HFN – 600 Master seminar

Non-Thermal processing of food

- Pulsed Electric Field

- Pulsed Visible Light

presented by Tamilselvan.T

51094

Thermal processing of food:

This method helps in processing of food with the help

of thermal energy i.e., Heat.

The basic purpose of thermal processing are

Used to reduce or destroy microbial activity.

Used to destroy or inactivate enzyme activity.

Used to produce physical or chemical changes to make the food

meet a certain quality standard.

Thermal processing is widely used in industries all over the

world.

Disadvantages of thermal processing are:

It gives cooked flavor to food ex: milk

It also change organoleptic properties of food.

Alteration in nutritional properties occurs.

Ex: Protein denaturation, Loss of Heat liable

vitamins and some volatile flavors.

It is also energy expensive one.

Some thermal processing methods are

Ohmic heating , Microwave heating , Infrared heating , Radio

frequency heating , Drying , Extrusion .

Non-Thermal processing of food

Also called Alternative thermal processing

This method of processing commonly does not require

any heat for processing although some amount of heat is produced

during processing.

Non-Thermal processing of food stuffs now become center of

interest for scientists as it has more advantages than thermal

processing.

NTP has specific applications in terms of type of food processed.

It gives consumers high quality and minimally processed food

products.

New Non thermal processing methods are

High pressure processing

Oscillating magnetic field

Electron beam

PULSED ELECTRIC FIELD

PULSED VISIBLE LIGHT

Pulsed X - ray

Ultrasonic

Irradiation

Dense phased Carbon di-oxide

High Voltage Arc discharge

Cold Plasma

Ozone

Overall advantages of NTP

Low processing temperature

i.e., the NTP allows processing of foods below temperature

used during thermal pasteurization.

Low energy utilization

No need of continuous supply of energy.

Retention of flavors and taste

Gives consumer a fresh like taste.

Inactivates enzymes and Micro organisms.

Safe and environmentally acceptable

PULSED ELECTRIC FIELD

Pulsed electric field

It is also called High Electric Field Pulses (HELP)

It is the application of very high field strength for

a very short time to foods placed between electrodes.

It uses short electric field pulses to preserve food.

It works in intensity of 10-80 kV/cm with duration of micro to

milli seconds.

Today, about 20 research groups worldwide are working in this

PEF, but still there is no commercial, industrial system available.

(Pulse - A pulse is a single disturbance that moves through a

medium from one point to the next point)

History :

The bactericidal effect of electric current has already been tested

in 19th century (Prochownick and spaeth, 1890).

In 1920’s a process called ‘Electropure’ was introduced in

Europe and the USA.

In milk pasteurization it is used by passing current

within carbon electrode treatment chamber.

In 1950’s pulse discharges of high voltage electricity across two

electrodes for microbial inactivation is first investigated.

In 1967- First non thermal lethal effect of homogeneous PEF on

microbes by Sale and Hamilton.

Early patents by Krupp in Germany for inactivation of vegetative

microorganisms in milk and fruit juices with an electric field

strength up to 30 kV/cm.

1987 - Pure Pulse Technologies, USA use electric fields and their

effect on fruit juice quality was investigated by Dunn and

Pearlman.

Components needed :

High voltage power source

Capacitor bank

Treatment chamber

Electrical switch

Principle:

It is based on the principle of Electroporation i.e., Membrane

permeabilization.

The use of an external electric field for a few micro to milli

seconds induces local structural changes and a rapid breakdown of

the cell membrane which is important component on cell.

After electroporation, the components of surroundings enter into

cell and makes it rupture.

Cells that undergo PEF can respond to pulses reversibly or

irreversibly.

Working:

The pulses based on type of food is applied through the electrodes to

the food placed in treatment chamber.

In the two electrodes, one on high voltage and other on ground

potential separated by insulating material.

To avoid exposure to electrode surface, a glass coil surrounding the

electrode is used.

There are three types for passing pulses to the food placed in

treatment chamber.

They are Parallel plate, Coaxial, Coplanar.

Parallel plate Coaxial Coplanar

Food is capable of transferring electricity because of the presence

of several ions.

So, when an electric filed is applied, electric current flows into

the liquid food and is transferred to each point in the liquid

because of 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.

