium hypochlorite solutions reduced populations of E. coli, however, these reductions were not sufficient to completely inactivate the bacteria attached to red meat .     

Portable Electronic Nose for Detection of Spoiling Alaska Pink Salmon (Oncorhynchus gorbuscha)

ABSTRACT:  The ability of a portable hand-held electronic nose (EN) in detecting spoilage of whole Alaska pink salmon ( Oncorhynchus gorbuscha ) stored at 14 °C and in slush ice (1 °C) was investigated. Fish were sampled daily at 14 °C for up to 3 d, while fish stored in slush ice were sampled at various intervals up to 16 d. Sensory evaluations indicated that fish were rejected at day 3 when stored at 14 °C and at day 12 when stored in slush ice. Aerobic bacteria counts for fish skin at 14 °C ranged from 3.4 log₁₀ colony-forming units (CFU)/cm² (day 0) to 4.8 log₁₀ CFU/cm² (day 3) and for fish stored in slush ice ranged from 3.4 log₁₀ CFU/cm² (day 0) to 5.5 log₁₀ CFU/cm² (day 16). The correct classification rate using forward stepwise general discriminate analysis was 85% and 92% for EN analysis of belly cavity volatiles for fish held at 14 °C and in slush ice, respectively. A predictive model may be developed for spoilage of whole Alaska pink salmon by analyzing belly cavity odors using the EN.     

Behavior of Listeria monocytogenes inoculated on cantaloupe surfaces and efficacy of washing treatments to reduce transfer from rind to fresh-cut pieces

Attachment and survival of Listeria monocytogenes on external surfaces (rind) of inoculated cantaloupe, resistance of the surviving bacteria to chlorine or hydrogen peroxide treatments, transfer of the pathogen from unsanitized and sanitized rinds to fresh-cut tissues during cutting and growth, and survival of L. monocytogenes on fresh-cut pieces of cantaloupe were investigated. Surface treatment with 70% ethanol to reduce the native microflora on treated melon, followed by immersion in a four-strain cocktail of L monocytogenes (10(8) CFU/ml) for 10 min, deposited 4.2 log10 CFU/cm2 and 3.5 log10 CFU/cm2 of L monocytogenes on treated and untreated cantaloupe rinds, respectively. L. monocytogenes survived on the treated or untreated cantaloupe rinds for up to 15 days during storage at 4 and 20 degrees C, but populations declined by approximately 1 to 2 log10 CFU/cm2. Fresh-cut pieces prepared from inoculated whole cantaloupes stored at 4 degrees C for 24 h after inoculation were positive for L. monocytogenes. Washing inoculated whole cantaloupes in solutions containing 1,000 ppm of chlorine or 5% hydrogen peroxide for 2 min at 1 to 15 days of storage at 4 degrees C after inoculation resulted in a 2.0- to 3.5-log reduction in L. monocytogenes on the melon surface. Fresh-cut pieces prepared from the sanitized melons were negative for L. monocytogenes. After direct inoculation onto fresh-cut pieces, L. monocytogenes survived, but did not grow, during 15 days of storage at 4 degrees C. Growth was evident by 4 h of storage at 8 and 20 degrees C. It is concluded that sanitizing with chlorine or hydrogen peroxide has the potential to reduce or eliminate the transfer of L. monocytogenes on melon surfaces to fresh-cut pieces during cutting.     

MICROBIOLOGICAL STATUS OF BEEF CARCASS MEAT IN INDONESIA

The microbiological status of beef carcass meat was investigated at a traditional and a semi-modern abattoir in Indonesia. Carcasses from the traditional abattoir were generally less contaminated than those from the semi-modern abattoir. The average total aerobic viable bacterial count of carcasses produced at the traditional abattoir, (log₁₀ 3.62/cm²) was found to be significantly lower (p = 0.02) at the semi-modern abattoir (log₁₀ 4.02/cm²). More than 70% of carcasses at both abattoirs were found to be positive for Escherichia coli (> 10 organisms/cm²), while Salmonellae were found on approximately 15% of carcasses at both locations.     

