Report 1

Title: Reduction on Listeria monocytogenes on Deli Ham Surfaces Using a Radiant Heat Oven

Principal Investigator:
Peter M. Muriana
Associate Professor
Dept. Animal Science & Food and Ag Products Ctr.
Oklahoma State University
Stillwater, OK 74078-6055
405-744-5563 TEL
405-744-6313 FAX
muriana@okstate.edu

Objectives:
To determine microbial reduction conditions for Listeria monocytogenes on deli hams passed through a radiant heat oven/tunnel:

a)Microbial reduction at various select residence times (depends on product).
b)Temperature will be set at maximum (can be adjusted down if need be).
c)Surface-inoculated trials with 4-strain cocktail of Listeria monocytogenes.

Background:
Listeria monocytogenes is a psychrothermic microorganism, capable of growing at temperatures as low as 0.1oC and can tolerate NaCl levels as high as 8-10%. It has higher thermal inactivation temperatures than most Salmonella and/or E. coli (i.e., it is comparable to the most heat-resistant salmonella, S. senftenburg). It can form biofilms on processing equipment and is persistant in most food processing environments. It has high mortality rates as indicated in large outbreaks (i.e., 25-35%), has a death:case ratio equivalent to botulinum intoxication, and can result in abortion of fetuses in infected pregnant women; it is most susceptible to immuno-compromised individuals but even otherwise healthy people have become infected. Listeria monocytogenes is considered to be eliminated by processing temperatures of ready-to-eat (RTE) processed meats. However, it is fairly uqibuitous on raw meats and in food processing enivironments, requiring increased vigilance in worker and facility sanitation practices. It likely gains access to processed meats during the packaging/re-packaging process through either food contact surfaces, worker handling, and/or possibly air contamination.

General Approach:
The proposed project will examine microbial reduction of L. monocytogenes inoculated on the surface of bologna-type products passing through a radiant heat oven. Products will be tested by surface inoculation with a L. monocytogenes multiple strain “cocktail” mixture. The tests will be done using a high inoculation level of listeria cells (i.e, 106-108 CFU/cm2). Product will be ‘dipped’ in a pool of inoculum in a round bowl and allowed to drip-dry before passage through the oven.

Report 2

Using Unitherm Food System’s “InfraRed Grill”, Contact Inoculation, and Sodium Chlorite Spray

Objectives:
To determine microbial reduction conditions for Listeria monocytogenes on roast beef surfaces passed through the IR Grill with/without sodium chlorite spray treatment:

• Microbial reduction at 1 min residence time
• Surface-inoculated (contact inoculation) trials with 4-strain cocktail of Listeria monocytogenes
• Microbial reduction of L. monocytogenes in combination with sodium chlorite spray treatment.
• Microbial reduction of L. monocytogenes in combination with sodium chlorite spray treatment and IR Grill heating.

Protocol:Prior testing using dip and contact inoculation showed greater reduction using the contact inoculation method (sponge application) which is more representative of the type of contact contamination product will acquire prior to packaging.

In this trial, we tested the effect of spray-applied sodium chlorite (NaClO2) alone, and in combination with IR Grill heating (1 min in all cases), both before or after heating. We also tested the effect of replacing NaClO2 with ordinary buffer water because of the potential effect of rinsing off some of the surface inoculum that may falsely appear to be heat-mediated reduction.

Results:
The results show that the IR Oven alone (2nd bar) gives a –2.17-log10 reduction whereas NaClO2 + IR Grill, either before (-3.12-log10 reduction) or after (-3.62-log10 reduction) heating gave higher reductions. However, the Buffer + IR oven trial (-2.85 log10 reduction) shows that more than half of the reduction attributed to NaClO2 can be attributed to ‘rinsing off’ of the surface inoculum during spray application of the NaClO2. We would have also run “Buffer alone” as well as “IR Grill + Buffer”, but we didn’t have enough pieces of roast beef. If Giordano’s would like us to repeat this with sufficient number of product pieces to accommodate all controls, we would be happy to do this at no additional cost.

Report 3

COMBINATION PASTEURIZATION APPROACH

Report 4

Compliance Guidelines to Control Listeria Monocytogenes in Post-Lethality Exposed Ready-To-Eat Meat and Poultry Products

The following is an excerpt from the above mentioned document (pages 10 & 11).

Pre-Package Pasteurization and Post Package Surface Pasteurization

Muriana et. al., (2002) used a stainless steel water bath (similar to the Unitherm commercial Aquaflow Food processor) to submerge cooked RTE deli-style whole or formed turkey, ham and roast beef, removed from their package, inoculated with L. monocytogenes and vacuum packaged. Results show a 2 - 4 log decrease in the levels of L. monocytogenes in inoculated products post-cooked at 195 -205 F for 2 -10 min.

Pre-package surface pasteurization treatment of the fully cooked meat removed from their packaging wrap and inoculated with L. monocytogenes resulted in a 1.25 to 3.5 log reduction with a treatment time of 60-120 s at 475 to 750 F air temperature (Gande and Muriana, 2003). Surface Pasteurization was applied on cooked whole and split roast beef, whole corned beef, and whole and formed ham using a radiant oven ("Infrared Grill", Unitherm Food Systems). Pre-package pasteurization (60 sec) combined with post-package submerged water pasteurization using formed ham (60 or 90 sec), turkey bologna (45 or 60 sec), and roast beef (60 or 90 sec), resulted in a 3.2 to 3.9 log reduction for ham, 2.7-4.3 log reduction for bologna, or a 2.0 - 3.75 log reduction fro roast beef. The level of reduction varied depending on the method of inoculation, type of product used, treatment temperature, and residence time.

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