Titanium dioxide/UV photocatalytic disinfection in fresh carrots

Increased occurrences of fresh produce-related outbreaks of foodborne illness have focused attention on effective washing processes for fruits and vegetables. A titanium dioxide (TiO2) photocatalytic reaction under UV radiation provides a high rate of disinfection. The photo-killing effects of TiO2 on bacteria in liquid cultures under experimental conditions have been widely studied. However, the disinfection effects of the TiO2 photocatalytic reaction on fresh vegetables during a washing process have not been evaluated. Our objectives were to design a pilot-scale TiO2/UV photocatalytic reactor for fresh carrots and to compare the bactericidal effects of the TiO2/UV reaction against bacteria in liquid media and on carrots. TiO2/UV photocatalytic reactions for 40, 60, and 30 s were required for the complete killing of Escherichia coli, Salmonella Typhimurium, and Bacillus cereus (initial counts of approximately 6.7 log CFU/ml), respectively. The counts of total aerobic bacteria in fresh carrots and foodborne pathogenic bacteria in inoculated carrots were also measured. Counts of total aerobic bacteria were reduced by 1.8 log CFU/g after TiO2/UV photocatalytic disinfection for 20 min compared with a 1.1-log CFU/g reduction by UV alone. E. coli, Salmonella Typhimurium, and B. cereus (8 log CFU/ml) were inoculated onto carrots, and the number of surviving bacteria in carrots was determined after treatment. The TiO2/UV treatment exhibited 2.1-, 2.3-, and 1.8-log CFU/g reductions in the counts of E. coli, Salmonella Typhimurium, and B. cereus, respectively, compared with 1.3-, 1.2-, and 1.2-log CFU/g reductions by UV alone. The TiO2/UV photocatalyst reaction showed significant bactericidal effects, indicating that this process is applicable to nonthermal disinfection of fresh vegetables.     

Effects of Lactic Acid and Commercial Chilling Processes on Survival of Salmonella, Yersinia enterocolitica, and Campylobacter coli in Pork Variety Meats

Current industry chilling practices with and without the application of 2% L-lactic acid were compared for their effectiveness at reducing levels of Salmonella, Yersinia enterocolitica, and Campylobacter coli on pork variety meats. Pork variety meats (livers, intestines, hearts, and stomachs) were inoculated individually with one of the three pathogens and subjected to five different treatment combinations that included one or more of the following: water wash (25°C), lactic acid spray (2%, 40 to 50°C), chilling (4°C), and freezing (-15°C). Samples were analyzed before treatment, after each treatment step, and after 2, 4, and 6 months of frozen storage. Results showed that when a lactic acid spray was used in combination with water spray, immediate reductions were approximately 0.5 log CFU per sample of Salmonella, 0.8 log CFU per sample of Y. enterocolitica, and 1.1 log CFU per sample of C. coli. Chilling, both alone and in combination with spray treatments, had little effect on pathogens, while freezing resulted in additional 0.5-log CFU per sample reductions in levels of Salmonella and Y. enterocolitica, and an additional 1.0-log CFU per sample reduction in levels of C. coli. While reductions of at least 1 log CFU per sample were observed on variety meats treated with only a water wash and subsequently frozen, samples treated with lactic acid had greater additional reductions than those treated with only a water spray throughout frozen storage. The results of this study suggest that the use of lactic acid as a decontamination intervention, when used in combination with good manufacturing practices during processing, causes significant reductions in levels of Salmonella, Y. enterocolitica, and C. coli on pork variety meats.     

Inactivation of salmonella in biofilms and on chicken cages and preharvest poultry by levulinic Acid and sodium dodecyl sulfate

