Microwave (and RF) Heating in Food

Processing Applications

Juming Tang, Ph.D.

Professor of Food Engineering

Department of Biological Systems Engineering

Washington State University, Pullman WA

OUTLINE

1. Microwave and Radio Frequency (RF) Heating Principles

2. Established Applications in Food Processing

3. Development of Microwave Sterilization Technology for Pre-packaged Foods

Electromagnetic Spectrum

Very restricted bands

Can be used for ISM

applications

13.56 MHz(+/- 0.05%)

27.12 MHz (+/- 0.6%)

40.68 MHz (+/- 0.05%)

RF

915 MHz

2450 MHz Domestic Ovens

10 – 12 – 18 GHz (plasma)

MW

The wavelength l = c/f with c = 3.108m/s

f

l

SPECTRUM

•Generation of microwave

•Magnetron

•Magnetron

•Waveguide

•Microwave cavity (applicator)

•Domestic Microwave Oven (2450 MHz)

Microwave Cooking of Meat Patties (APV system)

RF Heating Systems

Food

Plate Electrodes in RF Heater

Food Dryer

Source: Strayfield, UK

Industrial Applications of RF Technology

- typical up to 85 kW per module

- Product temperature in electromagnetic field:

''21110563.5 Eft

TC p

=

- Dielectric property:

Dielectric heating of foods

- Contributions of dipole rotation and ionic conduction:

Loss factor

Dielectric constant

Multi-mode Systems

•Electric field pattern for a loaded microwave cavity at 2.4295 GHz.

•(Chan and Reader, 2000)

Single - mode Systems

TM010 cavity resonator, 915 MHz (adopted from Regier and Schubert)

How Does RF or Microwaves Heat Foods?

Space charge polarization Orientation polarization

Alternating Electric field

Mechanism of Dielectric Heating

MWRF

Ref: Tang et al., 2002, Scientific Press, New York

Ref: Wang et al.,2003. J. Food Eng. 57: 257-268.

Penetration Depth (mm)

RF Microwaves

2. Industrial Microwave (MW) and Radio

Frequency (RF) Technologies

-- Better quality

-- Reduced process times

-- New products?

Cooking of desserts in pots

Microwave Tunnel 22 000 Pots / hour Power : 144 KW.

MW COOKING DESSERTS

Nutripack (a French Company) solution with valve Valvo-PackTM

The valve allows a thermal treatment and the cooling of the product in the packing without

counter-pressure.

The valve is adhesive and is installed on the upper part (heat sealing film, cover…) of a

packing (plastic, metal, paper, cardboard) that has been previously pierced.

Opening limit : 10 mbar 3 mbar

Closing limit : 5 mbar 2 bars

MW COOKING/PASTEURIZATION OF VEGS

From their website:

MicVac develops, markets and sells two methods

for processing and packaging convenience food.

Both solutions (for pasteurised and unpasteurised

foods respectively) use a valve that offers several

benefits for both the producer and the consumer.

The MicVac method is based on the principle of

cooking and pasteurising food using microwaves

directly in the sealed consumer package. The film

cover on the package has a valve that opens

during cooking, releasing the overpressure in the

form of steam and oxygen. After cooking, the

valve closes and a natural vacuum is created in

the package – another of the product’s many

advantages.

•http://www.micvac.com/

•A similar concept developed by MicVac, Sweden

EXAMPLES OF PRODUCTS

MW COOKING/PASTEURIZATION

50kW RF Post Baking Unit - Courtesy of Fox’s Biscuits, UK

Wokingham, UKRF Finish Drying of Bakery Products

Moisture profile at exit of an industrial bakery

oven, and after RF drying for 5 mins

1.25

1.45

1.65

1.85

2.05

Working Side Middle Non-working Side

Mo

istu

re %

BD

W

Before RF After RF At Packing

RF Post-Baking

Virtually Eliminates Checking!

Sponge Products

• Reduces Mold Spores• Increases Shelf Life• Increases Production

RF DRYING OF BAKERY

PRODUCTS• Appetisers snack

• Meringue

•Puff pastry

•Breakfast cereal

•Bread crouton

•Sponge product

•Pretzel

•Short bread

•Profiterole

Manufacturers using RF

Heating and Drying

• Kraft (Nabisco) (USA)

• United Biscuits (UK)

• Kelloggs (Keebler) (USA)

• Fox’s Biscuits (UK)

• Weetabix (UK, Canada)

• Arnotts (Australia/ New Zealand/ Indonesia

• National Biscuits (S.Africa)

• Safeway (USA)

• Ferrero (Italy)

• Dancake (Portugal)

• Ulker (Turkey)

• Pepperidge Farms (USA)

• M&M Mars (USA)

