Prepackage surface pasteurization of ready-to-eat meats with a radiant heat oven for reduction of Listeria monocytogenes

In this paper, a thermal process for the surface pasteurization of ready-to-eat (RTE) meat products for the reduction of Listeria monocytogenes on such products (turkey bologna, roast beef, corned beef, and ham) is described. The process involves the passage of products through a "tunnel" of heated coils on a stainless steel conveyor belt at various treatment times relevant to the manufacture of processed meat for the surface pasteurization of RTE meat products. Two inoculation procedures, dip and contact inoculation, were examined with the use of a four-strain cocktail of L. monocytogenes prior to heat processing. With the use of radiant heat prepackage surface pasteurization, 1.25 to 3.5-log reductions of L. monocytogenes were achieved with treatment times of 60 to 120 s and air temperatures of 475 to 750 degrees F (246 to 399 degrees C) for these various RTE meats. Reduction levels differed depending on the type of inoculation method used, the type of product used, the treatment temperature, and the treatment time. Prepackage pasteurization (60 s) was also combined with postpackage submerged water pasteurization for formed ham (60 or 90 s), turkey bologna (45 or 60 s), and roast beef (60 or 90 s), resulting in reductions of 3.2 to 3.9. 2.7 to 4.3, and 2.0 to 3.75 log cycles, respectively. These findings demonstrate that prepackage pasteurization, either alone or in combination with postpackage pasteurization, is an effective tool for controlling L. monocytogenes surface contamination that may result from in-house handling.     

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.     

Reduction and survival of Listeria monocytogenes in ready-to-eat meats after irradiation

A five-strain Listeria monocytogenes culture was inoculated onto six different types of ready-to-eat (RTE) meats (frankfurters, ham, roast beef, bologna, smoked turkey with lactate, and smoked turkey without lactate). The meats were vacuum packed and stored at 4 degrees C for 24 h prior to irradiation. Populations of L. monocytogenes were recovered by surface plating on nonselective and selective media. The margins of safety studied include 3-log (3D) and 5-log (5D) reduction of pathogenic bacteria to achieve an optimal level of reduction while retaining organoleptic qualities of the meats. A 3-log reduction of L. monocytogenes was obtained at 1.5 kGy when nonselective plating medium was used. The dosages for 3-log reduction were 1.5 kGy for bologna, roast beef, and both types of turkey and 2.0 kGy for frankfurters and ham on the basis of use of selective medium. The D10-values ranged from 0.42 to 0.44 kGy. A 5-log reduction of L. monocytogenes was obtained at 2.5 kGy with nonselective medium. With selective medium, the dosages were 2.5 kGy for bologna, roast beef, and both types of turkey and 3.0 kGy for frankfurters and ham. Survival of L. monocytogenes in the same RTE meat types after irradiation was also studied. Meats were inoculated with 5 log L. monocytogenes per g and irradiated at doses of 2.0 and 4.0 kGy. Recovery of the surviving organisms was observed during storage at temperatures of 4 and 10 degrees C for 12 weeks. Preliminary results showed no growth in meats irradiated at 4.0 kGy. Survivors were observed for irradiated meats at 2.0 kGy stored at 10 degrees C after the second week. No growth was observed in samples irradiated at 2.0 kGy stored at 4 degrees C until the fifth week.     

Growth of L. monocytogenes strain F2365 on ready-to-eat turkey meat does not enhance gastrointestinal listeriosis in intragastrically inoculated A/J mice

There have been significant outbreaks of listeriosis associated with consumption of contaminated ready-to-eat (RTE) turkey meat products. In this study, we investigated whether growth on RTE deli turkey meat sends environmental signals to listerial cells that makes them more virulent in the gastrointestinal tract of mice. L. Listeria monocytogenes strain F2365 grew from a starting inoculum of 10(3) CFU/mL to final numbers of 10(8)-10(9) CFU/mL (within 12 days at 10 degrees C) when inoculated onto sliced processed, or whole muscle, turkey breast, or into emulsified whole turkey breast. We did not observe any difference in the numbers of CFU recovered from the spleens and livers of A/J mice inoculated intragastrically with L. monocytogenes grown on sliced turkey meat, in emulsified turkey meat, or in brain heart infusion broth. These results suggest that growth on RTE sliced deli turkey, or in RTE emulsified deli turkey, does not enhance the ability of L. monocytogenes F2365 to cause gastrointestinal listeriosis in intragastrically challenged A/J mice.     

