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.     

Application of predictive models to estimate Listeria monocytogenes growth on frankfurters treated with organic acid salts

Organic acid salts including sodium lactate, sodium diacetate, potassium benzoate, potassium sorbate, and their combinations were assessed as potential inhibitors of Listeria monocytogenes growth on frankfurters. Predictive models for L. monocytogenes growth on frankfurters treated with these salts were compared to select a proper L. monocytogenes growth curve model under these conditions. Sigmoidal equations, including logistic and Gompertz equations, are widely used to describe bacterial growth. In this study, the reparameterized Gompertz model provided a better fit to the L. monocytogenes growth data compared with the other models that were included in this study. Rather than a fixed value for the maximum number of organisms, the reparameterized Gompertz model allows this quantity to be estimated from the data to determine the effect, if any, of the treatments on maximum population density. This information is expected to improve practical methodology for hazard characterization of microbial pathogens on ready-to-eat meat products.     

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.     

Inhibitory effects of organic acid salts for control of Listeria monocytogenes on frankfurters

Sodium diacetate (SD), sodium diacetate plus potassium benzoate (SD-PB), and sodium lactate plus sodium diacetate plus potassium benzoate (SL-SD-PB) were selected for initial effectiveness against Listeria monocytogenes on frankfurters. Treatments were evaluated at -2.2, 1.1, 4.4, 10.0, and 12.8 degrees C for up to 90 days. The compounds were applied as 3 or 6% (total concentration) dipping solutions for surface treatment of the frankfurters. The treated frankfurters were inoculated with a five-strain cocktail of L. monocytogenes (Scott A 4b, H7764 1/2a, H7962 4b, H7762 4b, and H7969 4b) using 1 ml of 10(4) cells for each 90.8-g package of two frankfurters. The maximum population of L. monocytogenes was decreased and generation time and lag phase were increased after surface treatments with 6% SD, 6% SL-SD-PB, 3% SD-PB, and 6% SD-PB solutions at 1.1 degrees C. Surface treatment of frankfurters with SD at 6% was more effective for inhibiting L. monocytogenes growth than were the other treatments. Under the conditions of this study, L. monocytogenes survived in refrigerated storage even in the presence of the additives tested.     

Considerations for post-lethality treatments to reduce Listeria monocytogenes from fully cooked bologna using ambient and pressurized steam

During processing of ready-to-eat (RTE) deli meats, any secondary processing procedures such as peeling and cutting introduce the distinct possibility of cross-contamination between equipment, personnel, and food. To eliminate or reduce pathogens such as Listeria monocytogenes and ensure food safety, RTE deli meats can be pasteurized prior to or after packaging. In this study, ambient steam in-package pasteurization was compared with pressurized steam prepackaging pasteurization to reduce L. monocytogenes from fully cooked RTE bologna. The bologna (14 cm diameter×1.5 cm thickness) samples were surface-inoculated to contain about 8 log₁₀ of L. monocytogenes. To achieve 2 log reductions for L. monocytogenes, the bologna samples needed to be treated for about 10 s in pressurized steam at 131 °C or for about 2.5 min in ambient steam at 100 °C. The pasteurization time using pressurized steam treatment was about 75–90% shorter than using ambient steam treatment. Pressurized steam treatment may be integrated into a vacuum packaging unit to effectively eradicate L. monocytogenes from RTE meats just prior to sealing the retail packages to further reduce the treatment time, avoid post-treatment recontaminations by pathogens, and improve food safety without detrimentally affecting meat quality.     

Optimization of E-beam irradiation treatment to eliminate Listeria monocytogenes from ready-to-eat (RTE) cooked ham

The inactivation kinetics of death of five Listeria monocytogenes and one Listeria innocua by E-beam irradiation have been studied in order to optimize the treatment for the sanitation of ready-to-eat (RTE) cooked ham. Treatments of 1 and 2.5 kGy were calculated to reach the food safety objective (FSO) according to the EU and USDA statements. These doses do not modify the sensory properties (appearance, odour and flavour) in such a way that they were detected by consumers, excepting the odour when 2.5 kGy are applied to meet the USDA criterion.Industrial relevanceThe application of E-beam irradiation at low dose (< 2.0 kGy) to packed ready-to-eat (RTE) cooked ham was found to be an effective treatment to reach the food safety objective (FSO) in this product. This treatment provides a great opportunity from an industrial point of view. Several reasons may be adduced to support this opinion, such as, it is a clean, cheap and rapid treatment, it works at continuous flow, no sensory changes are detected by the consumer and it is environmentally friendly. Additionally, this procedure could be applied for the sanitation of a broad range of similar RTE meat products.     

