Microwave processing is a technique that uses electromagnetic waves to heat and cook food. Microwaves work by causing water and other polar molecules in food to vibrate rapidly, generating heat. A typical microwave oven contains a magnetron that generates microwaves which pass into a cooking cavity to heat food. Microwave heating is more energy efficient than conventional heating as it heats food directly rather than heating the surrounding air. Common applications of microwave processing in the food industry include cooking, baking, thawing, tempering, drying, blanching, pasteurization and sterilization. However, some controversies exist around the effects of microwaves on food quality and potential health impacts from leakage.

1. MICROWAVE PROCESSING
Presented By:
Ruchika Zalpouri
PhD (PFE)
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2. Content
1. Introduction to Microwave
2.Working of Microwave oven
3. Established Applications in Food
Processing
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3. 3
Microwaves
(very short wave)
Electromagnetic waves whose frequencies range
from about 300 MHz – 300 GHz or wavelengths
in air ranging from 100 cm –1 mm.
The shortest wavelength region of the radio
spectrum and a part of the electromagnetic
spectrum.

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History
• The first continuous magnetron was invented
by Randall and Boot, who worked on
producing a radar source to power radar sets
for the British military during World War II.
• A patent was issued in 1950 for “a method of
treating foodstuffs” in which a closed
microwave oven was described for the first
time.

6. •The first major applications:
1. Drying of potato chips
2. Pre-cooking of poultry and bacon
3. Tempering of frozen food and
4. Drying of pasta (Decareau, 1985).
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• While the first patent describing an industrial
conveyor belt microwave heating system was
issued in 1952 (Spencer, 1952)
Cont..

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Properties of
Microwave
• Electromagnetic radiation of short
wavelength
• Reflected by conducting surfaces
• Not reflected by ionosphere.

8. Heating Mechanism
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IONIC
INTERACTION
DIPOLAR
INTERACTION
HEAT GENERATION

9.  A microwave oven is a kitchen appliance
that cooks or heat food by dielectric
heating.
 It is accomplished by using microwave
radiation to heat water and other
polarized molecules in the food.
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MICROWAVE
OVEN

10. BASIC STRUCTURE OF MICROWAVE OVEN
Stirrer
Waveguide
Magnetron
Power
supply
Cooking
Cavity
Turntable
Door and choke
WORKING
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12. MAGNETRON OSCILLATOR
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Have low efficiency and are useful only at low
frequencies (< 500 MHz).
Negative
resistance
Magnetrons
Useful only for frequencies greater than 100 MHz
Cyclotron
frequency
Magnetrons
Provide oscillations of very high peak power and
useful in radar applications
Cavity
Magnetrons

13. MICROWAVE HEATING DEPENDS UPON
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MOISTURE
CONTENT
• High moisture content generally
translate into greater microwave
absorption and decreased penetration
depth.
• Moisture content is high, product will
heat more efficiently due to larger
dielectric loss factor
• Products of lower moisture content
may also heat well due to lower
specific heat capacity

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FREQUENCY
• The frequency of microwave greatly
influences the depth of penetration.
• Frequency increases and depth of
penetration decreases.
• The surface heating effect is more
prominent in 2450MHz whereas center
heating effect in more prominent in
915MHz.

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PRODUCT
PARAMETER
• A direct relationship exists between the
mass and the amount of absorbed
microwave power.
• Density affects microwave heating;
direct relationship exists between
density and dielectric constant.
• It affects the depth of microwave
penetration, and the heating rate and
uniformity

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TEMPERATURE
• As temperature increases,
evaporation will serve to decrease
the moisture content.
• Temperature effects the dielectric
property.
• Ohlsson (1983) observed that
temperature increased, less
microwave energy was absorbed

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CONTACT
MATERIAL
Glass
Stainless
steel
Ceramics
Plastic
Polypropylene Crystalline polyethylene
terephthalate

