pulsed electric field for food processing technology

Emerging Food Technologies Presentation Series - 2016

University of Sri Jayewardanepura

Pulsed Electric Fields for Food Processing Technology

MMA. SHAKOORAFSTUSJP



Name: M.M. Aaysha Shakoora

School attended: KM/ Mahmud Ladies College

Hobbies: Reading, handicraft & travelling

Interested in: Archery, Horseback riding & Swimming

Believes ,

“THE BEST AMONG YOU ARE THOSE WHO HAVE THE BEST MANNERS & CHARACTER”



OVERVIEW

INTRODUCTION SYSTEM COMPONENTS PRINCIPLES OF PEF FACTORS AFFECTING THE OUTCOME OF PEF ADVANTAGES & DISADVANTAGES OF PEF REFERENCES



PEF is a non-thermal method of physical food preservation that uses short pulses of electricity for microbial inactivation.

Pulse-burst of current/ voltage/ electromagnetic field energy. A pulse may last from a nanoseconds to several seconds.

Offer High-quality foods.

For food quality attributes, PEF technology is considered superior to traditional thermal processing methods because it avoids or greatly reduces detrimental changes in the sensory and physical properties of foods.

INTRODUCTION



Use of electricity in food preservation already has more than a 100 year history, since investigations in to bactericidal effect of current carried out by Prochowchik & Spaeth. In the 1940s, treatment of apple mash by DC & AC current was used for increasing juice yield.

In the beginning of 1960s, application of pulsed electric fields (PEF) for disruption of cells in food material was patented by Doevenspeck. He also reported achievement of up to 96% inactivation of Salmonella bacteria suspended in marination brine.

HISTORY………..



.

foods most often treated in PEF: Fruit juices Apple sauce Milk Liquid egg productsYogurt drinks Salad dressingTomato juice Liquid whole egg

The sensory attributes of foods well preserved & retain a fresh-like quality with extended shelf life after processing



System components High-voltage power source - a high voltage DC generator, converts (low)voltage from

an utility line (in Sri Lanka230 V) into high voltage AC, then rectifies to a high voltage DC.

capacitor bank - energy storage

Treatment chamber - hold the food during processing and house the discharging electrodes to generate an electric field in the food material

Electrical switch - to discharge energy from the capacitor across the food

An oscilloscope - used to observe the pulse waveform

former - used to charge a capacitor bank



Flow chart of a PEF food processing system with basic component.

Schematic diagram of a pulsed electric fields operation



Two electrodes are connected together with a nonconductive material to avoid electrical flow from one to the other.

Apart from those major components, some adjunct parts are also necessary. In case of continuous systems,

Pump - to convey the food through the treatment chamber Chamber cooling system - diminish the ohmic heating effect & control food

temperature during treatment.

High-voltage & high-current probes - measure the voltage & current delivered to the chamber



The Principles of Pulsed Electric

Field The process is based on pulsed electrical currents delivered to a product placed between a set of electrodes.

Food is capable of transferring electricity because of the presence of several ions. So, when an electrical field is applied, electrical current flows into the liquid food and is transferred to each point in the liquid because of the charged molecules present.

The food product experiences a force per unit charge, the so-called electric field, which is responsible for the dielectric cell membrane breakdown in MOs & interaction with the charged molecules of food

Application of pulsed electric fields of high intensity and duration from microseconds to milliseconds may cause temporary or permanent permeabilization of cell membranes enables inactivation of vegetative cells of bacteria and yeasts in various foods.



A microbiology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs or DNA to be introduced into the cell.

ELECTROPORATION OR ELECTROPERMEABILIZATION

Process of the cell electroporation by PEF :(1) building the transmembrane potential up by the applied external electric field(2) creation of small metastable hydrophilic pores (3) Evolution of the pore population(4) post-treatment stage (leakage of intracellular compounds, pore shrinkage and disappearance, etc.)



Electroporation can be either: reversible (cell membrane discharge) or irreversible (cell membrane breakdown or lysis)

but this effect can be controlled depending on the application.

.Treatment packaged aseptically stored under refrigeration.



