Acidified sodium chlorite treatment for inhibition of Listeria monocytogenes growth on the surface of cooked roast beef

The effects of acidified sodium chlorite (ASC) against Listeria monocytogenes on the surface of cooked roast beef were investigated. L. monocytogenes, strain V7, serotype 1/2a, was inoculated at numbers of 6.0 log CFU/g onto 5-g cubes of cooked regular or spicy roast beef. The samples were allowed to air dry for 1 h. The cooked roast beef samples were dipped into ASC or sprayed with ASC solutions of 250, 500, 750, or 1,000 ppm, then placed in bags with or without a vacuum and refrigerated at 4 degrees C. L. monocytogenes counts were determined after 0, 7, 14, 21, and 28 days of storage by spread plating roast beef samples onto Oxford agar plates that were incubated at 37 degrees C for 48 h. At day 28, the number of L. monocytogenes on the > or = 500 ppm ASC-treated spicy roast beef samples had count reductions that were >4.0 log CFU/g, whereas the same concentrations of ASC-treated regular roast beef samples had approximately a 2.5 log CFU/g reduction in L. monocytogenes counts when compared with the untreated samples. No significant differences (P > 0.05) were observed in L. monocytogenes counts between the vacuum- or nonvacuum-packaged ASC-treated cooked roast beef samples. Sensory evaluation showed no significant differences (P > 0.05) between ASC-treated and untreated roast beef. ASC can be used as a processing aid in the form of a dip or spray treatment to control L. monocytogenes on the surface of cooked roast beef.     

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

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

Efficacy of cetylpyridinium chloride against Listeria monocytogenes and its influence on color and texture of cooked roast beef

Sliced (cut) and exterior (intact) surfaces of restructured cooked roast beef were inoculated with Listeria monocytogenes, treated with cetylpyridinium chloride (CPC; immersion in 500 ml of 1% solution for 1 min), individually vacuum packaged, and stored for 42 days at 0 or 4 degrees C. Noninoculated samples were similarly treated, packaged, and stored to determine effects on quality (color and firmness) and on naturally occurring bacterial populations, including aerobic plate counts and lactic acid bacteria. Immediately after CPC treatment, regardless of inoculation level, L. monocytogenes populations were reduced (P = 0.05) by about 2 log CFU/cm2 on sliced surfaces and by about 4 log CFU/cm2 on exterior surfaces. Throughout 42 days of refrigerated storage (at both 0 and 4 degrees C), L. monocytogenes populations on CPC-treated samples remained lower (P = 0.05) than those of nontreated samples for both surface types. After 42 days of storage at both 0 and 4 degrees C, aerobic plate count and lactic acid bacteria populations of treated samples were 1 to 1.5 log CFU/cm2 lower (P = 0.05) than those of nontreated samples for both surface types. CPC treatment resulted in negligible effects (P > 0.05) on the color (L*, a*, and b* values) of exterior and sliced roast beef surfaces during storage. For both sliced and exterior surfaces, CPC-treated samples were generally less firm than nontreated samples. CPC treatment effectively reduced L. monocytogenes populations on roast beef surfaces and resulted in relatively minor impacts on color and texture attributes. CPC treatment, especially when applied to products prior to slicing, may serve as an effective antimicrobial intervention for ready-to-eat meat products.     

Acid adaptation does not promote survival or growth of Listeria monocytogenes on fresh beef following acid and nonacid decontamination treatments

The objective of this study was to evaluate the survival and growth of acid-adapted and nonadapted Listeria monocytogenes inoculated onto fresh beef subsequently treated with acid or nonacid solutions. Beef slices (2.5 by 5 by 1 cm) from top rounds were inoculated with acid-adapted or nonadapted L. monocytogenes (4.6 to 5.0 log CFU/cm2) and either left untreated (control) or dipped for 30 s in water at 55 degrees C, water at 75 degrees C, 2% lactic acid at 55 degrees C, or 2% acetic acid at 55 degrees C. The beef slices were vacuum packaged and stored at 4 or 10 degrees C and were analyzed after 0, 7, 14, 21, and 28 days of storage. Dipping in 75 degrees C water, lactic acid, and acetic acid resulted in immediate pathogen reductions of 1.4 to 2.0, 1.8 to 2.6, and 1.4 to 2.4 log CFU/cm2, respectively. After storage at 10 degrees C for 28 days, populations of L. monocytogenes on meat treated with 55 degrees C water increased by ca. 1.6 to 1.8 log CFU/cm2. The pathogen remained at low population levels (1.6 to 2.8 log CFU/cm2) on acid-treated meat, whereas populations on meat treated with 75 degrees C water increased rapidly, reaching levels of 3.6 to 4.6 log CFU/cm2 by day 14. During storage at 4 degrees C, there was no growth of the pathogen for at least 21 days in samples treated with 55 and 75 degrees C water, and periods of no growth were longer for acid-treated samples. There were no differences between acid-adapted and nonadapted organisms across treatments with respect to survival or growth. In conclusion, the dipping of meat inoculated with L. monocytogenes into acid solutions reduced and then inhibited the growth of the pathogen during storage at 4 and 10 degrees C, while dipping in hot water allowed growth despite initial reductions in pathogen contamination. The results of this study indicate a residual activity of acid-based decontamination treatments compared with water-based treatments for refrigerated (4 degrees C) or temperature-abused (10 degrees C) lean beef tissue in vacuum packages, and these results also indicate that this activity may not be counteracted by prior acid adaptation of L. monocytogenes.     

