Food Processing and Cooking Recipes

FUNT–1011 4(2–4)

Dr. Sanaullah Iqbal Miss Amina Chughtai

Department of Food & Nutrition

University of Veterinary and Animal Sciences, Lahore

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Food Processing Food processing is the set of methods and techniques

used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry.

Food processing typically takes clean, harvested crops or slaughtered or butchered animal products and uses these to produce attractive, market able and often long life food products.

Similar processes are used to produce animal feeds.

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Why Food Processing? 1. To increase shelf-life or storage of food and to avoid food spoilage

2. To achieve and maintain microbial food safety e.g. mycotoxins

3. To reduce volume, for example, Blanching of leafy vegetables

4. To increase variety in the diet by providing a range of attractive flavour, color, aroma and texture (organoleptic quality) in food

5. To improve the nutritional quality and digestability of the food

6. To acquire seasonal commodities on a year round basis

7. To utilize raw materials whom physical appearance is not good e.g. de-shaped and unripe apples for jams

8. To make food available at difficult locations e.g. Siachin glacier

9. To generate income by manufacturing company

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Food Processing Food processing is divided into two groups:

1. Unit operations: A combination of procedures to achieve the intended

changes to the raw materials.

2. Process:

Unit operations are grouped together to form a process. The combination and sequence of operations determines the nature of the final product.

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Principles of Food Preservation

Autolysis may be prevented or delayed by the destruction or inactivation of enzymes and to inhibit the reactivity of chemically active molecules.

Spoilage in foods as a result of microbial activity may be prevented or delayed by either prohibiting the entry of m.o. into the food, physically removing them from food, hindering their growth and activity or even destroying them.

Quality defects and losses in food caused by insects, rodents and birds may be controlled by adequate packaging and pest control program.

Physical deterioration during processing, handling and storage may be reduced by development of optimal conditions.

The principles of food preservation are based on this knowledge and on the understanding of how chemical reactions, physical changes and insect-pest attack collectively reduced the quality of foods.

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Food preservation Microorganisms and enzymes are the main agents

responsible for food spoilage and therefore the targets of preservation techniques. An “ideal” method of food preservation has the following characteristics:

It improves shelf life and safety by inactivating spoilage and pathogenic microorganisms.

It does not change organoleptic and nutritional attributes.

It does not leave residues.

It is cheap and convenient to apply.

It encounters no objections from consumers and legislators.

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Non-Thermal Food Preservation

Food Biopreservation

Ultra sound

Pulsed Electric Field (PEF)

Dense Gases – Supercritical Carbon Dioxide

High Hydrostatic Pressure

High-intensity Electric-field Pulse

Nano-technology in food processing

Thermo ultrasonication

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Food Biopreservation Use of micro-organisms and / or

their natural products for the preservation of foods.

Microbial processes Lactic acid fermentation Propionic acid fermentation Alcoholic fermentation

Addition of Organic acids Antimicrobial substances Enzymes Inhibitors

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Food Biopreservation Most fermented foods around the world depend on Lactic acid bacteria

End products of these fermentations by LAB not only contribute to preservation but also add flavour, aroma, texture, etc.

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Principles of food biopreservation

Preservation through fermentation is based on mainly four different effects:

1. Reduction of the pH through the formation of organic acids which results in a larger fraction of undissociated acids (more pronounced antimicrobial effect.) Weak acids are more effective at constant pH than strong acids e.g. 0.2% lactic acid (~ 22 mM) inhibits growth of Listeria monocytogenes at 7°C

2. Secretion of compounds that inhibit microbial metabolism (Hydrogen peroxide, Diacetyl, alcohol, organic acids)

3. Formation of antimicrobial substances like bacteriocins

4. Competition for the available nutrients

Food Biopreservation

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BACTERIOCINS:

These are ribosomally synthesized antimicrobial peptides produced by one bacterium that are active against other bacteria, either in the same species (narrow spectrum), or across genera (broad spectrum).

Producer organisms are immune to their own bacteriocin(s), a property that is mediated by specific immunity proteins.

