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Thermal processes used in making whole-muscle beef jerky include a drying step, which may result in enhanced pathogen thermotolerance and evaporative cooling that reduce process lethality. Several salmonellosis outbreaks have been associated with beef jerky. In this study, a standardized process was used to inoculate beef strips with five-strain cocktails of either Salmonella serovars or Escherichia coli O157:H7, to marinate the strips at pH 5.3 for 22 to 24 h at 5 degrees C, and to convert the strips to jerky using various heating and drying regimes. Numbers of surviving organisms were determined during and after heating and drying. Salmonella reductions of > or = 6.4 log CFU and similar reductions in E. coli O157:H7 were best achieved by ensuring that high wet-bulb temperatures were reached and maintained early in the process (51.7 or 54.4 degrees C for 60 min, 57.2 degrees C for 30 min, or 60 degrees C for 10 min) followed by drying at 76.7 degrees C (dry-bulb temperature). Processes with less lethality that reduced counts of both pathogens by > or = 5.0 log CFU were (i) heating and drying at 76.7 degrees C (dry bulb) within 90 min of beginning the process, (ii) heating for successive hourly intervals at 48.9, 54.4, 60, and 76.7 degrees C (dry bulb), and (iii) heating at 51.7 degrees C (dry bulb) and then drying at 76.7 degrees C (dry bulb), starting before the product water activity dropped below 0.86. In several trials, separate beef strips were inoculated with a commercial Pediococcus acidilactici starter culture as a potential surrogate for evaluating pathogen thermotolerance. The results of these trials suggested that this experimental approach may be useful for in-plant validation of process lethality.

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In the manufacture of beef jerky, a thermal lethality step is followed by drying to prevent growth of pathogenic bacterial postprocessing contaminants on the finished product. Recent guidelines from the U.S. Department of Agriculture have raised the question of the maximum water activity (a(w)) in jerky products that will inhibit growth of pathogenic bacteria. The survival of the potential postprocessing contaminants Staphylococcus aureus and Listeria monocytogenes was evaluated on 15 vacuum-packaged beef jerky and related products with a(w) values ranging from 0.47 to 0.87, just below the 0.88 limit reported for anaerobic growth of S. aureus. Small individual product pieces were inoculated on the outer surface with five strains each of S. aureus and L. monocytogenes, repackaged under vacuum, and stored at room temperature (21 degrees C) for 4 weeks. Pathogen numbers were determined before storage and after 1 and 4 weeks. None of the 15 jerky products supported growth of either pathogen. Counts of S. aureus fell by 0.2 to 1.8 log CFU after 1 week of storage and by 0.6 to 5.3 log CFU after 4 weeks of storage. Numbers of L. monocytogenes fell by 0.6 to 4.7 log CFU and by 2.3 to 5.6 log CFU after 1 and 4 weeks of storage, respectively. Although factors other than a(w) may have some effect on pathogen survival, the results of the present study clearly support drying beef jerky to an a(w) of < or = 0.87 to ensure that bacterial pathogens cannot grow on vacuum-packaged product stored at room temperature.

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This study was conducted to evaluate small-scale hot-water postpackaging pasteurization (PPP) as a postlethality (post-cooking) treatment for Listeria monocytogenes on ready-to-eat beef snack sticks and natural-casing wieners. Using a commercially available plastic packaging film specifically designed for PPP applications and 2.8 liters of boiling water (100 degrees C) in a sauce pan on a hot plate, an average reduction in L. monocytogenes numbers of > or = 2 log units was obtained using heating times of 1.0 min for individually packaged beef snack sticks (three brands) and 4.0 min for packages of four sticks (two brands) and seven sticks (three brands). Average product surface temperatures, measured as soon as possible after PPP and opening the package, were 47 to 51.5, 58 to 61.5, and 58.5 to 61 degrees C for the beef snack sticks packages of one, four, and seven sticks per package, respectively. A treatment of 7.0 min for packages of four natural-casing wieners (three brands) achieved L. monocytogenes reductions of > or = 1.0 log unit and average product surface temperature of 60.5 to 63.5 degrees C. Cooked-out fat and moisture resulting from tested treatments ranged from 0.2 to 1.1% by weight for beef snack sticks and from 0.4 to 1.2% by weight for natural-casing wieners. For natural-casing wieners, PPP had no detrimental effect on overall product desirability to consumers; results suggested that PPP may significantly enhance appearance of this product. However, for beef snack sticks the cooking out of fat and moisture during PPP had a significant negative effect on consumer opinions of product appearance.

