Acid Adaptation Enhances Tolerance of Escherichia coli O157:H7 to High Voltage Atmospheric Cold Plasma in Raw Pineapple Juice.

Pathogens that adapt to environmental stress can develop an increased tolerance to some physical or chemical antimicrobial treatments. The main objective of this study was to determine if acid adaptation increased the tolerance of Escherichia coli O157:H7 to high voltage atmospheric cold plasma (HVACP) in raw pineapple juice. Samples (10 mL) of juice were inoculated with non-acid-adapted (NAA) or acid-adapted (AA) E. coli to obtain a viable count of ~7.00 log10 CFU/mL. The samples were exposed to HVACP (70 kV) for 1-7 min, with inoculated non-HVACP-treated juice serving as a control. Juice samples were analyzed for survivors at 0.1 h and after 24 h of refrigeration (4 °C). Samples analyzed after 24 h exhibited significant decreases in viable NAA cells with sub-lethal injury detected in both NAA and AA survivors (p < 0.05). No NAA survivor in juice exposed to HVACP for 5 or 7 min was detected after 24 h. However, the number of AA survivors was 3.33 and 3.09 log10 CFU/mL in juice treated for 5 and 7 min, respectively (p < 0.05). These results indicate that acid adaptation increases the tolerance of E. coli to HVACP in pineapple juice. The potentially higher tolerance of AA E. coli O157:H7 to HVACP should be considered in developing safe juice processing parameters for this novel non-thermal technology.

A Review of Regulatory Standards and Advances in Essential Oils as Antimicrobials in Foods.

As essential oils (EOs) possess GRAS status, there is a strong interest in their application to food preservation. Trends in the food industry suggest consumers are drawn to environmentally friendly alternatives and less synthetic chemical preservatives. Although the use of EOs has increased over the years, adverse effects have limited their use. This review aims to address the regulatory standards for EO usage in food, techniques for delivery of EOs, essential oils commonly used to control pathogens and molds, and advances with new active compounds that overcome sensory effects for meat products, fresh fruits and vegetables, fruit and vegetable juices, seafood, dairy products, and other products. This review will show adverse sensory effects can be overcome in various products by the use of edible coatings containing encapsulated EOs to facilitate the controlled release of EOs. Depending on the method of cooking, the food product has been shown to mask flavors associated with EOs. In addition, using active packaging materials can decrease the diffusion rate of the EOs, thus controlling undesirable flavor characteristics while still preserving or prolonging the shelf life of food. The use of encapsulation in packaging film can control the release of volatile or active ingredients. Further, use of EOs in the vapor phase allows for contact indirectly, and use of nanoemulsion, coating, and film wrap allows for the controlled release of the EOs. Research has also shown that combining EOs can prevent adverse sensory effects. Essential oils continue to serve as a very beneficial way of controlling undesirable microorganisms in food systems.

Shiga Toxin-Producing Escherichia coli in the Long-Term Survival Phase Exhibit Higher Chlorine Tolerance and Less Sublethal Injury Following Chlorine Treatment of Romaine Lettuce.