Genes responsible for production and immunity are generally found clustered in operons.

It has been suggested that between 30–99% of the Bacteria and Archaea make at least one bacteriocin.

Five classes of bacteriocins but majority fall in class I and II.

Food Biopreservation

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Suitability for food preservation: generally recognised as safe substances not active and nontoxic on eukaryotic cells become inactivated by digestive proteases, having little

influence on the gut microbiota (probiotics), usually pH and heat-tolerant, relatively broad antimicrobial spectrum, against many food-

borne pathogenic and spoilage bacteria, bactericidal mode of action, usually acting on the bacterial

cytoplasmic membrane: no cross resistance with antibiotics, genetic determinants are usually plasmid-encoded, facilitating

genetic manipulation

Food Biopreservation BACTERIOCINS

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Benefits of bacteriocins in food preservation: An extended shelf life of foods

Provide extra protection during temperature abuse conditions

Decrease the risk for transmission of foodborne pathogens through the food chain

Ameliorate the economic losses due to food spoilage

Reduce the application of chemical preservatives

Permit the application of less severe heat treatments without compromising food safety: better preservation of food nutrients and vitamins, as well as organoleptic properties of foods,

Food Biopreservation BACTERIOCINS

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Application of bacteriocins in food system: Foods can be supplemented with ex situ produced bacteriocins

o Bacteriocin is produced through fermentation and subsequent recovery and purification process → Costly

o Needs approval as food preservative

o Only nisin is approved as purified bacteriocin (E234)

o Ex situ produced bacteriocins can also be added as part of more complex mixtures (Microgard)

o Application in form of immobilized preparations, e.g., on packaging material such as polyethylene films (for packaging of ground meat, sausage, etc.)

Food Biopreservation BACTERIOCINS

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Application of bacteriocins in food system: Alternative is inoculation with bacteriocin-producing strain, in

situ bacteriocin production

o Advantageous with respect to legal aspects and costs; if the producer strain has GRAS status then no approval necessary

o Bacteriocinogenic strain can be added o directly as starter culture

o As co-culture in combination with a starter culture

o As protective culture (esp. for non-fermented foods)

o Protective cultures can for example be used to inhibit spoilage or pathogenic bacteria during the shelf life or even during temperature abuse conditions of frozen foods

Food Biopreservation BACTERIOCINS

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Food Biopreservation BACTERIOCINS

Application of bacteriocins in food system: Hurdle technology:

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Food Biopreservation BACTERIOCINS

Biosynthesis: Genes encoding bacteriocin production and immunity are generally

organised in operon clusters

These genes are located on plasmids (e.g., sakacin A, divergicin A), transposons (e.g. nisin, lacticin 481) or on the chromosom (e.g. subtilin)

Actual bacteriocin peptide is synthesized on the ribosome as a prepeptide which undergoes extensive posttranslational modifications to form the bioactive peptide (lantibiotics)

Lantibiotics (Lanthionine-containing antibiotic)

Best studied example for a lantibiotic is nisin

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Food Biopreservation BACTERIOCINS

Biosynthesis: Operon for lantibiotic biosynthesis contains genes for:

Structural gene coding for the prepeptide (LanA)

Enzymes for posttranslational modifications (LanB, LanC)

Protease to remove the leader peptide (LanP)

Regulatory proteins (LanK, kinase; LanR, response regulator)

Transport proteins involved in peptide translocation (LanT, putative ABC transporter - ATP-binding cassette)

Immunity (LanI, LanFEG)

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Food Biopreservation BACTERIOCINS Biosynthesis:

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Cyclic conformations resulting from amino acid modifications are essential for: maintaining peptide rigidity

Insensitivity to proteolytic degradation

Increase of thermostability

Antimicrobial function, e.g. removal of ring A in nisin (through site-directed mutagenesis) results in almost complete loss of activity

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Food Biopreservation BACTERIOCINS Biosynthesis:

Nisin was first isolated from culture broth of Lactococcus lactis in 1947

Commercially available in 1953 (Nisaplin®; Aplin and Barrett, UK)

