Radiation (gamma) resistance and postirradiation growth of Listeria monocytogenes suspended in beef bologna containing sodium diacetate and potassium lactate

Listeria monocytogenes, a psychrotrophic foodborne pathogen, is a frequent postprocessing contaminant of ready-to-eat (RTE) meat products, including frankfurters and bologna. Ionizing radiation can eliminate L. monocytogenes from RTE meats. When they are incorporated into fine-emulsion sausages, sodium diacetate (SDA) and potassium lactate (PL) mixtures inhibit the growth of L. monocytogenes. The radiation resistance of L. monocytogenes, and its ability to proliferate during long-term refrigerated storage (9 degrees C), when inoculated into beef bologna that contained 0% SDA-0% PL, 0.07% SDA-1% PL, and 0.15% SDA-2% PL, were determined. The radiation doses required to eliminate 90% of the viable L. monocytogenes cells were 0.56 kGy for bologna containing 0% SDA-0% PL, 0.53 kGy for bologna containing 0.07% SDA-1% PL, and 0.46 kGy for bologna containing 0.15% SDA-2% PL. L. monocytogenes was able to proliferate on bologna containing 0% SDA-0% PL during refrigerated storage, but the onset of proliferation was delayed by the addition of the SDA-PL mixtures. An ionizing radiation dose of 3.0 kGy prevented the proliferation of L. monocytogenes and background microflora in bologna containing 0.07% SDA-1% PL and in bologna containing 0.15% SDA-2% PL over 8 weeks of storage at 9 degrees C. Little effect on lipid oxidation and color of the control bologna, or bologna containing SDA-PL mixtures, was observed upon irradiation at either 1.5 or 3.0 kGy.     

EFFECT OF IONIZING RADIATION ON BEEF BOLOGNA CONTAINING SOY PROTEIN CONCENTRATE

Soy protein concentrate (SPC), an extender, is a common additive in ready-to-eat (RTE) meat products. SPC contains antioxidants that could potentially interfere with the ability of ionizing radiation to eliminate Listeria monocytogenes from RTE meat products. When L. monocytogenes was inoculated into cooked beef bologna emulsion containing 0, 1.75, or 3.5% SPC the gamma radiation D₁₀ values, at radiation doses of 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 kGy, were 0.66, 0.68, and 0.71kGy, respectively. Soluble antioxidant power, as determined by the Ferric Reducing Antioxidant Power (FRAP) assay was 1958, 3572, and 5494 mol in bologna emulsion containing 0, 1.75 and 3.5% SPC, respectively. Soluble antioxidant power was not affected by ionizing radiation. SPC did not prevent ionizing radiation induced lipid oxidation as determined by Thiobarbituric Acid Reactive Substance (TBARS) assay. Hunter color analysis of both unirradiated and irradiated bologna slices containing SPC indicated decreased a value as a result of irradiation, while the addition of SPC helped maintain b-value and L-value. The inclusion of SPC did not represent a barrier to ionizing radiation pasteurization of fine emulsion sausages for the parameters examined.     

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.     

Radiation Resistance of Listeria monocytogenes in the Presence or Absence of Sodium Erythorbate

ABSTRACT: Listeria monocytogenes is a common contaminant of ready-to-eat meat products that can be eliminated by low dose ionizing radiation. Sodium erythorbate (SE), an antioxidant, is commonly included in cured meat emulsions or applied to the surfaces of cured meats as a solution prior to packaging. The radiation resistance (D_γ) of L. monocytogenes increased when suspended in SE solutions of 0.1% and greater. However, no differences in D_γ, which ranged from 0.67 kGy to 0.70 kGy, were observed when L. monocytogenes was inoculated onto cooked cured meat products (frankfurters or bologna slices) which contained no SE, 0.05% SE in the emulsion, or a 10% SE solution applied to the product surface. Surface antioxidant power of the cured meats did not reach a level sufficient to protect L. monocytogenes against the lethal effects of ionizing radiation. Therefore, the industrial practice of applying SE to the surfaces of cured meat products would not compromise the efficacy of irradiation as an antimicrobial process.     