Resistance of Listeria monocytogenes F2365 cells to synthetic gastric fluid is greater following growth on ready-to-eat deli turkey meat than in brain heart infusion broth

Ready-to-eat (RTE) deli meats have been categorized as high-risk foods for contraction of foodborne listeriosis. Several recent listeriosis outbreaks have been associated with the consumption of RTE deli turkey meat. In this study, we examined whether the growth of Listeria monocytogenes F2365 on commercially prepared RTE deli turkey meat causes listerial cells to become more resistant to inactivation by synthetic gastric fluid (SGF). Listerial cells grown on turkey meat to late logarithmic-early stationary phase were significantly more resistant to SGF at pH 7.0, 5.0, or 3.5 than listerial cells grown in brain heart infusion (BHI) broth. The pH was lower in the fluid in packages of turkey meat than in BHI broth (6.5 versus 7.5). However, listerial cells grown in BHI broth adjusted to a lower pH (6.0) did not exhibit enhanced resistance to SGF. The lesser resistance to SGF of listerial cells grown in BHI broth may be due, in part, to the presence of glucose (0.2%). This study indicates the environment presented by the growth of L. monocytogenes on deli turkey meat affects its ability to survive conditions it encounters in the gastrointestinal tract.     

Growth of Listeria monocytogenes in different retail delicatessen meats during simulated home storage

Delicatessen meats are reported to be the leading vehicle of foodborne listeriosis in the United States. Listeria monocytogenes can reach high numbers in these products during storage, and the growth rate is largely dictated by product formulation and storage temperature. To assess the impact of product age on Listeria growth, five commercial brands each of cured and uncured turkey breast, ham, and roast beef (three lots per brand) were sliced (approximately 25 g per slice) at the beginning of the shelf life, the midpoint, and the last allowable day of sale, surface inoculated with an eight-strain cocktail of L. monocytogenes (approximately 40 CFU/g), and then quantitatively examined for Listeria, lactic acid bacteria, and mesophilic aerobic bacteria during aerobic storage at 4, 7, or 10°C. As expected, L. monocytogenes grew faster in deli meats without rather than with Listeria inhibitors (lactate and/or diacetate) and at the highest storage temperature (10°C). Lag-phase durations for L. monocytogenes in deli meats with and without Listeria inhibitors were 9.21, 6.96, and 5.00 and 6.35, 3.30, and 2.19 days at 4, 7, and 10°C, respectively. Generation times for L. monocytogenes in deli meats with and without Listeria inhibitors were 1.59, 1.53, and 0.85 and 0.94, 0.50, and 0.36 at 4, 7, and 10°C, respectively. Maximum population densities for L. monocytogenes in deli meats with and without Listeria inhibitors were 5.26, 5.92, and 5.97 and 8.47, 8.96 and 9.34 log CFU/g at 4, 7, and 10°C, respectively. Although lactate and diacetate suppressed L. monocytogenes growth, the extent of inhibition differed, ranging from total inhibition in roast beef to only partial inhibition in ham and cured turkey. Listeria growth was also impacted by lot-to-lot variation in the concentrations of Listeria inhibitors, product pH, and background microflora. These data will be useful for developing recommendations for "best consumed by" dating for deli meats using a risk-based approach.     

Elimination of Listeria monocytogenes from ready-to-eat turkey and cheese tortilla wraps using ionizing radiation

