Fate of Listeria monocytogenes during freezing,thawing and home storage of frankfurters

Little information is available regarding the fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters even though recent surveys show that consumers regularly store unopened packages in home freezers. This study examined the effects of antimicrobials, refrigerated storage, freezing, thawing method, and post-thawing storage (7 °C) on L. monocytogenes on frankfurters. Inoculated (2.1 log CFU/cm²) frankfurters formulated without (control) or with antimicrobials (1.5% potassium lactate plus 0.1% sodium diacetate) were vacuum-packaged, stored at 4 °C for 6 or 30 d and then frozen (−15 °C) for 10, 30, or 50 d. Packages were thawed under refrigeration (7 °C, 24 h), on a countertop (23 ± 2 °C, 8 h), or in a microwave oven (2450 MHz, 1100 watts, 220 s followed by 120 s holding), and then stored aerobically (7 °C) for 14 d. Bacterial populations were enumerated on PALCAM agar and tryptic soy agar plus 0.6% yeast extract. Antimicrobials completely inhibited (p < 0.05) growth of L. monocytogenes at 4 °C for 30 d under vacuum-packaged conditions, and during post-thawing aerobic storage at 7 °C for 14 d. Different intervals between inoculation and freezing (6 or 30 d) resulted in different pathogen levels on control frankfurters (2.1 or 3.9 log CFU/cm², respectively), while freezing reduced counts by <1.0 log CFU/cm². Thawing treatments had little effect on L. monocytogenes populations (<0.5 log CFU/cm²), and post-thawing fate of L. monocytogenes was not influenced by freezing or by thawing method. Pathogen counts on control samples increased by 1.5 log CFU/cm² at d-7 of aerobic storage, and reached 5.6 log CFU/cm² at d-14. As indicated by these results, consumers should freeze frankfurters immediately after purchase, and discard frankfurters formulated without antimicrobials within 3 d of thawing and/or opening.     

Effect of fat content on survival of Listeria monocytogenes during simulated digestion of inoculated beef frankfurters stored at 7 °C

Potential effects of the fat content of frankfurters on the gastrointestinal survival of Listeria monocytogenes were investigated. At various stages of storage (7 °C, up to 55 days), inoculated frankfurters of low (4.5%) and high (32.5%) fat content were exposed to a dynamic gastrointestinal model (37 °C) and L. monocytogenes counts were determined at intervals during exposure in each gastrointestinal compartment (gastric, GC; intestinal, IC). Bacterial survival curves in each compartment were fitted with the Baranyi and Roberts mathematical model. L. monocytogenes populations on low- and high-fat frankfurters exceeded 8.0 log CFU/g at 39 and 55 days of storage, respectively. Major declines in populations occurred after 60 min on low-fat frankfurters in the GC, with reductions of 2.6 to >7.2 log CFU/g at 120 min on days 1 and 39 of storage, respectively. L. monocytogenes reductions in high-fat frankfurters ranged from 1.6 (day-1) to 5.2 (day-55) log CFU/g. Gastric inactivation rates were 0.080–0.194 and 0.030–0.097 log CFU/g/min for low- and high-fat samples, respectively. Since gastric emptying began while the gastric pH was >5, initial counts (enumerated 30 min after ingestion) reaching the IC depended on initial contamination levels on each product, which increased during storage. Subsequent reductions during the intestinal challenge were 0.1–1.4 log CFU/g. Findings indicated protective effects of fat against gastric destruction of L. monocytogenes. However, since the effects of fat were observed mainly at later stages of gastric exposure, they did not influence numbers of viable cells reaching the IC.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

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).     