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

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

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

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

Inhibition of Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus on sliced roast beef by cetylpyridinium chloride and acidified sodium chlorite

The effects of 0.5% cetylpyridinium chloride (CPC), 0.12% acidified sodium chlorite (ASC) and a mix of equal volume of the two (0.25% CPC-0.06% ASC) on Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus were evaluated on inoculated sliced roast beef. The antimicrobial agents were, respectively, sprayed on the beef surfaces and tray absorbent pads, and samples were stored at 4 degrees C for 10 days (d). At 0 d, L. monocytogenes and S. aureus were reduced to undetectable levels in 2 h after spraying with CPC. CPC-ASC treatment reduced E. coli O157:H7, L. monocytogenes and S. aureus by 4.07, 6.37 and 4.32 log cfu/cm2, respectively, at 0 d. ASC treatment reduced the population of E. coli O157:H7 by 6.09 log cfu/cm2 at 10 d. CPC treatment caused a slight discoloration and ASC-treated beef surfaces demonstrated the lowest redness and highest lightness. The grey colour and off-odour were significant in the ASC-treated beef samples, while CPC-treated samples demonstrated less off-odor and brown colour from 0 to 4 d. Based on our results, it appears that the application of CPC on sliced roast beef can extend the shelf-life of the product without impairing its quality.     

Efficacy of washing meat surfaces with 2% levulinic, acetic, or lactic acid for pathogen decontamination and residual growth inhibition

We compared spray washing at 55.4 °C with 2% levulinic acid to that with lactic or acetic acid for decontamination of pathogenic bacteria inoculated onto meat surfaces, and their residual protection against later growth of pathogenic bacteria. The model systems included Escherichia coli O157:H7 on beef plate, Salmonella on chicken skin and pork belly, and Listeria monocytogenes on turkey roll. In the decontamination studies, acid washes lowered recoverable numbers of pathogens by 0.6 to 1 log/cm(2) as compared to no-wash controls, and only lactic acid lowered the number of pathogens recovered as compared to the water wash. Washing with levulinic acid at 68.3 or 76.7 °C did not result in additional decontamination of E. coli. Acetic acid prevented residual growth of E. coli and L. monocytogenes, and it reduced numbers of Salmonella on chicken skin to below recoverable levels. Overall, levulinic acid did not provide as effective decontamination as lactic acid nor residual protection as acetic acid.     

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.     

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.     

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

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

Influence of marinades on survival during storage of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on beef jerky

The objective of the present study was to investigate the survival of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on dried beef slices (beef jerky), which were treated (24 h, 4 degrees C) with the following marinades before drying at 60 degrees C for 10 h: (1) control (C), (2) traditional marinade (TM), (3) modified marinade; double the amount of TM with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (4) dipping into 5% acetic acid and then TM (AATM), and (5) dipping into 1% Tween 20 and then into 5% acetic acid followed by the TM (TWTM). Dried meat slices were inoculated with acid-adapted or nonadapted L. monocytogenes (ca. 5.7 log CFU/cm(2)) prior to aerobic storage at 25 degrees C for 60 days. Survivors were determined using tryptic soy agar with 0.1% pyruvate (TSAP) and PALCAM agar. Results showed that surviving bacterial populations on TWTM, AATM, and MM treatments were significantly (P<0.05) lower than those surviving on C and TM until 42 days of storage. By the end of 60 days of storage, bacterial populations in all treatments were not different regardless of acid adaptation or recovery media, except for treatment C inoculated with nonadapted cultures, which had significantly higher TSAP counts than other treatments. There was no significant (P> or =0.05) difference in survival of previously acid-adapted and nonadapted bacterial populations in samples of TWTM, AATM, and MM treatments. However, bacterial populations that were nonadapted were significantly higher than those that were acid-adapted on products of C and TM treatments on days 60 and 24, respectively. The earliest complete elimination (enrichment negative) of the pathogen occurred by day 28 (AATM) in products inoculated with acid-adapted cultures and by day 42 (TWTM and AATM) in products inoculated with nonadapted cultures. These results indicate that use of modified marinades in jerky processing and low water activity provided antimicrobial effects against possible post-processing contamination with L. monocytogenes.     