Antioxidant power,lipid oxidation,color, and viability of Listeria monocytogenes in beef bologna treated with gamma radiation and containing various levels of glucose

Ionizing radiation can be used to pasteurize ready-to-eat (RTE) meat products. Thermal processing of RTE meats that contain dextrose results in the production of antioxidants that may interfere with ionizing radiation pasteurization of RTE meat products. Beef bologna was manufactured with dextrose concentrations of 0, 2, 4, 6, and 8%. Antioxidant activity, as measured by the Ferric Reducing Antioxidant Power assay, increased with dextrose concentration but was unaffected by ionizing radiation. Lipid oxidation increased significantly in irradiated bologna (4 kGy) that contained dextrose. Hunter color analysis indicated that the addition of dextrose reduced the ionizing radiation-induced loss of redness (a-value) but promoted the loss of brightness (L-value). The radiation resistance, D10-value, of Listeria monocytogenes that was surface-inoculated onto bologna slices was not affected by dextrose concentration. L. monocytogenes strains isolated from RTE meats after listeriosis outbreaks were utilized. Increased antioxidant activity generated by thermal processing of dextrose in fine emulsion sausages does not present a barrier to radiation pasteurization of RTE meats. However, a high dextrose concentration in combination with gamma irradiation increases lipid oxidation significantly.     

Inactivation of avirulent Yersinia pestis in beef bologna by gamma irradiation

Yersinia pestis, a psychrotrophic pathogen capable of growth at refrigeration temperatures, can cause pharyngeal and gastrointestinal plague in humans that consume contaminated foods. Because Y. pestis is listed as a select agent for food safety and defense, evaluation of food safety intervention technologies for inactivation of this pathogen is needed. Ionizing (gamma) radiation is a safe and effective intervention technology that can inactivate pathogens in raw and processed meats, produce, and seafood. In this study, we investigated the effect of temperature on the ability of ionizing radiation to inactivate avirulent Y. pestis in beef bologna. The mean (±standard error of the mean) radiation D(10)-values (the radiation dose needed to inactivate 1 log unit or 90% of the population of a microorganism) for avirulent Y. pestis suspended in beef bologna samples were 0.20 (±0.01), 0.22 (±0.01), 0.25 (±0.02), 0.31 (±0.01), 0.35 (±0.01), and 0.37 (±0.01) kGy at temperatures of 5, 0, -5, -10, -15, and -20°C, respectively. When incorporated into a three-dimensional mesh, the predictive model followed a parabolic fit (R(2) = 0.84), where the log reduction = -0.264 - (0.039 × temp) - (3.833 × dose) - (0.0013 × temp(2)) - (0.728 × dose(2)). These results indicate that ionizing radiation would be an effective technology for control of Y. pestis in ready-to-eat fine emulsion sausage products.     

Effect of citric acid on the radiation resistance of Listeria monocytogenes and frankfurter quality factors

Listeria monocytogenes is a common contaminant of ready-to-eat meat products, including frankfurters. Ionizing (gamma) radiation can eliminate L. monocytogenes from frankfurters. Citric acid (CA) is an antioxidant synergist and anti-microbial agent that can be applied to the surfaces of cured meat products prior to packaging. The effect of CA on the radiation resistance of L. monocytogenes that was surface-inoculated onto frankfurters was determined. The D(10) values, the radiation doses required to inactivate 90% of viable L. monocytogenes, were 0.61, 0.60, 0.54, and 0.53 kGy, on frankfurters dipped in 0, 1, 5 or 10% CA solution, respectively. CA, although an antioxidant synergist, did not increase antioxidant activity (AA) on frankfurter surfaces as determined by the ferric reducing antioxidant power (FRAP) assay. Lipid oxidation, as determined by the Thiobarbituric acid reactive substances (TBARS) assay, was not affected by CA or ionizing radiation. Color of frankfurters, determined by Hunter L, a, b, indicated that ionizing radiation induced a small, but visually imperceptible, loss of redness (a-value). Frankfurter firmness, as measured by maximum shear force, was not affected by ionizing radiation or CA. CA enhanced the lethality of ionizing radiation without negatively impacting frankfurter color, lipid oxidation, firmness, or antioxidant activity.     

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 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.     