The extent of chlorine inactivation and sublethal injury of stationary-phase (STAT) and long-term survival-phase (LTS) cells of Shiga toxin-producing Escherichia coli (STEC) in vitro and in a lettuce postharvest wash model was investigated. Four STEC strains were cultured in tryptic soy broth supplemented with 0.6% (w/v) yeast extract (TSBYE; 35°C) for 24 h and 21 d to obtain STAT and LTS cells, respectively. Minimum bactericidal concentration (MBC) and dose-response assays were performed to determine chlorine's antibacterial efficacy against STAT and LTS cells. Chlorine solutions (pH 6.5) and romaine lettuce were each inoculated with STAT and LTS cells to obtain initial populations of ∼7.8 log colony-forming units (CFU)/mL. Survivors in chlorine solutions were determined after 30 s. Inoculated lettuce samples were held at 22°C ± 1°C for 2 h or 20 h and then exposed to chlorine (10-40 ppm) for 60 s. Survivors were enumerated on nonselective and selective agar media following incubation (35°C, 48 h). The MBC for STAT and LTS cells was 0.04 and 0.08 ppm, respectively. Following exposure (30 s) to chlorine at 2.5, 5.0, and 10 ppm, STAT cells were reduced to <1.0 log CFU/mL, whereas LTS survivors were at 5.10 (2.5 ppm), 3.71 (5.0 ppm), and 2.55 (10 ppm) log CFU/mL. At 20 and 40 ppm chlorine, greater log CFU reductions of STAT cells (1.64 and 1.85) were observed compared with LTS cells (0.94 and 0.83) after 2 h of cell contact with lettuce (p < 0.05), but not after 20 h. Sublethal injury in STEC after chlorine (40 ppm) treatment was lower in LTS compared with STAT survivors (p < 0.05). Compared with STAT cells, LTS cells of STEC seem to have higher chlorine tolerance as planktonic cells and as attached cells depending on cell contact time on lettuce. In addition, a higher percentage of LTS cells, compared with STAT cells, survive in a noninjured state after chlorine (40 ppm) treatment of lettuce.

Thyme Oil Enhances the Inactivation of Salmonella enterica on Raw Chicken Breast Meat During Marination in Lemon Juice With Added Yucca schidigera Extract.

Enteric pathogens such as Salmonella enterica can survive in low pH conditions and pose a food safety threat during marinating of raw poultry meat. A study was conducted to investigate the effectiveness of thyme oil for killing S. enterica on raw chicken during marination in lemon juice containing yucca extract. Samples of raw chicken breast were inoculated with a five-serovar mixture of S. enterica (~108 CFU/mL) and immersed for 2, 4, 6, and 8 h in four lemon-based marinades at 22°C: lemon juice alone (L), L with added 0.5% yucca extract (L + Y), L + Y and 0.5% thyme oil (L + Y + 0.5% TO) and L + Y + 1.0% TO. The L and L + Y served as controls. Survivors were determined by surface plating chicken homogenates on xylose-lysine tergitol-4 (XLT4) agar and XLT4 agar overlaid with non-selective agar (TAL) and counting bacterial colonies after 48 h of incubation (35°C). Marinades containing Y and TO significantly reduced initial viable populations of S. enterica compared to control (L and L + Y) solutions (P < 0.05). Based on S. enterica survivors on TAL medium, the L and L + Y reduced initial populations by 1.12 and 1.42 Log CFU/sample, respectively, after 8 h whereas, Log reductions caused by L + Y + 0.5% TO and L + Y + 1.0% TO, respectively, were 2.62 and 3.91 (P < 0.05). Numbers of survivors were higher on TAL compared to XLT4 agar (P < 0.05); however, the extent of sub-lethal injury caused by the marinades was not statistically significant (P > 0.05). The death rate of S. enterica increased significantly (P < 0.05) in the marinades containing TO (0.5 or 1.0%) compared to control (L + Y). Based on these results, thyme oil has good potential to increase the antimicrobial efficacy of lemon juice marinade against Salmonella on raw chicken breast and enhance the microbial safety of this popular poultry product.

In-package decontamination of chicken breast using cold plasma technology: Microbial, quality and storage studies.

Atmospheric cold plasma (ACP) is a promising non-thermal technology for controlling food spoilage. In this study, ACP treatment at 100 kV for 1, 3 and 5 min was applied to chicken breast samples. Approximately 2 log CFU/g reduction in natural microflora of chicken was achieved within 5 min of treatment and 24 h of storage. The observed reduction was attributed to the reactive oxygen and nitrogen species in cold plasma. For shelf-life study, control and ACP treated samples (100 kV for 5 min) were analysed for the population of mesophiles, psychrotrophs and Enterobacteriaceae as well as sample colour and pH over a storage period of 24 days. On day 24, the population of mesophiles, psychrotrophs and Enterobacteriaceae in treated chicken was respectively 1.5, 1.4 and 0.5 log lower than the control. These results suggest that in-package ACP is an effective technology to extend the shelf-life of poultry products.