Viability of a five-strain mixture of Listeria monocytogenes in vacuum-sealed packages of frankfurters, commercially prepared with and without 2.0 or 3.0% added potassium lactate, during extended storage at 4 and 100 degrees C

The viability of Listeria monocytogenes was monitored on frankfurters containing added potassium lactate that were obtained directly from a commercial manufacturer. Eight links (ca. 56 g each) were transferred aseptically from the original vacuum-sealed bulk packages into nylon-polyethylene bags. Each bag then received a 4-ml portion of a five-strain mixture of the pathogen. Frankfurters containing 2.0 or 3.0% potassium lactate were evaluated using 20 CFU per package, and frankfurters containing 3.0% potassium lactate were evaluated using 500 CFU per package. The packages were vacuum-sealed and stored at 4 or 10 degrees C for up to 90 or 60 days, respectively. During storage at 4 degrees C, pathogen numbers remained at about 1.6 log10 CFU per package over 90 days in packages containing frankfurters with 2.0% potassium lactate that were inoculated with about 20 CFU. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 20 CFU and stored at 4 degrees C, pathogen numbers remained at about 1.4 log10 CFU per package over 90 days. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 500 CFU and stored at 4 degrees C, pathogen numbers remained at about 2.4 log10 CFU per package over 90 days. However, in the absence of any added potassium lactate, pathogen numbers increased to 4.6 and 5.0 log10 CFU per package after 90 days of storage at 4 degrees C for starting levels of 20 and 500 CFU per package, respectively. During storage at 10 degrees C, pathogen numbers remained at about 1.4 log10 CFU per package over 60 days in packages containing frankfurters with 2.0% potassium lactate that were inoculated with about 20 CFU. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 20 CFU and stored at 10 degrees C, pathogen numbers remained at about 1.1 log10 CFU per package over 60 days of storage. In the absence of any added potassium lactate, pathogen numbers increased to 6.5 log10 CFU per package after 28 days and then declined to 5.0 log10 CFU per package after 60 days of storage at 10 degrees C. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 500 CFU per package, pathogen numbers remained at about 2.4 log10 CFU per package over 60 days of storage at 10 degrees C, whereas in the absence of any added potassium lactate, pathogen numbers increased to about 6.6 log10 CFU per package within 40 days and then declined to about 5.5 log10 CFU per package after 60 days of storage. The viability of L. monocytogenes in frankfurter packages stored at 4 and 10 degrees C was influenced by the pH and the presence or levels of lactate but not by the presence or levels of indigenous lactic acid bacteria or by the proximate composition of the product. These data establish that the addition of 2.0% (P < 0.0004) or 3.0% (P < 0.0001) potassium lactate as an ingredient in frankfurters can appreciably enhance safety by inhibiting or delaying the growth of L. monocytogenes during storage at refrigeration and abuse temperatures.     

Evaluation of nisin-coated cellulose casings for the control of Listeria monocytogenes inoculated onto the surface of commercially prepared frankfurters

Commercially prepared frankfurters were formulated with and without approximately 1.4% potassium lactate and 0.1% sodium diacetate and were subsequently processed in cellulose casings coated with and without nisin (approximately 50,000 IU per square inch of internal surface area) to control the outgrowth of Listeria monocytogenes during refrigerated storage. The frankfurters were inoculated with approximately 5 log CFU per package of a five-strain mixture of L. monocytogenes and then vacuum sealed before being stored at 4 degrees C for 60 to 90 days. Surviving organisms were recovered and enumerated by rinsing each package with 18 ml of sterile 0.1% peptone water and plating onto MOX selective agar. The data for each of two trials were averaged. In packages that contained frankfurters formulated with potassium lactate and sodium diacetate and prepared in nisin-coated casings, L. monocytogenes levels decreased by 1.15 log CFU per package after 90 days of storage. L. monocytogenes levels decreased by 0.95 log CFU per package in frankfurters that were prepared in casings that were not coated with nisin. In packages of frankfurters that were formulated without potassium lactate and sodium diacetate and prepared in nisin-coated casings, L. monocytogenes levels decreased by 0.88 log CFU per package after 15 days of storage but then increased appreciably thereafter over a 60-day period of refrigerated storage. There was also an appreciable increase in pathogen numbers during 60 days of storage in otherwise similar frankfurters formulated without potassium lactate and sodium diacetate prepared in casings that were not coated with nisin. These data confirm that potassium lactate and sodium diacetate display listeriostatic activity as an ingredient of commercial frankfurters. These data also establish that cellulose casings coated with nisin display only moderate antilisterial activity in vacuum-sealed packages of commercially prepared frankfurters during storage at 4 degrees C.     

