This document presents a comparative study of ohmic and microwave heating in food processing. Ohmic heating directly utilizes electrical resistance to generate heat in food, offering high energy efficiency and rapid, uniform heating, while microwave heating uses electromagnetic waves to heat food through molecular friction, though it has limitations such as non-uniform heating and low penetration depth. The conclusion emphasizes that both heating methods are beneficial for food preservation, enhancing shelf life, and inactivating microbes, while suggesting further research for optimization.

1. A COMPARATIVE STUDY
OF OHMIC AND
MICROWAVE HEATING IN
FOOD PROCESSING
PRESENTED BY -
MARIAH SADAF
(13003417----)
SESSION- 2017-2021

2. INTRODUCTION
• Ohmic heating, a thermal electrical
heating method, is also termed as
resistance heating.
• Ohmic heating is direct heating method
where food is in contact with the
electrodes.
• The concept of ohmic heating is quite
simple. The passage of electric current
through an electrically conductive food
material obeys Ohm’s law (V = IR); and
heat is generated due to the electrical
resistance of the food.
• Almost all electric power is transformed
into heat.
• Microwaves are part of electromagnetic
spectrum in the frequency range falling
between radio and infrared region.
• Frequency 2450MHz – 915MHz(for
food)
• Microwave heating is a method that
offers technique of heating requiring
intermolecular friction ,conduction and
convection. Microwave generates heat
within the food rapidly raising the
temperature to the desired extent.
• The waves can be absorbed by water,
fat or sugar in foods and thus is
converted into Heat
OHMIC HEATING MICROWAVE HEATING

3. Increase In Kinetic Energy Thereby Heating The Product
Momentum Transfer To These Molecules
Collision Of Molecules
Conducts Electricity
Food Product
OHMIC HEATING
PROCESS DIAGRAMMECHANISM

4. The interaction
between the local field
strength and local
electrical conductivity
will govern the local
heat generation by
this equation
The actual heating
rate for the substance
can then be
calculated from the
equation
Q = E²k
= λJ²
Where Q is heat generation
rate per unit volume (W/m³)
E is the electric field strength
(V/cm)
k is the electrical conductivity
(S/m)
λ is the resistivity (ohm-meter)
J is the current density
(A/m²)
dT /dt =
Q/ ρC
Where T is temperature in degree
Celsius
t is the time in second
ρ is the density (kg/m³)
C is the specific heat
capacity(kJ/kg-
C)
ρC is the volumetric heat capacity
OHMIC HEATING

5. OHMIC HEATING : APPLICATION
• Pasteurize egg
• Reduce fouling
• Prevent coagulation
• Prevents denaturation
• Prevents coagulation
• Provides uniform heating
• Effective pasteurization
• No additional protein
destruction
• Juice extraction
• Juice preservation
• Blanching
• Dehydration
• Peeling

6. OHMIC HEATING
ADVANTAGES
DISADVANTAGES
 High energy efficiency (90% electrical energy
is converted into heat).
 Rapid and uniform heating
 Better nutrient and vitamins retention
 No theoretical upper temperature limit.
 No hot surface for heat transfer; less risk of
surface fouling and burning of the product.
 Reduced maintenance cost
 Process can simply be controlled with switch
on and off.
 Environmentally friendly.
 Product with large size (15mm) and high
concentration of solid (up to 80%) can easily
be processed
 Electrolysis of product and corrosion of
electrode occur at low frequency that may
result in metal contamination to food which
may be hazardous at high concentration.
 Too high installation and initial operating
cost.
 This system is unable to heat a product with
high fat and oil and dried food system. Since
fats are non-conductive (due to absence of
water and ions), it may bypass current and
slow heating may occurs.
 Runaway heating may occur at high
temperature due to increase in electrical
conductivity.

