Validation of a commercial process for inactivation of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on the surface of whole muscle beef jerky

Inactivation of Avian Influenza Virus Inoculated into Ground Beef Patties Cooked on a Commercial Open-Flame Gas Grill

With the emergence of clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus (AIV) infection of dairy cattle and its subsequent detection in raw milk, coupled with recent AIV infections affecting dairy farm workers, experiments were conducted to affirm the safety of cooked ground beef related to AIV because such meat is often derived from cull dairy cows. Specifically, retail ground beef (percent lean:fat = ca. 80:20) was inoculated with a low pathogenic AIV (LPAIV) isolate to an initial level of 5.6 log10 50% egg infectious doses (EID50)  per 300 g patty. The inoculated meat was pressed into patties (ca. 2.54 cm thick, ca. 300 g each) and then held at 4 °C for up to 60 min. In each of the two trials, two patties for each of the following three treatments were cooked on a commercial open-flame gas grill to internal instantaneous temperatures of 48.9 °C (120°F), 62.8 °C (145°F), or 71.1 °C (160°F), but without any dwell time. Cooking inoculated ground beef patties to 48.9 °C (ave. cooking time of ca. 15 min) resulted in a mean reduction of ≥2.5 ± 0.9 log10 EID50 per 300 g of ground beef as assessed via quantification of virus in embryonating chicken eggs (ECEs). Likewise, cooking patties on a gas grill to 62.8 °C (ave. cooking time of ca. 21 min) or to the USDA FSIS recommended minimum internal temperature for ground beef of 71.1 °C (ave. cooking time of ca. 24 min) resulted in a reduction to nondetectable levels from initial levels of ≥5.6 log10 EID50 per 300 g. These data establish that levels of infectious AIV are substantially reduced within inoculated ground beef patties (20% fat) using recommended cooking procedures.

Inactivation of Listeria monocytogenes and Salmonella spp. During Cooking of Country Ham and Fate of L. monocytogenes and Staphylococcus aureus During Storage of Country Ham Slices

Thermal inactivation studies were undertaken on Listeria monocytogenes and Salmonella spp. inoculated on the surface of country ham. Hams (average = ca. 3.4 ± 0.5 kg each; average = ca. ≥18% shrinkage) were used as provided by the processor (i.e., "salted hams"), desalted in tap water (i.e., "desalted hams"), or dried for an additional period (i.e., "extra-dried hams"). Hams were surface inoculated (ca. 9.5 log CFU/ham) with a multistrain cocktail of L. monocytogenes or Salmonella spp. and cooked within a bag ina circulating water bath to an internal temperature of 130°F (54.4°C) instantaneous, 145°F (62.8°C) and held for 4 min, 153°F (67.2°C) and held for 34 s, or 160°F (71.1°C) instantaneous. Regardless of ham type, all four time and temperature combinations tested herein delivered a ≥6.7-log reduction of cells of L. monocytogenes or Salmonella spp. Differences in product pH, moisture content, or aw did not have an appreciable impact on the thermal inactivation of L. monocytogenes or Salmonella spp. on country ham. In addition, shelf-life studies were undertaken using slices of "salted" country ham that were surface inoculated (ca. 5.5 log CFU/slice) with a multistrain cocktail of L. monocytogenes or Staphylococcus aureus and then stored at 20°C. Levels of S. aureus increased by ca. ≤1.4 log CFU/slice during storage for 90 days, whereas levels of L. monocytogenes remained relatively unchanged (≤0.2 log CFU/slice increase). Our data validated that cooking parameters elaborated in the U.S. Department of Agriculture's Food Safety and Inspection Service Cooking Guideline for Meat and Poultry Products (Revised Appendix A) are sufficient to deliver significant reductions (ca. ≥6.8 log CFU/ham) in levels of L.monocytogenes and Salmonella spp. on country ham. In addition, in the event of postprocessing contamination, country ham may support the outgrowth of S. aureus or survival of L. monocytogenes during storage at 20°C for 90 days.

