Effect of inhibitory extracts derived from liquid smoke combined with postprocess pasteurization for control of Listeria monocytogenes on ready-to-eat meats

Surface pasteurization was examined in combination with low-phenolic antimicrobial extracts derived from liquid smoke to inhibit and prevent the growth of Listeria monocytogenes during the shelf life of ready-to-eat meats. In preliminary trials with retail frankfurters, one smoke derivative (2-min dip) produced a 0.3-log reduction of L. monocytogenes and a 1-min in-bag pasteurization (73.9 degrees C) produced a 2.9-log reduction, whereas a combination of the two treatments produced a 5.3-log reduction that resulted in no detectable Listeria by week 3 under accelerated shelf-life conditions (10 degrees C). In trials with frankfurters manufactured without lactate or diacetate that were treated with a shortened 1-s dip, this smoke extract and one with reduced smoke flavor and color both produced a > 4.5-log reduction of L. monocytogenes on frankfurters when heated at 73.9 degrees C for 1 min, with no recoverable Listeria detected for 10 weeks when stored at 6.1 degrees C. When deli turkey breast chubs manufactured without lactate, diacetate, or nitrite were treated with a 1-s dip in combination with radiant-heat pasteurization (270 degrees C), growth of L. monocytogenes was retarded but not prevented. However, in a similar study in which smoke extract treatment of deli turkey breast was combined with in-bag postpackage pasteurization (water submersion at 93.3 degrees C), a 60-, 45-, or even 30-s heat treatment resulted in a 2- to 3-log reduction of L. monocytogenes, with no growth on the meat during 10 weeks of storage at 6.1 degrees C. These findings indicate that reduced-acid low-phenolic antimicrobial liquid smoke derivatives combined with surface pasteurization are capable of reducing or preventing growth of L. monocytogenes to meet the criteria for the U.S. Department of Agriculture Food Safety and Inspection Service Alternative 1 process for ready-to-eat deli meat products manufactured without lactate or diacetate.     

Chemical effects of smoke processing on frankfurter quality and palatability characteristics

Frankfurters were made by standard commercial practices except for the smoke treatment which involved four different methods: solid smoke-aerosol, liquid smoke-aerosol, liquid smoke-external dip and liquid smoke-internal mix. For control purposes, frankfurters were prepared without any smoke treatment. All frankfurters were packaged and stored at 5°C with samples removed for analyses weekly for three weeks. All smoke-processing treatments resulted in products assessed as overall acceptable with the experienced sensory panel unable to detect differences among the various methods of manufacture except for the franks made by mixing liquid smoke in the emulsion. However, the flavour scores of those products subjected to external smoke-processing treatments were higher and more acceptable than the other two treatments. Frankfurters manufactured using aerosol smoke treatments were rated by sensory panellists as the most tender. However, shear force measurements indicated that those franks processed with external liquid smoke treatments were somewhat less tender. Liquid smoke-processing techniques favoured the development of a more desirable cured colour. The most stable colour was attributed to the liquid smoke-processing system in which the smoke materials were mixed in the emulsion. All palatability properties (sensory and colour) were highly correlated with the smokiness of the product. Generally, storage time had little effect on frankfurter palatability characteristics.     

Effectiveness of acidic calcium sulfate with propionic and lactic acid and lactates as postprocessing dipping solutions to control Listeria monocytogenes on frankfurters with or without potassium lactate and stored vacuum packaged at 4.5 degrees C

