This document discusses various non-thermal food processing methods including ohmic heating, pulsed electric fields, high pressure processing, pulsed light, ultrasound, oscillating magnetic fields, and irradiation. It describes the objectives and mechanisms of each method, providing details on how each technique works to reduce microbes while maintaining quality attributes like color, flavor and texture. The conclusion states that non-thermal methods are useful for liquid foods and large-scale production but have high equipment costs, and that reducing costs could enable broader application in small industries.

1. Paper No.: 02
Paper Title: Principles of The food processing & preservation
Module – 23: Processing and Preservation by Non-thermal Methods
Paper Coordinator: Dr. P. Narender Raju,
Scientist, National Dairy Research Institute, Karnal, Haryana
Content Writer: Dr. Kuna Aparna,
Asst. Professor, Prof. Jayashankar Telangana State
Agricultural University, Hyderabad

2. Module 23
PROCESSING & PRESERVATION BY
NON THERMAL METHODS

3. Introduction
• Newly developed food technologies usually focus on
preservation while keeping food quality attributes.
• Although thermal preservation provides safer food, there
exists loss of food properties like nutrients and sensory
attributes.
• The main objectives of new techniques are, to retain the
nutrients, sensory properties and to increase the shelf
life without any adverse effect on its quality.
• The other objective of preservation is to increase the shelf
life by reducing the microbial load and also the water
activity.
• Both can be achieved by either traditional method of
preservation methods or by non thermal treatments like
microwave heating, Pulsed Electric Field (PEF) Technology,
High Pressure Processing(HPP), Pulsed Light Technology,
Ohmic Heating, Irradiation, Ultra sonics, Pulsed X-Rays,
Oscillating Magnetic Fields (OMF).

4. Objectives of Non thermal food processing are:
• Render foods free of pathogenic & spoilage
organisms
• Retain color, flavor
• Improve shelf life
• Improve texture

5. Types of Non thermal food processing
Ohmic heating
• Ohmic heating is a thermal method that minimizes
equipped with several electrodes.
• The advantage of ohmic heating is its ability to heat
materials rapidly and uniformly, including products
containing particulates.
• The principal mechanisms of microbial inactivation in
ohmic heating are thermal while some evidence exists for
non-thermal effects of ohmic heating as well.
• A large number of potential future applications exist for
ohmic heating, including its use in blanching, evaporation,
dehydration, fermentation and extraction.
• Ohmic heating is employed in pasteurising and sterilising of
liquid and particulate foods, especially of ready-to-serve
meals, fruits, vegetables, meat, poultry or fish, and is an
alternative to sterilisation of foods by means of
conventional heat exchangers or autoclaves.

6. High electric field pulses
• High intensity pulsed electric field (PEF or HELP) processing involves
the application of pulses of high voltage (typically 20–80 kV/cm) to
foods placed between two electrodes.
• HELP may be applied in the form of exponentially decaying, square
wave, bipolar, or oscillatory pulses and at ambient, sub-ambient, or
slightly above-ambient temperature for less than 1second.
• Energy loss due to heating of foods is minimised, reducing the
detrimental changes of the sensory and physical properties of foods.
• Electric high-voltage impulses generate a trans-membrane potential
across the cell membrane of, for example, a bacterial cell which
overlays the natural membrane potential.
• If the difference between outer and inner membrane potential rises
above a critical value of about 1 V, polarisation and in the end
breakdown of the membrane is induced.
• At sufficient high field-strength (above 10 kV/cm) and duration of
the pulses (usually between nano-and microseconds) vegetative
micro-organisms in liquid media are inactivated due to irreversible
membrane destruction. Bacterial spores, however, are not
inactivated.

7. Light pulses
• Pulsed light is a method of food preservation
that involves the use of intense and short-
duration pulses of broad spectrum ‘‘white
light’’ (ultraviolet to the near infrared region).
• For most applications, a few flashes applied in
a fraction of a second provide a high level of
microbial inactivation.
• This technology is applicable mainly in
sterilising or reducing the microbial
population on packaging or food surfaces.

8. Oscillating magnetic fields
• Experiments have shown, that strong static (SMF) or
oscillating (OMF) magnetic fields (5–50 Tesla) have the
energy input and thus reduces thermal damage to food.
• If an electric current is passing through a conductive
medium, in this case the food, the medium warms up as
a result of the movement of ions.
• The conductive electric resistance heating—ohmic
heating—utilises the effect of the electrical resistance
within a conductive liquid or solid material.
• In this manner a direct conversion of electric energy into
heat takes place.
• The impulse duration is between 10 ms and several
miiliseconds.
• The effects of magnetic fields on microbial populations
have produced controversial results.

9. Ultrasound
• Ultrasonic waves (energy generated by sound waves of 20,000
Hz or more) generate gas bubbles in liquid media, that produce
a high temperature-and pressure increase when they
immediately burst.
• The bactericidal effect of ultrasound is attributed to
intracellular cavitation, that is, micro-mechanical shocks that
disrupt cellular structural and functional components up to the
point of cell lysis.
• Critical processing factors are the nature of the ultrasonic
waves, the exposure time with the microorganisms, the type of
micro-organism, the volume of food to be processed, the
composition of the food, and the temperature.
• The effects, however, are not severe enough for a sufficient
reduction of micro-organisms so most applications use
combinations with other preservation methods.
• Although ultrasound technology has a wide range of current
and future applications in the food industry, including
inactivation of micro-organisms and enzymes, presently, most
developments for food applications are non-microbial.