Long-Term Survival Phase Cells of Salmonella Typhimurium ATCC 14028 Have Significantly Greater Resistance to Ultraviolet Radiation in 0.85% Saline and Apple Juice.

Nonendospore-forming pathogenic bacteria in the long-term survival (LTS) phase can remain viable for months or years and may show reduced susceptibility to various antimicrobial interventions. In the present study, we investigated the response of LTS phase Salmonella enterica serovar Typhimurium (ATCC 14028) to ultraviolet (UV) radiation in 0.85% (w/v) saline and apple juice and the extent of sublethal injury in LTS phase survivors. The LTS-phase Salmonella Typhimurium cells were cultured at 35°C for 14 days in tryptic soy broth with 0.6% (w/v) yeast extract (TSBYE). Exponential- and stationary-phase cells, cultured in TSBYE (35°C) for 2.5 and 18 h, respectively, served as control samples. Cells (107 CFU [colony-forming unit]/mL) from each physiological state were exposed to UV light in saline (80 µW/cm2) and apple juice (1500 µW/cm2). The Salmonella Typhimurium survivors were plated for enumeration on either tryptic soy agar with 0.6% yeast extract or xylose-lysine-tergitol 4 (XLT4) agar and colonies counted after incubation (35°C, 24 h). Of all the growth phases tested, LTS phase cells were consistently impacted the least by UV treatment (p < 0.05). In saline, D-values of exponential, stationary, and LTS Salmonella Typhimurium were 0.35, 0.38, and 0.49 min, respectively. D-values in apple juice at pH 3.63 and pH 5.65 were 2.52, 3.19, and 3.57 min and 3.24, 3.50, and 4.18 min, respectively. UV radiation (80 µW/cm2) of Salmonella Typhimurium in saline for 2.5 min reduced the number of exponential- and stationary-phase cells by ∼7.19 and 6.30 log10 CFU/mL, respectively. In contrast, LTS cells were only reduced by 5.08 log10 CFU/mL. Among the three physiological states, LTS phase cells had the least sublethal injury in the surviving population (p < 0.05). These results indicate that the LTS state cross-protects Salmonella Typhimurium against UV radiation and should be considered in determination of the UV radiation D-value for this pathogen.

Antimicrobial Efficacy of Cinnamaldehyde Against Escherichia coli O157:H7 and Salmonella enterica in Carrot Juice and Mixed Berry Juice Held at 4°C and 12°C.

The effectiveness of cinnamaldehyde for inactivating Salmonella enterica and Escherichia coli O157:H7 in carrot juice (CRJ) and mixed berry juice (MBJ) was investigated. Brain heart infusion broth (BHI), CRJ, and MBJ, with concentrations of added cinnamaldehyde ranging from 0.15 to 1.5 µL/mL, 0.25 to 2.0 µL/mL, and 0.25 to 1.5 µL/mL, respectively, were each inoculated with a 5-strain mixture of Salmonella enterica or Escherichia coli O157:H7 to give an initial viable count of 5.07 log10 colony-forming units/mL. Inoculated BHI or juices without cinnamaldehyde served as controls. Growth of the pathogens in BHI (35°C) was monitored by taking absorbance readings (optical density [OD] 600 nm) for 24 h. The inoculated juices were held at 4°C or 12°C for 24 h, and numbers of viable pathogens were determined at 0, 2, 4, 8, and 24 h by plating samples on selective agar followed by incubation (35°C) and counting bacterial colonies at 48 h. The minimum inhibitory concentration of cinnamaldehyde for both pathogens in BHI was 0.25 µL/mL. The pathogens were more sensitive to cinnamaldehyde in MBJ compared with CRJ, irrespective of storage temperature (p < 0.05). At 4°C, cinnamaldehyde (1.5 µL/mL) completely inactivated S. enterica and E. coli in MBJ (negative by enrichment) within 2 h and 8 h, respectively; whereas both pathogens were detected in CRJ (4°C; with 2.0 µL/mL cinnamaldehyde) at 8 and 24 h. At 12°C, S. enterica and E. coli were undetected in MBJ (1.5 µL/mL cinnamaldehyde) within 2 and 4 h, respectively; however, in CRJ (12°C; 2.0 µL/mL cinnamaldehyde), complete inactivation of S. enterica and E. coli occurred within 4 and 24 h, respectively. Cinnamaldehyde is an effective antimicrobial from natural sources that can be used for inactivating bacterial pathogens in fruit and vegetable juices to enhance microbial safety of these nutritious food products.