Surface contamination (skin and feathers) of broilers with Salmonella occurs primarily during growth and transportation. Immediately after transporting chickens, chicken cage doors were sprayed with a foam containing 3% levulinic acid plus 2% sodium dodecyl sulfate (SDS). Samples were collected for Salmonella assay after 45 min. Salmonella on cage doors was reduced from 19% (19 of 100 doors) before treatment to 1% (1 of 100 doors) after treatment, coliform counts were reduced from 6 to 8 to 2 to 4 log CFU/9 cm(2), and aerobic plate counts were reduced from 7 to 9 to 4 to 6 log CFU/9 cm(2). Whole chicken carcasses with feathers were inoculated with 10(8) CFU of Salmonella Enteritidis, soaked for 5 min at 21°C in 72 liters of a treatment or control solution, and assayed for Salmonella. Salmonella counts on chickens treated with water were 6.8 to 8.5 log CFU/9 cm(2), those treated with 50 ppm of calcium hypochlorite were 7.6 to 8.9 log CFU/9 cm(2), and those treated with 3% levulinic acid plus 2% SDS were <1.7 to 2.8 CFU/9 cm(2) (>4-log reduction). Results of biofilm studies on surfaces of various materials revealed that a 3% levulinic acid plus 2% SDS treatment used as either a foam or liquid for 10 min effectively reduced Salmonella populations by 5 and >6 log CFU/cm(2), respectively.     

Package systems and storage times serve as postlethality controls for Listeria monocytogenes on whole-muscle beef jerky and pork and beef smoked sausage sticks

To validate how packaging and storage reduces Listeria monocytogenes on whole-muscle beef jerky and smoked pork and beef sausage sticks, four packaging systems (heat sealed [HS] without vacuum, heat sealed with oxygen scavenger, nitrogen flushed with oxygen scavenger [NFOS], and vacuum) and four ambient temperature storage times were evaluated. Commercially available whole-muscle beef jerky and smoked pork and beef sausage sticks were inoculated with a five-strain L. monocytogenes cocktail, packaged, and then stored at 25.5 °C until enumerated for L. monocytogenes at 0, 24, 48, and 72 h and 30 days after packaging. The interaction of packaging and storage time affected L. monocytogenes reduction on jerky, but not on sausage sticks. A >2-log CFU/cm(2) reduction was achieved on sausage sticks after 24 h of storage, regardless of package type, while jerky had <2-log reductions for all packaging types. At 48 h, log reductions were similar (P. 0.05) for all types of jerky packaging, ranging from 1.26 to 1.72 log CFU/cm(2); however, at 72 h, mean L. monocytogenes reductions were >2 log CFU/cm(2), except for NFOS (1.22-log CFU/cm(2) reduction). Processors could package beef jerky in HS packages with oxygen scavenger or vacuum in conjunction with a 24-h holding time as an antimicrobial process to ensure a >1-log CFU/cm(2) L. monocytogenes reduction or use a 48-h holding time for HS- or NFOS-packaged beef jerky. A >3-log CFU/cm(2) mean reduction was observed for all beef jerky and sausage stick packaging systems after 30 days of 25.5 °C storage.     

Antimicrobials for reduction of Salmonella contamination in uncooked, surface-browned breaded chicken products

Surface-browned but uncooked frozen breaded chicken products have been associated with salmonellosis outbreaks due to inadequate or no cooking of the products before consumption. This study was conducted to evaluate the effect of three antimicrobials against Salmonella during manufacture of a surface-browned, uncooked frozen breaded chicken meat product. Fresh chicken breast meat portions (5 by 5 by 5 cm) were inoculated (4 to 5 log CFU/g) with Salmonella and mixed with caprylic acid (CAA; 0.5 and 1.0%), carvacrol (CAR; 0.3 and 0.5%), ε-polylysine (POL; 0.125 and 0.25%), or distilled water (control). Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all treatments, and the mixtures were ground (5% total moisture enhancement level) and formed into portions (9 by 5 by 3 cm). The products were breaded and surface browned by baking in an oven (208°C for 15 min) or deep frying in vegetable oil (190°C for 15 s), packaged in polyethylene bags, and stored at -20°C for 7 days. Total reductions of inoculated Salmonella in untreated control oven- or fryer-browned products after frozen storage were 1.2 and 0.8 log CFU/g, respectively. In comparison, treatment with CAA, CAR, or POL reduced initial pathogen counts by 3.3 to >4.5, 4.1 to >4.7, and 1.1 to 1.6 log CFU/g, respectively, regardless of the antimicrobial concentration and browning method. Treatment with 1.0% CAA (oven browned) or 0.5% CAR (oven or fryer browned) reduced Salmonella to nondetectable levels (<0.3 log CFU/g) in stored frozen products. These data may be useful for development of suitable antimicrobial treatments to reduce the risk of Salmonella contamination in surface-browned, uncooked frozen breaded chicken products.     

