Postprocessing antimicrobial treatments to control Listeria monocytogenes in commercial vacuum-packaged bologna and ham stored at 10 degrees C

The antilisterial effect of chemical dipping solutions on commercial bologna and ham slices, inoculated (3 to 4 log CFU/ cm2) after processing, was evaluated during storage in vacuum packages at 10 degrees C. Samples were inoculated with a 10-strain composite of Listeria monocytogenes and subsequently immersed (25+/-2 degrees C) for 2 min in 2.5% acetic acid (AA), 2.5% lactic acid (LA), 5% potassium benzoate (PB), or 0.5% Nisaplin (commercial form of nisin, equivalent to 5,000 IU/ml of nisin) solutions, either singly or sequentially (Nisaplin plus AA, Nisaplin plus LA, or Nisaplin plus PB), and then vacuum packaged and stored at 10 degrees C for 48 days. In addition to microbiological analysis, sensory evaluations were performed on uninoculated samples treated with AA, LA, or PB. Initial reductions (day 0) of the pathogen, compared with the controls, on bologna and ham samples treated with AA, LA, or PB ranged from 0.4 to 0.7 log CFU/cm2. Higher (P < 0.05) initial reductions (2.4 to 2.9 log CFU/cm2) were obtained for samples treated with Nisaplin alone and when followed by AA, LA, or PB. L. monocytogenes populations on control bologna and ham samples increased from 3.4 log CFU/cm2 (day 0) to 7.4 and 7.8 log CFU/ cm2, respectively, in 8 days at 10 degrees C. Listericidal effects were observed for all treatments tested, except for Nisaplin applied on its own, during storage at 10 degrees C. The sequential treatment of Nisaplin plus LA reduced L. monocytogenes to undetectable levels in both products at the end of storage. The sequential treatments were also found to inhibit growth of spoilage microorganisms. Sensory evaluations indicated that dipping (2 min) of ham samples in AA (2.5%), LA (2.5%), or PB (5%) led to lower sensory scores. However, since results of this study indicated that these treatments caused extensive listericidal effects, there is possibly a potential to reduce the levels of chemicals applied and still achieve adequate antilisterial activity without major negative effects on product quality.     

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.     

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.     

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

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

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

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

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.     

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

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

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.     

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 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.     

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.     

Post-processing application of chemical solutions for control of Listeria monocytogenes, cultured under different conditions, on commercial smoked sausage formulated with and without potassium lactate-sodium diacetate

This study evaluated post-processing chemical solutions for their antilisterial effects on commercial smoked sausage formulated with or without 1.5% potassium lactate plus 0.05% sodium diacetate, and contaminated (approximately 3-4 log cfu/cm(2)) with 10-strain composite Listeria monocytogenes inocula prepared under various conditions. Inoculated samples were left untreated, or were immersed (2 min, 25 +/- 2 degrees C) in solutions of acetic acid (2.5%), lactic acid (2.5%), potassium benzoate (5%) or Nisaplin (0.5%, equivalent to 5000 IU/ml of nisin) alone, and in sequence (Nisaplin followed by acetic acid, lactic acid or potassium benzoate), before vacuum packaging and storage at 10 degrees C (48 days). Acetic acid, lactic acid or potassium benzoate applied alone reduced initial L. monocytogenes populations by 0.4-1.5 log cfu/cm(2), while treatments including Nisaplin caused reductions of 2.1-3.3 log cfu/cm(2). L. monocytogenes on untreated sausage formulated with antimicrobials had a lag phase duration of 10.2 days and maximum specific growth rate (mu(max)) of 0.089 per day, compared to no lag phase and mu(max) of 0.300 per day for L. monocytogenes on untreated product that did not contain antimicrobials in the formulation. The immersion treatments inhibited growth of the pathogen for 4.9-14.8 days on sausage formulated without potassium lactate-sodium diacetate; however, in all cases significant (P < 0.05) growth occurred by the end of storage. The antilisterial activity of chemical solutions was greatly enhanced when applied to product formulated with antimicrobials; growth was completely inhibited on sausage treated with acetic or lactic acid alone, and in sequence with Nisaplin. In general, habituation (15 degrees C, 7 days) of L. monocytogenes cells, planktonically or as attached cells to stainless-steel coupons in sausage homogenate prior to contamination of product, resulted in shorter lag phase durations compared with cells cultivated planktonically in a broth medium. Furthermore, when present, high levels of spoilage flora were found to suppress growth of the pathogen. Findings of this study could be useful to US meat processors in their efforts to select required regulatory alternatives for control of post-processing contamination in meat products.     