The antimicrobial properties of chitosan in mayonnaise and mayonnaise-based shrimp salads

The potential for using chitosan glutamate as a natural food preservative in mayonnaise and mayonnaise-based shrimp salad was investigated. Mayonnaise containing 3 g/liter of chitosan combined with acetic acid (0.16%) or lemon juice (1.2 and 2.6%) was inoculated with log 5 to 6 CFU/g of Salmonella Enteritidis, Zygosaccharomyces bailii, or Lactobacillus fructivorans and stored at 5 and 25 degrees C for 8 days. In mayonnaise containing chitosan and 0.16% acetic acid, 5 log CFU/g of L. fructivorans were inactivated, and numbers remained below the sensitivity limit of the plate counting technique for the duration of the experiment. Z. bailii counts were also reduced by approximately 1 to 2 log CFU/g within the first day of incubation at 25 degrees C, but this was followed by growth on subsequent days, giving an overall growth delay of 2 days. No differences in counts of Z. bailii in mayonnaise stored at 5 degrees C or of Salmonella Enteritidis stored at either temperature were observed. In mayonnaise containing lemon juice at both 1.2 and 2.6%, no substantial differences were observed between the controls and the samples containing chitosan. In shrimp salads stored at 5 degrees C, the presence of a coating of chitosan (9 mg/g of shrimp) inhibited growth of the spoilage flora from approximately log 8 CFU/g in the controls to log 4 CFU/g throughout 4 weeks. However, at 25 degrees C, chitosan was ineffective as a preservative. The results demonstrated that chitosan may be useful as a preservative when combined with acetic acid and chill storage in specific food applications.     

Antimicrobial effect of herb extracts against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium associated with beef

The effects of plant extracts against pathogenic bacteria in vitro are well known, yet few studies have addressed the effects of these compounds against pathogens associated with muscle foods. A series of experiments was conducted to determine the effectiveness of a commercially available, generally recognized as safe, herb extract dispersed in sodium citrate (Protecta One) or sodium chloride (Protecta Two) against Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes associated with beef. In the first experiment, E. coli O157:H7, Salmonella typhimurium, and L. monocytogenes inoculated onto beef and subjected to surface spray treatments with 2.5% solutions of Protecta One or Protecta Two were not affected by immediate application (day 0) of the herbal extracts. However, after 7 days of storage at 4 degrees C, E. coli O157:H7 was reduced by >1.3 log10 CFU/cm2 by Protecta Two; L. monocytogenes was reduced by 1.8 and 1.9 log10 CFU/cm2 by Protecta One and Protecta Two, respectively; Salmonella typhimurium was not reduced >0.3 log10 CFU/cm2 by either extract by day 7. In the second experiment, 2.5% Protecta Two (wt/vol or wt/wt) added to inoculated lean and adipose beef trim, processed, and packaged as ground beef chubs (80% lean, 20% adipose), did not reduce pathogen populations >0.5 log10 CFU/g up to 14 days at 4 degrees C. In the third experiment, surface spray treatments of beef with 2.5% lactic acid or 2.5% solutions of Protecta One or Protecta Two, vacuum packaged, and stored up to 35 days at 4 degrees C did reduce E. coli O157:H7, L. monocytogenes, and Salmonella Typhimurium slightly. These studies suggest that the use of herb extracts may afford some reductions of pathogens on beef surfaces; however, the antimicrobial activity may be diminished in ground beef by adipose components.     