Antimicrobial activity of apple, hibiscus, olive, and hydrogen peroxide formulations against Salmonella enterica on organic leafy greens

Salmonella enterica is one of the most common bacterial pathogens implicated in foodborne outbreaks involving fresh produce in the last decade. In an effort to discover natural antimicrobials for use on fresh produce, the objective of the present study was to evaluate the effectiveness of different antimicrobial plant extract-concentrate formulations on four types of organic leafy greens inoculated with S. enterica serovar Newport. The leafy greens tested included organic romaine and iceberg lettuce, and organic adult and baby spinach. Each leaf sample was washed, dip inoculated with Salmonella Newport (10(6) CFU/ml), and dried. Apple and olive extract formulations were prepared at 1, 3, and 5% concentrations, and hibiscus concentrates were prepared at 10, 20, and 30%. Inoculated leaves were immersed in the treatment solution for 2 min and individually incubated at 4°C. After incubation, samples were taken on days 0, 1, and 3 for enumeration of survivors. Our results showed that the antimicrobial activity was both concentration and time dependent. Olive extract exhibited the greatest antimicrobial activity, resulting in 2- to 3-log CFU/g reductions for each concentration and type of leafy green by day 3. Apple extract showed 1- to 2-log CFU/g reductions by day 3 on various leafy greens. Hibiscus concentrate showed an overall reduction of 1 log CFU/g for all leafy greens. The maximum reduction by hydrogen peroxide (3%) was about 1 log CFU/g. The antimicrobial activity was also tested on the background microflora of organic leafy greens, and reductions ranged from 0 to 2.8 log. This study demonstrates the potential of natural plant extract formulations to inactivate Salmonella Newport on organic leafy greens.     

Membrane damage and viability loss of Escherichia coli K-12 in apple juice treated with radio frequency electric field

The need for a nonthermal intervention technology that can achieve microbial safety without altering nutritional quality of liquid foods led to the development of a radio frequency electric fields (RFEF) process. In order to understand the mechanism of inactivation of bacteria by RFEF, apple juice purchased from a wholesale distributor was inoculated with Escherichia coli K-12 at 7.8 log CFU/ml and then treated with RFEF. The inoculated apple juice was passed through an RFEF chamber operated at 20 kHz, 15 kV/cm for 170 micros at a flow rate of 540 ml/min. Treatment condition was periodically adjusted to achieve outlet temperatures of 40, 45, 50, 55, and 60 degrees C. Samples at each outlet temperature were plated (0.1 ml) and the number of CFU per milliliter determined on nonselective and selective agar media was used to calculate the viability loss. Bacterial inactivation and viability loss occurred at all temperatures tested with 55 degrees C treatment, leading to 4-log reductions. No significant effect was observed on bacterial population in control samples treated at 55 degrees C with a low-RFEF (0.15 kV/cm) field strength. These observations suggest that the 4-log reduction in samples treated at 15 kV/cm was entirely due to nonthermal effect. RFEF treatment resulted in membrane damage of the bacteria, leading to the efflux of intracellular ATP and UV-absorbing materials. Populations of injured bacteria recovered immediately (<30 min) from the treated apple juice averaged 0.43 log and were below detection after 1 h of RFEF treatment and determination using selective plates (tryptic soy agar containing 5% sodium chloride). The results of this study suggest that mechanism of inactivation of RFEF is by disruption of the bacterial surface structure leading to the damage and leakage of intracellular biological active compounds.     

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.     

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 hot water and hydrogen peroxide treatments on survival of salmonella and microbial quality of whole and fresh-cut cantaloupe