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The U.S. Department of Agriculture has established standards for the composition and shelf stability of various ready-to-eat meat products. These standards may include product pH, moisture:protein ratio, and water activity (aw) values. It is unclear how closely these standards are based on the potential for pathogen growth or toxin production. Because the vacuum packaging used on most ready-to-eat meat products inhibits mold, Staphylococcus aureus is the pathogen most likely to grow on products with reduced aw and increased percentage of water-phase salt. In this study, 34 samples of various ready-to-eat meat products were inoculated with a three-strain mixture of S. aureus, vacuum packaged, and stored at 21 degrees C for 4 weeks. S. aureus numbers decreased by 1.1 to 5.6 log CFU on fermented products (pH < or = 5.1) with a wide range of salt concentrations and moisture content. Similarly, S. aureus numbers decreased by 3.2 to 4.5 log CFU on dried nonacidified jerky (aw < or = 0.82; moisture:protein ratio of < or =0.8). Products that were not fermented or dried clearly supported S. aureus growth and cannot be considered shelf stable. The product pH and moisture:protein ratio were the two compositional factors most highly correlated (R2 = 0.84) with S. aureus survival and growth for the types of products tested, but pH and aw or pH and percentage of water-phase salt also may provide useful predictive guidance (R2 = 0.81 and 0.77, respectively).

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Food regulatory agencies advise against thawing frozen meat and poultry at room temperature. In this study, whole chickens (1,670 g) and ground beef (453 and 1,359 g) were inoculated with Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus on the surface (all products) and in the center (ground beef). After freezing at -20 degrees C for 24 h, products were thawed at 22 or 30 degrees C for 9 h. Pathogen growth was predicted using product time and temperature data and growth values from the U.S. Department of Agriculture Agricultural Research Service Pathogen Modeling Program 7.0 predictive models of pathogen growth. No pathogen growth was predicted for whole chicken or 1,359 g of ground beef thawed at 30 degrees C or 453 g of ground beef thawed at 22 degrees C. Growth (< or = 5 generations) was predicted for 453 g of ground beef at 30 degrees C. Inoculation study data corroborated the predictions. No growth occurred on whole chickens or 1,359-g portions of ground beef thawed at 30 degrees C for 9 h. Pathogen numbers increased an average of 0.2 to 0.5 log on the surface of 453-g ground beef portions thawed for 9 h at 22 or 30 degrees C. Our results suggest that thawing > or = 1,670 g of whole chicken at < or = 30 degrees C for < or = 9 h and thawing >453 g ground beef portions at < or = 22 degrees C for < or = 9 h are not particularly hazardous practices. Thawing smaller portions at higher temperatures and/or for longer times cannot be recommended, however. Use of values derived from the Pathogen Modeling Program 7.0 model provided realistic predictions of pathogen growth during thawing of frozen ground beef and chicken.