Listeria monocytogenes is a common postprocess contaminant on ready-to-eat foods including premade ready-to-eat sandwiches. One popular type of sandwich product is the tortilla wrap, which contains sliced luncheon meats and cheeses rolled within a flour tortilla. This study determined the radiation resistance of L. monocytogenes surface inoculated onto two types of commercially available wheat flour tortillas, processed cheese slices, and deli turkey meat. The D10-values for L. monocytogenes (the radiation dose required to inactivate 1 log of the pathogen) were 0.27 kGy when inoculated onto two flour tortilla types, 0.28 and 0.30 kGy when inoculated onto two types of sliced processed cheeses, and 0.58 and 0.65 kGy when inoculated onto two types of sliced deli turkey meat. When two types of tortilla wraps were assembled from the individual components and L. monocytogenes was inoculated into the interfaces between the individual components, the D10-values were 0.27 to 0.37 kGy in the tortilla and cheese interfaces, 0.33 to 0.41 kGy in the cheese and turkey interfaces, and 0.25 to 0.33 kGy in the turkey and tortilla interfaces. The ability of ionizing radiation to reduce pathogen levels on the complex tortilla, cheese, and luncheon meat product was limited by the higher radiation resistance of L. monocytogenes when inoculated onto the ready-to-eat turkey-meat component.     

Control of Listeria Monocytogenes by Lauric Arginate on Frankfurters Formulated with or without Lactate/Diacetate

ABSTRACT:  Listeria monocytogenes  (Lm) is a food safety concern that can be associated with ready-to-eat (RTE) meat and poultry products because of its persistence in the processing environment. Listeriosis has a fatality rate of 28% in immuno-compromised individuals. RTE meats receive a lethal heat treatment but may become contaminated by Lm after this treatment. Federal regulators and manufacturers of RTE meats are working to find additional ways to control postprocess contamination by Lm in RTE meats. This research was initiated to validate combinations of antimicrobials that would produce an immediate lethality of at least 1 log of Lm on artificially contaminated frankfurters, and also suppress Lm growth to less than 2 logs throughout the extended shelf life at refrigerated temperatures (4 °C). Based on our studies, 22-ppm lauric arginate (LAE, ethyl-N-dodecanoyl-L-arginate hydrochloride) gave more than a 1-log reduction of Lm surface inoculated onto frankfurters within 12 h. The combination of either 1.8%/0.13% or 2.1%/0.15% potassium lactate/sodium diacetate (L/D) in combination with 22 ppm LAE caused more than a 2-log reduction at 12 h. Storage studies revealed that complementary interactions of L/D and LAE also met the 2nd requirement. This combination initially reduced Lm by 2 logs and suppressed growth to less than 2 logs even at the end of the 156-d storage life for frankfurters. These results confirmed that the combination of L/D with LAE as a postprocessing–prepackaging application could be useful in complying with the USDA's Alternative 1 that requires validation for the control of Lm on RTE frankfurters.     

Use of vacuum-steam-vacuum and ionizing radiation to eliminate Listeria innocua from ham

Listeria spp. are a frequent postprocess contaminant of ready-to-eat (RTE) meat products, including ham. Vacuum-steam-vacuum (VSV) technology has been used successfully to eliminate Listeria innocua from hot dogs. Ionizing radiation can eliminate Listeria spp. from RTE meats. However, the excessive application of either technology can cause changes in product quality, including structural changes, changes in cure color (redness), and lipid oxidation. In this study, two cycles of VSV were combined with 2.0 kGy of ionizing radiation to obtain 4.40- and 4.85-log10 reductions of L. innocua on ham meat and skin, respectively. The use of both treatments resulted in an additive, as opposed to synergistic, reduction of L. innocua on ham. The combination treatment did not cause statistically significant changes in product structure, color (redness), or lipid oxidation.     

Impact of dilution ratios on Listeria monocytogenes growth during University of Vermont medium enrichment of deli meats

In the U.S. Department of Agriculture (USDA) method for Listeria detection, a 25-g composite food sample is enriched in 225 ml of University of Vermont medium (UVM), giving a detection limit of 0.04 CFU/g. However, in a recent large-scale four-state deli meat survey for L. monocytogenes, 125-g samples enriched in 1,125 ml of UVM were requested to increase the detection limit to 0.008 CFU/g. To circumvent problems associated with large volumes of UVM, the impact on L. monocytogenes growth of lower dilution ratios used for enrichment and most-probable-number (MPN) detection was compared with the results obtained using the conventional 1:10 dilution. In this study, 125-g samples of cured turkey, uncured turkey, ham, and roast beef were inoculated with a six-strain L. monocytogenes cocktail to contain approximately 1 x 10(3) CFU/g. This cocktail was then diluted 1:3, 1:5, or 1:10 in UVM, homogenized, enriched at 30 degrees C, and periodically plated on modified Oxford agar to determine generation times during 24 h of incubation. The same enrichment protocol was also assessed in a three-tube MPN assay using 125-g samples inoculated with L. monocytogenes to contain approximately 1 CFU/g. The effects of two homogenization methods, stomaching and pulsifying, on Listeria growth were compared using oven-roasted turkey breast diluted 1:3, 1:5, and 1:10 in UVM. Overall, the growth rates, generation times, and MPN values for each of the four selected deli meats were similar (P > 0.05) using UVM enrichment ratios of 1:3, 1:5, and 1:10, with no significant (P > 0.05) differences in L. monocytogenes growth rate or generation time between experiments using pulsifying and stomaching. These findings indicate that lower volumes of UVM can be used in the USDA procedure when examining deli meats without compromising Listeria recovery.     