Cantaloupe melon has been associated with outbreaks of salmonellosis. Contamination might be introduced into the flesh from the rind by cutting or by contact of cut pieces with contaminated rinds. Our objectives were to investigate the efficacy of hot water or hot 5% hydrogen peroxide treatments in reducing the population of native microflora and inoculated Salmonella on cantaloupe rind and transfer to fresh-cut tissue during cutting. Whole cantaloupes, inoculated with a cocktail of Salmonella serovars to give 4.6 log CFU/cm2 and stored at 5 or 20 degrees C for up to 5 days, were treated with hot water (70 or 97 degrees C) or 5% hydrogen peroxide (70 degrees C) for 1 min at 0, 1, 3, or 5 days postinoculation. Aerobic mesophilic bacteria and yeast and mold on treated whole melon and fresh-cut pieces were significantly (P < 0.05) reduced by all three treatments. Treatments with hot water (70 and 97 degrees C) caused a 2.0- and 3.4-log CFU/cm2 reduction of Salmonella on whole cantaloupe surfaces irrespective of days of postinoculation storage prior to treatment up to 5 days at 5 or 20 degrees C, respectively. Treatment with 5% hydrogen peroxide (70 degrees C) caused a 3.8-log CFU/cm2 reduction of Salmonella. Fresh-cut pieces prepared from untreated inoculated melons and those treated with 70 degrees C hot water were positive for Salmonella. However, fresh-cut pieces prepared from inoculated whole melon dipped in water (97 degrees C) or hydrogen peroxide (70 degrees C) for 60 s were negative for Salmonella, as determined by dilution plating onto agar medium, but were positive after enrichment at days 3 and 5 of storage at 5 degrees C. The ability to detect Salmonella in fresh-cut pieces was dependent on the initial level of inoculation. The results of this study indicate that the use of hot water (97 degrees C) or heated hydrogen peroxide to reduce the population of Salmonella on contaminated whole cantaloupes will enhance the microbial safety of the fresh-cut product.     

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.     

Use of nisin-coated plastic films to control Listeria monocytogenes on vacuum-packaged cold-smoked salmon

Cold-smoked (Salmo salar) salmon samples were surface-inoculated with a cocktail of three nisin-resistant strains of L. monocytogenes (PSU1, PSU2 and PSU21) to a level of approximately 5 x 10(2) or 5 x 10(5) CFU/cm2 of salmon surface. The inoculated smoked salmon samples were vacuum-packaged with control film (no nisin) or nisin-coated plastic films and stored at either 4 or 10 degrees C. When the inoculated smoked salmon samples were packaged with film coated with 2000 IU/cm2 of nisin, a reduction of 3.9 log CFU/cm2 (compared with control) was achieved at either temperature for samples inoculated with 5 x 10(2) CFU/cm(2 of L. monocytogenes after 56 (4 degrees C) and 49 (10 degrees C) days of storage while reductions of 2.4 and 0.7 log CFU/cm2 were achieved for samples inoculated with a high level of L. monocytogenes (5 x 10(5) CFU/cm2) after 58 (4 degrees C) and 43 (10 degrees C) days, respectively. For samples packaged in film coated with 500 IU/cm2 of nisin, reductions of 0.5 and 1.7 log CFU/cm2 were achieved for samples inoculated with a low level of L. monocytogenes (5 x 10(2) CFU/cm2) after 56 (4 degrees C) and 49 (10 degrees C) days of storage while reductions of 1.8 and 0.8 log CFU/cm2 were achieved for samples inoculated with high level of L. monocytogenes after 58(4 degrees C) and 43 (10 degrees C) days, respectively. In addition, nisin inhibited the proliferation of background microbiota on smoked salmon in a concentration-dependent manner at both storage temperatures although the bacteriostatic effect was more pronounced at refrigeration temperature. This work highlights the potential for incorporating nisin into plastic films for enhancing the microbial safety of smoked salmon as well as controlling its microbial spoilage.     

Eradicating Listeria monocytogenes from fully cooked franks by using an integrated pasteurization-packaging system

Surface pasteurization by applying steam or hot water before or after packaging of processed foods may be used to eliminate pathogens such as Listeria monocytogenes from ready-to-eat meat and poultry products. Surface pasteurization treatment with a mixture of pressurized steam and hot water was integrated into a continuous vacuum-packaging system to reduce L. monocytogenes from fully cooked franks. The franks (2.54 cm diameter by 15.24 cm length) were surface inoculated to contain up to 6 log CFU/cm2 L. monocytogenes. The inoculated franks were treated at 121 degrees C for 1.5 s in an arrangement of six franks per packaging chamber followed by immediate vacuum sealing of the top films of food packages in the same unit. A 3-log CFU/cm2 reduction of L. monocytogenes on fully cooked franks was obtained using the integrated pasteurization-packaging system. The pasteurization depth was 1.27 mm below the surfaces of the franks. This process provides a commercially applicable means of ensuring food safety by effectively eradicating L. monocytogenes from ready-to-eat meat and poultry products at the very last possible step of food packaging before reaching retail consumers.     