Bactericidal activity of lauric arginate in milk and Queso Fresco cheese against Listeria monocytogenes cold growth

Lauric arginate (LAE) at concentrations of 200 ppm and 800 ppm was evaluated for its effectiveness in reducing cold growth of Listeria monocytogenes in whole milk, skim milk, and Queso Fresco cheese (QFC) at 4°C for 15 to 28 d. Use of 200 ppm of LAE reduced 4 log cfu/mL of L. monocytogenes to a nondetectable level within 30 min at 4°C in tryptic soy broth. In contrast, when 4 log cfu/mL of L. monocytogenes was inoculated in whole milk or skim milk, the reduction of L. monocytogenes was approximately 1 log cfu/mL after 24 h with 200 ppm of LAE. When 800 ppm of LAE was added to whole or skim milk, the initial 4 log cfu/mL of L. monocytogenes was nondetectable following 24 h, and no growth of L. monocytogenes was observed for 15 d at 4°C. With surface treatment of 200 or 800 ppm of LAE on vacuum-packaged QFC, the reductions of L. monocytogenes within 24 h at 4°C were 1.2 and 3.0 log cfu/g, respectively. In addition, the overall growth of L. monocytogenes in QFC was decreased by 0.3 to 2.6 and by 2.3 to 5.0 log cfu/g with 200 and 800 ppm of LAE, respectively, compared with untreated controls over 28 d at 4°C. Sensory tests revealed that consumers could not determine a difference between QFC samples that were treated with 0 and 200 ppm of LAE, the FDA-approved level of LAE use in foods. In addition, no differences existed between treatments with respect to flavor, texture, and overall acceptability of the QFC. Lauric arginate shows promise for potential use in QFC because it exerts initial bactericidal activity against L. monocytogenes at 4°C without affecting sensory quality.     

Effects of natural antimicrobials on inhibition of Listeria monocytogenes and on chemical, physical and sensory attributes of naturally-cured frankfurters

Due to regulations for natural and organic processed meats, sodium nitrite and many antimicrobials cannot be used. Therefore, natural and organic processed meats are more susceptible to pathogenic bacterial growth, and natural alternatives to chemical preservatives are needed. Inhibition of Listeria monocytogenes, and quality characteristics of frankfurters manufactured with 3% cranberry powder, or with 1% or 2% cranberry powder each with either cherry powder (0.6%), lime powder (60 mg/kg), or a blend of cherry, lime and vinegar (1.4%) were investigated. Cranberry powder at 3% significantly reduced L. monocytogenes growth by 5.3 log CFU/g compared to the uncured co006Etrol (P < 0.05). However, cranberry addition over 1% also resulted in significant product pH decline and negatively impacted the color, texture and sensory attributes of the frankfurters.     

Effect of lactoferrin and its derivatives against gram-positive bacteria in vitro and, combined with high pressure, in chicken breast fillets

The bactericidal activity of lactoferrin (LF), amidated lactoferrin (AMILF), pepsin digested lactoferrin (PDLF), and its activated (ALF) commercial form, against six strains of three gram-positive bacterial species was investigated. Listeria monocytogenes was most sensitive in vitro, Staphylococcus aureus showed a moderate resistance, and Enterococus faecalis was highly resistant to antimicrobials. When chicken breast fillets were inoculated with L. monocytogenes CECT5725 and treated with antimicrobials, reductions were below 0.5 log CFU/ml in all cases. In combination with high pressure (HHP) treatment at 400 MPa for 10 min, antimicrobials showed a slight additional bactericidal effect, always below 1 log CFU/g. Incorporation of antimicrobials 18 h before or 1 h after HHP treatment generally yielded better results than incorporation 1 h before HHP treatment, although reductions remained below 1.5 log CFU/g in all cases. LF and its derivatives showed a limited potential for pathogen control in meat.     

Spray application of liquid smoke to reduce or eliminate Listeria monocytogenes surface inoculated on frankfurters

In a simulated post process contamination scenario liquid smoke was sprayed on the frankfurters after peeling, and then inoculated with Listeria monocytogenes (Lm). Samples that did not receive a liquid smoke spray remained at approximately 2 log cfu/cm² during the 48 h of storage while the levels on the liquid smoke treated frankfurters continued to decline until they were below detection level (1 cfu/100 cm²). A shelf-life study lasting 140 days indicated that liquid smoke suppressed the growth of Lm for up to 130 days. An application of 2 or 3 ml liquid smoke at packaging resulted in at least a 1 log reduction of Lm within 12 h post packaging.     