The safety of ready-to-eat meat products such as frankfurters can be enhanced by treating with approved antimicrobial substances to control the growth of Listeria monocytogenes. We evaluated the effectiveness of acidic calcium sulfate with propionic and lactic acid, potassium lactate, or lactic acid postprocessing dipping solutions to control L. monocytogenes inoculated (ca. 10(8) CFU/ml) onto the surface of frankfurters with or without potassium lactate and stored in vacuum packages at 4.5 degrees C for up to 12 weeks. Two frankfurter formulations were manufactured without (control) or with potassium lactate (KL, 3.3% of a 60% [wt/wt] commercially available syrup). After cooking, chilling, and peeling, each batch was divided into inoculated (four strains of L. monocytogenes mixture) and noninoculated groups. Each group was treated with four different dips: (i) control (saline solution), (ii) acidic calcium sulfate with propionic and lactic acid (ACS, 1:2 water), (iii) KL, or (iv) lactic acid (LA, 3.4% of a 88% [wt/wt] commercially available syrup) for 30 s. Noninoculated frankfurters were periodically analyzed for pH, water activity, residual nitrite, and aerobic plate counts (APCs), and L. monocytogenes counts (modified Oxford medium) were determined on inoculated samples. Surface APC counts remained at or near the lower limit of detection (<2 log CFU per frank) on franks with or without KL and treated with ACS or LA throughout 12 weeks at 4.5 degrees C. L. monoctogenes counts remained at the minimum level of detection on all franks treated with the ACS dip, which indicated a residual bactericidal effect when L. monocytogenes populations were monitored over 12 weeks. L. monocytogenes numbers were also reduced, but not to the same degree in franks made without or with KL and treated with LA. These results revealed the effectiveness of ACS (bactericidal effect) or LA (bacteriostatic effect) as postprocessing dipping solutions to inhibit or control the growth of L. monocytogenes on vacuum-packaged frankfurters stored at 4.5 degrees C for up to 12 weeks.     

Combining pediocin (ALTA 2341) with postpackaging thermal pasteurization for control of Listeria monocytogenes on frankfurters

Frankfurters packaged in 1-link, 5-link, or 10-link packages were surface-inoculated with a five-strain mixture of Listeria monocytogenes (3.40 or 5.20 log CFU/g) after treatments with 3,000 arbitrary units (AU) or 6,000 AU pediocin (in ALTA 2341) per link. The frankfurters were vacuum packaged, after which the packages were heated in hot water at 71, 81, or 96 degrees C for 30, 60, or 120 s. L. monocytogenes was enumerated following the treatments. Selected treatments were subsequently evaluated during storage at 4, 10, and 25 degrees C for up to 12 weeks. L. monocytogenes was reduced by all treatments, but 81 degrees C or more for at least 60 s in combination with pediocin (Pdn-6000) was necessary to achieve a 50% reduction of initial inoculations. Heat treatments were most effective for 1-link packages and least effective for 10-link packages. Little or no growth of L. monocytogenes occurred on frankfurters for 12 weeks at 4 or 10 degrees C, and for 12 days at 25 degrees C. Generally, the treatments mentioned above did not significantly (P > 0.05) affect the sensory qualities of frankfurters. Therefore, pediocin (in ALTA 2341) in combination with postpackaging thermal treatment offers an effective treatment combination for improved control of L. monocytogenes on frankfurters.     

Control of Listeria monocytogenes on turkey frankfurters by generally-recognized-as-safe preservatives

Generally-recognized-as-safe chemicals applied to the surfaces of turkey frankfurters were evaluated for their ability to reduce populations of or inhibit the growth of Listeria monocytogenes. Frankfurters were treated prior to inoculation by dipping for 1 min in a solution of one of four preservatives (sodium benzoate, sodium propionate, potassium sorbate, and sodium diacetate) at three different concentrations (15, 20, and 25% [wt/vol]), with < 0.3% of the preservative being present for each frankfurter. Subsequently, 0.1 ml of a five-strain mixture of L. monocytogenes (10(6) CFU/ml) was used to surface inoculate each frankfurter separately in a sterile stomacher bag. Inoculated frankfurter bags were held at 4, 13, and 22 degrees C, and L. monocytogenes cells were enumerated at 0, 3, 7, 10, and 14 days of storage. The results of this study revealed that at all three concentrations of all four preservatives, the initial populations of L. monocytogenes decreased immediately by 1 to 2 log10 CFU/g. After 14 days of storage at 4 degrees C, L. monocytogenes counts for all treated frankfurters were 3 to 4 log10 CFU/g less than those for the untreated frankfurters. After 14 days of storage at 13 degrees C, L. monocytogenes counts for frankfurters treated with 25% sodium benzoate or 25% sodium diacetate were 3.5 to 4.5 log10 CFU/g less than those for untreated frankfurters, and those for frankfurters treated with 25% sodium propionate or 25% potassium sorbate were 2.5 log10 CFU/g less than those for untreated frankfurters. In all instances, the degree of growth inhibition was directly proportional to the concentration of the preservative. Only frankfurters treated with 25% sodium diacetate or sodium benzoate were significantly inhibitory to L. monocytogenes when held at 22 degrees C for 7 days or longer. Interestingly, the untreated frankfurters held at 22 degrees C were spoiled within 7 days, with copious slime formation, whereas there was no evidence of slime on any treated frankfurters after 14 days of storage.     

