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V.B. Alvarez/PEF/10-2007

PULSED ELECTRICPULSED ELECTRICPULSED ELECTRICPULSED ELECTRICPULSED ELECTRICPULSED ELECTRICPULSED ELECTRICPULSED ELECTRICFIELD PROCESSINGFIELD PROCESSINGFIELD PROCESSINGFIELD PROCESSINGFIELD PROCESSINGFIELD PROCESSINGFIELD PROCESSINGFIELD PROCESSING

Valente B. AlvarezFood industries Center

Department of food Science andTechnology

PULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSING

Contents Principle Processing

parameters Applications and

effects


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Application of short burst of high voltage(approx. 20-80 kV/cm) to foods placedbetween two electrodes pulses applied at ambient or refrigerated

temperatures for short treatment time ofseconds or less

Square wave, bipolar, oscillatory pulses orof exponentially decaying waves

Aseptic packaging and refrigerated storageafter treatment

Nonthermal method of food preservation

Pulse electric field (PEF)Pulse electric field (PEF)Pulse electric field (PEF)Pulse electric field (PEF)Pulse electric field (PEF)Pulse electric field (PEF)Pulse electric field (PEF)Pulse electric field (PEF)basic principlebasic principlebasic principlebasic principlebasic principlebasic principlebasic principlebasic principle

PEF PrinciplePEF Principle

Non-thermal inactivationof microorganisms thatresults from thepermeabilization orelectroporation of the cellmembrane

Depends on electric fieldintensity, pulse duration,and number of pulses.

DesbalanceOsmotico

Hinchamiento

Celula

Ruptura de laMembrana

Mechanism of inactivation


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Critical process parametersCritical process parameters

PROCESS RELATED Electric field strength Total treatment time Pulse width Pulse polarity Treatment temperature Pulsed shape (Square

wave, exponentialdecay, oscillatorypulses)

Flow rate

PRODUCT RELATED Electrical conductivity pH Water activity (a w)

Bacteria > Yeasts Gram (+) > Gram (-) Bacterial spores & Mold ascospores > Vegetative

cells

Stationary or Lag growth phase > Logarithmicphase

Microbiological resistanceMicrobiological resistance


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Log phase cells are more sensitivethan stationary phase cells

Spores are not inactivated(Mertens & Knorr, 1992; Gould, 2001)

Pulse electric field (PEF)Microbiology

Intrinsic and extrinsic factorsinfluencing effectiveness:

More inactivation with risingtemperatures

Low ionic strength favors inactivation Reduction in pH increase

inactivation(Qin et al., 1994; Jayaram et al., 1992)

Pulse Electric Field (PEF)Pulse Electric Field (PEF)Process ConditionsProcess Conditions


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Resistivity in general decreases astemperature increases

Resistivity decreases as ionic strengthincreases Hulsheger and Niemann (1980) found the same level of E.

coli inactivation in buffers of NaCl, Na 2S 2O3, NaH 2PO 4,

The bactericidal effect of PEF is generallyinversely proportional to the ionicstrength of the material treated Wouters and Smelt, 1997

PEF process conditionsPEF process conditions

PEF: less thermal damage toPEF: less thermal damage tofoodsfoods

FLAVOR Cranberry juice treated with PEF was not

distinguishable from raw juice, although heattreated juice was.

Apple cider treated with PEF had nodetectable flavor differences from untreatedproduct when fresh

Orange juice PEF treated at 65 oC was preferredover heat pasteurized product, but not overuntreated product


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COLOR Cranberry juice retained more

anthocyanin pigments after PEFprocessing than after heat treatment

Tomato salsa processed with PEFretained a brighter red color than heatprocessed product

No significant color differences were

seen in orange juice or in apple cider


NUTRITIONAL COMPONENTS Vitamin C loss was more significant in heat

treated orange juice than in PEF treated juice

PROTEIN COAGULATION

Coagulation in the treatment chamber leads toreduced flow, non-uniform or over- treatmentand eventually plugging of the chamber.