Efficacy of bacteriophage LISTEXP100 combined with chemical antimicrobials in reducing Listeria monocytogenes in cooked turkey and roast beef

The aim of this study was to verify the effectiveness of the commercially available anti-Listeria phage preparation LISTEX^™P100 in reducing Listeria monocytogenes on ready-to-eat (RTE) roast beef and cooked turkey in the presence or absence of the chemical antimicrobials potassium lactate (PL) and sodium diacetate (SD). Sliced RTE meat cores at 4 and 10 °C were inoculated with cold-adapted L. monocytogenes to result in a surface contamination level of 10³ CFU/cm². LISTEX^TMP100 was applied at 10⁷ PFU/cm² and samples taken at regular time intervals during the RTE product's shelf life to enumerate viable L. monocytogenes. LISTEX^™P100 was effective during incubation at 4 °C with initial reductions of L. monocytogenes of 2.1 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef without chemical antimicrobials (there was no significant difference to the initial L. monocytogenes reductions in the presence of LISTEX^TMP100 for cooked turkey containing PL and roast beef containing SD-PL). In the samples containing no chemical antimicrobials, the presence of phage resulted in lower L. monocytogenes numbers, relative to the untreated control, of about 2 log CFU/cm² over a 28-day storage period at 4 °C. An initial L. monocytogenes cell reduction of 1.5 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef containing no chemical antimicrobials was achieved by the phage at 10 °C (abusive temperature). At this temperature, the L. monocytogenes cell numbers of samples treated with LISTEX™ P100 remained below those of the untreated control only during the first 14 days of the experiment for roast beef samples with and without antimicrobials. On day 28, the L. monocytogenes numbers on samples containing chemical antimicrobials and treated with LISTEX^TMP100 stored at 4 and 10 °C were 4.5 log₁₀ CFU/cm² and 7.5 log₁₀ CFU/cm², respectively, for cooked turkey, and 1.2 log₁₀ CFU/cm² and 7.2 log₁₀ CFU/cm², respectively, for roast beef. In both cooked turkey samples with and without chemical antimicrobials stored at 10 °C, the phage-treated samples had significantly lower numbers of L. monocytogenes when compared to the untreated controls throughout the 28-day storage period (P < 0.0001). For roast beef and cooked turkey containing chemical antimicrobials treated with LISTEX^TMP100 and stored at 4 °C, no more than a 2 log CFU/cm² increase of L. monocytogenes was observed throughout the stated shelf life of the product. This study shows that LISTEX^™P100 causes an initial reduction of L. monocytogenes numbers and can serve as an additional hurdle to enhance the safety of RTE meats when used in combination with chemical antimicrobials.     

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.     

Application of an active alginate coating to control the growth of Listeria monocytogenes on poached and deli turkey products

The relatively high prevalence of Listeria monocytogenes in ready-to-eat (RTE) turkey products is of great concern. The overall objective of this study was to develop antimicrobial edible coating formulations to effectively control the growth of this pathogen. The antimicrobials studied were nisin (500 IU/g), Novagard CB 1 (0.25%), Guardian NR100 (500 ppm), sodium lactate (SL, 2.4%), sodium diacetate (SD, 0.25%), and potassium sorbate (PS, 0.3%). These were incorporated alone or in binary combinations into five edible coatings: alginate, κ-carrageenan, pectin, xanthan gum, and starch. The coatings were applied onto the surface of home-style poached and processed deli turkey discs inoculated with ~ 3 log CFU/g of L. monocytogenes. The turkey samples were then stored at 22 °C for 7 days. For poached and processed deli turkey, the coatings were found to be equally effective, with pectin being slightly less effective than the others. The most effective poached turkey treatments seemed to be SL (2.4%)/SD (0.25%) and Nisin (500 IU/g)/SL (2.4%), which yielded final populations of 3.0 and 4.9 log CFU/g respectively compared to the control which was 7.9 log CFU/g. For processed deli turkey, the most effective antimicrobial treatments seemed to be Nisin (500 IU/g)/SD (0.25%) and Nisin (500 IU/g)/SL (2.4%) with final populations of 1.5 and 1.7 log CFU/g respectively compared to the control which was 6.5 log CFU/g. In the second phase of the study, home-style poached and store-purchased roasted (deli) turkey inoculated with the pathogen at a level of ~ 3 log CFU/g were coated with alginate incorporating selected antimicrobial combinations and stored for 8 weeks at 4 °C. Alginate coatings supplemented with SL (2.4%)/PS (0.3%) delayed the growth of L. monocytogenes with final counts reaching 4.3 log CFU/g (home-style poached turkey) and 6.5 log CFU/g (roasted deli turkey) respectively while the counts in their untreated counterparts were significantly higher (P < 0.05) reaching 9.9 and 7.9 log CFU/g, respectively. This study therefore demonstrates the effectiveness of using alginate-based antimicrobial coatings to enhance the microbiological safety and quality of RTE poultry products during chilled storage.     