Inactivation of Listeria innocua on frankfurters that contain potassium lactate and sodium diacetate by flash pasteurization

ABSTRACT:  Listeria monocytogenes , a psychrotrophic foodborne pathogen, is a recurring postprocess contaminant on ready-to-eat meat (RTE) products, including frankfurters. Potassium lactate (PL) and sodium diacetate (SDA) are FDA-approved antimicrobials that inhibit the growth of L. monocytogenes when incorporated into the formulation of fine emulsion sausage. Flash (steam) pasteurization (FP) has been shown to reduce levels of L. monocytogenes , and its surrogate L. innocua , on frankfurter surfaces. The ability of FP to inactivate and prevent the growth of the L. monocytogenes surrogate L. innocua in a pilot plant setting was investigated. FP treatment (1.5 s, 121 °C) of single layers of frankfurters that were surface-inoculated with either 5, 4, or 3 log CFU/g of L. innocua immediately before FP (1.5 s, 121 °C) resulted in log reductions of 1.97 (± 0.11), 2.03 (± 0.10), or 2.07 (± 0.14), respectively. Inoculum level had no effect on the inactivation of L. innocua . Following 8 wk of refrigerated storage (4 °C), L. innocua levels decreased by 0.5 log in non-FP-treated frankfurter packs, while the 2 log reduction of L. innocua was maintained for FP-treated frankfurters. FP (1.5 s, 121 °C) had no effect on frankfurter color or texture. Because the numbers of L. monocytogenes associated with contaminations of ready-to-eat meats are typically very low, the use of FP in combination with PL and SDA has the potential to reduce the number of frankfurter recalls and foodborne illness outbreaks.     

Control of Listeria monocytogenes in ready-to-eat meats containing sodium levulinate, sodium lactate, or a combination of sodium lactate and sodium diacetate

ABSTRACT:  This study investigated the use of sodium levulinate to prevent outgrowth of Listeria monocytogenes in refrigerated ready-to-eat (RTE) meat products. Turkey breast roll and bologna were formulated to contain 1%, 2%, or 3% (w/w) sodium levulinate, 2% sodium lactate, a 2% combination of sodium lactate and sodium diacetate (1.875% sodium lactate and 0.125% sodium diacetate), or no antimicrobial (control). Samples of the RTE products were sliced, inoculated with 10² to 10³ CFU/cm² of a 5-strain cocktail of L. monocytogenes , vacuum packaged, and stored at refrigeration temperature for 0 to 12 wk. Counts reached 10⁸ CFU/cm² on control turkey roll product after 8 wk, and over 10⁷ CFU/cm² on control bologna after 12 wk. Addition of 2% or more sodium levulinate to turkey roll and 1% or more sodium levulinate to bologna completely prevented growth of L. monocytogenes during 12 wk of refrigerated storage. A consumer taste panel with pathogen-free samples found no differences in the overall liking among the preparations of turkey roll or among preparations of bologna. These results show that sodium levulinate is at least as effective at inhibiting outgrowth of L. monocytogenes in RTE meat products as the current industry standards of lactate or lactate and diacetate, and levulinate addition does not alter the overall liking of the RTE meat products.     

Inhibition of Listeria monocytogenes using nisin with grape seed extract on turkey frankfurters stored at 4 and 10 degrees C

Recontamination of cooked ready-to-eat (RTE) chicken and beef products with Listeria monocytogenes has been a major safety concern. Natural antimicrobials in combinations can be an alternative approach for controlling L. monocytogenes. Therefore, the objectives of this study were to evaluate the inhibitory activities against L. monocytogenes of nisin (6,400 IU/ ml), grape seed extract (GSE; 1%), and the combination of nisin and GSE both in tryptic soy broth with 0.6% yeast extract (TSBYE) and on the surface of full-fat turkey frankfurters. TSBYE was incubated at 37 degrees C for 72 h and turkey frankfurters at 4 or 10'C for 28 days. Inocula were 6.7 or 5 log CFU per ml or g for TSBYE or frankfurters, respectively. After 72 h in TSBYE, nisin alone did not show any inhibitory activity against L. monocytogenes. The combination of nisin and GSE gave the greatest inhibitory activity in both TSBYE and on turkey frankfurters with reductions of L. monocytogenes populations to undetectable levels after 15 h and 21 days, respectively. This combination of two natural antimicrobials has the potential to control the growth and recontamination of L. monocytogenes on RTE meat products.     

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.     