Fate of Listeria monocytogenes, Salmonella spp., and Shiga Toxin-Producing Escherichia coli on Slices of an All-Beef Soppressata during Storage

Cells of Listeria monocytogenes, Salmonella spp., or Shiga toxin-producing Escherichia coli (STEC) were inoculated (ca. 4.0 log CFU/slice) onto slices (ca. 4 g each slice) of an all-beef soppressata (ca. pH 5.05 and a_w 0.85). The storage of vacuum-sealed slices of inoculated soppressata at 4 °C or 20 °C for 90 days resulted in reductions of all three pathogens by ca. 2.2 to 3.1 or ca. ≥3.3 log CFU/slice, respectively. When pathogen levels decreased to below detection (≤1.18 log CFU/slice) by direct plating, it was possible to recover each of the target pathogens by enrichment, albeit more frequently from slices stored at 4 °C (p < 0.05) compared to 20 °C. In summary, the slices of the commercially produced beef soppressata selected for this study did not provide a favorable environment for either survival or outgrowth of surface-inoculated cells of L. monocytogenes, Salmonella spp., or STEC during storage.

Viability of Shiga Toxin-Producing Escherichia coli, Salmonella spp., and Listeria monocytogenes during Preparation and Storage of Fuet, a Traditional Dry-Cured Spanish Pork Sausage

ABSTRACT

The primary objective of this study was to monitor viability of Shiga toxin-producing Escherichia coli (STEC), Salmonella spp., and Listeria monocytogenes during preparation and storage of fuet. Regarding methodology, coarse-ground pork (ca. 35% fat) was mixed with salt (2.5%), dextrose (0.3%), starter culture (ca. 7.0 log CFU/g), celery powder (0.5%), and ground black pepper (0.3%) and then separately inoculated with a multistrain cocktail (ca. 7.0 log CFU/g) of each pathogen. The batter was stuffed into a ca. 42-mm natural swine casing and fermented at 23 ± 2°C and ca. 95% ± 4% relative humidity to ≤pH 5.3 (≤48 h). Sausages were then dried at 12 ± 2°C and ca. 80% ± 4% relative humidity to a water activity (aw) of 0.89 (within 33 days) or aw 0.86 (within 60 days). A portion of each batch of fuet was subjected to high-pressure processing (HPP; 600 MPa for 3 min) before chubs were vacuum packaged and stored for 30 days at 20 ± 2°C. The results revealed that pathogen numbers remained relatively unchanged after fermentation (≤0.35 log CFU/g reduction), whereas reductions of ca. 0.8 to 3.2 log CFU/g were achieved after drying fuet to aw 0.89 or 0.86. Regardless of whether fuet was or was not pressure treated, additional reductions of ca. 2.2 to ≥5.3 log CFU/g after drying were achieved following 30 days of storage at 20°C. For non-HPP-treated fuet dried to aw 0.89 and stored for 30 days at 20°C, total reductions of ≥5.3 log CFU/g in levels of STEC or Salmonella spp. were achieved, whereas levels of L. monocytogenes were reduced by ca. 3.6 log CFU/g. Total reductions of ≥5.3 log CFU/g in levels of all three pathogens were achieved after drying non-HPP-treated fuet to aw 0.86. For fuet dried to aw 0.89 or 0.86, that were pressure treated and then stored for 30 days at 20°C, total reductions of >6.2 log CFU/g in levels of all three pathogens were achieved. In conclusion, the processing parameters tested herein, with or without application of HPP, validated that reductions of ≥2.0 or ≥5.0 log CFU/g in levels of STEC, Salmonella spp., and L. monocytogenes were achieved during preparation and storage of fuet.