Survival and death of Salmonella typhimurium and Campylobacter jejuni in processing water and on chicken skin during poultry scalding and chilling

Salmonella Typhimurium and Campylobacter jejuni were inoculated in scalding water, in chilled water, and on chicken skins to examine the effects of scalding temperature (50, 55, and 60 degrees C) and the chlorine level in chilled water (0, 10, 30, and 50 ppm), associated with the ages of scalding water (0 and 10 h) and chilled water (0 and 8 h), on bacterial survival or death. After scalding at 50 and 60 degrees C, the reductions of C. jejuni were 1.5 and 6.2 log CFU/ml in water and <1 and >2 log CFU/cm2 on chicken skins; the reductions of Salmonella Typhimurium were <0.5 and >5.5 log CFU/ml in water and <0.5 and >2 log CFU/cm2 on skins, respectively. The age of scalding water did not significantly (P > 0.05) affect bacterial heat sensitivity. However, the increase in the age of chilled water significantly (P < 0.05) reduced the chlorine effect. In 0-h chilled water. C. jejuni and Salmonella Typhimurium were reduced by 3.3 and 0.7 log CFU/ml, respectively, after treatment with 10 ppm of chlorine and became nondetectable with 30 and 50 ppm of chlorine. In 8-h chilled water, the reduction of C. jejuni and Salmonella Typhimurium was <0.5 log CFU/ml with 10 ppm of chlorine and ranged from 4 to 5.5 log CFU/ml with 50 ppm of chlorine. Chlorination of chilled water did not effectively reduce the bacteria attached on chicken skins. The D-values of Salmonella Typhimurium and C. jejuni were calculated for the prediction of their survival or death in the poultry scalding and chilling.     

Efficacy of home-style dehydrators for reducing Salmonella on whole-muscle chicken

Home-style dehydrators commonly used by consumers have limited relative humidity (RH) and temperature control. To evaluate the effect of dehydrator load on temperature and RH and subsequent reduction of Salmonella on whole-muscle chicken, chicken breasts were rolled and cut into samples (1 to 2 mm thick, 6 by 6 cm(2)) and inoculated with a five-strain Salmonella cocktail. The samples were allowed to air dry for 15 min and then were loaded into home-style three-tray (3T) or five-tray (5T) dehydrators, with 12 chicken pieces per tray. No difference (P > 0.05) was observed in RH or temperature between the 3T and 5T dehydrators. Peak RH was 38% and gradually deceased to 8.5% after 6 h of drying. Temperatures peaked at 57 °C after 6 h of drying. Dehydrator load had no effect (P > 0.05) on lethality for Salmonella. A reduction of 3.3 ± 0.2 log CFU/cm(2) was observed after 6 h of drying. However, sample location affected Salmonella reduction (P < 0.05). Samples from the bottom tray had a 1.5-log reduction, whereas samples from the top and middle trays had 4.1- and 3.9-log reductions, respectively. The water activity of samples after 6 h of drying was 0.71 ± 0.17 regardless of tray location or dehydrator type. When chicken was dried in home-style dehydrators, increasing the dehydrator load did not increase RH or achieve greater Salmonella lethality. Tray location had a significant impact on Salmonella lethality. Adequate reduction of Salmonella on chicken was not achieved when chamber temperatures were below 57 °C with limited RH throughout drying.     

Effect of combining nisin and/or lysozyme with in-package pasteurization on thermal inactivation of Listeria monocytogenes in ready-to-eat turkey bologna