First and one of the few bacteriocins that is commercially available

Wide acceptance, GRAS status

Nisin A, nisin Z: vary slightly in primary sequence, produced by different species of L. lactis

Cationic bacteriocin peptide, carries positive charge due to the presence of Lys and His residues

Small, elongated and flexible molecule

Amphiphilic, hydrophilic and hydrophobic properties of the molecule

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Food Biopreservation BACTERIOCINS Lantibiotic: Nisin

Food Biopreservation NISIN Mode of Action:

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Dual mode of action: They can bind to lipid II, the main transporter of peptidoglycan subunits from

the cytoplasm to the cell wall, and therefore prevent correct cell wall synthesis, leading to cell death. Nisin also binds to tichoic acid in the cell wall and activates autolytic degradation.

They can use lipid II as a docking molecule to initiate a process of membrane insertion and pore formation that leads to rapid cell death.

Food Biopreservation NISIN Mode of Action:

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1st Step: Binding of nisin to the (phospho) lipid bilayer of the membrane through electrostatic interaction between positively charged C-terminal region of nisin and negatively charged phospholipids

Association of nisin with membrane depends on the type of lipids present in the membrane and the charge carried by these lipids

2nd step: Insertion of nisin into the membrane

Energy-dependent process, energy is required both for the insertion of nisin and the opening of the pore

Electrical transmembrane potential is the major driving force for these processes

Energisation state of cells is therefore critical (threshold potential of –80 mV is required)

Food Biopreservation NISIN Mode of Action:

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3rd step: Pore formation Nisin is a small molecule and can span the membrane only once,

therefore several nisin molecules associate to form the pore Aggregation follows once the first nisin is inserted into the membrane,

dynamic, transient process, ‘barrel-stave’ model Peptides are aligning around a central channel (diameter approx. 1 nm

but varying), hydrophobic part facing lipid bilayer while hydrophilic part faces water-filled pore

‘Barrel-stave’ model of pore formation by nisin. Nisin monomers (‘staves’) bind, insert and aggregate within the membrane to form a water-filled pore (the ‘barrel’).

In vivo, nisin is killing sensitive bacteria when present in nanomolar concentrations

Potent inhibitor of several species of Gram-positive bacteria, outer cell membrane of Gram-negative bacteria is impermeable to nisin

Active against: Clostridum botulinum (vegetative cells and spores)

Clostridum butyricum

Listeria monocytogenes (10 to 2500 μg/mL needed for complete inhibition depending on food matrix and strain)

Bacillus species

Salmonella species 25

Food Biopreservation NISIN

Antimicrobial spectrum:

Processed cheese: 5–15 μg/g; inhibition of endospores from Bacillus and Clostridium spp.

Cottage cheese: 5-50 μg/g, inhibition of L. monocytogenes Soft fresh cheese: 5 μg/g, preservation of minimally process cheese

such as ricotta Yoghurts: 0.5–1.25 μg/g, reduction of over-acidity Milk and milk products: 0.25–1.25 μg/g, extension of shelf life of

pasteurised milk in developing countries Pasteurised fruit juice: 0.13–0.25 μg/g, inhibition of Alicyclobacillus

acidoterrestris Beer: 0.25–2.5 μg/g, selective inhibition of spoilage lactic acid bacteria Dressings and sauces: 1.25–5 μg/g, inhibition of various contaminants Canned food: 2.5–5 μg/g, destruction of clostridial and bacilal spores Fresh soup: control of spoilage flora

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Food Biopreservation NISIN

Selected Applications:

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Food Biopreservation NISIN Selected Applications:

Broughton, J.D. Nisin as food preservative. Food Australia 57 (12) - December, 2005

Ultrasound

Why use ultrasound? The sound as a diagnostic tool, e.g. in non-destructive evaluation

The sound as a source of energy, e.g. in sonochemistry

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Ultrasound can be defined as “sound waves with frequencies above that of human hearing (typically higher than 16 kHz)”

Frequency ranges of sound In recent years food technologists have discovered that it is possible to employ a more powerful form of ultrasound (>5W/cm2) at a lower frequency (generally around 40 kHz). This is usually referred to as power ultrasound.