HIGHLIGHTS

Guidance on validation of lethal control measures for foodborne pathogens in foods

Food manufacturers are required to obtain scientific and technical evidence that a control measure or combination of control measures is capable of reducing a significant hazard to an acceptable level that does not pose a public health risk under normal conditions of distribution and storage. A validation study provides evidence that a control measure is capable of controlling the identified hazard under a worst-case scenario for process and product parameters tested. It also defines the critical parameters that must be controlled, monitored, and verified during processing. This review document is intended as guidance for the food industry to support appropriate validation studies, and aims to limit methodological discrepancies in validation studies that can occur among food safety professionals, consultants, and third-party laboratories. The document describes product and process factors that are essential when designing a validation study, and gives selection criteria for identifying an appropriate target pathogen or surrogate organism for a food product and process validation. Guidance is provided for approaches to evaluate available microbiological data for the target pathogen or surrogate organism in the product type of interest that can serve as part of the weight of evidence to support a validation study. The document intends to help food manufacturers, processors, and food safety professionals to better understand, plan, and perform validation studies by offering an overview of the choices and key technical elements of a validation plan, the necessary preparations including assembling the validation team and establishing prerequisite programs, and the elements of a validation report.

Processing of Biltong (Dried Beef) to Achieve USDA-FSIS 5-log Reduction of Salmonella without a Heat Lethality Step

In the US, dried beef products (beef jerky) are a popular snack product in which the manufacture often requires the use of a heat lethality step to provide adequate reduction of pathogens of concern (i.e., 5-log reduction of Salmonella as recommended by the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS)). Biltong, a South African-style dried beef product, is manufactured with low heat and humidity. Our objectives were to examine processes for the manufacture of biltong that achieves a 5-log reduction of Salmonella without a heat lethality step and with, or without, the use of additional antimicrobials. Beef pieces (1.9 cm × 5.1 cm × 7.6 cm) were inoculated with a 5-serovar mixture of Salmonella (Salmonella Thompson 120, Salmonella Heidelberg F5038BG1, Salmonella Hadar MF60404, Salmonella Enteritidis H3527, and Salmonella Typhimurium H3380), dipped in antimicrobial solutions (lactic acid, acidified calcium sulfate, sodium acid sulfate) or water (no additional antimicrobial), and marinaded while vacuum tumbling and/or while held overnight at 5 °C. After marination, beef pieces were hung in an oven set at 22.2 °C (72 °F), 23.9 °C (75 °F), or 25 °C (77 °F) depending on the process, and maintained at 55% relative humidity. Beef samples were enumerated for Salmonella after inoculation, after dip treatment, after marination, and after 2, 4, 6, and 8 days of drying. Water activity was generally <0.85 by the end of 6–8 days of drying and weight loss was as high as 60%. Trials also examined salt concentration (1.7%, 2.2%, 2.7%) and marinade vinegar composition (2%, 3%, 4%) in the raw formulation. Nearly all approaches achieved 5-log₁₀ reduction of Salmonella and was attributed to the manner of microbial enumeration eliminating the effects of microbial concentration on dried beef due to moisture loss. All trials were run as multiple replications and statistical analysis of treatments were determined by repeated measures analysis of variance (RM-ANOVA) to determine significant differences (p < 0.05). We believe this is the first published report of a biltong process achieving >5.0 log₁₀ reduction of Salmonella which is a process validation requirement of USDA-FSIS for the sale of dried beef in the USA.

Meat Bars: A Survey To Assess Consumer Familiarity and Preparation Parameters and a Challenge Study To Quantify Viability of Shiga Toxin-Producing Escherichia coli Cells during Processing and Storage

