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Control of Listeria monocytogenes


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  • 1. Control of Listeriamonocytogenes
    Kelly J.K. Getty, Ph.D.
    Kansas State University
  • 2. Control and Growth of Listeriamonocytogenes
    Packaging effects on jerky, snack sticks, kippered beef steak, and turkey tenders
    Intrinsic factors in sliced deli turkey roast
    Effect of salts
  • 3. Package Systems and Storage Times Serve as Post-Lethality Controls for Listeria monocytogenes on Whole Muscle Beef Jerky and Pork and Beef Smoked Sausage Sticks
    J. Food Prot. (2011) 74:188-192
    Support provided by the USDA CSREES under agreement 2003-34211-12998, the Kansas Department of Commerce and Housing, Agriculture Marketing Division, and Oberto Sausage Company
  • 4. Background
    A “zero” tolerance policy is applied by USDA to Lm in ready-to-eat meat and poultry products
    USDA defines a post lethality treatment as a process that reduces Lm by at least 1 log
    Research has shown packaging can generate a 1 log Lm reduction following 1 or more weeks of storage at ambient temperature
  • 5. Objective
    To determine the effect of packaging environment and storage time on reducing Listeriamonocytogeneson whole muscle beef jerky and pork and beef smoked sausage sticks
  • 7. Experimental Design
    Jerky cut into square pieces
    Dipped into Lminoculum
    Dry Jerky ~ 1 h
    Enumeration of initial level of Lm
    Four packaging treatments applied
    Measure Water Activity
    Plates incubated for 24 hours at 35˚C
    Hold for 24, 48, 72 h and 30 days
    Enumeration after storage periods
    Plates incubated for 24 hours at 35˚C
  • 8. Inoculum Procedures
    Five strains of Lm were used to prepare a cocktail inoculum.
    One loopful of each strain placed into 9 mL test tubes of tryptic soy broth (TSB). Incubated for 24 hours at 35˚C.
    From the test tubes, 0.5 mL was pipetted into 200 mL jars of TSB. Incubated for 24 hours at 35˚C
    Contents of jars were combined to create 1 L 5 strain cocktail
  • 9. Sampling Procedures
    Jerky was aseptically cut into 4 x 4 cm2 pieces.
    Dipped for 1 minute in 5 strain cocktail of Lm.
    Allowed to air dry for 1 hour.
    Packaged using four treatments:
    - Nitrogen Flush with - Vacuum (VAC)
    oxygen scavenger (NFOS)
    - Heat Seal with - Heat seal (HS)
    oxygen scavenger (HSOS)
    Samples held for 0, 24, 48, 72 h and 30 days
  • 10. Enumeration of Listeriamonocytogenes
    4 x 4 cm2 was placed in a stomacher bag and 34 mL of peptone water was added.
    Samples were stomached for 1 minute.
    Serial dilutions were prepared.
    0.1 mL of each dilution was spread plated onto modified Oxford medium (MOX) plates.
    Plates were incubated at 35˚C for 24 hours.
  • 11. results
  • 12. Mean Log Reduction of Lm on Beef Jerky Packaged in Different Packaging Environments and Stored at Ambient Temperature
    abcde Means having a different superscript differ (P<0.05)
  • 13. Mean Lm Log Reduction (CFU/cm2) on Smoked Sausage Sticks Packaged in Different Packaging Environments
  • 14. Mean Lm Log Reduction (CFU/cm2) on Smoked Sausage Sticks During Ambient Temperature Storage
  • 15. Conclusions
    Jerky - Using these packaging environments in conjunction with at least a 48 h storage time is a Lm post lethality control treatment.
    Snack Sticks - Using these packaging environments in conjunction with at least a 24 h storage time is a Lm post lethality control treatment.