Parameters

Process parameters

Field strength

Pulse length

Number of pulses

Start temperature

End temperature

Treatment chamber

Volume

Gap

Flow rate

Residence time

Microbial parameters

Type of Microorganism

Medium composition

Oxygen concentration

Time of incubation

Product parameters

Conductivity

Composition

Ionic strength

pH

Aw

The operation are of two types – Flowing and Non-flowing.

Food products can be used for PEF

Milk , Yogurt , Liquid whole eggs, Soups, Brines,

Apple sauce, Tomato juice and foods that can withstand electric

fields.

Liquid egg E.coli 6

Coaxial chamber ,37°C

,4 µs pulse length, 2.6

V/µm, 0.5 l/min, 100

pulses

Skim milk Listeria innocua 2.5

Continuous flow,

5.0 V/µm,36 °C ,

32 pulses, 2 µs

pulse length,3.5 Hz.

Milk Listeria

monocytogenes4

Co- axial , 3.0 V/mm,50

°C ,600 µs treatment

time, pulse length 1.5 µs

,flow rate 7 ml/s,

Food product Microorganism Log

reduction

Process condition

Examples of Microbial Inactivation by PEF

Advantages:

Providing microbiologically safe food.

Minimal processing of food.

Enhance extraction of sugars and cellular contents, metabolites

from plant cells.

It helps in drying plant tissues.

Enzyme activity modification.

Can be used synergistically with pre heat method, HPP and with

antimicrobials like Nisin and lysosyme is under investigation.

Useful for processing of semisolid and liquid foods.

Since PEF kills cells and impairs water retention, it can aid in

filtration methods.

Can also be used for the extraction of sugars and starches from

root vegetables.

Continuous processing is possible.

Applicable for acid foods, as spores will not germinate in acid

foods.

Disadvantages:

It is an Expensive method.

Still under research and development.

Availability of commercial units is less.

The method of inactivation is still theoretical and not clearly

studied.

Effectively depends on electrical conductivity of food.

Not useful for solid foods.

A reduction in electrode lifetime the release of particles and heavy

metals from electrode may cause toxicity.

PEF has limited effects on microbial spores because some MO can

withstand this.

Not possible to use in products that contain or could form air

bubbles.

Not possible to use in foods with higher or variable electrical

conductivity .

PEF is a non-thermal process, there is an increase in temperature

occurs in treatment chamber.

Technical issues to be addressed before commercialize PEF :

Consistent generation of high strength PEF

Reliable data acquisition systems and measuring devices

Identification of the critical, maximum and optimum field strength for

microbial degradation, flow rate and dosages.

Temperature control and minimization of heat production during

processing.

The potential for gas bubbles and interference from suspended particles

The design of full scale treatment chamber

Aseptic packaging system that are compatible with the process

Inactivation of Microorganisms after PEF treatment in pH 7, Batch treatment, Field strength 2.2 V/ µs, pulse length 2 µs.

(Alvarez & Raso , unpublished data)

Energy required for cell disintegration with different techniques

for Potato tissue

Non thermal Inactivation of Saccharomyces cerevisiae in Apple Juice Using Pulsed Electric Fields (Swanson B. et.al., 1995)

Aim:

To study the use of High intensity electric fields in a continuous system for inactivation of Saccharomyces cerevisiae in apple juice.

Methods :

1). To determine microbial inactivation S. cerevisiae at a concentration of 2 × 106 cfu/mL was inoculated in commercial applejuice. Selected field intensities were 13,22,35,50 kV/cm , pulses selected were 2 to 10 with pulse duration of 2.5 µs.

2). For shelf life determination 5 × 103 cfu of S. cerevisiae per mL were initially inoculated in the commercial apple juice. Field intensity was 36 kV/cm and 10 pulses and duration of 2.5 µs. In 15 mL centrifuge tubes incubated at 4 °C or 25 °C (treated and untreated)

( LWT- food science and Technology, Volume 28, 564-568p, 1995)

Results:

1). 6D inactivation of inoculated S.cerevisiae was achieved. The temperature was only 29.6 °C with two 2.5 s pulses at 50kV/ cm.(which is lesser than heat pasteurization)

2). Untreated 4 °C and 25 °C shows undesirable fermented flavor within 9 day and 1 day. But for PEF treated apple juice shows over 3 week shelf life extension at 4 °C and 25 °C storage.

Inactivation of Escherichia coli and Staphylococcus aureus in model foods by pulsed electric field technology (Swanson B et.al., 1995)

Aim: To study the inactivation of E.coli and S.aureus when subjected to High voltage electric filed pulses.