Meat bars are dried snacks containing a mixture of meat, berries, and nuts. To explore consumer awareness of meat bars, we conducted two online, nationally representative surveys and established that 70.8% (743 of 1,050) of U.S. citizens were unfamiliar with this product. When asked to check all answers that applied, most of the 545 respondents (who were recruited based on their familiarity with meat bars) preferred beef (n = 385) as the protein source, followed by chicken (n = 293), pork (n = 183), and turkey (n = 179). Most meat bars were purchased from grocery stores (n = 447), followed by online orders (n = 130) and outdoor stores (n = 120). When asked specifically whether they made their own meat bars, 17.8% of respondents (97 of 545) replied "yes," the majority (52 of 97, 54%) of which obtained recipes online. Some 69.1% (67 of 97) measured the internal temperature of the meat during dehydration, but only 10.3% (10 of 97) confirmed the internal temperature by using a thermometer. Given the paucity of information available on the fate of pathogenic or spoilage bacteria associated with meat bars, as another component of this study, batter was prepared with or without encapsulated citric acid (ECA; 0.74%) added to a formulation of ground beef (65%; 90% lean, 10% fat), chopped pecans (15%), golden flaxseed flour (9.7%), chopped cranberries (5.0%), chopped sunflower seeds (3.1%), sea salt (1.1%), black pepper (0.8%), and celery powder (0.35%). Batter was inoculated (ca. 6.5 log CFU/g) with Shiga toxin-producing Escherichia coli (STEC), portioned by hand (40 ± 0.1 g each), and then dried in a commercial dehydrator. Regardless of the drying treatment, inclusion of ECA in the batter resulted in a pH decrease from ca. 5.5 to ca. 4.7 to 5.0 in the finished product. Without ECA, when meat bars were dried at 62.8°C for 6 h, 71.1°C for 4 h, or 62.8°C for 2 h and then 71.1°C for 2 h, levels of STEC decreased by ca. 6.2, 6.3, or 5.2 log CFU/g, respectively. With ECA, STEC decreased by ca. 6.0, 6.6, or 6.0 log CFU/g in meat bars dried at 62.8°C for 6 h, 71.1°C for 4 h, or 62.8°C for 2 h and then 71.1°C for 2 h, respectively. Our results confirmed that a ≥5.0-log reduction in STEC could be achieved in meat bars formulated with or without ECA under all dehydration conditions tested.

Thermal Inactivation of Salmonella in Pâté Made from Chicken Liver

HIGHLIGHTS

Cooking may reduce the potential risk of salmonellosis associated with liver pâté. A 5-log reduction was achieved when inoculated pâté was cooked to an internal temperature of ≥73.8°C. A 5-log reduction was achieved when pâté was made with inoculated liver fried for >8 min at 140°C. Findings of this study may be useful for establishing cooking guidelines for liver and pâté.

Adjusting Processing Parameters in an Entry-Level Commercial Dehydrator To Achieve a 5-Log Reduction of Salmonella during the Cooking Step

The U.S. Department of Agriculture, Food Safety and Inspection Service (FSIS) guidance encourages jerky processors to use a single lethality step that will achieve a 5-log reduction of Salmonella. Many processors rely on internal temperature-time combinations recommended in this guidance. However, the efficacy of convective heating is highly dependent on relative humidity (RH). RH recommendations are vague because of variability in processing conditions and limited available data. This study was conducted to establish processing conditions for an entry-level commercial dehydrator (Harvest Saver R5A) to achieve a 5-log reduction of Salmonella. Unseasoned, unmarinated top round beef strips (65 mm thick) were inoculated with Salmonella (>7 log CFU/g) and processed with the chamber temperature set to 82.2°C for a total cook time of 60 min with the intake closed (closed oven). Modifications (product load and fan speed) were made in subsequent trials to improve lethality. After incubation at 37°C for 24 to 48 h, surviving Salmonella populations were enumerated on tryptic soy agar. In trial A, the maximum fan speed (2.5 m/s) with 30 kg of product resulted in 45 to 48.5% RH at 60 min, and a 5-log reduction of Salmonella was achieved in only 35.5% of the meat samples (54 of 152 samples). Increasing the product load by 40% (42 kg; trial B) increased RH in the chamber (57 to 85%) and resulted in improved lethality; a 5-log reduction was achieved in 95.0% of samples (131 of 138 samples). Because samples with reduced lethality were located on the windward side of the chamber, the fan speed was reduced (0.9 m/s; trial C1) to increase the RH, resulting in a 5-log reduction in 100% of the samples (138 of 138 samples). A replicate trial (trial C2) was conducted, and a 5-log reduction again was achieved in 100% of the samples. All trials exceeded recommendations by the FSIS; however, adequate Salmonella reduction was achieved only when the RH was >65% throughout. Product load and fan speed are practical parameters for processors to manipulate to increase the RH in closed systems and thus improve Salmonella lethality.