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 on frankfurters with antimicrobials in the formulation and by dipping in organic acid solutions

The antilisterial activity of sodium lactate (SL) and sodium diacetate (SD) was evaluated in a frankfurter formulation and in combination with a dipping treatment into solutions of lactic acid or acetic acid after processing and inoculation. Pork frankfurters were formulated with 1.8% SL or 0.25% SD or combinations of 1.8% SL with 0.25 or 0.125% SD. After processing, frankfurters were inoculated (2 to 3 log CFU/cm2) with a 10-strain composite of Listeria monocytogenes and left undipped or were dipped (2 min) in 2.5% solutions of lactic acid or acetic acid (23 +/- 2 degrees C) before vacuum packaging and storage at 10 degrees C for 40 days. Total microbial populations and L. monocytogenes, lactic acid bacteria, and yeasts and molds were enumerated during storage. Sensory evaluations also were carried out on frankfurters treated and/or formulated with effective antimicrobials. The combination of 1.8% SL with 0.25% SD provided complete inhibition of L. monocytogenes growth throughout storage. Dipping in lactic acid or acetic acid reduced initial populations by 0.7 to 2.1 log CFU/cm2, but during storage (12 to 20 days), populations on dipped samples without antimicrobials in the formulation reached 5.5 to 7.9 log CFU/cm2. For samples containing single antimicrobials and dipped in lactic acid or acetic acid, L. monocytogenes growth was completely inhibited or reduced over 12 and 28 days, respectively, whereas final populations were lower (P < 0.05) than those in undipped samples of the same formulations. Bactericidal effects during storage (reductions of 0.6 to 1.0 log CFU/ cm2 over 28 to 40 days) were observed in frankfurters containing combinations of SL and SD that were dipped in organic acid solutions. Inclusion of antimicrobials in the formulation and/or dipping the product into organic acid solutions did not affect (P > 0.05) the flavor and overall acceptability of products compared with controls. The results of this study may be valuable to meat processors as they seek approaches for meeting new regulatory requirements in the United States.     

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.     

Numerical analysis of survival of Listeria monocytogenes during in-package pasteurization of frankfurters by hot water immersion

ABSTRACT:  The objective of this research was to develop and validate a more accurate method to analyze and calculate the inactivation of Listeria monocytogenes in frankfurter packages during postlethality hot water immersion heating and the subsequent cooling processes. Finite difference analysis with implicit scheme was used to simulate the heat transfer process during in-package pasteurization of frankfurters. A volumetrically distributed simulation method was developed to calculate the lethality of the thermal treatment. The simulation method was validated using frankfurter packages inoculated with a 4-strain cocktail of L. monocytogenes. Experimental results showed that the numerical analysis model could accurately simulate the heat transfer process during heating and cooling of frankfurter packages. The simulated temperatures on the surface or in the middle of the package matched very closely with the experimental observations. Using the simulated temperature distribution in the packages, the integrated lethality simulation method, based on the volumetric distribution of bacteria, could accurately predict the reduction in the bacterial counts. The calculation results were on average within 0.3 log(CFU/g) difference from the experimental observations, while the General Method systematically underestimated the bacterial reductions by approximately 0.9 log(CFU/g). The study shows that the integrated lethality method is more accurate than the General Method in calculating the lethality of thermal processes for conduction-heated foods.     

Thermal lethality of Salmonella Senftenberg and Listeria innocua in fully cooked and packaged chicken breast strips via steam pasteurization.