Effects of Tannic Acid on Lipid and Protein Oxidation, Color, and Volatiles of Raw and Cooked Chicken Breast Meat during Storage.

The objective of this study was to determine the effect of tannic acid (TA) on the oxidative stability and the quality characteristics of ground chicken breast meat. Five treatments including (1) control (none added), (2) 2.5 ppm TA, (3) 5 ppm TA, (4) 10 ppm TA, and (5) 5 ppm butylated hydroxyanisole (BHA) were added to boneless, skinless ground chicken breast meat, and used for both raw and cooked meat studies. For the raw meat study, the ground chicken breast meat was packaged in oxygen-permeable bags and stored at 4 °C for 7 days. For the cooked study, raw ground meat samples were vacuum-packaged in oxygen-impermeable vacuum bags, cooked in-bag to the internal temperature of 75 °C, re-packaged in oxygen-permeable bags, and then stored. Both raw and cooked meats were analyzed for lipid and protein oxidation, color, and volatiles (cooked meat only) at 0, 3, and 7 days of storage. Raw meats with 10 ppm of TA added had significantly (p ≤ 0.05) lower lipid and protein oxidation than other treatments during storage. In addition, TA at 10 ppm level maintained the highest color a*- and L*-values during storage. Cooked chicken breast meat with 5 and 10 ppm TA added produced significantly (p ≤ 0.05) lower amounts of off-odor volatiles than other treatments. Among the volatile compounds, the amount of hexanal increased rapidly during storage for cooked meat. However, meats with 5 and 10 ppm TA added showed the lowest amount of hexanal and other aldehydes related to lipid oxidation, indicating a strong antioxidant effect of TA in cooked chicken breast meat. Furthermore, the differences in aldehydes among the treatments were bigger in cooked than in raw meat, indicating that the antioxidant effect of TA in cooked meat was greater than that in raw meat. Therefore, TA at >5 ppm can be used as a good natural preservative in cooked chicken meat to maintain its quality during storage.

Effect of Oregano Essential Oil (Origanum vulgare subsp. hirtum) on the Storage Stability and Quality Parameters of Ground Chicken Breast Meat.

A study was conducted to investigate the effect of oregano essential oil on the oxidative stability and color of raw and cooked chicken breast meats. Five treatments, including (1) control (none added); (2) 100 ppm oregano essential oil; (3) 300 ppm oregano essential oil; (4) 400 ppm oregano essential oil; and (5) 5 ppm butylated hydroxyanisole (BHA), were prepared with ground boneless, skinless chicken breast meat and used for both raw and cooked meat studies. For raw meat study, samples were individually packaged in oxygen-permeable bags and stored in a cold room (4 °C) for 7 days. For cooked meat study, the raw meat samples were vacuum-packaged in oxygen-impermeable vacuum bags and then cooked in-bag to an internal temperature of 75 °C. After cooling to room temperature, the cooked meats were repackaged in new oxygen-permeable bags and then stored at 4 °C for 7 days. Both raw and cooked meats were analyzed for lipid and protein oxidation, volatiles, and color at 0, 3, and 7 days of storage. Oregano essential oil significantly reduced (p < 0.05) lipid and protein oxidation, and improved color stability of raw and cooked meat. However, oregano oil at 400 ppm showed the strongest effect for all these parameters. Hexanal was the major aldehyde, which was decreased significantly (p < 0.05) by oregano oil treatment, in cooked meat. Overall, oregano essential oil at 100-400 ppm levels could be a good preservative that can replace the synthetic antioxidant in chicken meat.