7. MICROWAVE HEATING
MECHANISM

8. MICROWAVE HEATING
The microwaves are generated by special oscillator tubes called "Magnetrons and Keltron”.
The electromagnetic energy, at microwave frequency is conducted through a coaxial tube or wave
guide at a point of usage.
Both Magnetron and Keltron are electron tubes which generate microwaves.
The Magnetron is a vacuum valve in which the
electron, emitted by the cathode, turn around
under the action of a continuous electric field
produced by the power supply and of a
continuous magnetic field. The movement
produces the electro-magnetic radiation.
Keltron uses the transit time between two given
points to produce this modulated electron stream
which then delivers pulsating energy to a cavity
resonator and sustain oscillation within the cavity.
1. Magnetron
2. Keltron

9. MICROWAVE HEATING : APPLICATION
Baking
Pasteurization and sterilization
Tempering
Blanching
Pre-cooking and Cooking
Dehydration

10. MICROWAVE HEATING
1. Low penetration depth
2. Product may hazardous to
health
3. High initial cost
4. Non uniform heating
5. Less energy efficient
1. Rapid heating
2. Reduced loss of nutrients
3. No contamination of foods
by products of combustion
4. Equipment is small,
compact, clean in operation
5. Surface of the food does not
overheat
6. Automatic process control
ADVANTAGES DISADVANTAGES

11. OHMIC HEATING MICROWAVE HEATING
Uses the electrical resistance of foods Forms of electromagnetic energy
Heat is generated due to electrical current Heat is generated by molecular friction
Depends on the electrical resistance of the food Depends on moisture content of the food
Penetrates throughout the food Limited penetration depth

12. SUGGESTIONS FOR IMPROVEMENT
 Develop predictive, determinable and reliable models.
 Reliable feedback control to adjust the supply power according to
the conductivity changes occurring.
 Developing real time-temperature monitoring techniques for
locating cold-spots and overheated regions during heating.
Developing adequate safety and quality-assurance protocols in
order to commercialize these heating technology.

13. CONCLUSION
Thus, individually or in combination these two types of heating
methods are very beneficial in the food industry.
 Helps in food preservation.
 Increases the shelf life.
 Inactivates microbes.
 Gives the scope to bring about innovation in terms of
preservation.
 High rate of heating during processing results in short
processing time.
 Higher retention of nutrients and vitamins
 Further research have to be carried out in order to identify
cold-spot, decrease cost and improve electrode so that
electrolysis is prevent

14. REFERENCES
• Microwave heating by By A.C. Metaxas
• Andrew Proctor, 2011. “Alternatives to Conventional Food Processing”. Royal Society of
Chemistry. 307-334.
• Ohmic heating in food processing. Ramaswamy, Hosahalli S. Boca Raton, FL: CRC Press.
2014.
• Varghese, K. Shiby; Pandey, M. C.; Radhakrishna, K.; Bawa, A. S. (October
2014). "Technology, applications and modelling of ohmic heating: a review"
• Ohmic Heating in food processing. CRC Press. 2014
• The Facts about Microwave Ovens by John R. Free, Popular Science, February 1973.
• Acierno, D., Barba, A. A., & d’ Amore, M. (2004). Heat transfer phenomena during
processing materials with microwave energy. Heat and Mass Transfer, 40(5), 413-420.
• Alajaji, S.A., & El-Adawy, T.A. (2006). Nutritional composition of chickpea (Cicer arietinum
L.) as affected by microwave cooking and other traditional cooking methods. Journal of
Food Composition and Analysis, 19, 806-812.
• Alibas, I. (2007). Microwave, air and combined microwave-air-drying parameters of
pumpkin slices. LWT-Food Science and Technology, 40, 1445-1451.
• Aparna, K., Basak, T., & Balakrishnan, A.R. (2007) Role of metallic and composite (ceramic-
metallic) supports on microwave heating of porous dielectrics. International Journal of Heat
and Mass Transfer, 50, 3072-3089

15. THANK
YOU!