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).     

Use of mild irradiation doses to control pathogenic bacteria on meat trimmings for production of patties aiming at provoking minimal changes in quality attributes

The objectives of the present work were to assess the use of moderate doses of gamma irradiation (2 to 5 kGy) and to reduce the risk of pathogen presence without altering the quality attributes of bovine trimmings and of patties made of irradiated trimmings. Microbiological indicators (coliforms, Pseudomonas spp and mesophilic aerobic counts), physicochemical indicators (pH, color and tiobarbituric acid) and sensory changes were evaluated during storage. 5 kGy irradiation doses slightly increased off flavors in patties. Two pathogenic markers (Listeria monocytogenes and Escherichia coli O157:H7) were inoculated at high or low loads to trimming samples which were subsequently irradiated and lethality curves were obtained. Provided that using irradiation doses ≤ 2.5 kGy are used, reductions of 2 log CFU/g of L. monocytogenes and 5 log CFU/g of E. coli O157:H7 are expected. It seems reasonable to suppose that irradiation can be successfully employed to improve the safety of frozen trimmings when initial pathogenic bacteria burdens are not extremely high.     

Microwave Oven Heating for Inactivation of Listeria Monocytogenes on Frankfurters before Consumption

ABSTRACT:  Microwave oven heating was evaluated for inactivation of  Listeria monocytogenes  on inoculated and stored frankfurters. Frankfurters formulated without/with 1.5% potassium lactate and 0.1% sodium diacetate were inoculated with  L. monocytogenes  (1.9 ± 0.2 log CFU/cm²), vacuum-packaged, and stored (4 °C) to simulate conditions prior to purchase by consumers. At storage days 18, 36, and 54, packages were opened and placed at 7 °C, simulating aerobic storage in a household refrigerator. At 0, 3, and 7 d of aerobic storage, 2 frankfurters were placed in a bowl with water (250 mL) and treated in a household microwave oven at high (1100 W) power for 30, 45, 60, or 75 s, or medium (550 W) power for 60 or 75 s. Frankfurters and the heating water were analyzed for total microbial counts and  L. monocytogenes  populations. Exposure to high power for 75 s reduced pathogen levels (0.7 ± 0.0 to 1.0 ± 0.1 log CFU/cm²) to below the detection limit (<−0.4 log CFU/cm²) on frankfurters with lactate/diacetate, even after 54 d of vacuum-packaged storage followed by 7 d of aerobic storage. For frankfurters without lactate/diacetate, high power for 75 s caused reductions between > 1.5 and 5.9 log CFU/cm² from control levels of 1.5 ± 0.1 to 7.2 ± 0.5 log CFU/cm². Depending on treatment and storage time, the water used to reheat the frankfurters had viable  L. monocytogenes  counts of <−2.4 to 5.5 ± 0.5 log CFU/mL. The results indicated that frankfurters should be reheated in a microwave oven at high power for 75 s to inactivate up to 3.7 log CFU/cm² of  L. monocytogenes  contamination.     