Fate of Listeria monocytogenes inoculated onto the surface of model Turkey frankfurter pieces treated with zein coatings containing nisin, sodium diacetate, and sodium lactate at 4 degrees C

The antimicrobial effects of zein coatings containing nisin, sodium lactate, and sodium diacetate against Listeria monocytogenes on turkey frankfurters at 4 degrees C were determined. Our objectives were to determine whether zein, nisin, lactate, and diacetate alone or in combination could control the growth of L. monocytogenes on full-fat turkey frankfurters at 4 degrees C and to determine whether lactate or diacetate had any synergistic effect on the activity of nisin. Turkey frankfurter pieces surface inoculated with L. monocytogenes strain V7 were treated with zein-ethanol-glycerol (ZEG), zein-propylene-glycol (ZPR), ethanol-glycerol (EG), propylene glycol (PR), nisin (N), sodium lactate (L), or sodium diacetate (D) alone or in combination. Over 28 days, treatment with N or D alone reduced L. monocytogenes counts on frankfurters by 6.6 or 6.3 log CFU/g, respectively. N-D treatment reduced L. monocytogenes by 6 log CFU/g. The zein solvents EG and PR reduced L. monocytogenes by about 5.6 and 5.2 log CFU/g, respectively, similar to the results obtained with ZEG and ZPR, which suggests that zein powder per se had no antimicrobial activity. After 28 days, ZEG-N-D, ZEG-N-D-L, ZPR-N-D, and ZPR-N-D-L yielded no detectable CFU. L alone was ineffective. No synergies were observed. N and D when used singly and the combinations of N-D, ZEG-N-D, ZEG-N-D-L, ZPR-N-D, ZPR-N-D-L, EG, and PR were effective as inhibitors of the growth of recontaminating L. monocytogenes cells on full-fat turkey 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.     

Reduction of Listeria monocytogenes populations during exposure to a simulated gastric fluid following storage of inoculated frankfurters formulated and treated with preservatives

The effect of a simulated gastric fluid (adjusted to pH 1.0 with HCl) on Listeria monocytogenes, inoculated postprocessing on pork frankfurters formulated with sodium lactate (SL) and sodium diacetate (SD) and not dipped or dipped in solutions of lactic acid or acetic acid, was evaluated during storage of the frankfurters at 10 degrees C for 40 days. Pork frankfurters containing 1.8% SL, 0.25% SD, 1.8% SL+0.125% SD, or 1.8% SL+0.25% SD were inoculated with 10(2)-10(3) CFU/cm2 of a 10-strain preparation of L. monocytogenes and were not dipped or dipped for 2 min in solutions of 2.5% lactic or acetic acid before they were vacuum-packaged and stored. Survival of L. monocytogenes was determined after exposure of frankfurters for 0, 20, 40, and 60 min to the simulated gastric fluid after storage for 0, 10, 20, 30, or 40 days. Growth of L. monocytogenes on frankfurters formulated with antimicrobials was inhibited in the order control 相似文献   

Inhibition of Listeria monocytogenes by sodium diacetate and sodium lactate on wieners and cooked bratwurst.

The inhibition of Listeria monocytogenes by sodium lactate and sodium diacetate was evaluated for wieners containing pork, turkey, and beef and for cooked bratwurst containing beef and pork. Both products were supplied by commercial manufacturers. Treated products were surface-inoculated with 10(5) CFU of L. monocytogenes per package and vacuum-packed in gas-impermeable pouches. Wieners were stored for 60 days at 4.5 degrees C, and bratwurst were stored for 84 days at 3 and 7degrees C. A surface treatment that consisted of dipping wieners into solutions containing < or = 6% lactate and < or = 3% diacetate for 5 s did not delay pathogen growth compared with that for untreated wieners. In additional trials, the antilisterial activity of lactate and diacetate in wiener and bratwurst formulations was evaluated. Lactate levels ranged from 1.32 to 3.4%, and diacetate was evaluated at 0.1 and 0.25%. The growth of L. monocytogenes was delayed for 4 and 12 weeks at 7 and 3 degrees C, respectively, on uncured, unsmoked bratwurst formulated with 3.4% lactate/0.1% diacetate, compared with 1 and 2 weeks, respectively, for the formulation containing 2% lactate. L. monocytogenes grew by > or = 1 log unit after 4 weeks' storage at 3 or 7 degrees C on cured, smoked bratwurst without lactate or diacetate, but growth was inhibited for 12 weeks on cured, smoked bratwurst formulated with 3.4% lactate and 0.1% diacetate. Sodium lactate levels of > or = 3% and combinations of > or = 1% lactate plus > or = 0.1% diacetate prevented listerial growth on wieners stored for 60 days at 4.5 degrees C. These results indicate that dipping wieners in lactate-diacetate solutions is not an efficient way to apply these antimicrobial agents to wieners. However, the inclusion of combinations of sodium lactate and sodium diacetate in wiener or bratwurst formulations inhibits the growth of L monocytogenes at < or = 7 degrees C, and an additional margin of safety was observed for products that are cured and smoked.     