10. High pressure processing
• The technology of high pressure processing (HPP), also
referred to as ultra high pressure UHP) or high hydrostatic
pressure (HHP) .
• Process temperature during pressure treatment can be from
below 0ᵒC to above 100ᵒC.
• Exposure times can range from a few seconds to over 20
min.
• Food treated in this way has been shown to keep its original
freshness, colour, flavour and taste.
• HPP acts instantaneously and uniformly throughout a mass
of food independent of size, shape and food composition.
• Pressure pasteurisation is feasible also at room temperature
and energy saving as compared to heat treatment.
Temperatures ranging from 90 to 110°C in conjunction with
pressures of 500–700 MPa have been used to inactivate
spore-forming bacteria such as Clostridium botulinum.

11. Summary of Non Thermal Food Processing Methods
Process Description Critical factors Mechanism of
inactivation Status
UV-
light/pulsed
light
UV radiant exposure, at
least 400 J/m2
Intense and short-duration
pulses of broad spectrum
(ultraviolet to the near
infrared region).
Transmissivity of the
product, the geometry, the
power, wavelength and
arrangement of light
source(s), the product flow
profile.
DNA mutations induced
by DNA absorption of the
UV light
Used for disinfection
of water supplies and
food contact surfaces
Ultrasound Energy generated by
sound waves of 20,000
Hz or more
The heterogeneous and
protective nature of food
(e.g. inclusion of
particulates) severely curtails
the singular use of ultrasound
for preservation
Intracellular cavitation
(micro-mechanical
shocks that disrupt
cellular structural and
functional components up
cell lysis)
Combination with
e.g. heat, pressure
has certain potential
Oscillating
magnetic field
(OMF)
Subjecting food sealed in
plastic bags to 1–100
OMF pulses (5–500 kHz,
0–50ᵒC, 25–100 ms)
Consistent results concerning
the efficacy of this method
are needed
Controversial results on
effects of magnetic fields
on microbial
populations
Application at the
moment not
considered
Pulsed
electric field
(PEF)
High voltage pulses to
foods between two
electrodes (<1 s; 20–80
kV/cm; exponentially
decaying, square wave,
bipolar, or oscillatory
pulses at ambient, sub-
ambient, or above
ambient temperature)
Electric field intensity, pulse
width, treatment time,
temperature, pulse wave
shapes, type, concentration
and growth stage of
microorganism, pH,
antimicrobials, conductivity
and medium ionic strength
Most theories studied are
electrical break down and
electroporation
Different laboratory-
and pilot-scale
treatment chambers
designed and used
for foods, only two
industrial-scale PEF
systems available
High pressure
processing
(HPP)
Liquid/solid foods,
with/without packaging
(100–800 MPa, below
0ᵒC to >100ᵒC, from a
few seconds to over 20
min Instantaneously and
uniformly throughout a
mass of food independent
of size, shape and food
composition
Pressure, time at pressure,
temperature (including
adiabatic heating), pH,
composition
Denaturation of enzymes,
proteins; breakdown of
biological membranes;
cellular mass transfer
affected
In use since 1990
(Japan, USA, France,
Spain) Current
pressure processes
include batch and
semi-continuous
systems

12. Conclusion
• The non thermal processing is used for all foods for its
better quality, acceptance, and for its shelf life.
• The new processing techniques are mostly employed
to the
liquid packed foods when compared to solid foods.
• Since the non thermal methods are used for
bulk quantities of foods, these methods of food
preservation are mainly used in the large scale
production.
• The cost of equipments used in the non thermal
processing is high when compared to equipments used
in thermal processing.
• After minimising the investment costs of non thermal
processing methods, it can also be employed in small
scale industries

13. Glossary
• High pressure processing (HPP): Subjects liquid or solid foods with or
without packaging to pressures between 40 and 1000 MPa ( 1-20 min).
• Cold Plasma: It is a novel non-thermal food processing technology
designed for the inactivation of pathogenic microoganisms and food
safety improvement.
• Pulsed Electric Field: It involves the discharge of high voltage electric
short pulses which causes a transitory or a permanent permeabilization
of the cell membranes and It is more efficient than traditional heat
treatments of food and consequently presents better retention of
flavour, colour and nutritional value, improved protein functionality,
increased shelf-life and reduced pathogen levels .
• Pulsed light: It is a method of food preservation that involves the use of
intense and short-duration pulses of broad spectrum ‘‘white light’’
(ultraviolet to the near infrared region).

14. Suggested Readings
• “Introduction to Food Engineering,” 4th Edition, R.P. Singh and D.R.
Heldman, Academic Press, NY, 2009.
• “Food Processing Technology: Principles and Practice,” P.J. Fellows, CRC
Press, Boca Raton, FL, 2000.
• Barbosa-Canovas, Food Preservation Technology Series, Technomic
Publications, Lancaster, PA, 2000.
• “Non-Thermal Preservation of Foods,” G.V. Barbosa-Canovas, U.R.
Pothakumary, E. Palou, B.G. Swanson, Marcel Dekker, New York, 1998.
• “Preservation of Food with Pulsed Electric Field,” G.V. Barbosa-Canovas,
M.M. Gongora-Nieto, U.R. Pothakumary, and B.G. Swanson, Academic
Press, San Diego, CA, 1999.
• “Emerging Technologies for Food Processing,” Da-Wen Sun (Ed.) Elsevier
Academic Press, U.K., 2005.