Effect of hydrogen peroxide treatment on microbial quality and appearance of whole and fresh-cut melons contaminated with Salmonella spp

The efficacy of hydrogen peroxide treatment on the inactivation of Salmonella spp. inoculated on the external surface of cantaloupe and honeydew melon was investigated. Salmonella was inoculated onto whole cantaloupe and honeydew melon to a final concentration of 4.65 log(10) CFU/cm(2) and 3.13 log(10) CFU/g, respectively. Inoculated whole melons stored at 5 degrees C for up to 7 days were washed with water, 2.5% and 5% hydrogen peroxide at day 0 and 5. Hydrogen peroxide (2.5% and 5%) treatments of whole melon for 5 min caused a 3 log(10) CFU/cm(2) reduction of the indigenous surface microflora and a 3.0 log(10) CFU/cm(2) reduction in Salmonella spp. on all melon surfaces. The efficacy of the hydrogen peroxide treatments was less when the interval between inoculation and treatment of cantaloupe exceeded 24 h. Unlike cantaloupe fresh-cut pieces, Salmonella was not recovered from fresh-cut pieces prepared from treated whole honeydew melon. Growth of Salmonella occurred in cantaloupe fresh-cut pieces stored at 10 or 20 degrees C, and by 2 weeks, levels reached approximately 1 log CFU/g. A rapid decline in appearance and overall acceptability was observed in fresh-cut pieces prepared from untreated whole cantaloupe. While Salmonella was recovered from fresh-cut pieces from and whole treated cantaloupe, sanitizing the surface of contaminated whole melons with hydrogen peroxide before and after cutting and storage of the fresh-cut pieces at 5 degrees C can enhance the microbial safety and acceptability rating for about 2 weeks after processing.     

EFFECT OF MARINADE AND DRYING TEMPERATURE ON INACTIVATION OF ESCHERICHIA COLI O157:H7 ON INOCULATED HOME DRIED BEEF JERKY

Beef slices were inoculated (5.7–7.5 log CFU/cm²) with a 4-strain composite of E. coli O157:H7, stored (4C, 24 h), marinated (4C, 24 h), dried for 10 h at 62.5C or 68.3C, and stored for 90 days at 21C. Unmarinated beef slices dried for 10 h at 62.5C were used to determine the relative contribution of the marinate versus temperature treatment in the 62.5C trials. Samples were analyzed (bacterial enumeration with selective and nonselective agar media, pH, and a_w) following inoculation, marinating, at 4, 6, 8 and 10 h of drying, and after 30, 60 and 90 days of storage. Marination resulted in slight changes in bacterial populations (−0.3 to + 0.6 log CFU/cm²), but did not enhance bacterial reduction during drying. For all treatments, most bacterial reductions occurred in the first 4 h of drying, with little reduction thereafter. After 10 h of drying, bacterial reductions were 3.2–3.4 log CFU/cm² for unmarinated beef slices dried at 62.5C. Reductions of 2.2 and 3.0–4.6 log CFU/cm² were achieved in marinated jerky slices dried at 62.5C and 68.3C, respectively. No treatment resulted in the recommended 5-log reduction at the end of 10 h drying. However, bacteria did become undetectable by direct plating (<10 CFU/cm²) following 30 days of storage in all treatments except the unmarinated beef slices plated on tryptic soy agar (TSA). Additional work is needed to develop procedures for adequate destruction of E. coli O157:H7 during drying of beef jerky.     

Modeling the Growth Characteristics of Listeria monocytogenes and Native Microflora in Smoked Salmon

ABSTRACT:  Smoked salmon contaminated with Listeria monocytogenes has been implicated in foodborne listeriosis. The objectives of this study were to model the growth characteristics and examine the growth relationship of L. monocytogenes and native microflora in smoked salmon. Smoked salmon samples with a native microflora count of 2.9 log₁₀ CFU/g were inoculated with a 6-strain mixture of L. monocytogenes to levels of log₁₀ 1.6 and log₁₀ 2.8 CFU/g, and stored at 4, 8, 12, and 16 °C. Growth characteristics (lag phase duration [LPD, h], growth rate [GR, log₁₀ CFU/h], and maximum population density [MPD, log₁₀ CFU/g]) of L. monocytogenes and native microflora were determined. At 4 to 16 °C, the LPD, GR, and MPD were 254 to 35 h, 0.0109 to 0.0538 log₁₀ CFU/h, and 4.9 to 6.9 log₁₀ CFU/g for L. monocytogenes , respectively, and were 257 to 29 h, 0.0102 to 0.0565 log₁₀ CFU/h, and 8.5 to 8.8 log₁₀ CFU/g for native microflora. The growth characteristics of L. monocytogenes or the native microflora were not significantly different ( P > 0.05), regardless the initial levels of L. monocytogenes . Mathematical equations were developed to describe the LPD, GR, and MPD of L. monocytogenes and native microflora as a function of storage temperature. The growth relationship between L. monocytogenes and native microflora was modeled and showed that the LPD and GR of L. monocytogenes were similar to those of native microflora. These models can be used to estimate the growth characteristics of L. monocytogenes in smoked salmon, and thereby enhance the microbiological safety of the product.     