Achieving a targeted lethality with minimum exposure to heat and preservation of product quality during pasteurization is a challenge. The objective of this study was to evaluate the effect of nisin and/or lysozyme in combination with in-package pasteurization of a ready-to-eat low-fat turkey bologna on the inactivation of Listeria monocytogenes. Sterile bologna samples were initially treated with solutions of nisin (2 mg/ml = 5,000 AU/ml = 31.25 AU/cm2), lysozyme (10 mg/ml = 80 AU/ml = 0.5 AU/cm2), and a mixture of nisin and lysozyme (2 mg/ml nisin + 10 mg/ml lysozyme = 31.75 AU/cm2). Bologna surfaces were uniformly inoculated with a Listeria suspension resulting in a population of approximately 0.5 log CFU/cm2. Samples were vacuum packaged and subjected to heat treatment (60, 62.5, or 65 degrees C). Two nonlinear models (Weibull and log logistic) were used to analyze the data. From the model parameters, the time needed to achieve a 4-log reduction was calculated. The nisin-lysozyme combination and nisin treatments were effective in reducing the time required for 4-log reductions at 62.5 and 65 degrees C but not at 60 degrees C. At 62.5 degrees C, nisin-lysozyme-treated samples required 23% less time than did the control sample to achieve a 4-log reduction and 31% less time at 65 degrees C. Lysozyme alone did not enhance antilisterial activity with heat. Results from this study can be useful to the industry for developing an efficient intervention strategy against contamination of ready-to-eat meat products by L. monocytogenes.     

High-pressure resistance variation of Escherichia coli O157:H7 strains and Salmonella serovars in tryptic soy broth, distilled water, and fruit juice

The effect of high pressure on the log reduction of six strains of Escherichia coli O157:H7 and five serovars of Salmonella enterica was investigated in tryptic soy broth, sterile distilled water, and commercially sterile orange juice (for Salmonella) and apple cider (for E. coli). Samples were subjected to high-pressure processing treatment at 300 and 550 MPa for 2 min at 6 degrees C. Samples were plated onto tryptic soy agar directly after pressurization and after being held for 24 h at 4 degrees C. At 300 MPa, little effect was seen on E. coli O157:H7 strains, while Salmonella serovars varied in resistance, showing reductions between 0.26 and 3.95 log CFU/ml. At 550 MPa, E. coli O157:H7 strains exhibited a range of reductions (0.28 to 4.39 log CFU/ml), while most Salmonella populations decreased beyond the detection limit (> 5-log CFU/ml reduction). The most resistant strains tested were E. coli E009 and Salmonella Agona. Generally, bacterial populations in fruit juices showed larger decreases than did populations in tryptic soy broth and distilled water. E. coli O157:H7 cultures held for 24 h at 4 degrees C after treatment at 550 MPa showed a significant log decrease as compared with cultures directly after treatment (P < or = 0.05), while Salmonella serovars did not show this significant decrease (P > 0.05). All Salmonella serovars tested in orange juice treated at 550 MPa for 2 min at 6 degrees C and held for 24 h showed a > 5-log decrease, while E. coli O157:H7 strains require a higher pressure, higher temperature, longer pressurization, or a chemical additive to achieve a 5-log decrease.     

Survival of Salmonella enteritidis phage type 30 on inoculated almonds stored at -20, 4, 23, and 35 degrees C

To evaluate the survival of Salmonella on raw almond surfaces, whole almond kernels were inoculated with Salmonella Enteritidis phage type (PT) 30 collected from a 24-h broth culture or by scraping cells from an agar lawn. Kernels inoculated with lawn-collected cells to 8, 5, 3, and 1 log CFU per almond after a 24-h drying period were stored for 161 days at 23 +/- 3 degrees C. Calculated rates of reduction were similar for the four inoculum levels (0.22, 0.28, 0.29, and 0.22 log CFU/month, respectively). Kernels inoculated to 7.1 or 8.0 log CFU per almond after drying were stored for 171 or 550 days, respectively, at selected temperatures, including -20 +/- 2 degrees C, 4 +/- 2 degrees C, 23 +/- 3 degrees C, and 35 +/- 2 degrees C. No significant reductions of Salmonella were observed during storage at -20 and 4 degrees C over 550 days. At 35 degrees C, a biphasic survival curve was observed, with calculated reductions of 1.1 log CFU/month from days 0 to 59 and no significant reduction from days 59 to 171. At 23 degrees C, reductions of 0.18 and 0.30 log CFU/month were calculated for 171 and 550 days of storage, respectively. When combined with data from the study of inoculum levels, an overall average calculated reduction at 23 degrees C was 0.25 +/- 0.05 log CFU/month. Significantly greater reductions were observed during the 24-h drying period when broth-collected cells were used as the inoculum, suggesting that cells collected from agar lawns were more resistant to drying. However, after initial drying, the rates of reduction at 23 degrees C did not differ significantly between the inoculum preparation methods. Salmonella Enteritidis PT 30 survives for long periods on almond kernels under a variety of commonstorage conditions.     

