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OhmicOhmic HeatingHeating(Electrical Resistance Heating(Electrical Resistance Heating(Electrical Resistance Heating(Electrical Resistance Heating(Electrical Resistance Heating(Electrical Resistance Heating(Electrical Resistance Heating(Electrical Resistance Heating

or Electro heating)or Electro heating)or Electro heating)or Electro heating)or Electro heating)or Electro heating)or Electro heating)or Electro heating)

Valente B. AlvarezFood industries Center

Department of food Science and

Technology

OhmicOhmic HeatingHeating

Contents

Ohmic principle

Processparameters

Microbial

inactivation

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Basic principleBasic principle

Dissipation of electrical energyinto heat

Results in internal energygeneration

- proportional to the square ofelectric field strength and theelectrical conductivity

Electrical conductivity functionof temperature, material, and

method of heating

Food is made as apart of electricalcircuit

Alternating electriccurrent is passedthrough the food

Food act as a resistorto passage ofelectrical current

This causes heatgenerationP = I2 R

(P power, I current,R resistance)

R

L

V

))(1(A

LR

=

R Product resistance (ohms)L - Length (m)

A - Area

- electrical conductivity

(S/m)

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Ohmic heating and

microbial inactivation Main mechanism

like thermal process, inactivation by heat

Additional non-thermal electroporation at50-60 Hz

Electrical charges build up and formpores across microbial cells

(Wang, W.C., 1995)

AdvantagesAdvantages

Rapid heating

Reduce the total thermal abuse

Benefit heat sensitive foods (able to heatproteinaceous materials)

Suitable for continuous processing

lower capital cost than microwave Environmentally friendly

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Potential commercialPotential commercialapplications:applications: Aseptic processing of high

value added foods

pre-heating productsbefore canning

blanching, evaporation,dehydration, fermentation,and extraction

Critical process parametersCritical process parameters

Temperature and time are the principalcritical process factors

Other factors of interest include electrical conductivity(ies) of the respective

phases of the food,

temperature dependence of electricalconductivity,

design of the heating device,

extent of interstitial fluid motion,

residence time distribution (if any),

thermo physical properties of the food, and

electric field strength.

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Electrical conductivity of foodsElectrical conductivity of foods

0.34

4.3

Starch

with 0.2% salt

with 2% salt

0.42Beef

0.17Pea

0.041Carrot

0.037Potato

Electrical conductivity (S/m)Food

Electrical conductivity of foods is a function of temperature

Ohmic heating andmicrobial inactivation

Limitations & On-going research

Coupling between temperature,electrical and flow field

Shape and orientation issues

Economically viable for premiumquality foods

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Ohmically processed

commercial products

In the U.S. Canned low-acid particulate product

Pasteurized liquid egg

Italy, Greece, France, Mexico, andJapan Sliced, diced, and whole fruit within

sauces

Regulations

For in-container process

Similar to that of traditional thermalprocessing

Continuous flow processing andaseptic packaging

Under development by FDA and USDA

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OhmicOhmic HeatingHeating

Summary Ohmic principle

Processparameters

Applications andmicrobialinactivation

References (References (OhmicOhmic heating)heating) Sastry, S.K. 2003. Ohmic heating. Encyclopedia of

Agricultural, Food and Biological Engineering, MarcelDekker, Inc. 707-711.

Ramaswamy, R., Balasubramaniam, V.M., andSastry, S.K. 2005. Ohmic heating Fact sheet forfood processors (FSE 4-05). The Ohio StateUniversity, Columbus, OH, U.S.A.(http://fst.osu.edu/Ohmicfactsheet.pdf)

Wang, D.C. 1995. Ohmic heating of foods: Physical

properties and applications. Ph.D. Dissertation. TheOhio State University, Columbus, OH.

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References (PEF)References (PEF)

Bendicho, S., Barbosa-canovas, G.V., and Martin, O.2002. Milk processing by high intensity pulsedelectric fields. Trends in Food Science & Technology,13, 195-204.

Ramaswamy, R., Jin, T., Balasubramaniam, V.M.,and Zhang, H. 2005. Pulsed electric field processing.Factsheet for food processors (FSE 2-05), The OhioState University, Columbus, OH, U.S.A.(http://ohioline.osu.edu/fse-fact/0002.html)

Wouters, P.C., Alvarez, I., and Raso, J. 2001.Critical factors determining inactivation kinetics bypulsed electric field food processing. Trends in FoodScience & Technology, 12, 112-121.