18. Microwave heating Conventional heating
Heating process Heated by
surrounding hot air.
Heated by alternating
magnetic field
Organoleptic
property of food
Induce browning or
crisping of food.
Cannot make food
brown and crispy.
Efficiency Heat is lost therefore
less efficient.
Heat is produced and
less energy loss.
(20% energy save)
Comparison Between Microwave And
Conventional Heating

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Applications of
Microwave
• Detect speeding cars
• Send telephone, radio communication
• Cure rubber
• Food processing

20. APPLICATIONS IN FOOD
PROCESSING INDUSTRY
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21. BAKING AND COOKING
Case study
MICROWAVE
COOKING
• Microwave cooking with sealed vessels
enabled a drastic reduction in cooking time,
from 110 to 11 min for chickpeas and from
55 to 9 min for common beans, compared
with conventional cooking.
MICROWAVE
BAKING
• Microwave baked cake was found to possess
high springiness, moisture content and the
low firmness as texture attributes compared
with the cake that baked in convection
method.

22. THAWING AND TEMPERING
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Microwave tempering Conventional tempering
Microwave tempering can be
performed in few minutes for a
large amount of frozen products
(5–10 min for 20–40 kg)
Tempering process takes a long
time (several days) with
considerable drip loss especially
resulting in loss of protein,
which represents an economic
loss.
The lower frequency (915 MHz
band) has an advantage for
tempering of thick products
because of its deeper
penetration and longer
wavelength compared to the
higher frequency (2450 MHz)
microwave.
Done with water or air, subject
the outer surfaces of the product
bulk to warmer temperatures for
long periods, for the heat to
penetrate to the center. This
results in large temperature
gradients.

23. CONTINUOUS MICROWAVE MEAT TEMPERING
SYSTEM
It contains multi-feed processor for meat tempering at 896MHz
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24. Microwave Drying
Microwave assisted Freeze Drying
Microwave-assisted vacuum Drying
Microwave assisted Hot air Drying
Methods
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Microwave
assisted air
drying
(MD)
• Microwave assisted air drying is one of the methods
where hot air drying is combined with microwave
heating in order to enhance the drying rate.
• Suitable for drying of high moisture foods in which
reduction in moisture content is time consuming in
final stage as compared to hot air drying process; since
the diffusion process is very slow.

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Microwave
assisted
freezing
drying
(MFD)
• Freeze drying accompanied concurrently with the help
of microwave
• Microwave drying applied after freeze drying (Duan,
Zhang, Mujumdar,& Wang, 2010a)
Microwave
assisted
vacuum
drying
(MVD)
• In the absence of convection, either conduction or
radiation or microwaves can be combined with vacuum
drying to improve its thermal efficiency (Zhang et al.,
2006).
• Prevents oxidation due to the absence of air, and
thereby maintains the color, texture and flavor of the
dried products

27. Comparison of energy consumption of
different drying methods
Pumpkin
slices
Air oven drying (50 and 75 °C for 45-
90 min)
0.61- 0.78
Microwave drying (with 160 and 350
W for 125-195 min )
0.24 – 0.26
Combined microwave- air drying for
31-51 min (160 W – 50°C, 160 W –
75°C and 350 W- 75°C )
0.33-0.40
Puligundla et al (2013) Potentials of Microwave Heating Technology for Select
Food Processing Applications - a Brief Overview and Update. J Food Process
Technol 4: 278. doi:10.4172/2157-7110.1000278

28. Microwave Blanching
• The first microwave blanching was reported by Proctor and Goldblith
using 3000 MHz for green vegetables, and it was found to retain maximum
amounts of vitamin C.
• Microwave blanching requires little or no water for efficient heat
transfer in food, therefore reduction in the amount of nutrients lost by
leaching.
Foodstuff Procedure Parameters Quantities
Broccoli Traditional
process (92°C
for 0.5-4 min)
Protein (%) 42.62 ±4.88
Vitamin C (mg /100 g dry
sample)
459.77 ± 0.77
Microwave
( 2450 MHz
with 950 W
for 3 min
Protein (%) 44.34 ±1.92
Vitamin C (mg /100 g dry
sample)
565.56 ± 1.49

29. Microwave Pasteurization and Sterilization:
•Firstly, use of microwave systems for pasteurization of
milk was studied by Hamid et al (1969)
•More uniform heating of foods (pasteurization) was
achieved using 915 MHz microwave radiation, and it
could be due to greater penetration depths of 915 MHz
microwaves.