Efficacy of pulsed UV-light for the decontamination of Escherichia coli O157:H7 and Salmonella spp. on raspberries and strawberries

ABSTRACT:  Small fruits are increasingly being implicated in outbreaks of foodborne illness, and fresh produce is now the 2nd leading cause of foodborne illness in the United States. Conventional methods of decontamination are not effective, and there is a need to evaluate novel technologies. Pulsed ultraviolet (UV)-light is one such technology. In this study, pulsed UV-light was applied to strawberries and raspberries at varying UV doses and times. On raspberries, maximum reductions of Escherichia coli O157:H7 and Salmonella were 3.9 and 3.4 log₁₀ CFU/g at 72 and 59.2 J/cm², respectively. On the surfaces of strawberries, maximum reductions were 2.1 and 2.8 log₁₀ CFU/g at 25.7 and 34.2 J/cm², respectively. There was no observable damage to the fruits at these UV doses. The results obtained in this study indicate that pulsed UV-light has the potential to be used as a decontamination method for raspberries and strawberries.     

Combining Antimicrobial and Steam Treatments in a Vacuum-packaging System to Control Listeria monocytogenes on Ready-to-eat Franks

ABSTRACT: This study was to evaluate the effectiveness of steam or steam in combination with an antimicrobial agent to control Listeria monocytogenes on ready-to-eat (RTE) franks. The franks were surface-inoculated to contain 6 or 3 log₁₀(colony-forming units [CFU])/cm² of L. monocytogenes and treated with steam or steam in combination with an antimicrobial agent, immediately followed by vacuum-sealing the top films of frank packages (6 franks per package in a single layer). Three log (CFU) /cm² of reductions were achieved at the both inoculation levels for L. monocytogenes on franks. At an inoculation level of 3 logs, no outgrowth of L. monocytogenes was obtained on the treated franks after storing at 4.4°C or 16°C for a combined 47 d. This study provided an alternative approach for controlling L. monocytogenes in packaged franks.     

Reduction of Escherichia Coli O157:H7 and Lactobacillus Plantarum Numbers on Fresh Beef by Polylactic Acid and Vacuum Packaging

ABSTRACT: The efficacy of 2% molecular weight 240, 2% molecular weight 360 polylactic acid (PLA), and an equal mix of both at reducing numbers of Escherichia coli O157:H7 and Lactobacillus plantarum on raw beef was determined. Fresh beef cubes inoculated with either organism were dipped in PLA solutions or wrapped in PLA-sprayed films. Samples were vacuum packaged and stored at 4°C for 42 d. Treated samples maintained a significantly lower pH than controls. Growth of E. coli O157:H7 was totally inhibited by both PLA treatments by up to 7.29 log₁₀ CFU/cm² when the spray method was used. However, PLA treatments against L. plantarum were not very effective.     

Effects of Shelf-Life Enhancers on E. coli K12 Survival in Solutions Used to Enhance Beef Strip Steaks

ABSTRACT:  The objective of this study was to evaluate the effects of enhancement solutions containing sodium lactate or sodium lactate/sodium diacetate on E. coli K12 transmission to beef strip steaks and in purge. Solutions containing salt, phosphate, and shelf-life enhancers were injected to 10% over initial weight of the steaks. Lactate or lactate/diacetate addition to a solution inoculated with 6 log₁₀ E. coli K12 CFU/mL was equally effective in limiting growth resulting in a 1-2 log₁₀ CFU/g reduction when compared to salt/phosphate in steaks. When inoculation level was 3 log₁₀ CFU/mL in the enhancement solution, microbial growth was detectable only in the purge of steaks enhanced with salt/phosphate only. Lactate increased CIE L* value and b* and decreased a* values when compared to the control. Lactate-/diacetate-containing solutions decreased L* values when compared to lactate alone. Lactate/diacetate also reduced purge loss from steaks compared to lactate and salt/phosphate solutions.     