Survival and growth of alkali-stressed Listeria monocytogenes on beef frankfurters and thermotolerance in frankfurter exudates

Cells of Listeria monocytogenes exposed at 4 degrees C to 1% solutions of two alkaline cleaners or alkali-adapted in tryptose phosphate broth (pH 10.0) at 37 degrees C for 45 min, followed by 4 degrees C for 48 h, were inoculated onto beef frankfurters containing high fat (16 g) and high sodium (550 mg) or low fat (8 g) and low sodium (250 mg) per 57-g serving. Frankfurters were surface inoculated (2.0 log10 CFU/g), vacuum packaged, stored at -20, 4, or 12 degrees C, and analyzed for populations of L. monocytogenes at 2-day to 2-week intervals. Populations did not change significantly on frankfurters stored at -20 degrees C for up to 12 weeks. After storage at 4 degrees C for 6 weeks (I week before the end of shelf life), populations of control cells and cells exposed to alkaline cleaners were ca. 6.0 log10 CFU/g of low fat, low sodium (LFLS) frankfurters and ca. 3.5 log10 CFU/g of high fat, high sodium (HFHS) frankfurters. Growth of alkali-adapted cells on both types of frankfurters was retarded at 4 degrees C. Growth of L. monocytogenes on frankfurters stored at 12 degrees C was more rapid than at 4 degrees C, but a delay in growth of alkali-adapted cells on HFHS and LFLS frankfurters was evident during the first 9 and 6 days, respectively. Alkali-adapted cells had a significantly (P < or = 0.05) lower logistic D59 degrees C-value (decimal reduction time) than alkaline cleaner-exposed cells, but the D59 degrees C-value was not different from that of control cells. Cells exposed to a nonbutyl alkaline cleaner, and then heated in LFLS frankfurter exudates, had a significantly lower D62 degrees C-value than cells that had been exposed to some of the other treatments. Growth characteristics of L. monocytogenes inoculated onto the surface of frankfurters may be altered by previous exposure to alkaline environments. Differences in growth characteristics of L. monocytogenes on HFHS versus LFLS beef frankfurters stored at refrigeration temperatures indicate that composition influences the behavior of both alkaline-stressed and control cells.     

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.     

Antimicrobial activity of cetylpyridinium chloride against Listeria monocytogenes on frankfurters and subsequent effect on quality attributest

Frankfurters inoculated with Listeria monocytogenes were treated with 1% cetylpyridinium chloride (CPC) or with 1% CPC followed by a water rinse at various combinations of spray temperatures (25, 40, and 55 degrees C), spray pressures (20, 25, and 35 psi), and times of exposure (30, 40, and 60 s). No significant differences (P > 0.05) were observed in the reductions achieved by 1% CPC + water wash and those achieved with 1% CPC treatment alone. L. monocytogenes populations were reduced by ca. 1.7 log CFU/g immediately following treatment, with no differences (P > 0.05) observed for different spray temperatures, pressures, or exposure times. The effectiveness of 1% CPC spray treatment (at 25 degrees C, 20 psi, and 30 s of exposure) against L. monocytogenes on vacuum-packaged frankfurters stored at 0 and 4 degrees C for 42 days was then evaluated. Application of a 1% CPC surface spray to frankfurters immediately prior to packaging reduced L. monocytogenes concentrations by 1.4 to 1.7 log CFU/g and further restricted growth of the pathogen during 42 days of refrigerated storage, thereby meeting U.S. Department of Agriculture alternatives 1 and 2 criteria for Listeria control. CPC treatment reduced aerobic plate counts, lactic acid bacteria, yeasts and molds, total coliforms, and Escherichia coli populations on noninoculated frankfurters to below detectable limits. The 1% CPC treatment did not affect the color (L*, a*, and b* values) of frankfurters stored for 42 days at 0 or 4 degrees C (P > 0.05). The effect of 1% CPC treatment on the firmness of frankfurters was also negligible.     