Fully cooked chicken breast strips were surface inoculated to contain 9 log10 (CFU/g) Salmonella Senftenberg or Listeria innocua. The inoculated products were vacuum packaged in 0.2-mm-thick barrier bags (241 by 114 mm), then steam pasteurized at 88 degrees C in a continuous process for 26 to 40 min or in a batch process for 33 to 41 min. After the treatments, the products were analyzed for the survivors of Salmonella or Listeria. The models were developed to correlate the surviving rate of Salmonella and Listeria with cooking time for both continuous and batch processes. A cooking time of 34 min was needed to achieve 7 logs of the reduction in a batch process. To achieve the same log reduction, a longer (6 min) cooking time was needed in a batch process than in a continuous process. The results from this study will be useful for processors to evaluate postcooking treatment procedures for ready-to-eat meat products.     

Inactivation of Listeria monocytogenes on frankfurters by monocaprylin alone or in combination with acetic acid

The antilisterial activity of monocaprylin (MC) and its combination with acetic acid (AA) on frankfurters was investigated. Each frankfurter was surface inoculated with a three-strain mixture of Listeria monocytogenes to obtain an inoculation level of 4.0 log CFU per frankfurter, and then dipped for 35 s in sterile deionized water (45 or 50 degrees C) containing 1% ethanol (control), 50 mM MC plus 1% ethanol, 1% AA plus 1% ethanol, or 50 mM MC plus 1% AA plus 1% ethanol. Samples were vacuum packaged, stored at 4 degrees C for 77 days, and analyzed for L. monocytogenes. Sensory odor and color of frankfurters were evaluated using a 9-point hedonic scale. Color was also objectively measured using the Minolta Chroma Meter. From day 0 to day 77, population counts of L. monocytogenes on frankfurters dipped in antimicrobial solutions at 50 degrees C were consistently lower than the control counts. Similar results were observed for samples treated at 45 degrees C. However, L. monocytogenes grew readily on control samples at both temperatures. Dipping of frankfurters in antimicrobial solutions (45 or 50 degrees C) significantly reduced (P < 0.05) the populations of L. monocytogenes. After 70 days of storage, L. monocytogenes was completely killed in samples dipped in MC+AA solution at 50 degrees C. The antimicrobial treatments did not affect the odor or color of the samples (P > 0.05). Overall, results indicated that dipping of frankfurters with MC reduced L. monocytogenes, and inclusion of AA further enhanced MC antilisterial activity, without any negative effect on odor or color.     

Survival of Listeria monocytogenes on sliced cooked sausage after treatment with pediocin AcH

A preparation with pediocin AcH bound to its heat-killed producer cells Lactobacillus plantarum WHE 92 (starter culture ALC01, Wisby, Denmark) by adjusting the pH of the preparation to 6.0 was studied for its effects against Listeria monocytogenes ATCC 7644 and (spoilage) lactic acid bacteria on sliced cooked sausage. The pediocin AcH preparation or 0.9% (w/w) NaCl dilution (as a control) were randomly distributed dropwise on the surface of the slices. Treated slices were vacuum-packed and stored at 6 degrees C. Microbiological analysis and determination of pH values were performed after 3, 6, 9, 14 and 21 days of storage. Flavour of the sausages was evaluated after 7 and 11 days of storage. The pediocin preparation had effect (p > 0.05) neither on the growth of lactic acid bacteria, on the pH value nor on the flavour of vacuum-packed sliced sausage during 21 days of storage compared to control. However, during 6 days of storage, the number of L. monocytogenes decreased from the initial level of 2.7 log cfu/g sausage to < 2 log cfu/g, while on the control sausages the number of L. monocytogenes remained at the inoculated level. The numbers of L. monocytogenes remained at those levels to the end of storage period (21 days). However, the treated samples were determined to be Listeria positive, which indicates that the pediocin preparation was not efficient enough to kill all L. monocytogenes.     

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.     

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.     

Lethality of Salmonella and Listeria innocua in fully cooked chicken breast meat products during postcook in-package pasteurization

The process lethality model was used to predict the thermal kill of Salmonella and Listeria innocua in fully cooked and vacuum-packaged chicken breast meat during hot-water postprocess pasteurization. Time-temperature profiles of the meat samples during treatment and D-values (decimal reduction times) and z-values (change in temperature required to change the D-value) for Salmonella and L. innocua in the same meat product were used in the prediction of lethality. The results of the model prediction were compared with those of the inoculation study for the same meat product at a 95% confidence level of up to 10(7) CFU/g for Salmonella and L. innocua. The thermal lethality predictions obtained with the process lethality model for Salmonella and L. innocua were within the 95% confidence level for the experimental data from the inoculation study, suggesting that the process lethality model was a useful tool for the determination of the kill of Salmonella or L. innocua at up to 10(7) CFU/g in fully cooked chicken breast meat products during postprocess pasteurization with hot water.     