Materials and methods : The cultures of E.coli and S.aureus inoculated in ( milk filtrate) and exposed to peak electric field strength of 16kV/cm and 60 pulses with pulse width ranging from 200 to 300 µs.

The temperature of cell suspension was kept below lethal temperature, to demonstrate the inactivation is not due to thermal effects by pulses but by electroporation.

Results:

The extent of Microbial inactivation increases when applied electric field strength increases. E.coli was inactivated upto 4 to 5 log cycles and S.aureus was inactivated upto 3 to 4 log cycles with a field strength of 16kV/cm. (At 82.2 °C - 5 log reduction achieved by thermal means but organoleptic properties change)

(Food Research International, Vol. 28(2), pp. 167-171, 1995 )

PULSED VISIBLE LIGHT

This technology known since 1980’s , and was approved by Food

and Drug Administration (FDA) in 1996.

Pulsed Light (PL) technology is an alternative to thermal

treatment for killing pathogenic and spoilage microorganisms in

foods, including bacteria, yeasts, molds, and viruses.

In the food industry, PLT can be applied to sterilize, sanitize or

reduce microbial load in foods, food packaging materials, as well

as surfaces, environments, plants, devices and media (water, air)

involved in food processes.

History

Many different PL devices were developed before 1970 for

different industrial purposes.

The use of inert-gas flash lamps generating intense and brief

pulses of UV light as a technique of microbial inactivation

definitely started during the late 1970s in Japan.

This technique was patented by Hiramoto (1984) .

A great increase in R&D of PLT increase when FDA approved the

use of PLT ‘for Production, Processing and Handling of foods’ and

recommended some conditions for such use.

The electromagnetic radiations are emitted and propagated by

means of waves which differ in wavelength, frequency and energy

(E).

The term light is generally used to mean radiations having

ranging about from 180 to 1100 nm.

It includes ultraviolet rays UV = 180–400 nm, (roughly

subdivided into UVA = 315–400 nm, UVB = 280–315 nm, UVC=

180–280 nm), visible light = 400–700 nm and infrared rays= 700–

1100 nm.

FDA about PLT

According to FDA - ‘Food treated with pulsed light shall

receive the minimum treatment reasonably required to accomplish

the intended technical effect’

FDA recommends, ‘The total cumulative treatment shall not

exceed 120 kJ/m2 which is more than sufficient to achieve a high

inactivation of a wide range of microorganisms including bacterial

and fungal spores’.

Principle

Photochemical Effect

When the pulsed light falls the DNA of microbial cells, it

absorbs some energy. Such absorbed energy is able to break organic

molecular bonds, causing DNA rearrangement, cleavage and

destruction and inhibit pyrimidine production.

These modifications finally result in mutations, damage to the

genetic information, impairment of replication and gene

transcription and then in the death of the microorganism cells.

Photo thermal effect

Most energy of the light pulses that penetrate through a food

product is absorbed by the layers nearest to the surface and dissipated

as heat, causing in such thin layers a certain increase in temperature.

Since microbial cells have a higher absorption of the pulsed light

than that of the surrounding medium (water), this determines a

localized rapid heating of microorganisms.

At very high pulse power values can reach temperatures

sufficient to cause their overheating, rupture and death and the

extremely short pulse duration prevents the microorganism cell surface

from being cooled by the surrounding medium .

Working

Pulsed light technology (PLT) involves the use of inert-gas flash

lamps which converts short-duration and high-power electric pulses,

as those used in PEF technology, into short-duration and high-

power pulses of radiation included in the spectra of UV , Visible,

IR.

The shorter the duration of each pulse, the higher the pulse power.

When compared with continuous light radiations, light pulses show

a much higher penetrating capability through the materials

During the pulse, this system delivers a spectrum that is 20,000

times more intense than sunlight at the earths surface.

It is measured in Jcm-1

Operating time : 100 – 400 µs.

No.of pulses – 1- 20/s

Energy difference between Continuous light and pulses of different duration

Components

1. The power supply

2. A storage capacitor

3. A pulse-forming network

4. The gas discharge flash lamp

5. A trigger signal

The obtained energy is finally delivered to the target by

various systems depending on the different applications.

Item Experimentals Results / Remarks

ShrimpF = 1-2 J/cm2

n = 4-8

1-3 lcr of Listeria,

results in shelf life

extension of 1 week

versus untreated one.