Viability of Listeria monocytogenes on commercially-prepared hams surface treated with acidic calcium sulfate and lauric arginate and stored at 4°C

We demonstrated the effectiveness of delivering an antimicrobial purge/fluid into shrink-wrap bags immediately prior to introducing the product and vacuum sealing, namely the “Sprayed Lethality In Container” (SLIC™) intervention delivery method. The pathogen was Listeria monocytogenes, the antimicrobials were acidic calcium sulfate (ACS; calcium sulfate plus lactic acid; 1:1 or 1:2 in dH₂O) and lauric arginate (LAE; Ethyl-N-dodecanoyl-l-arginate hydrochloride; 5% or 10% in dH₂O), and the product was commercially prepared “table brown” ham (ca. 3 pounds each). Hams were surface inoculated with a five-strain cocktail of L. monocytogenes (ca. 7.0 log₁₀ CFU per ham), added to shrink-wrap bags that already contained ACS or LAE, vacuum-sealed, and stored at 4 °C for 24 h. Pathogen levels decreased by 1.2, 1.6, 2.4, and 3.1 log₁₀ CFU/ham and 0.7, 1.6, 2.2, and 2.6 log₁₀ CFU/ham in samples treated with 2, 4, 6, and 8 mL of a 1:1 and 1:2 solution of ACS, respectively. In samples treated with 2, 4, 6, and 8 mL of a 5% solution of LAE, pathogen levels decreased by 3.3, 6.5, 5.6, and 6.5 log₁₀ CFU/ham, whereas when treated with a 10% solution of LAE pathogen levels decreased ca. 6.5 log₁₀ CFU/ham for all application volumes tested. The efficacy of ACS and LAE were further evaluated in shelf-life studies wherein hams were surface inoculated with either ca. 3.0 or 7.0 log₁₀ CFU of L. monocytogenes, added to shrink-wrap bags that contained 0, 4, 6, or 8 mL of either a 1:2 solution of ACS or a 5% solution of LAE, vacuum-sealed, and stored at 4 °C for 60 days. For hams inoculated with 7.0 log₁₀ CFU, L. monocytogenes levels decreased by ca.1.2, 1.5, and 2.0 log₁₀ CFU/ham and 5.1, 5.4, and 5.5 log₁₀ CFU/ham within 24 h at 4 °C in samples treated with 4, 6, and 8 mL of a 1:2 solution of ACS and a 5% solution of LAE, respectively, compared to control hams that were not treated with either antimicrobial. Thereafter, pathogen levels remained relatively unchanged (±1.0 log₁₀ CFU/ham ) after 60 days at 4 °C in hams treated with 4, 6, and 8 mL of a 1:2 solution of ACS and increased by ca. 2.0–5.0 log₁₀ CFU/ham in samples treated with 4, 6, and 8 mL of a 5% solution of LAE. For hams inoculated with 3.0 log₁₀ CFU, L. monocytogenes levels decreased by 1.3, 1.9, and 1.8 log₁₀ CFU/ham within 24 h at 4 °C in samples treated with 4, 6, and 8 mL of a 1:2 solution of ACS, respectively, compared to control hams that were not treated. Likewise, levels of the pathogen were reduced to below the limit of detection (i.e., 1.48 log₁₀ CFU/ham) in the presence of 4, 6, and 8 mL of a 5% solution of LAE within 24 h at 4 °C. After 60 days at 4 °C, pathogen levels remained relatively unchanged (±0.3 log₁₀ CFU/ham) in hams treated with 4, 6, and 8 mL of a 1:2 solution of ACS. However, levels of L. monocytogenes increased by ca. 2.0 log₁₀ CFU/ham in samples treated with 4 and 6 mL of a 5% LAE solution within 60 days but remained below the detection limit on samples treated with 8 mL of this antimicrobial. These data confirmed that application via SLIC™ of both ACS and LAE, at the concentrations and volumes used in this study, appreciably reduced levels of L. monocytogenes on the surface of hams within 24 h at 4 °C and showed potential for controlling outgrowth of the pathogen over 60 days of refrigerated storage.     