Effects of cell surface charge and hydrophobicity on attachment of 16 Salmonella serovars to cantaloupe rind and decontamination with sanitizers

Adherence of bacteria to cantaloupe rind is favored by surface irregularities such as roughness, crevices, and pits, thus reducing the ability of washing or sanitizer treatments to remove or inactivate attached cells. In this study, we compared the surface charge and hydrophobicity of two cantaloupe-related outbreak strains of Salmonella Poona (RM2350 and G-91-1595) to those of 14 additional Salmonella strains using electrostatic and hydrophobic interaction chromatography. The relative abilities of the 16 strains to attach to cantaloupe surfaces and resist removal by washing with water, chlorine (200 ppm), or hydrogen peroxide (2.5%) for 5 min after a storage period of up to 7 days at 5 to 20 degrees C also were determined. Whole cantaloupes were inoculated with each pathogen at 8.36 log CFU/ml, dried for 1 h inside a biosafety cabinet, stored, and then subjected to the washing treatments. Only the positive surface charge of the two cantaloupe-related strains of Salmonella Poona was significantly higher (P < 0.05) than that of the other strains. Initial bacterial attachment to cantaloupe surfaces ranged from 3.68 to 4.56 log CFU/cm2 (highest values for Salmonella Michigan, Newport, Oranienburg, and Mbandaka). The average percentage of the total bacterial population strongly attached to the cantaloupe surface for the Salmonella serovars studied ranged from 0.893 to 0.946 at 5 degrees C and from 0.987 to 0.999 at 25 degrees C. Washing inoculated melons with water did not produce a significant reduction in the concentration of the pathogens (P > 0.05). Chlorine and hydrogen peroxide treatments caused an average 3-log reduction when applied 20 to 40 min postinoculation. However, sanitizer treatments applied 60 min or more postinoculation were less effective (approximately 2.5-log reduction). No significant differences were noted in sanitizer efficacy against the individual strains (P > 0.05). The two cantaloupe-related outbreak Salmonella Poona strains did not significantly differ from the other Salmonella strains tested in negative cell surface charge or hydrophobicity, were not more effective in attaching to whole melon surfaces, and were not more resistant to the various washing treatments when present on rinds.     

Antimicrobial activity of cetylpyridinium chloride washes against pathogenic bacteria on beef surfaces

Cetylpyridinium chloride (CPC), a water-soluble, neutral pH, colorless compound, is widely used in oral hygiene products to inhibit bacteria responsible for plaque. Previously, researchers have demonstrated that CPC not only reduces Salmonella typhimurium on poultry but also prevents cross-contamination. To determine the effectiveness of CPC against pathogens associated with lean and adipose beef surfaces, several spray-washing experiments (862 kPa, 15 s, 35 degrees C) with 1% (wt/vol) CPC were conducted. On lean beef surfaces, CPC immediately reduced 5 to 6 log10 CFU/cm2 of Escherichia coli O157:H7 and Salmonella typhimurium to virtually undetectable levels (0 log10 CFU/cm2), as well as after 35 days of refrigerated (4 degrees C), vacuum-packaged storage. On adipose beef surfaces, 5 log10 CFU/cm2 Salmonella typhimurium and E. coli O157:H7 were reduced immediately (>2.5 log10 CFU/cm2) with 1% CPC; by day 35 the reduction was <1.3 log10 CFU/cm2. Further plate overlay analyses indicated that the effectiveness of CPC against pathogens on adipose surfaces was not hampered by the presence of meat components or fatty acids. Additional chemical and microbiological analyses of 1% CPC-treated beef surfaces subjected to a secondary water wash (following contact times of 0, 5, 10, 15, or 30 min) or grinding did reduce pathogenic bacteria and CPC levels. However, residual CPC levels following any of the treatments were considered excessive for human consumption. Despite the residual levels, this study is the first to demonstrate the effect of CPC on pathogenic bacteria associated with beef surfaces immediately after treatment and also after long-term, refrigerated, vacuum-packaged storage.