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

Thank YouThank You