it give the comparison between ohmic and microwave heating in the food processing with detailed study on its mechanism advantages and disadvantages

1. SEMINAR REPORT
On
A Comparative Study Of Ohmic And Microwave Heating
In Food Processing
Submitted by:
NAME - MARIAH SADAF
UNIVERSITY ROLL NO-1300341-----
2017-2021
Submitted at
Department of Food Technology
TECHNO MAIN SALT LAKE
EM-4/1, SALT LAKE, SECTOR – V
KOLKATA-700091
Affiliated To:
MAULANA ABUL KALAM AZAD UNIVERSITY OF
TECHNOLOGY, WB
BF-142, BIDHAN NAGAR, SECTOR -1, KOLKATA -64

2. INTRODUCTION
Thermal processing is a food sterilization technique in which the food is
heated at a temperature high enough to destroy microbes and enzymes. The
specific amount of time required depends upon the specific food and the
growth habits of the enzymes or microbes. Both the texture and the
nutritional content of the food may be altered due to thermal processing.
 OHMIC HEATING
Ohmic heating, a thermal electrical heating method, is also termed as
resistance heating. It 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. A
large number of potential applications exist for ohmic heating, including
blanching, evaporation, dehydration, fermentation, sterilization, pasteurization,
and heating of foods. Beyond heating, applied electric field under ohmic
heating causes electroporation of cell membranes, which increase extraction
rates, and reduce gelatinization temperature and enthalpy. Ohmic heating
results in faster heating of food along with maintenance of color and nutritional
value of food. Water absorption index, water solubility index, thermal
properties, and pasting properties are altered with the application of ohmic
heating.
 The interaction between the local field strength and local electrical
conductivity will govern the local heat generation by this 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)
 The actual heating rate for the substance can then be calculated from
the equation: dT /dt = Q/ ρC Where T is temperature in °C
t is the time in second
ρC is the volumetric heat capacity

3. MECHANISM & APPLICATION
Applications Advantages Food Items
Sterilization, heating liquid
foods containing large
particulates and heat sensitive
liquids, aseptic processing
Attractive appearance, firmness properties,
pasteurization of milk without protein
denaturation
Cauliflower florets, soups,
stews, fruit slices in syrups
and sauces, ready to cook
meals containing
particulates, milk, juices, and
fruit purees
Ohmic cooking of solid foods The cooking time could be reduced
significantly. The center temperature rises
much faster than in conventional heating,
improving the final sterility of the product,
less power consumption and safer product
Hamburger patties, meat
patties, minced beef,
vegetable pieces, chicken,
pork cuts
Ohmic thawing Thawing without increase in moisture
content of the product
Shrimp blocks
Inactivation of spores and
enzymes
To improve food safety and enhance shelf
life, increased stability and energy
efficiency, Reduced time for inactivation of
lipoxygenase and polyphenol oxidase,
inactivation of enzymes without affecting
flavor
Process fish cake, orange
juice, juices
Blanching and extraction Enhanced moisture loss and increase in
juice yield
Potato slices, vegetable
purees extraction of sucrose
from sugar beets, extraction
of soy milk from soy beans
Food Product
Conducts
Electricity
Collision Of
Molecules
Momentum
Transfer To
These
Molecules
Increase In
Kinetic
Energy
Thereby
Heating The
Product

4. OHMIC HEATING: ADVANTAGES AND
DISADVANTAGES

ADVANTAGES
 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
DISADVANTAGES
 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.

5.  MICROWAVE HEATING
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.
Microwave heating is caused by the ability of the materials to absorb microwave
energy and convert it to heat. Microwave heating is caused by the ability of the
materials to absorb microwave energy and convert it into heat. Microwave
heating of food materials mainly occurs due to dipolar and ionic mechanisms.
Presence of moisture or water causes dielectric heating due to dipolar nature of
water. When an oscillating electric field is incident on the water molecules, the
permanently polarized dipolar molecules try to realign in the direction of the
electric field. Due to high frequency electric field, this realignment occurs at
million times per second and causes internal friction of molecules resulting in
the volumetric heating of the material. Microwave heating might also occur due
to the oscillatory migration of ions in the food which generates heat in presence
of high frequency oscillating electric field.
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.
1. Magnetron: 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.
2. Keltron: 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.

6. MECHANISM & APPLICATION
Food
product(cont
aining
water,sugar
and fats
which act as
dipole)
Microwave
passes
through and
the polar
components
align
themselves
with electric
field
Intermolecular
friction and
Heat is
generated
Simultaneously
conduction
(solid),
convection
(liquid) takes
place and is
distributed
uniformly
Heated
product
APPLICATION USE FOOD ITEM
Baking For internal heating
microwave, for external heating
hot air (electric coil) or infrared
for crust formation
Cakes, cupcakes,
pastries and pattis
Concentrating Of heat sensitive fluids and
slurries at relatively short time
Fruit juice, syrup and
jam
Cooking It cooks relatively larger pieces
without high temperature
gradients between surfaces
and interior
Meat and meat
products
Blanching Rapid and uniform heating
inactivates enzymes without
leaching of essential nutrients.
Vegetables and fruits
Drying and
Pasteurization
Heats uniformly with little
amount of heat.
Milk and vegetables
Pre-cooking Is well suited for pre-cooking
‘heat and serve’ as there is no
cooking associated.
Bacon and tenderloin

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

8. COMPARISON BETWEEN OHMIC AND
MICROWAVE HEATING
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
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.

9. 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.
The usage of microwave and ohmic heating for food processing is
continuously developing globally. Shorter processing time, high
energy efficiency and faster heating are the main advantages that
the microwave and ohmic heating offer. Although there are still
some problems associated with the process. These are in terms of
food quality and the non-uniform heating of foods. Hence research
has been focused on avenues to overcome these problems.
Currently, the research terrains are directed on the new food
formulation, changing of the oven design and the amalgamation of
microwaves and other heating methods in order to achieve an
efficient material interaction.

10. 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