Combining pediocin with postpackaging irradiation for control of Listeria monocytogenes on frankfurters

Frankfurters, in 1-link, 5-link, or 10-link packages, were surface inoculated with a five-strain mixture of Listeria monocytogenes (3.40 or 5.20 log CFU/g) after treatment with 3,000 arbitrary units (AU) or 6,000 AU of pediocin (in ALTA 2341) per link. The frankfurters were vacuum packaged, after which the 1-link and 5-link packages were irradiated at 1.2 or 2.3 kGy and the 10-link packages were irradiated at 1.4 or 3.5 kGy. L. monocytogenes was enumerated following the treatments. Selected treatments were subsequently evaluated during storage at 4, 10, and 25 degrees C for up to 12 weeks. Combination of pediocin with postpackaging irradiation at 1.2 kGy or more was necessary to achieve a 50% reduction of L. monocytogenes on frankfurters in 1-link or 5-link packages. The combination of 6,000 AU of pediocin and irradiation at 2.3 kGy or more was effective in all package sizes for inhibition of the pathogen for 12 weeks at 4 or 10 degrees C. There was a synergistic effect between pediocin and irradiation for inhibition of L. monocytogenes. Storage at 4 degrees C enhanced the antilisterial effects of the treatment combinations, with little or no growth of the pathogen in 1-link or 5-link packages during 12 weeks of storage. In general, these treatments did not affect the sensory quality of frankfurters.     

Effects of Preblending, Reduced Fat and Salt Levels on Frankfurter Characteristics

Frankfurters were manufactured from preblended (PB) or nonpreblended (NPB) meats to contain traditional and reduced levels of salt (1.5, 2.0, or 2.5%) and/or fat (17%= low; 25%= high). Emulsions stability, color, Kramer shear and palatability were evaluated. Salt had a positive effect on emulsion stability (p<0.05). Low-fat frankfurters were darker, redder, less blue in color, drier and more resistant to shear than high-fat frankfurters. Low-fat franks containing 1.5% salt had a softer texture than those containing 2.0 or 2.5% salt. Preblending did not affect textural properties. With modification of the formulations, low fat-low salt franks can be manufactured.     

Control of Listeria monocytogenes on frankfurters and cooked pork chops by irradiation combined with modified atmosphere packaging

This study was conducted to investigate the efficacy of controlling Listeria monocytogenes on frankfurters and cooked pork chops with irradiation and modified atmosphere packaging (MAP) containing a high concentration of CO(2). Frankfurters and cooked pork chops were inoculated with a five-strain cocktail of L. monocytogenes and packaged in vacuum or high-CO(2) MAP. Irradiation was applied to each product at 0, 0.5, 1.0, or 1.5 kGy. No significant packaging effect was found for the radiation sensitivity of L. monocytogenes. Radiation D(10)-values for L. monocytogenes were 0.66 ± 0.03 and 0.70 ± 0.05 kGy on frankfurters and 0.60 ± 0.02 and 0.57 ± 0.02 kGy on cooked pork chops in vacuum and high-CO(2) MAP, respectively. High-CO(2) MAP was more effective than vacuum packaging for controlling the growth of survivors during refrigerated storage. These results indicate that irradiation and high-CO(2) MAP can be used to improve control of L. monocytogenes in ready-to-eat meats.     

USE OF PEDIOCIN (ALTATM2341) FOR CONTROL OF LISTERIA MONOCYTOGENES ON FRANKFURTERS

Frankfurters were surfaced-inoculated with a 5-strain mixture of Listeria monocytogenes ( 3.40 or 5.20 log CFU/g) and vacuum-packaged (as one link, 5 links or 10 links per package) after treatments with 3,000 AU or 6,000 AU of pediocin (in ALTA ^TM 2341) per link. Treatments were evaluated for L. monocytogenes counts initially and during storage (4C, 10C and 25C)for up to 12 weeks. The populations of L. monocytogenes were reduced by addition of pediocin but were unaffected by the number of frankfurters per package. Treatments stored at 4C with pediocin effectively prolonged the time prior to growth of L. monocytogenes for 7 weeks and reduced the growth of L. monocytogenes for up to 12 weeks.     

Post process control of Listeria monocytogenes on commercial frankfurters formulated with and without antimicrobials and stored at 10 degrees C