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The U.S. Department of Agriculture has cautioned against slow cooking meat such that the interior temperature increases from 10 degrees C (50 degrees F) to 54.4 degrees C (130 degrees F) in > or = 6 h. During a commercial ham-smoking process, the ham cold point is typically between 10 and 54.4 degrees C for 13 h, but the ham is subsequently exposed to heating sufficient to eliminate vegetative pathogenic bacteria. Thus, production of heat-stable staphylococcal enterotoxin is the primary biological hazard. For this study, uncooked surface and uncooked ground interior ham were inoculated with a three-strain Staphylococcus aureus mixture, exposed to simulated surface and interior slow-cook conditions, respectively, and analyzed periodically using the Baird-Parker agar and 3M Petrifilm Staph Express count plate methods. For the surface and interior conditions, S. aureus numbers increased by no more than 0.1 and 0.7 log units, respectively. Predictions derived from actual time and temperature data and S. aureus growth values from a computer-generated model (Pathogen Modeling Program 6.1, U.S. Department of Agriculture) were for 2.7 (ham surface) and 9.9 to 10.5 (ham interior) generations of S. aureus growth, indicating that use of model-derived growth values would not falsely indicate safe slow cooking of ham. The Baird-Parker method recovered significantly (P < 0.05) greater numbers of S. aureus than the Petrifilm Staph Express method. For hams pumped with brine to attain (i) 18% (wt/wt) weight gain, (ii) > or = 2.3% sodium lactate, (iii) > or = 0.8% sodium chloride, and (iv) 200 ppm ingoing sodium nitrite, slow-cooking critical limits of < or = 4 h between 10 and 34 degrees C, < or = 5 h between 34 and 46 degrees C, and < or = 5 h between 46 and 54.4 degrees C could be considered adequate to ensure safety.

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The survival of Listeria monocytogenes was evaluated on 15 ready-to-eat meat products made using drying, fermentation, and/or smoking. The products were obtained from six processors and included summer sausage, smoked cured beef, beef jerky, snack stick, and pork rind and crackling products. The water activity of the products ranged from 0.27 (pork rinds and cracklings) to 0.98 (smoked cured beef slices). Products were inoculated with a five-strain cocktail of L. monocytogenes, repackaged under either vacuum or air, and then stored either at room temperature (21degrees C) or under refrigeration (5 degrees C) for 4 to 11 weeks. Numbers of L. monocytogenes fell for all products during storage, ranging from a decrease of 0.8 log CFU on smoked cured beef slices during 11 weeks under vacuum at 5 degrees C to a decrease of 3.3 log CFU on a pork rind product stored 5 weeks under air at 21degrees C. All of the products tested could be produced under alternative 2 of the U.S. Department of Agriculture regulations mandating control of L. monocytogenes on ready-to-eat meat and poultry products. For many of the products, 1 week of postprocessing storage prior to shipment would act as an effective postlethality treatment and would allow processors to operate under alternative I of these regulations.

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Soudjouk-style batter was inoculated with a five-strain mixture of Escherichia coli O157:H7 at about 7.6 log10 CFU/g in each of two trials. The sticks were fermented and dried at 22 degrees C and 50% relative humidity (RH) for 3 days and then at 9 degrees C and 40% RH for 18 h. After being flattened to about 1.25 cm, the sticks were conditioned at 38 degrees C and 70% RH or at 22 degrees C and 50% RH for about 3 days. After the latter conditioning treatment, sticks either were cooked to an internal temperature of 63 degrees C or received no heat treatment. Final mean pH values after conditioning at 22 degrees C and 50% RH for soudjouk manufactured with a starter culture and dextrose (1.0%) and for soudjouk manufactured without a starter culture were about 4.9 and 6.0, respectively. For soudjouk produced with a starter culture, pathogen numbers were reduced by 4.53 and 0.88 log10 CFU/g after conditioning at 38 degrees C and 70% RH and at 22 degrees C and 50% RH, respectively. For soudjouk produced via natural fermentation, pathogen numbers were reduced by 1.39 and 0.09 log10 CFU/g after conditioning at 38 degrees C and 70% RH and at 22 degrees C and 50% RH, respectively. Cooking reduced pathogen numbers to below the levels detectable by direct plating (<1.0 log10 CFU/g) and by enrichment for soudjouk produced with a starter culture and also reduced pathogen numbers by 6.28 log10 CFU/g for soudjouk produced via natural fermentation. However, cooking also resulted in an unacceptable product. In general, the reduction in pathogen numbers achieved by storage at ambient temperature (25 degrees C) was greater than that achieved by storage at cooler temperatures (4 and 15 degrees C), particularly for soudjouk prepared with a starter culture (for which a final pH value of 4.8 and a 6.4-log10 reduction were obtained after 21 days at 25 degrees C) rather than for that prepared without a starter culture (for which a final pH value of 6.1 and a 2.6-log10 reduction were obtained after 21 days at 25 degrees C). These results indicate that naturally fermented old-country-type sausage may allow the survival of E. coli O157:H7 in the absence of controlled fermentation, postfermentation cooking, and/or an ambient-storage processing step.

