Microwave sterilization, a potential technology for MREsMicrowave sterilization, a potential technology for MREs
Juming Tang, Ph.D.Juming Tang, Ph.D.Professor of Food EngineeringProfessor of Food Engineering
Oct. 26, 2010Oct. 26, 2010
Department of Biological Systems EngineeringDepartment of Biological Systems EngineeringWashington State University, Pullman WAWashington State University, Pullman WA
Microwaveheating.wsu.eduMicrowaveheating.wsu.edu
Conventional Retorting Relies on Heat Convection and Conduction in Foods
RetortConvection
Target: C. botulinum spores
2450 MHz microwave heating system for food in plastic pouches at US Army Natick Soldier Center in 1970
A Multi-mode 2450 MHz Microwave Cavity
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Sept. 2010, WSU MW Lab.
OUTLINEOUTLINE
1.1. Instruction – microwavesInstruction – microwaves2.2. Industrial 2450 MHz multi-mode microwave Industrial 2450 MHz multi-mode microwave
sterilization systemssterilization systems3.3. Development of 915 MHz single-mode microwave Development of 915 MHz single-mode microwave
sterilization technologysterilization technology4.4. Examples of MW processed productsExamples of MW processed products5.5. A case study for FDA approval – salmon fillet in A case study for FDA approval – salmon fillet in
saucesauce
Electromagnetic Spectrum
Allocated by FCCfor Industrial, ScientificMedical (ISM) applications
RF
915 MHz Industrial (wavelength in free space=0.33 m)
2450 MHz Domestic Ovens & Industrial Uses (0.12 m)
MW
The wavelengthc/f with c = 3.108m/s
1. Microwave Heating
f
•Magnetron
•Waveguide
•Microwave cavity (applicator)
•Domestic Microwave Oven (2450 MHz)
Indices Modes Frequency / GHzm N P0 5 2 TE 2.43200 4 3 TE 2.43434 1 3 TE, TM 2.43905 3 0 TM 2.44642 0 4 TE 2.45184 4 1 TE, TM 2.45780 2 4 TE 2.46001 5 2 TE, TM 2.46741 4 3 TE, TM 2.46973 5 0 TM 2.4750
Possible modes for an empty non-cubical microwave oven (Chan and Reader, 2000)
•Electric field pattern for (a) TM350 and (b) TE204
•Frequency Spectrum of 2.45 GHz magnetron
Multi-mode Systems
•Electric field pattern for a loaded microwave cavity at 2.4295 GHz. •(Chan and Reader, 2000)
2. Development of Microwave Sterilization 2. Development of Microwave Sterilization Technology for Pre-packaged foods Technology for Pre-packaged foods
(>40 years) (>40 years) All past MW sterilization systems used 2450
MHz (~12 cm wavelength in free space)
2450 MHz microwave heating system for food in plastic pouches at US Army Natick Soldier Center in 1970
A Multi-mode 2450 MHz Microwave Cavity
•Tops Foods (Olen Belgium) 3rd Generation 2450 MHz Microwave Sterilization/Pasteurization System (2004)
Sterilized products produced by TOPS Foods
MW pasteurized, processed to 80Cshelf-life 35 days at 7C
MW sterilized, shelf-life 1 yearat room temperature
Major limitations of 2450 MHz systems
1. Shallow penetration depth (<1cm) – longer heating time
2. Multi-mode systems, leading to unpredictable and non-uniform heating patterns in foods
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
D. Scaling-up and economic viability
E. 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
waveguide
cavity
0 phase shift
WSU Single Mode Design for 915 MHz Microwave Sterilization Systems, patented in 2006
WSU 2nd generation system - four single mode cavities, 40 kW max MW power, assembled in 2008
MW sterilization of salmonApril 15, 2003
(Run-1)
0
20
40
60
80
100
120
140
0.00 2.00 4.00 6.00 8.00 10.00 12.00
time [min]
para
met
ers
temperature of salmon
circulating water tempture
F0=8.4MW heating: 2.4 min;Total processing time: 10 min.
77 min heating time (steam at 247 F)
Change of Shear Force in Pink Salmon Fillet Heated at 121˚C
30
50
70
90
110
130
150
170
0 20 40 60 80 100 120 140
Cooking time (min)
Sh
ear
forc
e (N
)
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
• Results from sensory evaluations at US Army Natick Soldier Center
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
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Promises of Microwave Sterilization Technology:
Examples of MW processed products
Microwave sterilized salmon and fried riceMicrowave sterilized salmon and fried rice
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On Oct. 7, 2009, WSU technology received FDA approval for pre-packaged food sterilization using microwave energy, first ever in USA history
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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
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4. Case Studies- ctivities related to 4. Case Studies- ctivities related to FDA filing of salmon fillets in sauceFDA filing of salmon fillets in sauce
Sept. 2009 - Sept. 2010
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Salmon filet, skinless and boneless
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8-oz Printpack pouch
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Placement of pouches on mesh belt conveyor and orientation of pouches in MW processing
•Moving direction of food pouches:
Cold spot validation with real foods
•Positioning Ellab sensor tip at the
location determined by heating pattern
Processing real food in MW system
•Data retrieval from Ellab temperature sensor
•Temperature profile overlay with MW system data
Heat penetration data collectionHeat penetration data collection
Pouch location on
the mesh belt
April 2-10-
test1
April 8-10-
test1
April 9-10-
test1
April 14-10-test4
April 15-10-test1
April 19-10-test1
April 20-10-test1
April 20-10-test2
April 21-10-test1
April 26-10-test1
April 26-10-test2
April 27-10-test1
April 27-10-test2
123 7.904 6.355 7.01 11.526 7.167 6.828 8.539 8.7810 7.7011 10.3012 11.001314 6.5115 11.9516 9.17 13.3617 14.9218 7.5419 13.4020 11.3421 10.012223 10.522425 6.672627 9.5028 13.802930 9.5631 11.7232 11.1533 8.90343536 9.1037 9.2838 9.583940 14.504142
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NFPA strain 3679 (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
Microbial validation of food safetyMicrobial validation of food safetyTargeted microorganism – C. botulinum spores
Inoculating PA 3679 spores to the cold spot in salmon fillets
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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 0.0065%).
– Level-5: No positive (expected 0.0000041%).
Conclusion:
The MW process delivered expected lethalities.
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Incubation in Walk-in Incubator (~ 36°C)
•Positive pouches
Recovery tests after 90 days incubation at 36CRecovery 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
Recovery tests
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Submitted filing for salmon fillets in sauce in 8 oz pouches Submitted filing for salmon fillets in sauce in 8 oz pouches
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 DIRECTIONSFUTURE DIRECTIONS
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