  • 16. Effect of Packaging and Storage Time on Survival of Listeriamonocytogeneson Kippered Beef Steak and Turkey Tenders
    J. Food Sci. (accepted)
  • 17. Objective
    Determine the effect of packaging environment and short term storage time on reducing Listeriamonocytogenesin meat or poultry snacks
  • 18. Materials and Methods
    • Two commercially obtained products:
    • 19. Kippered Beef Steak:
    • 20. Lean beef components, ground and formed
    • 21. Cured Product
    • 22. Turkey Tenders:
    • 23. Whole muscle turkey breast, sliced and marinated
    • 24. Uncured Product
  • Experimental Design
    4 packaging treatments X 4 storage times X 2 samples/treatment X 3 replications
    Packaging treatments:
    • Heat sealed (HS)
    • 25. Heat seal with oxygen scavenger (HSOS)
    • 26. Nitrogen flushed with oxygen scavenger (NFOS)
    • 27. Vacuum (VAC)
    Storage times:
    • 0, 24, 48, or 72 h
  • Procedures
    Product cut into squares or used as intact strips
    Dip into Lm inoculum for 1 min
    Dry Product ~1 h at ambient temperature
    Package in 1 of 4 treatments
    Measure aw
    Spread plate for initial Lm level (time 0 h)
    Hold for 24, 48, or 72 h at ambient temperature
    Incubate plates for 48 h at 35˚C
    Spread plate following storage time
  • 28. Product Characteristics
  • 29. Mean aw During Ambient Time Storage
  • 30. Mean log reductions (CFU/cm2) of Listeriamonocytogenes in kippered beef steak
  • 31. Mean log reductions (CFU/cm2) of Listeriamonocytogenes in turkey tenders
  • 32. Implications
    Processors of these products could use a combination of vacuum or nitrogen flushing and a hold time of 24 h prior to shipping to reduce potential Lm by at least 1 log.
    However, processors should be encouraged to hold product for at least 72 h to enhance the margin of safety.
  • 33. Effect of Intrinsic Factors on Growth of Listeriamonocytogenes in Sliced Deli Turkey Roast
    We acknowledge Cargill Meat Solutions for support of this project.
  • 34. Objectives
    Evaluate how sodium nitrite concentration, percent pump, and salt type affect the growth of L. monocytogenesin vacuum packaged sliced turkey deli roast stored at 4°C for up to 91 days.
  • 35. Materials and Methods
    Sliced turkey deli roasts were formulated with 1.5% sodium chloride (NaCl) or 0.75% NaCl and 0.75% potassium chloride, 10% or 45% pump, and 0 ppm or 200 ppm sodium nitrite (NaNO2) for a total of eight treatments.
    Turkey slices were inoculated with a 5-strain Lm cocktail (inoculated) or peptone water (control) and then vacuum packaged.
  • 36. Materials and Methods
    After 0, 7, 14, 21, 28, 42, 63, and 91 days of 4C storage, treatments were sampled for Lm populations on modified oxford media (MOX) and aerobic plate count (APC).
    pH, water activity (aw), residual nitrite, and percent fat, moisture, protein, and sodium was measured using control treatments for each sampling day.
  • 37. Results
    Lm populations in turkey deli roast slices containing 200 ppm NaNO2 were 0.70 to 2.39 log CFU/cm2 lower (P<0.05) compared with products formulated with 0 ppm NaNO2.
    Using 10% pump reduced (P<0.05) Lm populations by 0.62 to 1.50 log CFU/cm2 on days 7 to 28 and at day 63 compared with products pumped to 45%.
  • 38. Results
    Incorporating 1.5% NaCl or 0.75% NaCl and 0.75% KCl into turkey formulations did not affect (P>0.05) Lm or APC growth during 91 days of 4C storage.
  • 39. Conclusion
    Growth of Lm and APC were reduced with higher nitrite concentrations and lower percent pump, while salt type did not affect Lm growth during 4°C storage.
  • 40. Effect of Salt and Salt Replacements on Listeriamonocytogenes Growth in a Broth System
    Nigel Harper, Ph.D. candidate
  • 41. Objectives
    To determine the effect that different salts have on the growth of L. monocytogenes
    Replacement salt
    Sea salt
  • 42. Materials and Methods
    Four chemical salts [sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl2) and magnesium chloride (MgCl2)] and two industrial salts (replacement salt and sea salt) at 0.5%, 1%, and 2.5.
    Listeriaenrichment broth used in this study was made without the sodium chloride and dipotassium phosphate.
  • 43. Results
    Results showed that MgCl2 actually induced growth (P > 0.05) compared to control (no salt) and other salt solutions.
    The industrial salts both yielded greater (P > 0.05) populations than the controls.
    These results show that replacing pure NaCl with a salt that contains magnesium could cause outgrowth of Lm.
  • 44. Next Steps
    Effect of salts on ground beef, ground turkey, and ground pork
    Effects of salts in more complex meat systems
  • 45. Acknowledgements
    Dr. Elizabeth Boyle
    Dr. James Higgins
    Dr. Ann Brackenridge, Cargill Meat Solutions
    Bruce Barry, Oberto Sausage Company
    Kim Uppal, Oberto Sausage Company
    Tyler Axman
    Shayne Lobaton-Sulabo
    Nigel Harper
    Dr. Melissa Weber