Seminar Presentation by Ram Niwas Jhajhria on the topic of Ohmic Heating & Extraction Processing (M.Tech student in the department of Agricultural & Food Process Engineering, IIT Kharagpur)

1. Ohmic Heating & extraction processing
Ram Niwas Jhajhria
15AG63R29
Presented by:

2. Contents
Introduction
Concept and Principle
How is it different from conventional heating
Suitable products for ohmic heating
Advantages
Inactivation of microorganisms by ohmic heating
Design point
Factors affecting ohmic heating
Electrodes Used
Extraction processing using ohmic heating
References

3. Ohmic heating
 Ohmic heating is an advanced thermal processing method wherein
the food material, which serves as an electrical resistor, is heated by
passing electricity through it.
 In the ohmic process two electrodes literally pass electric current
through the food, where it flows on a continuous basis in a static
column.
 Electrical energy is dissipated into heat, which results in rapid and
uniform heating.
 The heating occurs in the form of internal energy generation within
the material.

4. Ohmic heating
• Joule heating,
• electrical resistance heating,
• direct electrical resistance heating,
• electro heating,
• electro conductive heating

5. Concept of Ohmic Heating

7. How is ohmic heating different from
conventional thermal processing?
• During conventional thermal processing for particulate foods,
significant product quality damage may occur due to slow
conduction and convection heat transfer.
• Ohmic heating volumetrically heats the entire mass of the food
material, thus the resulting product is of far greater quality than
its canned counterpart.
• It is possible to process large particulate foods (up to 1 inch).
• In ohmic heater cleaning requirements are comparatively less
than those of traditional heat exchangers due to reduced product
fouling on the food contact surface.

8. Products suitable for ohmic
heating
 Ohmic heating can be used for heating liquid foods containing
large particulates, such as soups, stews, and fruit slices in syrups
and sauces, and heat sensitive liquids.
 The technology is useful for the treatment of protenacious
foods, which tend to denature and coagulate when thermally
processed.
 Juices can be treated to inactivate enzymes without affecting the
flavor.
 Other potential applications of ohmic heating include blanching,
thawing, online detection of starch gelatinization, fermentation,
peeling, dehydration, and extraction.

9. Advantages
• Fast
• More uniform heating
• Higher temperature in particulates than liquid can be achieved,
which is impossible for conventional heating
• Minimum mechanical damage
• High energy efficiency
• Ease of process control & reducing maintenance cost.

10. How does ohmic heating inactivate
microorganisms?
• The principal mechanisms of microbial inactivation in ohmic
heating are thermal in nature.
• A mild electroporation mechanism may occur during ohmic
heating. The principal reason for the additional effect of
ohmic treatment may be its low frequency (50 - 60 Hz),which
allows cell walls to build up charges and form pores.

11. Electroporation
• Electroporation is the formation of holes in a cell membrane
due to individual ion pressure, which cause change in
permeability of cell membrane, due to the varying the electric
field
• The low frequency used in ohmic heating (50-60Hz) allows
cell wall to build up charges and form pores, which is not the
case with high frequency methods such as microwave
heating, where the electric field is reversed before sufficient
charge buildup occurs at the cell walls.

12. Design points
 Electrical conductivities of solid and liquid phases & their
important coefficients
 A close matching of conductivities would be highly desirable
 If σ (elec. conductivity) of solid phase is lower than the liquid
phase
 particle concentration
 Particle orientation important if particle aspect ratio are far from
unity
 For cubic and spherical particles the effects are negligible.

13. Design points
 If all the particles are of low σ ,and particle conc. Is high,
than the entire mixture heats slowly
 Problem in regulating sufficient voltage to ensure heating
 Unlike conventional heating, particle size has relatively
minor effects on heating rates.
 Particles containing fat must be handled with care.
 Fat melts and separates from solid in the mixture.

14. Factors affecting ohmic heating
 Electrical conductivity
Two phase system
Bulk elect conductivity values and individual values must be
considered
Food materials electrical conductivity varies from 10 2
m S to
10 3
m S/cm
 Shape and orientation of the particle
 Volumetric heat capacity
 Thermal conductivity and solid liquid heat transfer coefficient
 Heating rate

15. Electrodes used in ohmic heaters
• Electrodes in ohmic heating can be regarded as a ‘junction’ between
a solid-state conductor (i.e. current feeder) and a liquid-state
conductor (i.e. heating medium).
• play a vital role by conveying the current uniformly into the heating
medium.
• Various materials used as electrodes in different ohmic heating
studies and applications include
• platinized-titanium (Stirling, 1987; Tzedakis et al., 1999),
• platinum (Tzedakis et al., 1999), titanium (Assiry, 1996),
• carbon/graphite (Gatchell, 1935; Moses, 1938),
• stainless steel (Assiry, 1996; Wu et al., 1998; Assiry et al.,
2003),
• rhodium plated stainless steel (Palaniappn et al., 1991).
• During ohmic heating at low-frequency (50 - 60 Hz) alternating
currents, it was reported that corrosion of electrodes and apparent
(partial) electrolysis were often encountered with most of those
electrodes.

16. Extraction Processing
 Pre-treatment process in solvent extraction processing
 Extraction time is reduced
 Amount of extracted product is significantly increased.
Oil extraction from rice bran:
Rice variety – : Basmati rice
Solvent – : n-hexane
Voltage- : 270 V
Conducting medium- : Sodium Chloride
(1M, 0.1M, 0.01M)

17. Procedure:
1. Ohmic heating chamber
2. Thermometer
3. Wattmeter
4. Ammeter
5. Variac
6. Current source

18.  Took 25g rice bran
 Add 150ml sodium chloride as a conducting material in three
different concentrations 1M, 0.1M, 0.01M in three different
experiments
 Switch on the power source and fixed the current value to heat
the material
 Power is controlled in throughout the process to control the
current
 During process the parameters i.e. temperature with time,
current and power is noted
 After ohmicaly heating, the rice bran samples were taken out
from ohmic heating chamber and washed with fresh water to
drain out the sodium chloride solution and then heated in hot air
oven at 75 ° C for 5 min.
 Then this pre treated rice bran is subjected to solvent extraction
in soxhlet apparatus at 72ºC, and extract the oil.

19. Result and Discussions
Twenty-five grams of rice bran was taken and oil extraction was
conducted. The volume of n-Hexane used for the extraction was 200
ml. The quantity of rice bran oil extracted was 0.53 ml with an
extraction time of 185 min (Without ohmic heating)
Ohmic heating was introduced as a pre treatment before
solvent extraction then the time of extraction was 54min only and
the yield of oil 0.8 ml
Extraction time reduced to approx 70-75%
Oil yield increased significantly

20. References:
Marcos Camargo Knirsch, Carolina Alves dos Santos, António
Augusto Martins de Oliveira Soares Vicente,Thereza Christina
Vessoni Penna, Trends in Food Science & Technology-Ohmic
heating, a review, 2012.
https://en.wikipedia.org/wiki/Joule_heating
https://www.youtube.com/watch?v=pPhvE5f-KwE
Gopu Raveendran Nair, V.R Divya, Liji Prasannan, V. Habeeba,
M.V. Prince, G.S.V. Raghavan, Ohmic heating as a pre treatment in
solvent extraction of rice bran, June 2012