REMOVAL OF SALMONELLA TYPHIMURIUM ATTACHED TO CHICKEN SKIN BY RINSING WITH TRISODIUM PHOSPHATE SOLUTION: SCANNING ELECTRON MICROSCOPIC EXAMINATION

The effect of trisodium phosphate (TSP) on Salmonella typhimurium attached to chicken skin was investigated by using scanning electron microscopy (SEM). Chicken drumsticks were inoculated with Salmonella typhimurium (2 × 10⁸ CFU/mL) for 30 min. Both inoculated and non-inoculated drumsticks were rinsed with 10% TSP solution at 10 or 50C for 15 s, and skin pieces were cut and fixed for SEM examination. For inoculated skins, a significant difference was noticed between TSP-rinsed and control skins (water-rinsed) at both temperatures. While control skins were covered with salmonellae (4 × 10⁵∼ 1 × 10⁶ CFU/cm²) and miscellaneous debris, TSP-rinsed skins, either at 10 or 50C, showed clean skin surfaces (<8×10³ CFU/cm²). For non-inoculated skins, it was difficult to see the difference in the number of attached bacteria due to their low numbers, however, water-rinsed skins still showed the debris on the surface. Above observations suggest that one of the major mechanisms of TSP on salmonellae reduction is detachment of contaminants from the skin surface.     

INHIBITION OF STAPHYLOCOCCUS AUREUS AND BACILLUS CEREUS ON A VEGETARIAN FOOD TREATED WITH NISIN COMBINED WITH EITHER POTASSIUM SORBATE OR SODIUM BENZOATE

Various amounts of nisin (0, 10³ and 5 × 10³ IU/g) in combination with either potassium sorbate (0, 2, and 3%) or sodium benzoate (0, 0.06 and 0.12%) were tested for effectiveness in inhibiting growth of Staphylococcus aureus C10 and Bacillus cereus B7 inoculated on a vegetarian food. The strains used were isolated from vegetarian foods obtained commercially in Taiwan, and the test food, spice and dried bean curd, was selected for the study based on ability to support the growth of these organisms. After treatment with a preservative combination, the surfaces of sterilized food samples were inoculated, samples were stored in vacuum or nonvacuum packages at either 4C or 30C, and at appropriate times, tested for microbial growth. Growth of both isolates was unaffected by vacuum-packaging treatment; however, a bacteriostatic effect was found at 4C. Data indicated that during the 14-day storage at 4C, vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 0.12% sodium benzoate significantly (p < 0.05) decreased the counts of S. aureus C10 and B. cereus B7 by 2.61 and 3.02 log₁₀ CFU/g, respectively. In the vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 3% potassium sorbate, counts for C10 and B7 were decreased by 2.35 and 2.64 log₁₀ CFU/g, respectively. Thus, the combined treatment extended the shelf-life of the vegetarian food .     

INCIDENCE AND GERMICIDE SENSITIVITY OF SALMONELLA TYPHI AND VIBRIO CHOLERAE O1 IN ALFALFA SPROUTS

The prevalence of some enteric bacteria in alfalfa sprouts obtained from public markets and supermarkets in Queretaro City was determined. In addition, the antimicrobial effect of several commercial germicides was tested on alfalfa sprouts for reduction of native coliforms and inoculated Vibrio cholerae Ol or Salmonella typhi. Escherichia coli and Salmonella sp. were detected in 74% and 1.1% of 90 of samples, respectively, and no sample tested positive to V. cholerae Ol. Coliforms ranged from 7.3 to 8.5 log₁₀ CFU/g. Treatment of alfalfa sprouts with 200 mg/L of hypochlorite, of a commercial iodophor, or of chlorine dioxide, or with 100 mg/L of Citricidal® for 5 min, reduced native coliforms only by 1–2 log₁₀ CFU/g. Reductions of S. typhi and V. cholerae O1 with 200 mg/L of sodium hypochlorite and 100 mg/L Citricidal® were also no more than J.5 log₁₀ CFU/g. Sprouts from seeds contaminated with V. cholerae O1 that were irrigated daily with water containing 100 mg/L chlorine dioxide, showed significantly lower V. cholerae Ol counts than seeds irrigated with tap water (p<0.05). However , V. cholerae O1 persisted after 8 days of sprouting, when the sprouts are ready for marketing. Treatment of seeds and sprouts with antimicrobials does not appear to be effective for reducing pathogens to safe levels.     