The antilisterial effect of postprocess antimicrobial treatments on commercially manufactured frankfurters formulated with and without a 1.5% potassium lactate-0.05% sodium diacetate combination was evaluated. Frankfurters were inoculated (ca. 3 to 4 log CFU/cm2) with 10-strain composite Listeria monocytogenes cultures originating from different sources. The inocula evaluated were cells grown planktonically in tryptic soy broth plus 0.6% yeast extract (30 degrees C, 24 h) or in a smoked sausage homogenate (15 degrees C, 7 days) and cells that had been removed from stainless steel coupons immersed in an inoculated smoked sausage homogenate (15 degrees C, 7 days). Inoculated frankfurters were dipped (2 min, 25 +/- 2 degrees C) in acetic acid (AA; 2.5%), lactic acid (LA; 2.5%), potassium benzoate (PB; 5%), or Nisaplin (commercial form of nisin; 0.5%, equivalent to 5,000 IU/ml of nisin) solutions, or in Nisaplin followed by AA, LA, or PB, and were subsequently vacuum packaged and stored for 48 days at 10 degrees C. In addition to microbiological analyses, sensory evaluations were performed with uninoculated samples that had been treated with AA, LA, or PB for 2 min. Initial L. monocytogenes populations were reduced by 1.0 to 1.8 log CFU/cm2 following treatment with AA, LA, or PB solutions, and treatments that included Nisaplin reduced initial levels by 2.4 to >3.8 log CFU/ cm2. All postprocessing treatments resulted in some inhibition of L. monocytogenes during the initial stages of storage of frankfurters that were not formulated with potassium lactate-sodium diacetate; however, in all cases, significant (P < 0.05) growth occurred by the end of storage. The dipping of products formulated with potassium lactate-sodium diacetate in AA or LA alone--or in Nisaplin followed by AA, LA, or PB-increased lag-phase durations and lowered the maximum specific growth rates of the pathogen. Moreover, depending on the origin of the inoculum, this dipping of products led to listericidal effects. In general, differences in growth kinetics were obtained for the three inocula that were used to contaminate the frankfurters. Possible reasons for these differences include the presence of stress-adapted subpopulations and the inhibition of the growth of the pathogen due to high levels of spoilage microflora. The dipping of frankfurters in AA, LA, or PB did not (P > 0.05) affect the sensory attributes of the product when compared to the control samples. The data generated in this study may be useful to U.S. ready-to-eat meat processors in their efforts to comply with regulatory requirements.     

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.     

Survival and growth of Listeria monocytogenes in broth as a function of temperature, pH, and potassium lactate and sodium diacetate concentrations

The objective of this study was to determine the antimicrobial effect of a combination of potassium lactate and sodium diacetate (0, 1.8, 3, and 4.5%; PURASAL P Opti.Form 4, 60% solution) on the survival and growth of Listeria monocytogenes Scott A in pH-adjusted broth (5.5, 6.0, 6.5, and 7.0) stored at 4, 10, 17, 24, 30, and 37 degrees C. Appropriate dilutions of broth were enumerated by spiral plating on tryptose agar and counted with an automated colony counter. Growth data were iteratively fit, using nonlinear regression analysis to a three-phase linear model, using GraphPad PRISM. At pH 5.5, the combination of lactate-diacetate fully inhibited (P < 0.001) the growth of L. monocytogenes at all four levels and six temperatures. At pH 6.0, addition of 1.8% lactate-diacetate reduced (P < 0.001) the specific growth rate of L. monocytogenes and increased lag time; however, 3 and 4.5% completely inhibited the growth at the six temperatures studied. Efficacy of the lactate-diacetate mixture was decreased as pH increased and incubation temperature increased. Thus, at pH 6.5, at least 3% was required to retard (P < 0.001) the growth of L. monocytogenes in broth. There was a limited effect of the lactate-diacetate level on the specific growth rate of the pathogen at pH 7.0. However, 1.8 and 3% significantly lengthened the lag time at 4 and 10 degrees C. These results suggest that 1.8% of lactate-diacetate mixture can be used as a substantial hurdle to the growth of L. monocytogenes when refrigerated temperatures are maintained for products with pH less than 6.5.     

Fate of Listeria monocytogenes in commercial ham, formulated with or without antimicrobials, under conditions simulating contamination in the processing or retail environment and during home storage