Da-Wen Sun, Emerging technologies for food processing, Elsvier Academic Press, USA , 2005

Whatever type of system is used to apply power ultrasound to foods, it will consist of three basic parts:

1. Generator: this is an electronic or mechanical oscillator that needs to be rugged, robust, reliable and able to operate with and without load.

2. Transducer: this is a device for converting mechanical or electrical energy into sound energy at ultrasonic frequencies.

3. Coupler: the working end of the system that helps transfer the ultrasonic vibrations to the substance being treated (usually liquid).

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Ultrasound Generation of Power Ultrasound

Mechanical effects crystallization of fats, sugars etc.

degassing

destruction of foams

extraction of flavourings

filtration and drying

freezing

mixing and homogenization

precipitation of airborne powders

tenderization of meat

Chemical and biochemical effects

bactericidal action

effluent treatment

modification of growth of living cells

alteration of enzyme activity

sterilization of equipment

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Ultrasound Some uses of power ultrasound in food processing

Da-Wen Sun, Emerging technologies for food processing, Elsvier Academic Press, USA , 2005

Like any sound wave, ultrasound is propagated via a series of compression and rarefaction waves induced in the molecules of the medium through which it passes.

At sufficiently high power the rarefaction cycle may exceed the attractive forces of the molecules of the liquid and cavitation bubbles will form.

Such bubbles grow by a process known as rectified diffusion, i.e. small amounts of vapour (or gas) from the medium enters the bubble during its expansion phase and is not fully expelled during compression.

The bubbles, distributed throughout the liquid, grow over the period of a few cycles to an equilibrium size for the particular frequency applied.

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Ultrasound Principle of ultrasound in food processing

Da-Wen Sun, Emerging technologies for food processing, Elsvier Academic Press, USA , 2005

If the bubbles were only subject to that particular frequency they would remain as oscillating bubbles, however, the acoustic field that influences an individual bubble among the many thousands generated in a cavitating fluid is not uniform.

Each bubble will slightly affect the localized field experienced by neighbouring bubbles through the creation of microcurrent.

Under such circumstances the irregular field will cause the cavitation bubble to become unstable and collapse. This shear force is one of the modes of action, which leads to disruption of microbial cells.

Based on theoretical considerations, extremely high temperatures and pressures are momentarily delivered to the liquid media during the collapse of bubbles

This collapse, generate the energy for chemical and mechanical effects. 32

Ultrasound Principle of ultrasound in food processing

Da-Wen Sun, Emerging technologies for food processing, Elsvier Academic Press, USA , 2005

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Ultrasound Principle of ultrasound in food processing

High intensity acoustic fields in liquids lead to rupture of the liquid and the formation of cavities or bubbles, a phenomenon called acoustic cavitation

Homogenous liquid-phase system Pulling of molecules to create cavity – intermolecular spaces are less

A pure liquid would require very high power levels to initiate cavitation.

However, most normal liquids contain some discontinuities, such as gas bubbles or dust motes, which act as weak spots and allow the bubbles to form.

Solid-liquid system Collapse of a cavitation bubble on or near to a surface is asymmetrical because

the surface provides resistance to liquid flow from that side.

Liquid –liquid system The general mechanical effects of cavitation at or close to a liquid–liquid

interface lead to very effective emulsification/homogenization.

Gases Greater power loss in the transmission of sound

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Ultrasound Power ultrasound in different phase systems

Da-Wen Sun, Emerging technologies for food processing, Elsvier Academic Press, USA , 2005

1. Laboratory scale Whatever food processing application

is to be studied or developed, the essential requirement is a source of ultrasound.

sonicate liquid samples in vessels immersed in the bath

Vibrations directly into the sample

To dissolve chemicals in solvents

Sonicator for microbial cell disruption

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Ultrasound Ultrssonic processing equipments

2. Large scale 2.1 Batch type

Batch systems will generally be based upon the ultrasonic cleaning bath using the whole bath as the reactor.

Examples can be found in cleaning and decontamination of equipment, e.g. in the cleaning of chicken shackles to avoid cross-contamination.