Empirical Distribution Models for Escherichia coli 57:H7 in Ground Beef Produced by a Mid-size Commercial Grinder

ABSTRACT: The purpose of this research was to develop empirical models that describe the amount and distribution of ground beef contaminated with Escherichia coli O157:H7 when a contaminated beef trim is introduced into a batch of uncontaminated beef before processing in a mid-size commercial grinder (34 g/s). A beef trim was inoculated with a rifampacin-resistant strain of E. coli O157:H7 and added to a batch of noncontaminated trims at the grinding step. To study the distribution of the E. coli O157:H7^rif in the ground beef, 6 treatments with different inoculum levels (1 to 6 log₁₀ colony-forming units [CFU]) were tested. Removal or pick up of the residual contamination with E. coli O157:H7^rif left in the grinder was evaluated. E. coli O157:H7^rif was detected in 9% to 86% of the total ground beef for the 1 to 6 log₁₀ CFU inoculum levels, respectively. E. coli O157:H7^rif contamination was detected in the collar that fixes the grinder's die and blade to the hub. An exponential algorithm described the relationship between the quantities of ground beef containing E. coli O157:H7^rif and the inoculum level ( R ²= 0.82). Distribution models based on a Chi-squared algorithm were developed for each inoculum level describing the contamination level as a function of the batch fraction processed ( R ²= 0.81 to 0.99). The results of this study corroborate that when beef processors test for pathogenic contamination in a mid-scale grinder, they should test the beef residues in the collar that fixes the grinder's die and blade to the hub.     

Effect of sanitizer treatments on Salmonella Stanley attached to the surface of cantaloupe and cell transfer to fresh-cut tissues during cutting practices

The ability of Salmonella Stanley to attach and survive on cantaloupe surfaces, its in vivo response to chlorine or hydrogen peroxide treatments, and subsequent transfer to the interior tissue during cutting was investigated. Cantaloupes were immersed in an inoculum containing Salmonella Stanley (10(8) CFU/ml) for 10 min and then stored at 4 or 20 degrees C for up to 5 days. Periodically, the inoculated melons were washed with chlorine (1,000 ppm) or hydrogen peroxide (5%), and fresh-cut tissues were prepared. The incidence of Salmonella Stanley transfer from the rinds to the fresh-cut tissues during cutting practices was determined. A population of 3.8 log10 CFU/cm2 of Salmonella Stanley was recovered from the inoculated rinds. No significant (P < 0.05) reduction of the attached Salmonella population was observed on cantaloupe surfaces stored at 4 or 20 degrees C for up to 5 days, and the population was not reduced after washing with water. Salmonella Stanley was recovered in fresh-cut pieces prepared from inoculated whole cantaloupes with no sanitizer treatment. Washing with chlorine or hydrogen peroxide solutions was most effective immediately after inoculation, resulting in an approximate 3.0-log10 CFU/cm2 reduction, and the level of recovered Salmonella population transferred to fresh-cut samples was reduced to below detection. The effectiveness of both treatments diminished when inoculated cantaloupes stored at 4 or 20 degrees C for more than 3 days were analyzed, and the fresh-cut pieces prepared from such melons were Salmonella positive. Salmonella outgrowth occurred on inoculated fresh-cut cubes stored above 4 degrees C.     

SURVIVAL OF SALMONELLA TYPHIMURIUM, LISTERIA MONOCYTOGENES AND INDICATOR BACTERIA ON COOKED UNCURED TURKEY LOAF STORED UNDER VACUUM AT 3°C

Sterile slices of cooked uncured turkey loaf were inoculated with 10⁶ CFU of either Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Enterococcus faecalis, Citrobacter freundii, Klebsiella pneumoniae, or Enterobacter cloacae. Inoculated samples were vacuum-packaged and stored at 3 ± 1°C. Microorganisms were enumerated at 0, 3, 6, 9, 12, and 15 days on nonselective media . K. pneumoniae exhibited the least cold-tolerance with a log₁₀ 1.70 decrease in numbers. The coliforms E. cloacae, E. coli, and C. freundii had a survival pattern similar to that of S. typhimurium, with population decreases of log₁₀ 0.65, 0.82, 1.13, and 0.79, respectively . E. faecalis and L. monocytogenes were significantly more cold-resistant, with a decrease of log₁₀ 0.20 and no significant change in numbers, respectively. Survival of E. faecalis was not significantly (p < 0.01) different than that of L. monocytogenes, suggesting the use of enterococci as indicators of L. monocytogenes contamination of processed meats .     