Survival and recovery of Listeria monocytogenes on ready-to-eat meats inoculated with a desiccated and nutritionally depleted dustlike vector

Dust from construction was theorized to serve as a vector for L. monocytogenes transmission to ready-to-eat (RTE) meats after heat processing but before packaging. A five-strain Listeria monocytogenes culture including serotype 4b was continually stressed on a sand vector under four sets of nutritionally depleted and dry conditions to simulate postprocessing contamination by dustlike particulates. The stresses included that associated with sand stored at different temperatures (10 and 22 degrees C) and levels of humidity (40% relative humidity [RH], 88% RH, or complete desiccation). Irradiated RTE meats, including frankfurters, bologna, chopped ham, and deli-style roast beef, were inoculated with the L. monocytogenes-contaminated sand every 2 to 3 days over a period of 1 1/2 months. After inoculation, the RTE meats were vacuum packed and stored at 4 degrees C for 24 h. Populations of L. monocytogenes were enumerated by surface plating on nonselective and selective media to recover cells on the basis of the different stresses presented (osmotic or antibiotic). L. monocytogenes was demonstrated to be capable of surviving on the sand vector for > 151 days at 10 degrees C and 88% RH, 136 days at 10 degrees C and 0% RH, 73 days at 22 degrees C and 40% RH, and 82 days at 22 degrees C and 0% RH. These results show that under the most conservative scenario, the 73-day-old L. monocytogenes-contaminated sand was able to attach to and be recovered from the RTE meats. This study illustrated that dust contaminated with L. monocytogenes, once in contact with meat surfaces, can survive and grow, posing a health hazard to consumers.     

Hot water postprocess pasteurization of cook-in-bag turkey breast treated with and without potassium lactate and sodium diacetate and acidified sodium chlorite for control of Listeria monocytogenes

Surface pasteurization and food-grade chemicals were evaluated for the ability to control listeriae postprocess on cook-in-bag turkey breasts (CIBTB). Individual CIBTB were obtained directly from a commercial manufacturer and surface inoculated (20 ml) with a five-strain cocktail (ca. 7.0 log) of Listeria innocua. In each of two trials, the product was showered or submerged for up to 9 min with water heated to 190, 197, or 205 degrees F (ca. 87.8, 91.7, or 96.1 degrees C) in a commercial pasteurization tunnel. Surviving listeriae were recovered from CIBTB by rinsing and were then enumerated on modified Oxford agar plates following incubation at 37 degrees C for 48 h. As expected, higher water temperatures and longer residence times resulted in a greater reduction of L. innocua. A ca. 2.0-log reduction was achieved within 3 min at 205 and 197 degrees F and within 7 min at 190 degrees E In related experiments, the following treatments were evaluated for control of Listeria monocytogenes on CIBTB: (i) a potassium lactate-sodium diacetate solution (1.54% potassium lactate and 0.11% sodium diacetate) added to the formulation in the mixer and 150 ppm of acidified sodium chlorite applied to the surface with a pipette, or (ii) a potassium lactate-sodium diacetate solution only, or (iii) no potassium lactate-sodium diacetate solution and no acidified sodium chlorite. Each CIBTB was inoculated (20 ml) with ca. 5 log CFU of a five-strain mixture of L. monocytogenes and then vacuum sealed. In each of two trials, half of the CIBTB were exposed to 203 degrees F water for 3 min in a pasteurization tunnel, and the other half of the CIBTB were not; then, all CIBTB were stored at 4 degrees C for up to 60 days, and L. monocytogenes was enumerated by direct plating onto modified Oxford agar. Heating resulted in an initial reduction of ca. 2 log CFU of L. monocytogenes per CIBTB. For heated CIBTB, L. monocytogenes increased by ca. 2 log CFU per CIBTB in 28 (treatment 1), 28 (treatment 2), and 14 (treatment 3) days. Thereafter, pathogen levels reached ca. 7 log CFU per CIBTB in 45, 45, and 21 days for treatments 1, 2, and 3, respectively. In contrast, for nonheated CIBTB, L. monocytogenes levels increased from ca. 5 log CFU per CIBTB to ca. 7 log CFU per CIBTB in 28, 21, and 14 days for treatments 1, 2, and 3, respectively. Lastly, in each of three trials, we tested the effect of hot water (203 degrees F for 3 min) postprocess pasteurization of inoculated CIBTB on the lethality of L. monocytogenes and validated that it resulted in a 1.8-log reduction in pathogen levels. Collectively, these data establish that hot water postprocess pasteurization alone is effective in reducing L. monocytogenes on the surface of CIBTB. However, as used in this study, the potassium lactate-sodium diacetate solution and acidified sodium chlorite were only somewhat effective at controlling the subsequent outgrowth of this pathogen during refrigerated storage.     