Viability of Listeria monocytogenes on uncured turkey breast commercially prepared with and without buffered vinegar during extended storage at 4 and 10°C

We determined the viability of Listeria monocytogenes on uncured turkey breast containing buffered vinegar (BV) and surface treated with a stabilized solution of sodium chlorite in vinegar (VSC). Commercially produced, uncured, deli-style turkey breast was formulated with BV (0.0, 2.0, 2.5, or 3.0%), sliced (ca. 100 g and ca. 1.25 cm thick), and subsequently surface inoculated (ca. 4.3 log CFU per slice) in each of two trials with a five-strain cocktail of L. monocytogenes. Next, 1 ml per side of a 2 or 10% solution of VSC was added to each package before vacuum sealing and storing at 4 or 10°C. Without antimicrobials, L. monocytogenes numbers increased by ca. 6.2 log CFU per slice after 90 and 48 days of storage at 4 or 10°C, respectively. At 4°C, L. monocytogenes numbers increased by ca. 0.4 to 1.9 log CFU per slice on turkey breast formulated with 2.0 or 2.5% BV and treated or not with 2% VSC, whereas when treated with 10% VSC, L. monocytogenes levels remained relatively unchanged over 90 days. However, when turkey breast was formulated with 3.0% BV and treated or not with VSC, pathogen numbers decreased by ca. 0.7 to 1.3 log CFU per slice. At 10°C, L. monocytogenes numbers increased by ca. 1.5 to 5.6 log CFU per slice after 48 days when formulated with 2.0 to 3.0% BV and treated or not with 2% VSC. When formulated with 2.0% BV and treated with 10% VSC, L. monocytogenes numbers increased by ca. 3.3 log CFU per slice, whereas when formulated with 2.5 or 3.0% BV and treated with 10% VSC, L. monocytogenes decreased by ca. 0.3 log CFU per slice. Inclusion of BV as an ingredient in uncured turkey breast, alone or in combination with VSC added to the package, appreciably suppressed outgrowth of L. monocytogenes during an extended refrigerated shelf life.

Validation of ground-and-formed beef jerky processes using commercial lactic acid bacteria starter cultures as pathogen surrogates

Beef jerky has been linked to multiple outbreaks of salmonellosis and Escherichia coli O157:H7 infection over the past 40 years. With increasing government scrutiny of jerky-making process lethality, a simple method by which processors can easily validate the lethality of their ground-and-formed beef jerky process against Salmonella' and E. coli O157:H7 is greatly needed. Previous research with whole-muscle beef jerky indicated that commercial lactic acid bacteria (LAB) may be more heat resistant than Salmonella and E. coli O157:H7, suggesting the potential use of LAB as pathogen surrogates. Of six commercial LAB-containing cultures evaluated for heat resistance in ground-and-formed beef jerky, Saga 200 (Pediococcus spp.) and Biosource (Pediococcus acidilactici) were identified as consistently more heat resistant than Salmonella and E. coli O157:H7. Six representative ground-and-formed beef jerky commercial processes, differing widely in lethality, were used to identify an appropriate level of LAB reduction that would consistently indicate a process sufficiently lethal (> or = 5.0-log reduction) for Salmonella and E. coli O157:H7. Both Saga 200 and Biosource consistently predicted adequate process lethality with a criterion of > or = 5.0-1og reduction of LAB. When either LAB decreased by > or = 5.0 log CFU, processes were sufficiently lethal against Salmonella and E. coli O157:H7 in 100% of samples (n=39 and 40, respectively). Use of LAB as pathogen surrogates for ground-and-formed beef jerky process validation was fieldtested by three small meat processors, who found this technique easy to use for process validation.

