1. Microwave sterilization, a potential technology for MREs
Juming Tang, Ph.D.
Professor of Food Engineering
Oct. 26, 2010
Department of Biological Systems Engineering
Washington State University, Pullman WA
Microwaveheating.wsu.edu

2. Conventional Retorting Relies on Heat Convection and Conduction in Foods
Target: C. botulinum spores

3. A Multi-mode 2450 MHz Microwave Cavity
2450 MHz microwave heating system for food in plastic pouches at US Army Natick Soldier Center in 1970

4. Sept. 2010, WSU MW Lab.

5. OUTLINE Instruction – microwaves
Industrial MHz multi-mode microwave sterilization systems
Development of 915 MHz single-mode microwave sterilization technology
Examples of MW processed products
A case study for FDA approval – salmon fillet in sauce

6. l f 1. Microwave Heating Electromagnetic Spectrum
The wavelength l = c/f with c = 3.108m/s l
Electromagnetic Spectrum RF
915 MHz Industrial (wavelength in free space=0.33 m)
2450 MHz Domestic Ovens & Industrial Uses (0.12 m) MW f
Allocated by FCC
for Industrial, Scientific
Medical (ISM) applications

7. Domestic Microwave Oven (2450 MHz)
Waveguide
Magnetron
Microwave cavity (applicator)
Domestic Microwave Oven (2450 MHz)

8. Possible modes for an empty non-cubical microwave oven (Chan and Reader, 2000)
Indices
Modes
Frequency / GHz m N P 5 2 TE
2.4320 4 3
2.4343 1
TE, TM
2.4390 TM
2.4464
2.4518
2.4578
2.4600
2.4674
2.4697
2.4750
Electric field pattern for (a) TM350 and (b) TE204
Frequency Spectrum of 2.45 GHz magnetron

9. Electric field pattern for a loaded microwave cavity at 2.4295 GHz.
Multi-mode Systems
Electric field pattern for a loaded microwave cavity at GHz.
(Chan and Reader, 2000)

11. 2. Development of Microwave Sterilization Technology for Pre-packaged foods (>40 years)
All past MW sterilization systems used 2450 MHz (~12 cm wavelength in free space)

12. A Multi-mode 2450 MHz Microwave Cavity
2450 MHz microwave heating system for food in plastic pouches at US Army Natick Soldier Center in 1970

13. Tops Foods (Olen Belgium) 3rd Generation 2450 MHz Microwave Sterilization/Pasteurization System (2004)

14. Sterilized products produced by TOPS Foods

15. MW pasteurized, processed to 80C
shelf-life 35 days at 7C
MW sterilized, shelf-life 1 year
at room temperature

16. Major limitations of 2450 MHz systems
Shallow penetration depth (<1cm) – longer heating time
Multi-mode systems, leading to unpredictable and non-uniform heating patterns in foods

17. 3. Development of 915 MHz Single-Mode Microwave Sterilization/Pasteurization Technology at WSU
A. System design to provide stable and predictable electromagnetic field patterns with high energy efficiency
Single –mode, high coupling efficiency
B. FDA approval for low acids shelf-stable foods
Stability of system and processes
Scientific base/means for process development
Food Safety
Scaling-up and economic viability
Suitable Packaging Materials
14 year activities supported by DoD Dual Use Program (2001-), US Army Natick Solider Center,
WSU, USDA NRI Programs, MW Consortium Members, and Print-Pack

18. 0 phase shift cavity waveguide WSU Single Mode Design for 915 MHz
Microwave Sterilization Systems, patented in 2006
0 phase shift
cavity
waveguide

19. WSU 2nd generation system - four single mode cavities, 40 kW max MW power, assembled in 2008

21. 77 min heating time (steam at 247 F)

22. Change of Shear Force in Pink Salmon Fillet Heated at 121˚C

23. Example:
10 oz trays (Rexam containers) containing chicken breast in sauce, processed by the WSU 915 MHz sterilization system for accelerated shelf-life/sensory studies at US Army Natick Soldier Center

24. Results from sensory evaluations at US Army Natick Soldier Center

25. Example:
Chicken and dumplings in 8 oz pouches (Print-pack) processed with WSU Microwave Sterilization System, produced for sensory studies at US Army Natick Soldier Center
Chicken and dumplings in 8 oz foil pouches by retort (control) for the sensory studies

28. Promises of Microwave Sterilization Technology:
Examples of MW processed products
After MW processing

29. Microwave sterilized salmon and fried rice

30. On Oct. 7, 2009, WSU technology received FDA approval for pre-packaged food sterilization using microwave energy, first ever in USA history

31. On July 18, 2010, the Institute of Food Technologists presented the 2010 R&D Award to WSU Consortium for “contributions to food technology that results in foods of improved quality and nutrition”. Juming Tang (WSU), C. Patrick Dunne (Natick Soldier Center); Douglas Hahn (Hormel), Kenny Lum (Seafood Products Association); and Evan Turek (Kraft ) received the award on behalf of the team

33. 4. Case Studies- ctivities related to FDA filing of salmon fillets in sauce Sept. 2009 - Sept. 2010

34. Salmon filet, skinless and boneless

35. 8-oz Printpack pouch

36. Placement of pouches on mesh belt conveyor and orientation of pouches in MW processing
Moving direction of food pouches:

37. Cold spot validation with real foods
Processing real food in MW system
Data retrieval from Ellab temperature sensor
Positioning Ellab sensor tip at the location determined by heating pattern
Temperature profile overlay with MW system data

38. Heat penetration data collection

40. Microbial validation of food safety Targeted microorganism – C
Microbial validation of food safety Targeted microorganism – C. botulinum spores
NFPA strain (P.A. 3679) as the surrogate.
It needs to be 100 times more heat resistant than C. botulinum spores, so that we use smaller number of surrogate to validate at least 12 log reduction in C. botulinum spore populations

41. Inoculating PA 3679 spores to the cold spot in salmon fillets

42. Observations Incubation results (after 90 days’ incubation)
Control: all 30 unprocessed inoculated control pouches were positive after 1 day incubation; All the 10 un-inoculated pouches processed at each level were negative.
Level-1: 47 out of 50 pouches (94%) were positive (expected:100% positive).
Level-2: 12 out of 50 pouches (24%) were positive (expected 65% positive).
Level-3: No positive (expected 0.041%).
Level-4: No positive (expected %).
Level-5: No positive (expected %).
Conclusion:
The MW process delivered expected lethalities.

43. Incubation in Walk-in Incubator (~ 36°C)
Positive pouches

44. Recovery tests after 90 days incubation at 36C
25% of pouches of Level 3 (target) and 25% of negative pouches of Level 2 (under processed) taken for enrichment tests

45. Recovery tests

46. Submitted filing for salmon fillets in sauce in 8 oz pouches

47. WSU licensed exclusive rights for commercialization of this technology to Food Safety Chain (FSC) corporation (Maple Valley, WA). We are forming a second consortium (Nov. 2, 2010, consortium meeting in Seattle). WSU is expanding the technology to address a broad food safety issues for various entrees and convenient meals, frozen, chilled or shelf stable.
FUTURE DIRECTIONS

48. Thank You