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.     

The Effectiveness of Sanitizer Treatments in Inactivation of Salmonella spp. from Bell Pepper, Cucumber, and Strawberry

ABSTRACT: Four different postharvest treatments for removal of Salmonella from bell pepper and cucumber were examined, including washes with chlorinated water (HOCl; 200 ppm), acidified sodium chlorite (ASC; 1200 ppm), and peroxyacetic acid (PAA; 75 ppm), and treatment with gaseous chlorine dioxide (ClO₂; total 100 mg). Only ClO₂ gas was evaluated for decontamination of strawberries. Each produce was inoculated with approximately 1.0 × 10⁷ colony-forming units (CFU) of a 5-serovar cocktail of Salmonella on artificially created wounds, smooth surfaces, and stem scar tissue. For tests involving smooth surface inoculation, ASC and PAA treatments decreased contamination to undetectable levels on bell pepper and cucumber, while the chlorine treatment of bell pepper reduced contamination by approximately 2-logs. For stem scar contamination on bell pepper, ASC and PAA treatments both showed >2-log unit reductions, and chlorine treatment showed a <1-log unit reduction. For puncture wounds on bell pepper, HOCl, ASC, and PAA treatments reduced bacterial levels approximately 2-, 3-, and 1-log units, respectively, indicating that HOCl and ASC were more effective than PAA. These aqueous treatments of cucumber with puncture wounds reduced bacterial levels approximately 1-, 2-, and 2-log units, respectively. ClO₂ treatment decreased counts to undetectable levels on all inoculation sites on cucumber and on strawberry smooth surfaces, but failed to completely eliminate Salmonella from bell pepper and from the stem scar and the puncture wounds of strawberry. ASC treatment of bell pepper and ClO₂ gas treatments of cucumber showed the best efficiency for inactivation of Salmonella. ClO₂ treatments effectively reduced Salmonella cells inoculated on the smooth surface and stem scar of strawberries compared with unsanitized control.     

Use of hydrogen peroxide in combination with nisin, sodium lactate and citric acid for reducing transfer of bacterial pathogens from whole melon surfaces to fresh-cut pieces

Hydrogen peroxide (2.5%) alone or hydrogen peroxide (1%) in combination with nisin (25 microg/ml), sodium lactate (1%), and citric acid (0.5%) (HPLNC) were investigated as potential sanitizers for reducing Escherichia coli O157:H7 or Listeria monocytogenes populations on whole cantaloupe and honeydew melons. Whole cantaloupes inoculated with E. coli O157:H7 and L. monocytogenes at 5.27 and 4.07 log10 CFU/cm2, respectively, and whole honeydew melons inoculated with E. coli O157:H7 and L. monocytogenes at 3.45 and 3.05 log10 CFU/cm2, respectively, were stored at 5 degrees C for 7 days. Antimicrobial washing treatments were applied to inoculated whole melons on days 0 or 7 of storage and surviving bacterial populations and the numbers transferred to fresh-cut pieces were determined. At days 0 and 7 treatment with HPLNC significantly (p<0.05) reduced the numbers of both pathogens, by 3 to 4 log CFU/cm2 on both types of whole melon. Treatment with HPLNC was significantly (p<0.05) more effective than treatment with 2.5% hydrogen peroxide. While fresh-cut pieces prepared from stored whole melons were negative for the pathogens by both direct plating and by enrichment, fresh-cut pieces from cantaloupe melons treated with 2.5% hydrogen peroxide were positive for both pathogens and pieces from honeydew melons were positive for E. coli 0157:H7. The native microflora on fresh-cut melons were also substantially reduced by HPLNC treatment of whole melons. The results suggest that HPLNC could be used to decontaminate whole melon surfaces and so improve the microbial safety and quality of fresh-cut melons.