Validation of commercial processes for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on the surface of whole-muscle turkey jerky

Three strips of turkey breast meat were separately inoculated with multistrain mixtures of Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes and placed on the top, middle, and bottom levels of a loading rack. The strips on the rack were then loaded into a smokehouse and cooked-dried for either 2.5 or 3.5 h at 73.8 degrees C (165 degrees F) or 1.5 or 2.5 h at 82.2 degrees C (180 degrees F) with constant hickory smoking and without addition of humidity. Cooking-drying marinated turkey jerky at 73.8 degrees C (165 degrees F) or 82.2 degrees C (180 degrees F) resulted in a >or= 7.1 log(10) cfu/strip reduction of all 3 pathogens. For nonmarinated jerky strips that were inoculated with E. coli O157:H7 or L. monocytogenes and cooked-dried at 82.2 degrees C (180 degrees F), a reduction of >or= 7.4 log(10) cfu/strip was observed, whereas for strips that were inoculated with Salmonella, a reduction of >or= 6.8 log(10) cfu/strip was observed. Cooking-drying nonmarinated turkey breast strips at 73.8 degrees C (165 degrees F) for 3.5 h resulted in a reduction of ca. 7.1 to 7.6 log(10) cfu/strip for all 3 pathogens, whereas for strips that were cooked-dried for 2.5 h, a reduction of ca. 5.4 to 6.2 log(10) cfu/strip was observed. Only marinated turkey jerky that was cooked-dried for 3.5 h at 73.8 degrees C (165 degrees F) satisfied the USDA-FSIS standard of identity (moisture: protein <or= 0.75:1.0) or shelf-stability (water activity of <or= 0.80), or both, requirements for jerky.

Behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in teewurst, a raw spreadable sausage

The fate of Listeria monocytogenes, Salmonella Typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on teewurst, a traditional raw and spreadable sausage of Germanic origin. Multi-strain cocktails of each pathogen (ca. 5.0 log CFU/g) were used to separately inoculate teewurst that was subsequently stored at 1.5, 4, 10, and 21 degrees C. When inoculated into commercially-prepared batter just prior to stuffing, in general, the higher the storage temperature, the greater the lethality. Depending on the storage temperature, pathogen levels in the batter decreased by 2.3 to 3.4, ca. 3.8, and 2.2 to 3.6 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, during storage for 30 days. When inoculated onto both the top and bottom faces of sliced commercially-prepared finished product, the results for all four temperatures showed a decrease of 0.9 to 1.4, 1.4 to 1.8, and 2.2 to 3.0 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, over the course of 21 days. With the possible exceptions for salt and carbohydrate levels, chemical analyses of teewurst purchased from five commercial manufacturers revealed only subtle differences in proximate composition for this product type. Our data establish that teewurst does not provide a favourable environment for the survival of E. coli O157:H7, S. Typhimurium, or L. monocytogenes inoculated either into or onto the product.

Fate of surface-inoculated Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium on kippered beef during extended storage at refrigeration and abusive temperatures

The behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium on kippered beef was evaluated. Individual pieces of the product were separately inoculated on the top and bottom surfaces with each three- to six-strain pathogen cocktail at ca. 6.0 log CFU per piece and stored at 4, 10, 21, or 30 degrees C for up to 28 days in each of two trials. When kippered beef was inoculated with E. coli O157:H7, Salmonella Typhimurium, or L. monocytogenes and stored at 4, 10, 21, or 30 degrees C for up to 28 days, pathogen numbers decreased ca. 0.4 to 0.9, 1.0 to 1.8, 3.0 to > or = 5.25, and > or = 5.0 to 5.25 log CFU per piece, respectively. Average D-values for E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes stored at 4 to 30 degrees C for 28 days were ca. 41 to 4.6, 40.8 to 5.3, and 29.5 to 4.3 days, respectively. As expected, the higher the storage temperature, the greater the level and rate of inactivation for all three pathogens. These data establish that kippered beef does not provide an environment conducive to proliferation of these pathogens.