Effects of high-pressure processing on the safety, quality, and shelf life of ready-to-eat meats

Ready-to-eat (RTE) meats (low-fat pastrami, Strassburg beef, export sausage, and Cajun beef) were pressure treated at 600 MPa, 20 degrees C, for 180 s to evaluate the feasibility of using high-pressure processing (HPP) for the safe shelf-life extension of these products. After processing, samples were stored at 4 degrees C for 98 days during which time microbiological enumeration and enrichments were performed. Additionally, sensory analyses were undertaken to determine consumer acceptability and purchase intent over the duration of storage. Counts of aerobic and anaerobic mesophiles, lactic acid bacteria, Listeria spp., staphylococci, Brochothrix thermosphacta, coliforms, and yeasts and molds revealed that there were undetectable or low levels for all types of microorganisms throughout storage. Comparison of consumer hedonic ratings for unprocessed and processed meats revealed no difference in consumer acceptability, and no deterioration in the sensory quality was evident for any of the products tested during the study. Additionally, inoculated pack studies were conducted to determine if HPP could be used as a postlethality treatment to reduce or eliminate Listeria monocytogenes and thus assess the potential use of HPP in a hazard analysis critical control point plan for production of RTE meats. Inoculated samples (initial level of 10(4) CFU/g) were pressure treated (600 MPa, 20 degrees C, for 180 s) and stored at 4 degrees C, and survival of L. monocytogenes was monitored for 91 days. L. monocytogenes was not detected by plating methods until day 91, but selective enrichments showed sporadic recovery in three of the four products examined. The results show that HPP at 600 MPa, 20 degrees C, for 180 s can extend the refrigerated shelf life of RTE meats and reduce L. monocytogenes numbers by more than 4 log CFU/g in inoculated product.     

Determination of thermal lethality of Listeria monocytogenes in fully cooked chicken breast fillets and strips during postcook in-package pasteurization

Fully cooked chicken breast fillets and strips were surface inoculated with a cocktail of Listeria monocytogenes culture. The inoculation level was 10(7) to 10(8) CFU/g meat. The inoculated products were vacuum packaged and pasteurized at 90 degrees C with a pilot-scale steam or hot water cooker. After heat treatment, the survivors of L. monocytogenes were enumerated. No significant difference was found on survivors of L. monocytogenes between steam- and hot water-treated products. To achieve a 7-log10 (CFU/g) reduction, approximately 5, 25, and 35 min were needed for single-packaged fillets, 227-g package strips, and 454-g strips, respectively. The results from this study were subsequently verified by a computer model that could predict the thermal lethality of pathogens in fully cooked meat and poultry products during postcook in-package pasteurization.     