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Beef carcass quarters and fat-covered subprimal cuts were suspended vertically and inoculated with a bovine manure slurry containing a five-strain mixture of Escherichia coli O157:H7 to deliver about 4 to 5 log10 CFU/cm2. To identify treatments that would improve the effectiveness of spraying with lactic acid (LA), the inoculated quarters and cuts were treated as follows: experiment A, (i) not treated (control), (ii) sprayed with 2% (vol/vol) LA, (iii) tempered at 21 degrees C for 4 h, and (iv) tempered and then sprayed with LA; experiment B, (v) sprayed with water, (vi) sprayed with LA, (vii) sprayed with LA containing 0.5% (vol/vol) sodium benzoate (SB), and (viii) sprayed with LA containing SB and 5% (vol/vol) Tween 20 (TW20); and experiment C, (ix) sprayed with water (no prespray), (x) presprayed with TW20 and then sprayed with LA, and (xi) presprayed with TW20 and then sprayed with LA containing SB. In experiment A, spraying carcasses with LA significantly (P < 0.05) reduced the numbers of E. coli Biotype I and serotype O157:H7 after 1 and 3 days of storage, respectively. The tempering process employed did not affect the effectiveness of the LA spray on either type of E. coli. In experiment B, there was no significant difference in the reduction of E. coli O157:H7 on subprimal cuts sprayed with water and that on cuts sprayed with LA alone or with LA in combination with SB and TW20 after 1 or 3 days of storage (total reductions ranged from about 1.6 to 2.8 log10 CFU/cm2). In experiment C, prespraying subprimal cuts with TW20 significantly (P < 0.05) increased the effectiveness of LA (reductions of 2.8 and 3.2 log10 CFU/cm2, respectively) and that of LA with SB (reductions of 2.6 and 3.3 log10 CFU/cm2, respectively) compared with spraying with water alone (reductions of ca. 1.0 and 2.0 log10 CFU/cm2, respectively) after I and 3 days of storage, respectively. In a separate experiment, the incorporation of TW20 (0.1 or 0.25%) into buffered peptone water prior to the maceration of excised carcass surface samples resulted in the recovery of significantly larger numbers (ca. 5.1 to 5.2 log10 CFU/cm2) of E. coli O157:H7 cells than did the control treatment without added TW20 (ca. 3.8 to 4.6 log10 CFU/cm2). These results demonstrate that the treatment of beef carcasses with LA reduces the number of viable E. coli O157:H7 cells and that this inactivation or removal by LA is enhanced by prespraying of the carcass with a 5% solution of TW20.