2.2 Flow type One of the oldest devices used to achieve emulsification through cavitation is the

liquid whistle. Process material is forced under pressure generated by a powerful pump through an orifice from which it emerges and expands into a mixing chamber.

The systems that are particularly suitable for general usage in the food industry are resonating tube reactors. Essentially the liquid to be processed is passed through a pipe with ultrasonically vibrating walls. In this way the sound energy generated from transducers bonded to the outside of the tube is transferred directly into the flowing liquid. Generally, commercial tube reactors are constructed of stainless steel and the choices for pipe cross-section are rectangular, pentagonal, hexagonal and circular.

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Ultrasound Ultrssonic processing equipments

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Ultrasound Ultrssonic processing equipments

Liquid whistle

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Ultrasound Potential applications of ultrasound in food industry

James JB, Food Processing Handbook, Wiley VCH , Weinheim, 2006

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Ultrasound Potential applications of ultrasound in food industry

James JB, Food Processing Handbook, Wiley VCH , Weinheim, 2006

Ultrasound

Major cause for food deterioration Gram +ve more resistant than G-ve Aerobic are more resistant than anaerobe Younger cells more senstive than older Vegetative more senstive than spore Inactivation of emerging pathogenic

microbes Damage to cells caused by heat is

reversible but by monosonicati on is irreversible

Used with other non-thermal technologies such as magnetic field and high pressure

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Inactivation of microorganisms

Schematic view of a bacteria cell during cavitation, showing the lethal effects of ultrasound such as pore formation, cell membrane disruption, and cell breakage

Ultrasound

Has received less attention as compared to microbial destruction o Enzymes show great sensitivity toward ultrasonic irradiation o Inactivation of pepsin due to cavitation o MTS inactivate peroxidase by splitting its prosthetic heme group o Ultrasound in combination with heat and pressure for soybean

lipoxygnase, horseradish peroxidase, tomato pectic enzymes, orange, pectin methylesterase, lipase, and protease, among others.

o Mechanism of action o MTS responsible for particle size reduction and molecular breakage e.g.

Breakage of pectin molecules in a purified pectin solution o Changes in pressure generate streching and compression in the cells and

tissues o Free redical production i.e. H+ and OH- ions

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Inactivation of enzymes

Ultrasound

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Future of Power Ultrasound

Much more research is required to gain a greater understanding of issues such as:

equipment design to optimize microbial and enzyme inactivation; ultrasonic enhancement of heat transfer to augment existing thermal

processes; accurate mapping of field intensity variations within a treatment

chamber to develop reliable scheduled processes using ultrasound; inactivation mechanisms for vegetative cells, spores and enzymes, which

need to be clearly identified, especially when combination technologies are used;

development of mathematical models for the inactivation of microorganisms and enzymes involving ultrasound;

identifying the influence of food properties such as viscosity and particle size on process lethality as well as the implication of process deviations when using ultrasound.

Development of CCP´s like established technologies

ULTRASOUND

Pulsed Electric Field (PEF)

The use of an external electrical field for a few microseconds induces local structural changes and a rapid breakdown of the cell membrane. Based on this phenomenon, called electroporation, many applications of high intensity pulsed electric fields (PEF) have been studied in the last decades.

Definition: Pulsed electric field processing is a technique in which a food is placed between two electrodes and exposed to a pulsed high voltage field (typically 20–80 kV cm–1).

For preservation applications, treatment times are less than 1 s, achieved by multiple short duration pulses typically less than 5µs.

Heat may be generated in the food product (and may need to be controlled by cooling), microbiological inactivation is achieved by non-thermal means.

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Introduction

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Pulsed Electric Field (PEF) Electrical breakdown The bacterial cell membrane can be considered to be a capacitor that is filled

with a dielectric material. The normal resisting potential difference across the membrane (the transmembrane potential) is around 10 mV.

If an external electric field is applied, this increases the potential difference across the cell membrane.

This increase in potential difference causes a reduction in the membrane thickness. When the potential difference across the cell reaches a critical level (normally considered to be around 1 V), pores are formed in the membrane.