Radiation sensitivity and postirradiation growth of foodborne pathogens on a ready-to-eat frankfurter on a roll product in the presence of modified atmosphere and antimicrobials

Intervention technologies including ionizing radiation, antimicrobials, and modified atmospheres (MA) can be used to inhibit the growth of or inactivate foodborne pathogens on complex ready-to-eat foods such as sandwiches. However, the effect of these technologies when used in combination (the hurdle concept) on the survival of foodborne pathogens is unknown. The ability of ionizing radiation to inactivate Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus inoculated onto a frankfurter on a roll product containing the antimicrobials sodium diacetate and potassium lactate in the presence of an MA (100% N2, 50% N2 plus 50% CO2, or 100% CO2) was investigated. The radiation resistances (D10-values) of the foodborne pathogens were 0.43 to 0.47 kGy for E. coli O157:H7, 0.61 to 0.71 kGy for Salmonella, 0.53 to 0.57 for L. monocytogenes, and 0.56 to 0.60 for S. aureus. The MA had no effect on the radiation resistance of the pathogens. During a 2-week storage period under mild temperature abuse (10 degrees C), none of the pathogens were able to proliferate on the frankfurter on a roll product, regardless of the MA used. However, application of sublethal doses of ionizing radiation resulted in increased mortality of the gram-positive pathogens L. monocytogenes and S. aureus during the storage period regardless of the MA. Although the pathogens were unable to proliferate on the frankfurter on a roll product during the storage period, application of a postpackaging intervention step was needed to actually inactivate the foodborne pathogens. Ionizing radiation used in combination with sodium diacetate and potassium lactate resulted in additional mortality of L. monocytogenes and S. aureus, independent of the MA, during the 2-week storage period.     

Impact of nitrite on detection of Listeria monocytogenes in selected ready-to-eat (RTE) meat and seafood products

ABSTRACT:  The impact of sodium nitrite (NaNO₂) on detection and recovery of Listeria monocytogenes from select ready-to-eat (RTE) foods including smoked salmon, smoked ham, beef frankfurters, and beef bologna was assessed. Nitrite-containing (NC; 100 to 200 ppm NaNO₂) or nitrite-free (NF) foods were inoculated with a 5-strain cocktail of L. monocytogenes by immersion into Butterfield's buffer solution containing 5.4 to 7.4 × 10³ L. monocytogenes per milliliter. Inoculated products were vacuum-packaged and stored at 5 °C. A weekly comparative analysis was performed for presence of L. monocytogenes using 5 detection methods on products held at 5 °C for up to 8 wk. L. monocytogenes initially present at <100 CFU/g during the first 2 wk of storage increased throughout the study, attaining final populations of approximately 1 × 10⁴ to 1 × 10⁵ CFU/g. Lactic acid bacteria predominated throughout the study in all products. Exposure to NaNO₂ (100 to 200 ppm) resulted in 83% to 99% injury to the L. monocytogenes strains tested. The genetic-based BAX^® System (DuPont™ Qualicon, Wilmington, Del., U.S.A.) and modified USDA/FSIS methods detected 98% to 100% of Listeria -positive food samples and were consistently superior to and significantly different ( P < 0.05) from conventional cultural methods in recovering Listeria from NC samples. Data show that nitrite-induced injury adversely affects detection and recovery of L. monocytogenes from NC food, confirming earlier findings that nitrite-induced injury masks L. monocytogenes detection in NC RTE food products. Nitrite-injured Listeria can subsequently repair upon nitrite depletion and grow to high levels over extended refrigerated storage.     

SURVIVAL OF SURFACE‐INOCULATED LISTERIA MONOCYTOGENES ON COMMERCIALLY AVAILABLE FRANKFURTERS FOLLOWING GAMMA IRRADIATION1

Frankfurter is a generic term for a cured and cooked sausage, which may consist of almost any meat type and include a wide variety of nonmeat fillers and additives. When several “brands” or types of commercially available frankfurters were surface‐inoculated with Listeria monocytogenes and vacuum‐packed, gamma radiation D‐values ranged from 0.49 kGy to 0.71 kGy, with an average D‐value of 0.61 kGy. Differences in gamma radiation D‐value were observed for nine of twenty one pair‐wise comparisons (α= 0.01) as determined by analysis of covariance. Therefore, frankfurter formulation may affect radiation D‐values for surface inoculated L. monocytogenes. If low dose gamma irradiation, cold pasteurization, were to be used for control of L. monocytogenes on frankfurters, gamma radiation dosage should be based on individual product formulation.     