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The population of inoculated Escherichia coli O157:H7 was monitored during the manufacture and storage of a semidry beef summer sausage processed by fermentation and cooking at a low temperature by heating to an internal temperature of 130°F (54°C). The all-beef batter (11% fat and nonmeat ingredients) was inoculated with the commercial starter culture Pediococcus acidilactici HP (≥8.6 log CFU/g of batter) and a five-strain mixture of E. coli O157:H7 (≥7 log CFU/g) and then hand stuffed into 2.5-inch (64-mm) diameter fibrous casings. The sausages were fermented at an initial temperature of 85°F (29°C) to a final temperature of 105°F (41°C) over ca. 13 h at 80% relative humidity (RH) to pH 4.6 or pH 5.0. After fermentation to pH 4.6, the internal temperature of the chubs was raised to 130°F (54°C) instantaneous over 3.6 h at 60% RH. After fermentation to pH 5.0, the internal temperature of the chubs was raised to 130°F (54°C) over 3.6 h at 60% RH and the chubs were maintained under these conditions for 0, 30, or 60 min. he chubs were cold water showered for 15 min and then chilled at 39°F (4°C) for 6 h before being vacuum packaged and stored at 39°F (4°C) or 77°F (25°C) for 7 days. Regardless of the target pH, fermentation alone resulted in only a 1.39-log CFU/g decrease in pathogen numbers. However, fermentation to pH 4.6 and heating to an internal temperature of 130°F (54°C) instantaneous reduced counts of E. coli O157:H7 by ≥7.0 log units to below detection levels (<10 CFU/g). Pathogen numbers remained below levels detectable by direct plating, but viable E. coli O157:H7 cells were recovered by enrichment of samples during sausage storage at either refrigeration or abuse temperatures. In contrast, fermentation to pH 5.0 and heating to an internal temperature of 130°F (54°C) instantaneous resulted in a 3.2-log-unit decrease in counts of E. coli O157:H7. No appreciable reductions in pathogen numbers were observed thereafter following storage at either 39°F (4°C) or 77°F (25°C) for 7 days. Fermentation to pH 5.0 and heating to an internal temperature of 130°F (54°C) instantaneous followed by holding for 30 or 60 min resulted in about a 5- or 7-log reduction, respectively, in pathogen numbers. For chubs held for 30 min at 130°F (54°C), pathogen numbers decreased to 2.02 and <1.0 log CFU/g at 39°F (4°C) and 77°F (25°C), respectively, after 7 days; viable cells were only observed by enrichment after storage at 77°F (25°C). For chubs held for 60 min at 130°F (54°C), pathogen numbers remained below levels detectable by direct plating, but viable cells were recoverable by enrichment after 7 days at both storage temperatures. These data will be useful guidelines to manufacturers for developing processing conditions to further ensure the safety of this category of fermented sausages relative to food-borne pathogens such as serotype O157:H7 strains of E. coli .

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A study to compare procedures and interventions for removing physical and bacterial contamination from beef carcasses was conducted in six carcass conversion operations that were representative of modern, high-volume plants and located in five different states. Treatment procedures included trimming, washing, and the current industry practice of trimming followed by washing. In addition, hot (74 to 87.8°C at the pipe) water washing and rinsing with ozone (0.3 to 2.3 ppm) or hydrogen peroxide (5%) were applied as intervention treatments. Beef carcasses were deliberately contaminated with bovine fecal material at >4.0 log colony-forming units (CFU)/cm2 in order to be better able to observe the decontaminating effects of the treatments. Carcasses were visually scored by 2 to 3 trained personnel for the level of gross contamination before and after treatment. Samples (10 by 15 cm, 0.3 to 0.5 cm thick) for microbiological testing were excised as controls or after application of each procedure or intervention and analyzed for aerobic mesophilic plate counts, Escherichia coli Biotype I counts, and presence or absence of Listeria spp., Salmonella spp., and Escherichia coli O157:H7. Average reductions in aerobic plate counts were 1.85 and 2.00 log CFU/cm2 for the treatments of trimming-washing and hot-water washing, respectively. Hydrogen peroxide and ozone reduced aerobic plate counts by 1.14 and 1.30 log CFU/cm2, respectively. In general, trimming and washing of beef carcasses consistently resulted in low bacterial populations and scores for visible contamination. However, the data also indicated that hot- (74 to 87.8°C at the pipe) water washing was an effective intervention that reduced bacterial and fecal contamination in a consistent manner.