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ISSUEISSUE THERMALTHERMAL PEFPEF

Mode of operation Batch/continuous Primarily continuous

Process in Package Yes No

Chemical changes Many Limited

Physical changes Many None

Enzyme Inactivation Yes Limited

Comparison between thermalComparison between thermalComparison between thermalComparison between thermalComparison between thermalComparison between thermalComparison between thermalComparison between thermalprocessing and PEFprocessing and PEFprocessing and PEFprocessing and PEFprocessing and PEFprocessing and PEFprocessing and PEFprocessing and PEF

Potential Food ApplicationsPotential Food ApplicationsPotential Food ApplicationsPotential Food Applications

Juice Milk Liquid eggs Soups

Syrups, sauces Emulsion Flavor ingredients


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Electric resistivity of variousElectric resistivity of variousfood materialsfood materials

Zhang, et al., 1994

FoodsElectric

resistivity( -cm)

Conductivity

(mS/cm)

Testtemperature

(oC)

Apple juice 570 1.8 15Orange juice 234 4.3 42Orange juice conc. 300 3.3 15

Tomato ketchup 42 23.8 15Crushed tomatoes 125 8.0 50

Milk, skim 310 3.23 15Milk, raw 230 4.4 20

Yogurt 169 5.9 23Egg whites 155 6.5 15Liquid whole egg 170 5.9 21

The importance of pH in PEFThe importance of pH in PEFformulationsformulations

High acid foods are moresuccessfully treated with PEF Vegetative organisms are more effectively

treated at lower pH

product is a high acid or acidified food (pH


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PEF Advantages & disadvantagesPEF Advantages & disadvantages

Limitations due to thedifficulty of inactivatingendospores and lowconductivity caused bysolids in foods.

Regulatory requirementsdeveloping

Difficult to incorporatenecessary equipment intomost production areas

High quality fresh-likeliquid foods

Improve flavor, nutritionalvalue, and Shelf life

Foods retain their fresharoma, taste, andappearance

Energy efficient processcompare to thermal

processing(Ramaswamy, 2003)

Combination processesCombination processes

PEF may offer synergistic effect with Ultrasound Temperature Chemical & additives

e.g. Bacteriocin

High pressure Sequential or simultaneous


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PEF Work at OSU

Raw & UHT skim milk were PEFprocessed 0.3 to 3.0 log reduction of P.

fluorescens , L. lactis and B. cereus and of total m.o.s in raw skim milk

No changes in protein, total solids,color, pH, particle size, and densitydue to PEF effects

Overall effectiveness of PEF vs.

Pasteurization (73oC for 30s)(Alvarez et al., 2003)

Microbial Inactivation of Microbial Inactivation of Microbial Inactivation of Microbial Inactivation of Microbial Inactivation of Microbial Inactivation of Microbial Inactivation of Microbial Inactivation of Pulsed Electric Field Treated MilkPulsed Electric Field Treated MilkPulsed Electric Field Treated MilkPulsed Electric Field Treated MilkPulsed Electric Field Treated MilkPulsed Electric Field Treated MilkPulsed Electric Field Treated MilkPulsed Electric Field Treated Milk

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

047 94 141 188

Treatment Time ( s)

L o g r e

d u c

t i o n s ,

N / N o

( c f u m

L - 1

)

P.fluorescens L. lactis B. cereus Microorganisms in Raw Skim Milk

-6

-5

-4

-3

-2

-1

0P. fluorescens L. lactis B.cereus

Microorganisms inRaw Skim Milk

L o g r e

d u c

t i o n ,

N / N o ( c

f u m

L - 1

)

Pasteurization PEF

Source: Michalac, Alvarez..., 2003


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PULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPULSED ELECTRIC FIELDPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSINGPROCESSING

Summary Principle Processing

parameters Applications and

effects

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.

Michalac, S., Alvarez, V. B., Ji, T., and Zhang, Q.2003. Inactivation of Selected Microorganisms andProperties of Pulsed Electric Field Processed Milk. J.Food Proc. and Preservation . 27 (2). 137-151.

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.

1 pulsed electric field

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