Factors affecting the outcome of pulsed electric fields treatments

The lethality factors contributing to the effectiveness of PEF

technological biological media factors



TECHNOLOGICAL FACTORS

• FIELD STRENGTH - Microbial inactivation increases with an increase in the electric field intensity, above a critical trans membrane potential.

Evenly distributed electric field intensity efficient treatment. Electric field intensities of smaller than 4-8 kV/cm usually do not affect microbial inactivation. In general, the electric field intensity required to inactivate MOs in foods, in the range of 12-45 kV/cm.

• TREATMENT TIME• TREATMENT TEMPERATURE• PULSE SHAPE & SIZE - square waveforms may be more lethal, energy efficient than

exponentially decaying pulses. square pulses have longer peak voltage duration compared to exponential pulses.

short pulses - avoid excessive heating or undesirable electrolytic reactions.



BIOLOGICAL FACTORS

● Individual characteristics of target MOs ● Physiological characteristics

● Growth states Gram (+) cells more resistant to PEF than Gram(-)negative bacteria Yeasts - higher sensitivity than bacteria Larger cells - Induction of electric fields into cell membranes is greater



MEDIA FACTORS

The effects of PEF on the food system : PEF system - conductivity, resistivity, dielectric properties, ionic strength, pH & composition Properties of the food - physical and chemical

These factors most likely influence the recovery of injured microbial cells and their subsequent growth following PEF exposure, since the presence of food components, such as fats and proteins , has reportedly had a preventive effect on MOs against PEF treatment

Each of these parameter influences the PEF treatment either alone or in combination.

● But enzymes and proteins are generally more resistant to electric field intensity & pulses than microorganisms. This requires further investigation, especially on the effects of pH, temperature, resistivity and composition of the enzyme or protein-containing medium or food system. As bacterial spores are resistant to pulsed electric fields, applications of this technology mainly focus on food-borne pathogens and spoilage microorganisms, especially for acidic food products



Advantages of Pulsed Electric Fields Technology

Preservation of solid, semisolid & liquid food

pasteurization - temperatures below 30-40°C

(juices, milk, yogurt, soups, and liquid eggs) Economically & efficiently improve energy usage

Providing microbiologically safe and minimally processed foods.

Causes minimal detrimental effect on food quality attributes

Enhance extraction of sugars (sugar beet) and other cellular content from plant cells

(Improvement of metabolite extraction)

Enhance mass & heat transfer to assist drying of plant tissues



Enzyme activity modification

Reducing the solid volume of wastewater

Biotechnology and genetic engineering (electroporation in cell hybridization)



● Restricted to food products with air bubbles & low electrical conductivity. presence of bubbles lead to non-uniform treatment, operational & safety problems. When the applied electric field > dielectric strength of the gas bubbles, partial discharges take place inside the bubbles that can volatize the liquid and therefore increase the volume of the bubbles. The bubbles may become big enough to bridge the gap between the 2 electrodes and may produce a spark. Therefore, air bubbles in the food must be removed, particularly with batch systems. Vacuum degassing or pressurizing the treatment media during processing, using positive back pressure, can minimize the presence of gas.

● Continuous processing – so not suitable for solid food products that are not pumpable.

● The systems need to be scaled up to commercial systems.

● The lack of methods to accurately measure treatment delivery

● Costly

DISADVANTAGES



https://www.researchgate.net/publication/226595907_Electroporation_of_Cell_Membranes_The_Fundamental_Effects_of_Pulsed_Electric_Fields_in _Food_Processing

Pulsed Electric Fields for Food Processing Technology http://dx.doi.org/10.5772/48678

https://www.researchgate.net/publication/226595907_Electroporation_of_Cell_Membranes_The_Fundamental_Effects_of_Pulsed_Electric_Fields_in_ Food_Processing

REFERENCES

https://www.researchgate.net/publication/226595907_Electroporation_of_Cell_Membranes_The_Fundamental_Effects_of_Pulsed_Electric_Fields_in_Food_Processing




http://dx.doi.org/10.5772/48678

http://dx.doi.org/10.5772/48678

http://dx.doi.org/10.5772/48678





pulsed electric field for food processing technology

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