Effectiveness of Broad-Spectrum Chemical Produce Sanitizers against Foodborne Pathogens as In Vitro Planktonic Cells and on the Surface of Whole Cantaloupes and Watermelons.

Over the past few years, foodborne disease outbreaks linked to enteric pathogens present on cantaloupe and watermelon surfaces have raised concerns in the melon industry. This research evaluated the effectiveness of commercially available produce sanitizers against selected foodborne pathogens, both in cell suspensions and on the outer rind surface of melons. The sanitizers (65 and 200 ppm of chlorine, 5 and 35% hydrogen peroxide, 5 and 50 ppm of liquid chlorine dioxide, various hydrogen peroxide-acid combinations, 0.78 and 2.5% organic acids, and 300 ppm of quaternary ammonium) were tested against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella, and non-O157 Shiga toxin-producing E. coli (O26, O45, O103, O111, O121, and O145). The cell suspension study revealed the ability of all tested sanitizers to reduce all selected pathogens by 0.6 to 9.6 log CFU/ml in vitro. In the melon study, significant differences in pathogen reduction were observed between sanitizers but not between melon types. The most effective sanitizers were quaternary ammonium and hydrogen peroxide-acid combinations, with 1.0- to 2.2-log CFU/g and 1.3- to 2.8-log CFU/g reductions, respectively, for all pathogens. The other sanitizers were less effective in killing the pathogens, with reductions ranging from 0.0 to 2.8 log CFU/g depending on pathogen and sanitizer. This study provides guidance to the melon industry on the best produce sanitizers for use in implementing a broad-spectrum pathogen intervention strategy.

Survival of Escherichia coli on strawberries grown under greenhouse conditions.

Strawberries are soft fruit that are not recommended to have a post-harvest wash due to quality concerns. Escherichia coli O157:H7 has been linked to outbreaks with strawberries but little is known about the survival of E. coli during the growth cycle of strawberries. The survival of E. coli on strawberry plants during growing under greenhouses conditions was evaluated. Soil, leaves, and strawberries (if present) were artificially contaminated with an E. coli surrogate either at the time of planting, first runner removal (4 wk), second runner removal (8 wk), or one week prior to harvest. At harvest E. coli was recovered from the leaves, soil, and strawberries regardless of the contamination time. Time of contamination influenced (P < 0.05) numbers of viable E. coli on the plant. The highest survival of E. coli (P < 0.0001) was detected in soil that was contaminated at planting (4.27 log10 CFU g soil(-1)), whereas, the survival of E. coli was maximal at later contamination times (8 wk and 1 wk prior to harvest) for the leaves (4.40 and 4.68 log10 CFU g leaves(-1)) and strawberries (3.37 and 3.53 log10 CFU strawberry(-1)). Cross contamination from leaves to fruit was observed during this study, with the presence of E. coli on strawberries which had not been present at the time of contamination. These results indicate that good agricultural best practices to avoid contamination are necessary to minimize the risk of contamination of these popular fruit with enteric pathogens. Practices should include soil testing prior to harvest and avoiding contamination of the leaves.

Radiation resistance and injury in starved Escherichia coli O157:H7 treated with electron-beam irradiation in 0.85% saline and in apple juice.