This leads to an immediate discharge at the membrane pore and, consequently, membrane damage. Breakdown of the membrane is reversible if the pores are small in relation to the total membrane surface, but when pores are formed across large areas of the membrane then destruction of the cell membrane results.

PEF treatment of Bacillus cereus cell.

In the area of plant and microbial genetics pulsed electric fields (5-15 kV cm-1) are applied to cause an electroporation of cell membranes to infuse foreign material such as DNA into the cell. The lipid bilayer and proteins of the cell membrane are temporarily destabilized.

This process of reversible pore formation has to be controlled to maintain viability of the organisms during the application of the PEF.

Due to the reversible permeabilization the cells repair their membranes through resealing the electropores immediately after the PEF treatment.

At higher treatment intensity PEF (20-80 kV cm-1) can be utilized for the inactivation of microorganisms by an irreversible breakdown of the cell membrane.

In food technology this irreversible pore formation by PEF can be applied as a mild preservation technique for liquid food as well as a substitute for conventional cell disintegration methods.

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Pulsed Electric Field (PEF) Electroporation

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Pulsed Electric Field (PEF) A brief History

The inactivation of microorganisms and enzymes using electric discharges started as early as the 1920s with the ‘ElectroPure’ process for milk production. This process consisted of heating the milk to 70 °C by passing it through carbon electrodes in an electric heating chamber to inactivate Mycobacterium tuberculosis and E. coli. The electric field was small, only 220 V AC, and was not pulsed; and the inactivation mechanism was purely thermal. There were around 50 plants using the ElectroPure system in the USA up until the 1950s.

An ‘electrohydraulic’ process was developed in the 1950s as a method for inactivating microorganisms in liquid food products. A shock wave generated by an electric arc and the formation of highly reactive free radicals was thought to be the main mechanism for microbiological inactivation. The process did not find widespread use in the food industry because particulates within the food were damaged by the shock waves and there were issues surrounding electrode erosion and the potential for contaminating the food except waste water treatment.

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Pulsed Electric Field (PEF) PEF Treatment systems The main components required for a pulsed electric field

application are

An impulse generation system

Power supply

Energy storage element

Closing and opening switch

A treatment chamber

A pump to supply feed to treatment chamber

A cooling system to control the temperature

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Pulsed Electric Field (PEF) PEF Treatment systems Generation of PEF The impulse generation system transforms the electric power from a low

utility level voltage to pulsed high intensity electric fields.

The electric power is most commonly stored in a bank of capacitors connected in series or parallel and discharged into the treatment chamber across a high voltage switch and protective resistors within microseconds.

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Pulsed Electric Field (PEF) PEF Treatment systems Treatment chamber The treatment chamber, wherein the food is exposed to the electric field

pulses, consists of at least two electrodes, one on high voltage and the other on ground potential, separated by insulating material in different geometric configurations.

Configurations of treatment chambers for continuous PEF treatment: (a) parallel plate, (b) coaxial and (c) co-linear configuration

Electrodes should be food grade and autoclavable

The parallel plates provide the most uniform electric field in a large usable area between the plates, but treatment intensity is reduced in boundary regions.

In batch chambers without mixing or product flow leading to changes of position, a considerable part of the volume may remain under-processed, noticeable as tailing effects in microbial inactivation kinetics.

In continuous treatment chambers, this can be prevented by adding multiple treatment zones in line or baffled flow channels.

To achieve the high flow rates required for industrial applications, the pulses must be applied with a high repetition rate, leading to a fast temperature increase of the media. Maintaining a constant temperature may require high cooling efforts or intermediate cooling between multiple treatment zones.

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Pulsed Electric Field (PEF) PEF Treatment systems

Coaxial chambers consist of an inner and outer electrode with the product flowing between them.

The electrical current flow is perpendicular to the fluid flow.