Control of Listeria monocytogenes with combined antimicrobials on beef franks stored at 4 degrees C

Contamination of ready-to-eat meat products such as beef franks with Listeria monocytogenes has become a major concern for the meat processing industry and an important food safety issue. The objective of this study was to determine the effectiveness of combinations of antimicrobials as aqueous dipping solutions to control L. monocytogenes on vacuum-packaged beef franks stored at 4 degrees C for 3 weeks. Commercial beef franks were dipped for 5 min in three antimicrobial solutions: pediocin (6,000 AU), 3% sodium diacetate and 6% sodium lactate combined, and a combination of the three antimicrobials. Samples were then inoculated with 10(7) CFU/g of either four L. monocytogenes strains individually or a cocktail of the four strains, vacuum packaged, and stored at 4 degrees C for 3 weeks. Sampling was carried out at day 0 and after 2 and 3 weeks of storage. Individual strains, as well as the cocktail, exhibited different responses to the antimicrobial treatments. After 2 and 3 weeks of storage at 4 degrees C, pediocin-treated beef franks showed a less than 1-log reduction for all bacterial strains. Samples treated with the sodium diacetate-sodium lactate combination showed about a 1-log reduction after 2 weeks of storage for all strains and between a 1- and 2-log reduction after 3 weeks of storage, depending on the bacterial strain. When the three antimicrobials were combined, reductions ranged between 1 and 1.5 log units and 1.5 to 2.5 log units after 2 and 3 weeks of storage, respectively, at 4 degrees C. These results indicate that the use of combined antimicrobial solutions for dipping treatments is more effective at inhibiting L. monocytogenes than treatments using antimicrobials such as pediocin separately.     

Combining organic acid treatment with steam pasteurization to eliminate Listeria monocytogenes on fully cooked frankfurters

An organic acid solution of 2% acetic, 1% lactic, 0.1% propionic, and 0.1% benzoic acids was combined with steam surface pasteurization to treat frankfurters during vacuum packaging to eliminate potential postcook contamination with Listeria monocytogenes. The thermal lethality of L. monocytogenes from steam was evaluated at an inoculation concentration of 1 to 6 log CFU/cm2. About 3-log reductions of L. monocytogenes were achieved when frankfurters were treated by steam for 1.5 s. Combining organic acid treatment with steam pasteurization further inhibited the growth of surviving L. monocytogenes cells for 19 and 14 weeks when the packaged frankfurters were stored at 4 and 7 degrees C, respectively. The results from this study provide meat processors with useful information for controlling L. monocytogenes on ready-to-eat meats.     

Technologies and Mechanisms for Safety Control of Ready-to-eat Muscle Foods: An Updated Review

Ready-to-eat (RTE) muscle foods refer to a general category of meat and poultry products that are fully cooked and consumable without reheating. These products, including whole and sliced pork, beef, turkey, chicken, and variety of meats, in the forms of ham, roast, rolls, sausage, and frankfurter, are widely available in the delicatessen section of retail stores or various food service outlets. However, difficulties in avoidance of contamination by foodborne pathogens, notably Listeria monocytogenes, during product postlethality repackaging render RTE meats labile to outbreaks. Accordingly, the USDA-FSIS has established processing guidelines and regulations, which are constantly updated, to minimize foodborne pathogens in RTE products. Technologies that complement good manufacturing practice have been developed to control RTE meat safety. Among them, various antimicrobial product formulations, postpackaging pasteurization (thermal and nonthermal), and antimicrobial packaging are being used. Through these efforts, outbreaks linked to RTE meat consumption have substantially reduced in recent years. However, the pervasive and virulent nature of L. monocytogenes and the possible presence of other cold-tolerant pathogens entail continuing developments of new intervention technologies. This review updates existing and emerging physical and chemical methods and their mode of action to inactivate or inhibit threatening microorganisms in RTE muscle foods.     