• Parle (India)

• Britannia (India)

• Crown (Korea)

• Horizon Biscuits (UK)

• United Biscuits/Danone (Lu –France, Bagley Argentina)

• Tong Yang (Korea)

• Morinaga (Japan)

• Dare Foods (Canada/USA)

• Barilla (Italy)

• ETI (Turkey)

• Ralston Purina (Bremner) (USA)

• Griffin (New Zealand)

Approximately 500 RF food processing systems

sold over 37 years

3. Development of Microwave Sterilization

Technology for Pre-packaged foods

(~50 years)

All past MW sterilization systems used 2450

MHz

Conventional Retorting Relies on Heat

Convection and Conduction in Foods

Retort

Convection

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

• Microwave pasteurization equipment with module

open to show alternating placement of magnetrons

(Berstoff, 1992)

Microwave pasteurization line for prepared meals

(Berstoff, 1992)

Microwave sterilization unit with external covering removed

(overpressure of 2.5 bar,OMAC, 1992)

Continuous microwave sterilization system

(OMAC, 1992)

Otsuka plant

in Japan (2008)

TOP’S FOODS

Olen, Belgium (2000)

The 2nd generation Microwave Sterilization

System2000

•The 3d Generation of Microwave Technology at

Tops Foods, 2004

Sterilized products produced by TOPS Foods

MW pasteurized, processed to 80C

shelf-life 35 days at 7C

MW sterilized, shelf-life 1 year

at room temperature

4. Research on Microwave Sterilization

Technologies at Washington State University

4. Engineering and Scientific Challenges in

Developing MW Sterilization Processes

1. Technology/systems to provide stable

electromagnetic field patterns with high

energy efficiency

Single –mode, high coupling efficiency

2. FDA Approval

Stability of system and processes

Scientific base/means for process development

Food Safety

3. High quality foods

4. Scaling-up and economic viability

MW STERILIZATION CONSOTIUM (2001-)

Washington State University

Microwave Company: Ferrite Component, NH

Food Packaging Companies:

Rexam Container, MO

Graphic Packaging, CO

Food Processing Companies:

Kraft Foods, ILL

Hormel, MN

Masterfoods (MARS USA), CA

Ocean Beauty Seafood Inc., WA

Technical Consultant: NPA

Supported by DoD DUST Program and US Army Natick Soldier

Center

System development

Computer simulation

Process development

Industrial implementation

Development of Microwave Sterilization Technology

Microbial studies

Scaling-upFDA Approval

waveguide

cavity

0 phase shift

WSU 915 MHz Single-Mode 10 kW Pilot Scale Sterilization

System (2001-2008)

Steps involved in identification of cold and hot spots with mashed

potato sample

M-2 Kinetics

Fo vs M-2 yield relationship

Computer vision to measure

M-2 color of processed

trays.

Checking repeatability of

hot and cold spots with different

tray sizes and level of salt

Identification of cold/ hot location

For different tray size.

Verification of location

Using fiber optics probes

MW sterilization of salmon

April 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

mete

rs

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

ea

r fo

rce

(N

)

Eggs

Mashed Potato

Microwave sterilized salmon and fried rice

56

Process time

(min)

Max cook value

Min Cook value

Ideal 2.4 22 22

Retort 27+4 279 78

Microwave 3.9+4 36 32

•Maximum and minimum C values for food in a 10 oz tray after

• a F0=6 process, water temp=121 C

•C values for food in a 10 oz tray after a F0=6 process, water

temp =125 C

Process time (min)

Max cook value

Min Cook value

Ideal

Retort

6

33+4

39

212

39

93

Microwave 9+4 58 50

Sensory and self-life studies at US Army

Natick Soldier Center

50 trays chicken

were produced for

Natick in January

2004

– Chicken product:

Natick evaluation,

shelve study and

taste panels

Chicken Breast, OVERALL Acceptability

Averages over 6 months storage at 100o F

y = -0.0796x + 6.7086

R2 = 0.6015 (Microw ave)

y = -0.0865x + 5.4943

R2 = 0.946 (Retort)

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7

Months in 100o F Storage

He

do

nic

sc

ore

(1-9

sc

ale

)

Microwave

Retort

Linear (Microwave)

Linear (Retort)

WSU 2nd generation system developed for FDA approval- four single mode cavities, 40 kW max MW power

Potential applications for microwave sterilization/pasteurization technologies

- new processes

- new products

- new markets

For more information

http://www.microwaveheating.wsu.edu/

MW and RF Technologies are much more

complicated than conventional methods.

Successful development of new applications

requires extensive R&D efforts based on good

understanding of MW and RF heating principles

and the systems.

Pilot-scale studies are necessary for scaling up to

industrial processes

Thank You