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Pulsed Electric Field (PEF) PEF Treatment systems

It is possible to control the potential for electrochemical reactivity during PEF processing, it is also possible to control temperature conditions throughout the process. This is easily accomplished by using multiple treatment chambers. When performing PEF processing with a single treatment chamber, the normal thermal cycle would include:

1. use of a heat exchanger to preheat the product before entering into the PEF treatment chamber to benefit from thermal synergy (there is a clear benefit to PEF processing at temperatures above refrigeration, between 40–45◦C)

2. an increase in temperature as the product is PEF treated

3. use of a post-treatment heat exchanger to cool the product after treatment.

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Pulsed Electric Field (PEF) PEF Treatment systems

Preservation applications Juices:

The shelf life of apple juice (from concentrate) has been successfully extended from 21 days to 28 days using 50 kV cm–1, ten pulses, a pulse width of 2 s and a maximum process temperature of 45 °C. Sensory panellists could determine no significant differences between treated and untreated juice.

PEF could extend the shelf life of fresh apple juice and apple juice from concentrate to over 56 days and 32 days respectively when stored at 22–25°C.

with process conditions of 28.6, 32.0 and 35.8 kV cm–1 for 10.3–46.3 s, a 2.5 log reduction of Lactobacillus plantarum was achieved in orange/carrot juice (70% orange, 30% carrot).

Five-fold reduction of Saccharomyces cerevisiae was achievable in orange juice using five pulses at a field strength of around 6.5 kV cm–1.

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Pulsed Electric Field (PEF) Potential applications of PEF

Preservation applications Milk:

A number of studies have demonstrated PEF inactivation of microorganisms in milk.

3 log reduction of E. coli using 21 kV cm–1, a 4 log reduction of Salmonella dublin using 18 kV cm–1, a 2.5 log reduction of Streptomyces thermophilus using 25 kV cm–1 and a 4.5 log reduction of L. brevis using 23 kV cm–1.

More recently, the shelf life of skimmed milk treated with PEF was reported to be 2 weeks at 4 °C using a process of 40 kV cm–1, 30 pulses and a 2-s treatment time.

A hurdle approach was recommended for effective PEF processing using a combination of mild heat and PEF.

Liquid whole egg: PEF has been shown to have minimal effect on the colour of liquid whole egg.

Although undetectable levels of microbial populations were present in PEF-treated liquid whole egg, spoilage was found to occur within 25–28 days of storage at 4 C

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Pulsed Electric Field (PEF) Potential applications of PEF

Non-preservation applications a number of non-preservation applications using PEF could also prove useful

for the food industry

Baking Applications PEF-treated wheat dough (50 kV, 20 min) is reported to have decreased water

loss during baking and the shelf life of the bread subsequently baked from the dough is reported to be increased

Extraction/ Cell permeabilisation The irreversible permeabilisation of plant cell membranes and tissues using

PEF offers interesting possibilities for improving expression, extraction and diffusion processes.

Potential applications include extraction processes such as those found in starch production, sugarbeet processing and juice extraction.

Drying time can be reduced if product is pretreated with PEF 55

Pulsed Electric Field (PEF) Potential applications of PEF

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The tissue softening effect of PEF, based on cell membrane electropermeabilization and loss of turgor, can be utilized to reduce the energy required for cutting of plant material. With a continuous, short time and low energy (10 kJ/kg) PEF treatment of potato tissue, a reduction of grinding energy similar to that of thermal or enzymatic treatment can be achieved, indicating its potential to replace or enhance conventional processing techniques.

Pulsed Electric Field (PEF) Potential applications of PEF

Significant steps forward have been made for pulsed electric field processing and it has reached a point where it is very close to commercial realisation. Large-scale equipment is now not only feasible but can be built to specification by companies such as Diversified Technologies Inc. (Mass., USA). It seems likely that a PEF-processed product will be launched in the not too distant future.

There are of course still some issues to be resolved:

Establishing exactly how effective PEF really is with respect to microbial and enzyme inactivation.

Numerous laboratory and pilot-scale trials have been con-ducted using a range of custom-built PEF equipment. Unfortunately, this makes it extremely difficult to compare data obtained from different laboratories and assess exactly what levels of inactivation are truly achievable in a commercial system.

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Pulsed Electric Field (PEF) Future of PEF