Freshly baked cakes

in clear plastic

container

F = 16 J / cm2

n = 3

Absence of molds in

treated one at storage.

Shelf life extension

of 11 days.

Commercial raw eggs F = 0.5 J/cm2

n = 8

8 lcr of salmonella

enteritidis.

Inactivation effect

observed on egg

shells and little into

egg pores.

Examples for effect on Food products

Dunn et al. (1989) obtained 10 log reductions of Aspergillus

niger spores by 4 pulses of 40 kJ/m2 or 1 pulse of 120 kJ/m2 using

broad spectrum pulsed light (BSPL).

The PLT of two types :

1. Continuous system

2. Batch system both depending on usage.

Continuous Pulsed light system

Factors commonly affecting :

Treatment time

Distance of sample from light source

Number of lamps

Volume of sample

Orientation

Design of lamps

Presence of particulate materials.

Composition of emitting spectrum

Advantages

Uses less energy. (because of xenon-flash lamps)

No adverse effects on nutrients.

Can be used as a powerful sterilization agent

Environmental friendly

Extends shelf life of food products.

Does not leave any residue in food.

Can be used for sterilization of packaging materials and have

been used in other industries than food.

Does not cause temperature changes in food.

Disadvantages

Applicable only on liquid foods and surface of solid foods.(0.1 mm)

The fissures and folds in food prevent microorganisms.

It will give a ‘shadow effect’

Efficiency depends on microbial exposure.

Food composition also affects decontamination by PLT.

Ex: Part of radiation is affected by proteins and oils, reducing

effective radiation available for microbial inactivation. So, High protein

or oily foods not suitable for PLT.

Food packaging material must be transparent and also must be

chemically stable.

Due to failure of light to penetrate opaque and irregular surfaces,

there is generally less microbial inactivation with pulsed light,

compared to other technologies.

Sometimes reflection loss also possible which result in reduced

ability.

If excess UVC light, which causes undesirable photochemical

damage to foods or food packaging materials.

Impact of pulsed light treatments on antioxidant characteristics and quality

attributes of fresh-cut apples. (Karina R et.al., 2016)

Aim: The effect of PL treatments combined with quality stabilizing dip on the

quality and antioxidant property of fresh cut apples were studied.

Methods : Apple wedges were dipped into a solution of 1% w/v N-acetyl cysteine

and 0.5% w/v CaCl2 and flashed with broad-spectrum light with an overall radiant

exposure of 4, 8, 12 and 16 J.cm-2 .General microbial counts, color, firmness,

phenolic compounds and vitamin C contents were evaluated over 15 days at 5 °C.

Conclusion: Pulsed light treatments stand as a feasible alternative for extending the

microbiological shelf life of fresh-cut apples at 5 °C, while maintaining their quality

and antioxidant attributes.

Experimental result suggested that PL promotes antioxidant potential

and also vitamin C levels are also preserved. a treatment of 8 J.cm-2 in combination

with the immersion into a quality-stabilizing solution may be selected to extend the

microbiological shelf life of fresh-cut apples without dramatically affecting their

texture.

(Innovative food science and Emerging technologies,Vol 33,pp 206-215, 2016)

Effect of pulsed light treatment on structural and functional properties of

whey protein isolate (Maresca et.al., 2016)

Aim : To study the effects of Pulsed Light (PL) processing at different

fluences (from 4 to 16 J/cm2) on the structure and functional properties of Whey

Protein Isolate (WPI) solution.

Methods : The determination of the free and total sulfhydryl (SH) groups was

used to detect the variation of WPI tertiary and quaternary structure.

Additionally, PL-induced changes in secondary structure were determined by

FT-IR spectroscopy and the differential scanning calorimetry (DSC), and

primary structure by carbonyl content.

Conclusion: This study reveals the potentiality of PLT to induce changes in

conformational and functional properties of WPI.

The exposure to PL led to increase of concentration of SH groups

and formation of carbonyl groups, which suggest modification of WP tertiary

and primary structure. Only small changes to secondary structure occurs.

Solubility and functional properties were significantly improved by applying PL

treatments at fluences in the range from 8 to 12 J/cm2.All results show PL

treatment was able to partially unfold WPI samples.

(Food Research International, volume 87, pp 189-196, 2016)

Conclusion

The application of new preservation methods resulting

in a moderate to non-significant effect in food products. Further

research is essential to demonstrate and explain the effect of new

preservation technologies on the shelf life and safety of food

products.

References:

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