Cross-contamination between processing equipment and deli meats by Listeria monocytogenes

Contamination of luncheon meats by Listeria monocytogenes has resulted in outbreaks of listeriosis and major product recalls. Listeriae can survive on processing equipment such as meat slicers which serve as a potential contamination source. This study was conducted to determine (i) the dynamics of cross-contamination of L. monocytogenes from a commercial slicer and associated equipment onto sliced meat products, (ii) the influence of sample size on the efficacy of the BAX-PCR and U.S. Department of Agriculture-Food Safety and Inspection Service enrichment culture assays to detect L. monocytogenes on deli meat, and (iii) the fate of L. monocytogenes on sliced deli meats of different types during refrigerated storage. Three types of deli meats, uncured oven-roasted turkey, salami, and bologna containing sodium diacetate and potassium lactate, were tested. A five-strain mixture of L. monocytogenes was inoculated at ca.10(3) CFU onto the blade of a commercial slicer. Five consecutive meat slices were packed per package, then vacuum sealed, stored at 4 degrees C, and sampled at 1 and 30 days postslicing. Two sample sizes, 25 g and contents of the entire package of meat, were assayed. Total numbers of L. monocytogenes-positive samples, including the two sample sizes and two sampling times, were 80, 9, and 3 for turkey, salami, and bologna, respectively. A higher percentage of turkey meat samples were L. monocytogenes positive when contents of the entire package were assayed than when the 25-g sample was assayed (12.5 and 7.5%, respectively). Lower inoculum populations of ca. 10(1) or 10(2) CFU of L. monocytogenes on the slicer blade were used for an additional evaluation of oven-roasted turkey using two additional sampling times of 60 and 90 days postslicing. L. monocytogenes-positive samples were not detected until 60 days postslicing, and more positive samples were detected at 90 days than at 60 days postslicing. When BAX-PCR and enrichment culture assays were compared, 12, 8, and 2 L. monocytogenes-positive samples were detected by both the enrichment culture and BAX-PCR, BAX-PCR only, and enrichment culture only assays, respectively. The number of L. monocytogenes-positive samples and L. monocytogenes counts increased during storage of turkey meat but decreased for salami and bologna. Significantly more turkey samples were L. monocytogenes positive when the contents of the entire package were sampled than when 25 g was sampled. Our results indicate that L. monocytogenes can be transferred from a contaminated slicer onto meats and can survive or grow better on uncured oven-roasted turkey than on salami or bologna with preservatives. Higher L. monocytogenes cell numbers inoculated on the slicer blade resulted in more L. monocytogenes-positive sliced meat samples. In addition, the BAX-PCR assay was better than the enrichment culture assay at detecting L. monocytogenes on turkey meat (P < 0.05).     

Use of octanoic acid as a postlethality treatment to reduce Listeria monocytogenes on ready-to-eat meat and poultry products

The antilisterial efficacy and organoleptic impact of an octanoic acid (OA)-based treatment for ready-to-eat (RTE) meat and poultry products were investigated. Whole-muscle and comminuted RTE products were inoculated with a five-strain mixture of Listeria monocytogenes. The OA treatments were applied to the surface of RTE products by dispensing a specific volume of solution directly into the final package prior to vacuum sealing. Once sealed, the vacuum-packaged RTE products containing OA were immersed in water heated to 93.3 degrees C (200 degrees F) for 2 s to effect adequate film shrinkage. Extending the time at which the packaged, treated RTE products were exposed to water heated to 93.3 degrees C was also evaluated with a commercial cascading shrink tunnel fitted with a modified drip pan. Once treated, RTE products were examined for survivor populations of L. monocytogenes after 24 h of storage at 5 degrees C. Sensory evaluation was conducted with a 60-member trained panel on 11 uninoculated, treated RTE products. The OA treatment of RTE products reduced L. monocytogenes numbers to between 0.85 log CFU per sample (oil-browned turkey) and 2.89 log CFU per sample (cured ham) when compared with controls. The antilisterial activity of OA was improved by increasing the duration of the heat shrink exposure. Specifically, reductions of L. monocytogenes ranged from 1.46 log CFU per sample (oil-browned turkey) to 3.34 log CFU per sample (cured ham). Results from the sensory evaluation demonstrated that 10 of the 11 treated RTE products were not perceived as different (P < or = 0.05) from the untreated controls. Panelists detected reduced (P < or = 0.05) smoke flavor intensity with treated mesquite turkey, although the treated product was viewed as acceptable. Results demonstrate the effectiveness of OA as a postlethality treatment meeting U.S. Food Safety and Inspection Service regulatory guidelines for RTE meat and poultry products with minimal impact on sensory quality.