Commercial cured ham formulated with or without potassium lactate and sodium diacetate was inoculated with Listeria monocytogenes and stored to simulate conditions of processing, retail, and home storage. The ham was sliced, inoculated with a 10-strain composite of L. monocytogenes (1 to 2 log CFU/cm2), vacuum packaged, and stored at 4 degrees C to simulate contamination following lethality treatment at processing (first shelf life). After 10, 20, 35, and 60 days of storage, packages were opened, samples were tested, and bags with remaining slices were reclosed with rubber bands. At the same times, portions of original product (stored at 4 degrees C in original processing bags) were sliced, inoculated, and packaged in delicatessen bags to simulate contamination during slicing at retail (second shelf life). Aerobic storage of both sets of packages at 7 degrees C for 12 days was used to reflect domestic storage conditions (home storage). L. monocytogenes populations were lower (P < 0.05) during storage in ham formulated with lactate-diacetate than in product without antimicrobials under both contamination scenarios. Inoculation of ham without lactate-diacetate allowed prolific growth of L. monocytogenes in vacuum packages during the first shelf life and was the worst case contamination scenario with respect to pathogen numbers encountered during home storage. Under the second shelf life contamination scenario, mean growth rates of the organism during home storage ranged from 0.32 to 0.45 and from 0.18 to 0.25 log CFU/cm2/day for ham without and with lactate-diacetate, respectively, and significant increases in pathogen numbers (P < 0.05) were generally observed after 4 and 8 days of storage, respectively. Regardless of contamination scenario, 12-day home storage of product without lactate-diacetate resulted in similar pathogen populations (6.0 to 6.9 log CFU/cm2) (P > 0.05). In ham containing lactate-diacetate, similar counts were found during the home storage experiment under both contamination scenarios, and only in 60-day-old product did samples from the first shelf life have higher (P < 0.05) pathogen numbers than those found in samples from the second shelf life. These results should be useful in risk assessments and for the establishment of "sell by" and "consume by" date labels for refrigerated ready-to-eat meat products.     

Evaluating the growth of Listeria monocytogenes in refrigerated ready-to-eat frankfurters: influence of strain, temperature, packaging, lactate and diacetate, and background microflora

This research was conducted to study the growth of Listeria monocytogenes inoculated on frankfurters stored at different conditions as a basis for a safety-based consume by shelf life date label. Three L. monocytogenes strains were separately inoculated at 10 to 20 CFU/cm2 onto frankfurters that were previously formulated with or without high pressure and with or without added 2% potassium lactate (PL) and 0.2% sodium diacetate (SD). Inoculated frankfurters were air or vacuum packaged; stored at 4, 8, or 12 degrees C; and L. monocytogenes and psychrotrophic plate counts were determined for 90, 60, and 45 days, respectively, or until the stationary phase was reached. The data (log CFU per square centimeter versus time) were fitted using the Baranyi-Roberts model to determine maximum growth rates and lag-phase time. The maximum growth rates and the lag time under each growth condition were used to calculate the time to reach 100-fold the initial Listeria population. In frankfurters lacking PL and SD, the count of all strains increased by 2 log after 18 to 50 days at 4 degrees C and 4 to 13 days at 8 degrees C. The growth was inhibited at 4 and 8 degrees C in frankfurters containing PL and SD, but one ribotype was capable of growing, with the time to reach 100-fold the initial Listeria population ranging from 19 to 35 days at 12 degrees C. In most cases, the time to reach 100-fold the initial Listeria population of L. monocytogenes was significantly longer in vacuum-packaged frankfurters as compared with air-packaged samples. Inclusion of PL and SD also inhibited the growth of psychrotrophs, but at all temperatures the psychrotrophic plate counts were greater than 4 log CFU/cm2 at the end of the experiments. These results indicated that despite the use of antimicrobials, certain L. monocytogenes strains could be capable of growing under storage-abuse conditions. Growth kinetics data could be useful for establishing a shelf life date label protocol under different handling scenarios.     

Control of Listeria monocytogenes on vacuum-packaged frankfurters sprayed with lactic acid alone or in combination with sodium lauryl sulfate