Evaluation of Changes in Listeria monocytogenes Populations on Frankfurters at Different Stages from Manufacturing to Consumption

ABSTRACT: This study evaluated the fate of inoculated Listeria monocytogenes on frankfurters stored under conditions simulating those that may be encountered between manufacturing and consumption. Frankfurters with or without 1.5% potassium lactate and 0.1% sodium diacetate (PL/SD) were inoculated (1.8 ± 0.1 log CFU/cm²) with a 10‐strain composite of L. monocytogenes, vacuum‐packaged, and stored under conditions simulating predistribution storage (24 h, 4 °C), temperature abuse during transportation (7 h, 7 °C followed by 7 h, 12 °C), and storage before purchase (60 d, 4 °C; SBP). At 0, 20, 40, and 60 d of SBP, samples were exposed to conditions simulating delivery from stores to homes or food establishments (3 h, 23 °C), and then opened or held vacuum‐packaged at 4 or 7 °C for 14 d (SHF). Pathogen counts remained relatively constant on frankfurters with PL/SD regardless of product age and storage conditions; however, they increased on product without antimicrobials. In vacuum‐packaged samples, during SHF at 4 °C, the pathogen grew faster (P < 0.05) on older product (20 d of SBP) compared to product that was fresh (0 d of SBP); a similar trend was observed in opened packages. At 7 °C, the fastest growth (0.35 ± 0.02 log CFU/cm²/d) was observed on fresh product in opened packages; in vacuum‐packages, growth rates on fresh and aged products were similar. By day 40 of SBP the pathogen reached high numbers and increased slowly or remained unchanged during SHF. This information may be valuable in L. monocytogenes risk assessments and in development of guidelines for storage of frankfurters between package opening and product consumption.     

Behavior of Salmonella during fermentation,drying and storage of cocoa beans

Due to cocoa being considered a possible source of Salmonella contamination in chocolate, the behavior of Salmonella during some cocoa pre-processing stages (fermentation, drying and storage) was investigated. The fermentation process was carried out on a pilot scale (2 kg beans/box) for 7 days. Every day a fermentation box was inoculated with a Salmonella pool (ca. 4 log MPN/g). The results showed that Salmonella did not affect (P > 0.05) the growth of the main microorganism groups involved in cocoa fermentation. On the other hand, the pathogen was influenced (P < 0.05) by yeast, acetic acid bacteria and pH. In spite of Salmonella showing counts ≤ 1 log MPN/g in the first days, at the end of fermentation it grew in all samples, reaching counts as high as 7.49 log MPN/g. For drying and storage, cocoa beans were inoculated during the fermentation (experiment A) or during the drying (experiment B). In these stages the decline of the water activity affected the pathogen behavior. In experiment A during the drying, Salmonella count increased in most of the samples. In experiment B either a slight growth or no growth in the samples inoculated up to 48 h was observed, whereas the other samples showed reductions from the initial count. After 30 days of storage at room temperature, the water activity decreased to 0.68, and reductions of Salmonella ranged from 0.93 to 2.52 log MPN/g. Despite the reductions observed during the storage, the pathogen was detected even after 120 days. Therefore, the results showed that Salmonella growth or survival depends on when the contamination occurs.     

Survival of Escherichia coli O157:H7 in channel catfish pond and holding tank water

Survival of Escherichia coli O157:H7 in channel catfish (Ictalurus punctatus), pond and holding tank water was investigated. Water from three channel catfish ponds was inoculated with ampicillin/nalidixic acid-resistant E. coli O157:H7 transformed with a plasmid encoding for green fluorescent protein at 10⁵, 10⁶, and 10⁷ CFU/ml. Samples were taken from surface, internal organs, and skin scrape of fish and pond water for E. coli O157:H7 enumeration on brain heart infusion (BHI) agar containing ampicillin and nalidixic acid. To determine the survival of E. coli O157:H7 in catfish holding tank water from two farmers markets, the water was inoculated with 10⁷E. coli O157:H7 CFU/ml. E. coli O157:H7 were detected by direct plating for 33 and 69 d in pond and holding tank water, respectively. A rapid decrease of the pathogen was observed in the first 2 weeks to reach 2 log CFU/ml. When E. coli O157:H7 was not recovered by direct plating, the pathogen was isolated by enrichment in TSB for approximately another 30 d from pond and holding tank water. The populations of E. coli O157:H7 found in the internal organs and skin scrape were 5.5 log and 2.5 log CFU/ml, respectively. E. coli O157:H7 from internal organs and water were recovered for at least 12 d. Results suggest that E. coli O157:H7 can survive in channel catfish pond and holding tank water and channel catfish may become a potential carrier of the pathogen.