Effects of Calcium Ascorbate and Ionizing Radiation on the Survival of Listeria monocytogenes and Product Quality of Fresh-cut 'Gala' Apples

The interactive effects of calcium ascorbate (CaA) and ionizing radiation on viability of Listeria monocytogenes inoculated in solutions and on ‘Gala’ apple slices were investigated. The D10 values (radiation doses that inactivate 90% of bacterial population) for L. monocytogenes inoculated in water, 3.5%, and 7.0% CaA solutions were 0.32, 0.61, and 0.58 kGy, respectively. The D₁₀ values of the pathogen on the surface of apple slices treated with water, 3.5%, and 7.0% CaA were 0.24, 0.32, and 0.32 kGy, respectively. To determine the impact of CaA and irradiation on quality of apple slices, apple slices treated with 0%, 3.5%, and 7.0% CaA were exposed to 1.6 kGy gamma radiation (a dose that produced a 5‐log reduction of L. monocytogenes) and stored under modified atmosphere at 4 °C for 14 d. CaA at levels of both 3.5% and 7.0% prevented the browning of the apple slices. The apple aroma intensity, however, decreased as the concentration of CaA increased. Irradiation at 1.6 kGy did not significantly affect color, soluble solid content, titratable acidity, or apple aroma intensity. The only negative effect of irradiation on apple slices appeared to be a loss of firmness. Our results suggest that CaA, used as an antibrowning agent, protected L. monocytogenes from radiation both in solution and on apple slices, but radiation at doses sufficient to inactivate 5‐log of the bacterium did not significantly influence product quality attributes except for the loss in firmness.     

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.     

Inactivation of Listeria innocua on Frankfurters by Ultraviolet Light and Flash Pasteurization

ABSTRACT:  Listeria monocytogenes , a psychrotrophic foodborne pathogen, is a recurring postprocess contaminant on ready-to-eat meat (RTE) products including frankfurters. Flash (Steam) Pasteurization (FP) and ultraviolet light (254 nm-UVC) has been shown to reduce levels of L. monocytogenes and L. innocua on frankfurters. In this study, the use of UVC light followed by FP to inactivate L. innocua, a nonpathogenic surrogate for L.monocytogenes , on frankfurters that contained sodium diacetate and potassium lactate (SDA/PL) in a pilot-plant setting was investigated. Application of UVC (1.0 J/cm²), followed by FP (0.75 s steam/121 °C) resulted in inactivation of 3.19 log L. innocua , while application of UVC (4.0 J/cm²), followed by FP (3 s steam/121 °C) resulted in inactivation of 3.89 log of L. innocua . A refrigerated storage study (8 °C) of frankfurters that contained SDA/PL that were treated with UVC followed by FP revealed the growth of L. innocua was inhibited for approximately 8 wk following application of the interventions. The use of UVC in combination with FP had little effect on frankfurter color and texture. The combination of UVC, FP, and SDA/PL was found to be an effective hurdle process for decontamination of frankfurter surfaces.     

Effect of Gamma Radiation on Furan Formation in Ready-to-Eat Products and their Ingredients

ABSTRACT:  Besides meat as the major component, ready-to-eat (RTE) meat and poultry products often contain ingredients such as Na-ascorbate, Na-erythorbate, glucose, honey, corn syrup, and Na-nitrite. Furan is a potential carcinogen and information is needed on its formation in irradiated RTE products. In the present study, we investigated the generation of irradiation-induced furan in aqueous solutions of those ingredients, and in 9 RTE food products (8 meat and poultry-based and 1 vegetable burger). Irradiation at doses up to 4.5 kGy induced formation of furan in aqueous solutions of Na-ascorbate, Na-erythorbate, glucose, honey, and corn syrup. Addition of Na-nitrite into these solutions prior to irradiation completely eliminated, or significantly reduced, furan formation. Most of the nonirradiated RTE products contained less than 1 ng/g of furan, except for beef and turkey frankfurters which contained 6 to 8 ng/g furan. Exposure of RTE food products to 4.5 kGy radiation in the nonfrozen state (5 °C) or to 10 kGy radiation in the frozen state (−18 °C) did not significantly increase furan levels in most of the samples. Furthermore, the irradiation treatments reduced furan levels in samples (that is, frankfurters) that contained more than 3 ng/g of furan. Our results suggested that irradiation induces furan formation in solutions of many RTE food ingredients, but not in RTE meat and poultry products themselves.