U.S. regulations require that processors employ lethal or inhibitory antimicrobial alternatives in production of ready-to-eat meat and poultry products that support growth of Listeria monocytogenes and may be exposed to the processing environment after a lethality treatment. In this study, lactic acid (LA; 5%, vol/vol) and sodium lauryl sulfate (SLS; 0.5%, wt/vol) were evaluated individually or as a mixture (LASLS) for control of L. monocytogenes on frankfurters. Frankfurters were inoculated with a 10-strain mixture of L. monocytogenes, sprayed for 10 s (20 bar, 23 +/- 2 degrees C) with antimicrobials or distilled water (DW) before (LASLS or DW) or after (LA, SLS, LASLS, or DW) inoculation (4.8 +/- 0.1 log CFU/cm2), vacuum packaged, and stored at 4 degrees C for 90 days. Samples were analyzed for numbers of the pathogen (on PALCAM agar) and for total microbial counts (on tryptic soy agar with yeast extract) during storage. Spraying with DW, LA, or SLS after inoculation reduced numbers of L. monocytogenes by 1.3 +/- 0.2, 1.8 +/- 0.5, and 2.0 +/- 0.4 log CFU/cm2, respectively. The LASLS mixture applied before or after inoculation reduced pathogen populations by 1.8 +/- 0.4 and 2.8 +/- 0.2 log CFU/cm2, respectively. No further reduction by any treatment was observed during storage. The bacterial growth curves (fitted by the model of Baranyi and Roberts) indicated that the lag-phase duration of the bacterium on control samples (13.85 to 15.18 days) was extended by spraying with all solutions containing LA. For example, LA suppressed growth of L. monocytogenes for 39.14 to 41.01 days. Pathogen growth rates also were lower on frankfurters sprayed after inoculation with LA or LASLS compared to those sprayed with DW. Therefore, spraying frankfurters with a mixture of LA and SLS may be a useful antilisterial alternative treatment for ready-to-eat meat and poultry products.     

Nitrite-induced injury of Listeria monocytogenes and the effect of selective versus nonselective recovery procedures on its isolation from frankfurters

Sodium nitrite (NaNO2) is used as a curing agent in frankfurters. Although previous studies have documented the bacteriostatic abilities of NaNO2 toward Listeria monocytogenes, few if any studies have been conducted that consider the possibility of sublethal injury to L. monocytogenes by exposure to NaNO2. The goals of this study were to determine whether NaNO2 has the ability to injure L. monocytogenes, to determine whether nitrite injury is reversible, and to compare the recovery of L. monocytogenes from frankfurters containing nitrite with Listeria repair broth (LRB) and University of Vermont modified Listeria enrichment broth (UVM). NaNO2, when used at concentrations of 100 and 200 ppm, was found to injure L. monocytogenes. The injury was completely reversible, or growth of uninjured Listeria occurred in LRB when injury was between 98.5 and 98.7%. However, total recovery was not observed in LRB when injury exceeded 99%. UVM was unable to reverse the effects of nitrite-injured L. monocytogenes. With respect to time, inoculum, and meat type, LRB was found to be consistently superior to UVM at recovering L. monocytogenes from frankfurters. Nitrite injury might be a factor influencing detection and recovery of L. monocytogenes from frankfurters.     

Behavior of Listeria monocytogenes at 7 degrees C in commercial turkey breast, with or without antimicrobials, after simulated contamination for manufacturing, retail and consumer settings

Uncured turkey breast, commercially available with or without a mixture of potassium lactate and sodium diacetate, was sliced, inoculated with a 10-strain composite of Listeria monocytogenes, vacuum-packaged, and stored at 4 degrees C, to simulate contamination after a lethal processing step at the plant. At 5, 15, 25 and 50 days of storage, packages were opened, slices were tested, and bags with remaining slices were reclosed with rubber bands; this simulated home use of plant-sliced and -packaged product. At the same above time intervals, portions of original product (stored at 4 degrees C in original processing bags) were sliced and inoculated as above, and packaged in delicatessen bags, simulating contamination during slicing/handling at retail or home. Both sets of bags were stored aerobically at 7 degrees C for 12 days to simulate home storage. L. monocytogenes populations were lower (P<0.05) during storage in turkey breast containing a combination of lactate and diacetate compared to product without antimicrobials under both contamination scenarios. Due to prolific growth of the pathogen under the plant-contamination scenario in product without lactate-diacetate during vacuum-packaged storage (4 degrees C), populations at 3 days of aerobic storage (7 degrees C) of such product ranged from 4.6 to 7.4 log cfu/cm(2). Under the retail/home-contamination scenario, mean growth rates (log cfu/cm(2)/day) of the organism during aerobic storage ranged from 0.14 to 0.16, and from 0.25 to 0.51, in product with and without lactate-diacetate, respectively; growth rates in turkey breast without antimicrobials decreased (P<0.05) with age of the product. Overall, product without antimicrobials inoculated to simulate plant-contamination and product with lactate-diacetate inoculated to simulate retail/home-contamination were associated with the highest and lowest pathogen levels during aerobic storage at 7 degrees C, respectively. However, 5- and 15-day-old turkey breast without lactate-diacetate stored aerobically for 12 days resulted in similar pathogen levels (7.3-7.7 log cfu/cm(2)), irrespective of contamination scenario.