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• Microwave sterilization process is a high-
temperature-short-time (HTST) type, used not only
to inactivate spoilage microorganisms in foods, but
also to minimize the quality deterioration of foods.
• Microwave sterilization process (128°C and 3 min
processing time) produced products superior to
those from conventional processes of canning
(120°C retort temperature and 45 min processing
time).
Cont..

31. Changes In Viable Counts Of
Microorganisms In Liquid Foods After
Microwave And Conventional Heating
Growth
medium
Treatment Microorganis
m
D value
Foods
Conventional
heating
E. Coli
17.8 min
Microwave
heating
11.6 s

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Microwave sterilization unit with
external covering
removed(overpressure of 2.5
bar,OMAC, 1992)
Microwave pasteurization line
for prepared meals
(Berstoff, 1992)

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• Microwave heating has also been used to
concentrate heat-sensitive solutions and slurries at
relatively low temperatures.
• Strawberry concentrate were heated to an internal
temperature of 82–88 °C for 3–4 min resulted in
improved color stability and had a protective effect
on anthocyanin pigment, reactive phenolics, and
ascorbic acid (Wrolstad et al., 1980).
Concentration

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A Federal standard limits the amount of microwaves that can leak from an
oven throughout its lifetime to 5 milliwatts (mW) of microwave radiation per
square centimeter at approximately 2 inches from the oven surface.

35. PENETRATION POWER
RAPID HEAT TRANSFER
MINIMUM FOULING DEPOSITION
HIGH HEATING EFFICIENCY
PERFECT GEOMATRY FOR CIP
SUITABLE FOR HEAT
SENSITIVE, VISCOUS FLUIDS
LOW COST MAINTAINANCE
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36. Non availability of actual temperature
profiles
Microwave-assisted process not
always results better quality retention
of food products
Leakage of microwaves from the microwave
ovens
Microwave cooking may also increase the
production of carcinogens in foods.
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• Many people believe that microwave ovens are
unsafe.
• Microwaving garlic for 60 seconds depleted allinase,
garlic’s primary cancer-fighting ingredient. (Song &
Milner 2001)
• Microwaves cause a higher degree of “protein
unfolding” than conventional heating. (George DF et
al, 2008)
CONTROVERSIES

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• Most of the studies are done for short exposure periods at higher
intensities. There is an immense shortage of studies using long
exposure periods with low-level radiation.
• Microwave (MW) Technologies are much more complicated than
conventional methods. Successful development requires
extensive R&D efforts based on good understanding of MW
heating principles and the systems.
• The main obstacles to industrial setup of MW heating processes
are the difficulties in controlling the process and the high energy
costs. Moreover the food industry and the consumer are very
conservative about the use of new technologies.
CONCLUSION

39. REFERENCES
• 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
• June 2005 Food and Environmental Hygiene Department The Government of the
Hong Kong Special Administrative Region MICROWAVE COOKING AND FOOD
SAFETY Risk Assessment Studies Report No. 19
• A.C. Metaxas Microwave heating IEE (1991). Power Engineering Journal 5(5) in
September
• Venkatesh M.S & Raghavan G.S.V. (2004). An Overview of Microwave Processing
and Dielectric Properties of Agri-food Materials Biosystems Engineering 88 (1), 1–18.
• Kouchakzadeh A& Safari. A. (2015). Studies on microwave energy absorption of
fresh green bell pepper (Capsicum) AgricEngInt: CIGR Journal 17(2): 105.
• YuanY, Xiong S L Q. Jiaqi Zhong Yuzhe Zhang Jiannan L. (2015). Temperature
Control Using Hybrid Control with MRAC and ECS into a MIMO Microwave
Heating Process. Journal of Microwave Power and Electromagnetic Energy, 49 (1):
46-54.
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