INHIBITION OF LISTERIA MONOCYTOGENES,SALMONELLA TYPHIMURIUM AND ESCHERICHIA COLI 0157:H7 ON BEEF MUSCLE TISSUE BY LACTIC OR ACETIC ACID CONTAINED IN CALCIUM ALGINATE GELS1

A method of applying organic acids contained in a calcium alginate gel was tested for inhibiting bacteria contaminating sterile lean beef tissue surfaces. Treated samples were incubated at 5C under controlled moisture conditions for up to 7 days and viable populations of the pathogens determined. For counts of L. monocytogenes, recovered on tryptic soy agar, alginate/lactic acid treatment reduced the log₁₀ counts 1.8 units vs 0.96 for acid treatment without alginate. With acetic acid, log₁₀ reductions were 1.51 vs 2.33 for the alginate/acetic acid vs acetic acid treatment alone. S. typhimurium was reduced 2.11 log₁₀ units vs 1.11 for alginate/lactic acid and acid treatments alone, respectively. The same trend held for E. coli 0157:H7, although the reduction was considerably less, 0.74 log₁₀ reduction vs 0.5 for alginate/lactic acid application vs acid alone. Both Gramnegative organisms were less inhibited by acetic acid treatments.     

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

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

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

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

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.     

Pathogen testing of ready-to-eat meat and poultry products collected at federally inspected establishments in the United States, 1990 to 1999

The Food Safety and Inspection Service (FSIS) conducted microbiological testing programs for ready-to-eat (RTE) meat and poultry products produced at approximately 1,800 federally inspected establishments. All samples were collected at production facilities and not at retail. We report results here for the years 1990 through 1999. Prevalence data for Salmonella, Listeria monocytogenes, Escherichia coli O157:H7, or staphylococcal enterotoxins in nine different categories of RTE meat and poultry products are presented and discussed. The prevalence data have certain limitations that restrict statistical inferences, because these RTE product-testing programs are strictly regulatory in nature and not statistically designed. The cumulative 10-year Salmonella prevalences were as follows: jerky, 0.31%; cooked, uncured poultry products, 0.10%; large-diameter cooked sausages, 0.07%; small-diameter cooked sausages, 0.20%; cooked beef, roast beef, and cooked corned beef, 0.22%; salads, spreads, and patés, 0.05%; and sliced ham and luncheon meat, 0.22%. The cumulative 3-year Salmonella prevalence for dry and semidry fermented sausages was 1.43%. The cumulative 10-year L. monocytogenes prevalences were as follows: jerky, 0.52%; cooked, uncured poultry products, 2.12%; large-diameter cooked sausages, 1.31%; small-diameter cooked sausages, 3.56%; cooked beef, roast beef, and cooked corned beef, 3.09%; salads, spreads, and patés, 3.03%; and sliced ham and luncheon meat, 5.16%. The cumulative 3-year L. monocytogenes prevalence for dry and semidry fermented sausages was 3.25%. None of the RTE products tested for E. coli O157:H7 or staphylococcal enterotoxins was positive. Although FSIS and the industry have made progress in reducing pathogens in these products, additional efforts are ongoing to continually improve the safety of all RTE meat and poultry products manufactured in federally inspected establishments in the United States.     

Postpackage pasteurization of ready-to-eat deli meats by submersion heating for reduction of Listeria monocytogenes

A mixed cocktail of four strains of Listeria monocytogenes was resuspended in product purge and added to a variety of ready-to-eat (RTE) meat products, including turkey, ham, and roast beef. All products were vacuum sealed in shrink-wrap packaging bags, massaged to ensure inoculum distribution, and processed by submersion heating in a precision-controlled steam-injected water bath. Products were run in pairs at various time-temperature combinations in either duplicate or triplicate replications. On various L. monocytogenes-inoculated RTE deli meats, we were able to achieve 2- to 4-log cycle reductions when processed at 195 degrees F (90.6 degrees C), 200 degrees F (93.3 degrees C), or 205 degrees F (96.1 degrees C) when heated from 2 to 10 min. High-level inoculation with L. monocytogenes (approximately 10(7) CFU/ml) ensured that cells infiltrated the least processed surface areas, such as surface cuts, folds, grooves, and skin. D- and z-value determinations were made for the Listeria cocktail resuspended in product purge of each of the three meat categories. However, reduction of L. monocytogenes in product challenge studies showed much less reduction than was observed during the decimal reduction assays and was attributed to a combination of surface phenomena, including surface imperfections, that may shield bacteria from the heat and the migration of chilled purge to the product surface. The current data indicate that minimal heating regimens of 2 min at 195 to 205 degrees F can readily provide 2-log reductions in most RTE deli meats we processed and suggest that this process may be an effective microbial intervention against L. monocytogenes on RTE deli-style meats.