This study evaluated the influence of starvation on the radiation resistance and injury in Escherichia coli O157:H7, following electron beam irradiation in 0.85% (wt/vol) saline and in apple juice. Washed exponential-phase cells of E. coli O157:H7 that were grown in tryptic soy broth (TSB) at 35°C were starved in 0.85% saline (25°C) for 10 days. Exponential- or stationary-phase cells grown in TSB (35°C) served as controls. Samples of 0.85% saline or pasteurized apple juice, inoculated with control cells or cells starved for 8 days, were exposed to electron beam irradiation at doses ranging from 0.0 (control) to 0.70 kGy. The E. coli survivors were enumerated by plating diluted samples on tryptic soy agar or on Sorbitol McConkey agar and counting bacterial colonies after incubation (35°C) for 24 h. Starved cells consistently exhibited higher irradiation D-values than controls (p<0.05). The D-values for control and starved E. coli O157:H7 in 0.85% saline were 0.11 and 0.26 kGy, respectively; D-values in apple juice were 0.16, 0.19, and 0.33 kGy for exponential, stationary, and starved cells, respectively. Irradiation (0.70 kGy) of E. coli O157:H7 in apple juice reduced numbers of exponential- and stationary-phase cells by ∼4.32 and 3.74 logs, respectively, whereas starved cells were reduced by only 2.20 logs. Exponential-phase cells exhibited the lowest resistance to irradiation, and sublethal injury in survivors of this group was higher than that of stationary-phase or starved cells irradiated at 0.50 or 0.70 kGy (p<0.05). The results of this study indicate that starvation-induced stress cross-protects E. coli O157:H7 from ionizing radiation and should be considered an important factor when determining irradiation D-values for this pathogen.

Investigating the control of Listeria monocytogenes on a ready-to-eat ham product using natural antimicrobial ingredients and postlethality interventions.

Ready-to-eat (RTE) meat and poultry products manufactured with natural or organic methods are at greater risk for Listeria monocytogenes growth, if contaminated, than their conventional counterparts due to the required absence of preservatives and antimicrobials. Thus, the objective of this study was to investigate the use of commercially available natural antimicrobials and postlethality interventions in the control of L. monocytogenes growth and recovery on a RTE ham product. Antimicrobials evaluated were cranberry powder (90MX), vinegar (DV), and vinegar/lemon juice concentrate (LV1X). Postlethality interventions studied were high hydrostatic pressure at 400 (HHP400) or 600 (HHP600) MPa, lauric arginate (LAE), octanoic acid (OA), and postpackaging thermal treatment (PPTT). Parameters evaluated through 98 days of storage at 4±1°C were residual nitrite concentrations, pH, a(w), and viable L. monocytogenes on modified Oxford (MOX) media. On day 1, OA, 90MX, DV, and LV1X yielded lower residual nitrite concentrations than the control, whereas HHP400, HHP600, and LAE did not. LAE, HHP400, and OA reduced L. monocytogenes population compared to the control after 1 day of storage by 2.38, 2.21, and 1.73 log10 colony-forming units per gram, respectively. PPTT did not achieve a significant reduction in L. monocytogenes populations. L. monocytogenes recovered and grew in all postlethality intervention treatments except HHP600. 90MX did not inhibit the growth of L. monocytogenes, while DV and LV1X did. Results of this study demonstrate the bactericidal properties of HHP, OA, and LAE and the bacteriostatic potential of natural antimicrobial ingredients such as DV and LV1X against L. monocytogenes.

Effects of different nitrite concentrations from a vegetable source with and without high hydrostatic pressure on the recovery of Listeria monocytogenes on ready-to-eat restructured ham.