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.     

Antimicrobial activity of lactic acid bacteria against Listeria monocytogenes on frankfurters formulated with and without lactate/diacetate

Contamination by Listeria monocytogenes has been a constant public health threat for the ready-to-eat (RTE) meat industry due to the potential for high mortalities from listeriosis. Lactic acid bacteria (LAB) have shown protective action against various pathogenic bacteria. The aim of this study was to evaluate the antilisterial activity of a combination of three LAB strains (Lactiguard®) on L. monocytogenes. The combination of the LAB was inhibitory to L. monocytogenes inoculated onto frankfurters not containing lactate/diacetate after 8 weeks of refrigerated storage (0.6 log reduction compared to L. monocytogenes only control), and when a cell free extract (CFS) of the LAB was added with LAB even more inhibition was obtained (1.2 log reduction compared with L. monocytogenes only). In frankfurters containing lactate/diacetate the LAB and the LAB plus CFS were more effective in reducing growth of L. monocytogenes after 8 weeks of refrigerated storage (2 and 3.3 log reductions respectively).     

Antimicrobial activity of lactic acid bacteria against Listeria monocytogenes on frankfurters formulated with and without lactate/diacetate

Contamination by Listeria monocytogenes has been a constant public health threat for the ready-to-eat (RTE) meat industry due to the potential for high mortalities from listeriosis. Lactic acid bacteria (LAB) have shown protective action against various pathogenic bacteria. The aim of this study was to evaluate the antilisterial activity of a combination of three LAB strains (Lactiguard®) on L. monocytogenes. The combination of the LAB was inhibitory to L. monocytogenes inoculated onto frankfurters not containing lactate/diacetate after 8 weeks of refrigerated storage (0.6 log reduction compared to L. monocytogenes only control), and when a cell free extract (CFS) of the LAB was added with LAB even more inhibition was obtained (1.2 log reduction compared with L. monocytogenes only). In frankfurters containing lactate/diacetate the LAB and the LAB plus CFS were more effective in reducing growth of L. monocytogenes after 8 weeks of refrigerated storage (2 and 3.3 log reductions respectively).     

Effectiveness of potassium lactate and sodium diacetate in combination with irradiation to control Listeria monocytogenes on frankfurters

ABSTRACT:  The use of antimicrobial ingredients in combination with irradiation is an effective antilisterial intervention strategy for ready-to-eat meat products. Microbial safety was evaluated for frankfurters formulated with 0% or 3% added potassium lactate/sodium diacetate solution and inoculated with Listeria monocytogenes before or after treatment with irradiation (0, 1.8, or 2.6 kGy). Frankfurters were stored aerobically or vacuum packaged and L. mo nocytogenes counts and APCs were determined while refrigerated. The incorporation of lactate/diacetate with or without irradiation had a strong listeriostatic effect for aerobically stored frankfurters. Outgrowth was suppressed and counts were not different from initial counts (5.2 log CFU/frank compared with 5.0 log CFU/frank); however, those without the additive increased steadily (5.4 to 9.3 log CFU/frank). Irradiation treatments alone had higher L. monocytogenes counts after 3 wk. For vacuum-packaged frankfurters, both the addition of lactate/diacetate and irradiation were effective at controlling growth after 8 wk. Large and incremental reductions in total counts were seen for irradiation treatments. Initial counts were reduced by 3 log CFU with the application of 1.8 kGy while 2.6 kGy decreased counts over 5 log CFU. These reductions were maintained throughout storage for lactate/diacetate-treated frankfurters. By 8 wk, L. monocytogenes counts on 1.8 and 2.6 kGy irradiated frankfurters without lactate/diacetate increased to 7.43 and 6.13 log CFU, respectively. Overall, lactate/diacetate retarded the outgrowth of L. monocytogenes on frankfurters throughout aerobic storage and the combination of irradiation and 3% lactate/diacetate reduced and retarded growth of L. monocytogenes , especially during the last 2 wk of vacuum-packaged storage.