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Pulse Electric Fields For Food Processing Technology

Department of Agricultural & Food Engineering IIT Kharagpur

Roll No 14AG63R11 Barun Kumar Yadav

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Introduction

• High voltages (≤ 100 kV ) in short ( 1-10 µs )

pulses ( up to 1000 Hz ) .

• Total Treatment time < 1 s (generally).

• Product expose to electric fields via electrodes.

• Effects includes permeabilisation of membranes.

• Classes as a “non –thermal” treatment.

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History of PEF (Scientific publication)

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Scientific publication vs other technologies

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Publication vs uptake of HPP

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Principle of Technology

• PEF processing for food preservation implies applying short

electric pulses.

• Usually 1±20 µs, but with a range of 50 ns to several

milliseconds.

• With a high field strength (15±80 kV/cm ) .

• Samples placed between two electrodes in a batch or

continuous treatment chamber.

• To generate such a fast electrical discharge, pulse-forming

networks (PFN) are used.

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The main components of a PFN

• Power supply: A high voltage generator which supplies electrical

energy at the selected voltage .

• One or several capacitor banks, inductors or/and resistors.

• One or several switch which deliver electrical energy to the

electrodes and the food sample.

• One (or several) treatment chamber(s) with two electrodes

between which the food sample either flows or is encased.

• An oscilloscope to measure voltage across the electrodes and

display pulse shape.

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Working

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Type of pulse wave form: PEF may be applied in the form of exponential decaying, Square , bipolar or oscillating pulses.

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Mechanism of Microbial inactivation • There are mainly two type of mechanism :

Electrical Breakdown

Electroporation

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Electrical breakdown

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Electroporation

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• Microbial inactivation increases with an increase in the

electric field strength.

• Gram-positive are more resistant to PEF than those that

are Gram-negative.

• Yeasts are more sensitive to electric fields than bacteria

due to their larger size.

• At low electric fields they seem to be more resistant than

Gram-negative cells.

• Spores are high resistant to PEF .

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Input requirement

Input requirements

of PEF

Microbial inactivatio

n15-40kV/

cm

Improvement of mass transfer in plant/anim

al cell0.7-

3.0kV/cm

In apple juice

22-34kV/cm

Sludge disintegration10-20kv/cm

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PEF Critical FactorsProcess- Electric field intensity- Pulse Width- Treatment time and temperature- Pulse wave shapes and polarity

Microbial entity- type, concentration, and growth stage of microorganism.

Treatment media- pH, antimicrobials, and ionic compounds, conductivity, and medium ionic

strength.- Food with large electrical conductivities generate smaller peak electric fields

across the treatment chamber and therefore are not feasible for PEF treatment.

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Comparison between technique ( Cost VS Technique )

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Advantage • Less treatment time and low treatment temperature.• Substitute for conventional heat pasteurization.• Increase shelf life and maintain food safety.• Minimally processed foods of fresh quality, which have

higher nutritional value because of color and flavor retention.

• PEF inactivates vegetative micro-organisms including yeasts, spoilage micro-organisms and pathogens.

• Reduction in microorganisms: 4-6 log• It can be used to pasteurize fluids such as juices, milk and

soups without using additives.• It increase the juice and oil extraction yeald.

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Disadvantage• High capital cost. • PEF treatment is effective for the inactivation of vegetative

bacteria only. • Micro-organisms are destroyed by PEF but spores, with their

tough protective coats, and dehydrated cells are able to survive.• Refrigeration is required to extend shelf-life.• Treatment does not inactivate enzymes.• PEF is a continuous processing method, which is not suitable for

solid food products that are not pump able.• PEF processing is restricted to food products with no air bubbles

and with low electrical conductivity.

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Aspects to be considered in PEF

• Generation of high electric field intensities.

• Design of chamber that impart uniform treatment to foods.

• Minimum increase in temperature.

• Design of electrodes that minimize the effect of

electrolysis.

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Application of PEF Technology

Juice processing:• Applying PEF to cellular tissue an increase in mass

transfer coefficients due to cell membrane permeabilisation.

• There is 10-12% increase of juice yield when applying electroplasmolysis to apple tissue.

• Application of PEF for juice processing provides a potential to replace or enhance conventional cell disintegration techniques.

• The shelf life of fresh orange juices is extended by PEF treatment from a few days to a few weeks.

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Sugar Processing• In Conventional procedures for production of sugar from

beets, disintegration and destruction of cell membranes a thermal treatment at temperatures in the range from 70 to 78°C is applied.

• The membrane de-naturation results in an acceleration of sugar release into the extraction media, but also cell wall components such as pectin may become soluble and can diminish juice purity and quality.

• A PEF treatment of sugar beets could increase mass transfer rates and could allow to reduce extraction temperatures and better quality of sugar can be obtained.

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PEF treatment of microalgae, seaweed, and other aquatic species

• Different varieties of macro- and microalgae are sources

of vitamins, pigments, proteins as well as antixodative and

bioactive substances.

• Algae extracts applying PEF treatment could provide a

potential toward a gentler downstream processing.

• There is an increasing in the yield after PEF treatment,

mainly in the case of extractability of growth hormones.

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Plant Oil ExtractionSitzmann and Munch (1988) reported an enhanced

separation of tankage emulsions when extracting protein and fat from animal tissue.

A similar effect can be expected after PEF treatment of oil seeds prior to recovery.

Yield and quality of oils has been studied and high oil yield was developed.

Oil recovery from olives was improved by 7.4% after a PEF treatment at 1.3 kV/cm in comparison to the control sample.

In soybean oil an increase in iso-flavonoid content was reported.

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Meat & Fish Treatment• Disintegration of animal cellular tissue is used to enhance

the curing of fish or meat products.• In case of raw ham a long-term curing and air drying is

applied. During such procedures a PEF treatment can be applied to improve mass transfer processes and to accelerate curing, reducing the time requirements.

• An increase in mass transfer rates, resulting in faster water transport to the product surface and therefore drying time can be reduced.

• This will lead to drastic saving of energy and better utilization of production capacities during convective air drying.

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References:

• Food preservation Techniques – Peter Zeuthen and Leif Bagh, Sarensen, CRC , Woodhead Publ. Ltd.

• Maged E.A. Mohamed and Ayman H. Amer Eissa (2012). Pulsed Electric Fields for Food Processing Technology, Structure and Function of Food Engineering, Prof. Ayman Amer Eissa (Ed.), ISBN: 978-953-51-0695-1, Intec, DOI: 10.5772/48678.

• Pulse electric field Technology for food industries , Fundamentels and application - Javier Raso and Volker Heinz , Springer publ Ltd.

• http://www.foodtech-international.com/papers/PulsedElectricField.htm• http://www.fda.gov/Food/FoodScienceResearch/

SafePracticesforFoodProcesses/ucm101662• http://worldfoodscience.com/cms/index.html@pid=1006021.html• https://www.youtube.com/watch?v=6LYAPgRyU0c