Sodium nitrite exerts an inhibitory effect on the growth of Listeria monocytogenes. The objective of this study was to investigate the effects of various nitrite concentrations from a vegetable source with and without high hydrostatic pressure (HHP) on the recovery and growth of L. monocytogenes on ready-to-eat restructured ham. A preconverted celery powder was used as the vegetable source of nitrite. Targeted concentrations of natural nitrite investigated were 0, 50, and 100 mg/kg. HHP treatments evaluated were 400 MPa for 4 min and 600 MPa for 1 or 4 min at 12 ± 2 °C (initial temperature of the pressurization fluid). Viable L. monocytogenes populations were monitored on modified Oxford medium and thin agar layer medium through 98 days of storage at 4 ± 1 °C. Populations on both media did not differ. The HHP treatment at 600 MPa for 4 min resulted in L. monocytogenes populations below the detection limit of our sampling protocols throughout the storage period regardless of the natural nitrite concentration. The combination of HHP at 400 MPa for 4 min or 600 MPa for 1 min with natural nitrite resulted in initial inhibition of viable L. monocytogenes. Ham formulations that did not contain natural nitrite allowed faster growth of L. monocytogenes than did those with nitrite, regardless of whether they were treated with HHP. The results indicate that nitrite from a vegetable source at the concentrations used in this study resulted in slower growth of this microorganism. HHP treatments enhanced the inhibitory effects of natural nitrite on L. monocytogenes growth. Thus, the combination of natural nitrite plus HHP appears to have a synergistic inhibitory effect on L. monocytogenes growth.

Evaluation of the thin agar layer method for the recovery of pressure-injured and heat-injured Listeria monocytogenes.

A sublethally injured bacterial cell has been defined as a cell that survives a stress such as heating, freezing, acid treatment, or other antimicrobial intervention but can repair the cellular damage exerted by the stressor and later regain its original ability to grow. Consequently, sublethally injured cells are not likely to be included in conventional enumeration procedures, which could result in unrealistically low counts unless efforts are made to encourage recovery of the injured cells before enumeration. The objective of this study was to evaluate the use of the thin agar layer (TAL) method for the recovery of pressure-injured and heat-injured Listeria monocytogenes in a tryptic soy broth with 0.6% yeast extract system. Pressure injury consisted of treatment of a culture of mixed L. monocytogenes strains with high hydrostatic pressure at 400 or 600 MPa for 1 s, 2 min, 4 min, or 6 min at a process temperature of 12±2 °C. Heat injury consisted of treatment of a culture of mixed L. monocytogenes strains at 60±1 °C for 3, 6, or 9 min. Growth media were tryptic soy agar (TSA) with 0.6% yeast extract, modified Oxford medium (MOX), and TAL, which consisted of a 7-ml layer of TSA overlaid onto solidified MOX. Counts of viable L. monocytogenes on TAL were higher than those on MOX in the heat-injury experiment but not in the pressure-injury experiment. Therefore, the effectiveness of the TAL method may be specific to the type of injury applied to the microorganism and should be investigated in a variety of cellular injury scenarios.

Investigating the control of Listeria monocytogenes on alternatively-cured frankfurters using natural antimicrobial ingredients or post-lethality interventions.

The objective of this study was to investigate natural antimicrobials including cranberry powder, dried vinegar and lemon juice/vinegar concentrate, and post-lethality interventions (lauric arginate, octanoic acid, thermal treatment and high hydrostatic pressure) for the control of Listeria monocytogenes on alternatively-cured frankfurters. Lauric arginate, octanoic acid, and high hydrostatic pressure (400 MPa) reduced L. monocytogenes populations by 2.28, 2.03, and 1.88 log 10 CFU per g compared to the control. L. monocytogenes grew in all post-lethality intervention treatments, except after a 600 MPa high hydrostatic pressure treatment for 4 min. Cranberry powder did not inhibit the growth of L. monocytogenes, while a dried vinegar and a vinegar/lemon juice concentrate did. This study demonstrated the bactericidal properties of high hydrostatic pressure, octanoic acid and lauric arginate, and the bacteriostatic potential of natural antimicrobial ingredients such as dried vinegar and vinegar/lemon juice concentrate against L. monocytogenes.