Control of Listeria monocytogenes with combined antimicrobials after postprocess contamination and extended storage of frankfurters at 4 degrees C in vacuum packages

Contamination of ready-to-eat foods, such as frankfurters, with Listeria monocytogenes, is a major concern that needs to be addressed in order to enhance the safety of these products. The objective of this study was to determine the effectiveness of combinations of antimicrobials included in the formulation of frankfurters against L. monocytogenes inoculated (10(3) to 10(4) CFU/cm2) on their surface after peeling and before vacuum packaging. In addition, the antilisterial effect of immersing the packaged products, prepared with or without antimicrobials, in hot (75 or 80 degrees C) water for 30 to 90 s was evaluated. Samples were stored at 4 degrees C for up to 120 days and periodically analyzed for pH and for microbial growth on tryptic soy agar plus 0.6% yeast extract (TSAYE) and PALCAM agar. Sodium lactate (1.8%; 3% of a 60% commercial solution) used alone inhibited growth of L. monocytogenes for 35 to 50 days, whereas when used in combination with 0.25% sodium acetate, sodium diacetate, or glucono-delta-lactone (GDL), sodium lactate inhibited growth throughout storage (120 days). Immersing packaged frankfurters in hot water (80 degrees C, 60 s) reduced inoculated populations of L. monocytogenes by 0.4 to 0.9 log CFU/cm2 and reduced its growth by 1.1 to 1.4 log CFU/cm2 at 50 to 70 days of storage in samples containing 1.8% sodium lactate alone. However, immersion of frankfurters containing no antimicrobials in hot water (75 or 80 degrees C) did not inhibit growth of the pathogen for more than 10 to 20 days, unless one frankfurter was placed per bag and heat treated for 90 s. These results indicate that the inclusion of 1.8% sodium lactate with 0.25% sodium acetate, sodium diacetate, or GDL in cured meat formulations may control L. monocytogenes growth during refrigerated (4 degrees C) storage. Additional studies are required to evaluate the effects of these combinations at abusive temperatures of storage, as well as on additional processed meat formulations and on the sensory quality and shelf life of products.     

Effect of selected generally recognized as safe preservative sprays on growth of Listeria monocytogenes on chicken luncheon meat

The ability of selected generally recognized as safe (GRAS) chemical preservatives to reduce populations or inhibit growth of Listeria monocytogenes on chicken luncheon meat was evaluated. Slices of luncheon meat were treated by evenly spraying onto their surfaces 0.2 ml of a solution of one of four preservatives (sodium benzoate, sodium propionate, potassium sorbate, and sodium diacetate) at one of three different concentrations (15, 20, or 25% [wt/vol]). Each slice was then surface inoculated with a five-strain mixture of 10(5) CFU of L. monocytogenes per ml, held at 4, 13, or 22 degrees C, and assayed for L. monocytogenes immediately after inoculation and at 3, 7, 10, and 14 days of storage. Initial reductions of L. monocytogenes populations ranged from 0.78 to 1.32 log10 CFU g(-1) at day 0 for sodium benzoate- or sodium diacetate-treated meat, whereas reductions for the sodium propionate or potassium sorbate treatments were only 0.14 to 0.36 log10 CFU g(-1). After 14 days of storage at 4 degrees C, L. monocytogenes populations on all treated slices were 1.5 to 3 log10 CFU g(-1) less than on the untreated slices. At 13 degrees C and after 14 days of storage, L. monocytogenes populations were 3.5 and 5.2 log10 CFU g(-1) less on luncheon meat slices treated with 25% sodium benzoate or 25% sodium diacetate, respectively, and ca. 2 log10 CFU g(-1) less when treated with 25% sodium propionate or 25% potassium sorbate than on untreated control slices. Only sodium diacetate was highly inhibitory to L. monocytogenes on meat slices held at 22 degrees C for 7 days or longer. Untreated luncheon meat held at 22 degrees C was visibly spoiled within 10 days, whereas there was no evidence of visible spoilage on any treated luncheon meat at 14 days of storage.     

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.     

Controlling Listeria monocytogenes on sliced ham and turkey products using benzoate, propionate, and sorbate

The objective of this study was to identify concentrations of sorbate, benzoate, and propionate that prevent the growth of Listeria monocytogenes on sliced, cooked, uncured turkey breast and cured ham. Sixteen test formulations plus a control formulation for each product type were manufactured to include potassium sorbate, sodium benzoate, or sodium propionate, used alone and combined (up to 0.3% [wt/wt]), or with sodium lactate-sodium diacetate combinations. Products were inoculated with L. monocytogenes (5 log CFU/100-g package) and stored at 4, 7, or 10 degrees C for up to 12 weeks, and triplicate samples per treatment were assayed biweekly by plating on modified Oxford agar. Data showed that 0.1% benzoate, 0.2% propionate, 0.3% sorbate, or a combination of 1.6% lactate with 0.1% diacetate prevented the growth of L. monocytogenes on ham stored at 4 degrees C for 12 weeks, compared with greater than a 1-log increase at 4 weeks for the control ham without antimicrobials. When no nitrite was included in the formulation, 0.2% propionate used alone, a combination of 0.1% propionate with 0.1% sorbate, or a combination of 3.2% lactate with 0.2% diacetate was required to prevent listerial growth on the product stored at 4 degrees C for 12 weeks. Inhibition was less pronounced when formulations were stored at abuse temperatures. When stored at 7 degrees C, select treatments delayed listerial growth for 4 weeks but supported significant growth at 8 weeks. All treatments supported more than a 1-log increase in listerial populations when stored at 10 degrees C for 4 weeks. These results verify that antimycotic agents inhibit the growth of L. monocytogenes on ready-to-eat meats but aremore effective when used in combination with nitrite.