Survival of methicillin-resistant Staphylococcus aureus during commercial heat treatment of slab bacon and consumer preparation of sliced bacon.

With the knowledge that retail pork products may be contaminated with methicillin-resistant Staphylococcus aureus (MRSA), the risk of consumers contracting a MRSA infection or foodborne illness from processed meats, especially bacon, is uncertain. Therefore, a study was designed to investigate the survival of MRSA during heat treatment of slab bacon at a commercial process and during cooking of sliced bacon at the consumer level. Fresh pork bellies were injected with a curing solution, inoculated, and heat treated to an internal temperature of 52°C. Three commercial brands of sliced bacon with similar "sell by" dates and fat-to-lean ratios were also inoculated and cooked at a temperature of 177°C for 0, 2, and 5 min on each side. Heat-treated slab bacon showed a log reduction of 1.89, which was significant (P < 0.05) compared with an uncooked inoculated control. Cooked sliced bacon had a reduction of viable MRSA cells of >6.5 log CFU/cm(2), and there was not a significant brand interaction (P > 0.05).

Survival of methicillin-resistant Staphylococcus aureus during thermal processing of frankfurters, summer sausage, and ham.

Infections from antibiotic-resistant bacteria are a major concern for human health professionals around the world. Methicillin-resistant Staphylococcus aureus (MRSA) is just one of the resistant organisms of concern. MRSA prevalence has also been recently reported in retail meat products at rates higher than originally thought. Although the risk of contracting an infection from handling contaminated meat products is thought to be low, very little is known about this organism from a food safety perspective. The objective of this study was to determine the survival of MRSA during thermal processing of frankfurters, summer sausage, and boneless ham. Frankfurters, summer sausage, and boneless ham were manufactured using formulations and processing procedures developed at the Iowa State University meat laboratory. Thermal processing resulted in a significant log reduction (p<0.05) for boneless ham, summer sausage, and frankfurters when compared to uncooked, positive controls for each of the three processed meat products. All products were thermally processed to an internal temperature of 70°C and promptly cooled to 7.2°C. Boneless ham showed the highest log reduction (7.28 logs) from cooking, followed by summer sausage (6.75 logs) and frankfurters (5.53 logs). The results of this study indicate that thermal processing of ham, summer sausage, and frankfurters to 70°C is sufficient to reduce the risk of MRSA as a potential food safety hazard.

Control of Campylobacter jejuni in chicken breast meat by irradiation combined with modified atmosphere packaging including carbon monoxide.

Campylobacter is one of the leading causes of human foodborne illnesses originating from meat and poultry products. Cross-contamination of this organism occurs in many poultry processing plants, and can occur in the kitchens and refrigerators of consumers. Therefore, new intervention strategies are needed for meat and poultry products to better protect consumers from this pathogen. Vacuum or modified atmosphere packaging is a common packaging technique used by the meat and poultry industry to extend the shelf life of meat products. In addition, irradiation has been well established as an antibacterial treatment to reduce pathogens on meat and poultry products. Irradiation in combination with high-CO(2) + CO modified atmosphere packaging (MAP) was investigated in this study for the control of Campylobacter jejuni in chicken breast meat. The radiation sensitivity (D(10)-value) of this foodborne pathogen in chicken breast meat was similar in vacuum or high-O(2) MAP (0.31 ± 0.01 kGy in vacuum packaging and 0.29 ± 0.03 kGy in MAP). C. jejuni survived in both vacuum and high-CO(2) MAP through 6 weeks of refrigerated storage. Irradiation was effective for eliminating C. jejuni from meat or poultry packaged in vacuum or MAP, and should reduce the chance of cross-contamination in retail stores or home kitchens. However, irradiated off-odor and sour aroma were observed for raw, irradiated chicken breast packaged with either vacuum or MAP. Therefore, additional means to mitigate quality changes appear necessary for these products.