Heat Energy, Ultrasound And Ohmic Heating, Their Heat Generation , Application And Heating Models

1. DEPARTMENT OF AGRICULTURAL PROCESSING AND
FOOD ENGINEERING,
SWAMI VIVEKANAND COLLEGE OF AGRICULTURAL
ENGINEERING AND TECHNOLOGY & RESEARCH STATION,
IGKV, RAIPUR
Submitted by
Yogesh Kumar
PhD. I Year
Heat Energy, Ultrasound And Ohmic Heating,
Their Heat Generation , Application And Heating Models

2. Food processing refers to the deliberate transformation of
agriculture produce, through numerous unit operations into more
palatable, shelf-stable, portable and useful, value-added products,
safe for human consumption.
Various traditional processing and preservation methods are still
abundantly and effectively used to process raw food products.
Drying.
Frying.
Smoking.
Salting.
Pickling.
Soaking. etc.
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Introduction

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Foods are complex materials containing proteins, vitamins,
carbohydrates, enzymes, fats, minerals, water and other organic
ingredients with differing compositions.
Processing and preservation of these foods require variety of
different applications/methods and cautions.
Use of ultrasound in food processing includes
•Extraction ,
•Drying ,
•Crystallizatio ,
•Filtration ,
•Defoaming ,
•Homogenization ,
•Meat tenderization ,
Introduction

4. Ultrasound also use of as preservation technique.
Microbial and enzyme inactivation by use of ultrasound makes it
possible to use in food preservation.
Preservation techniques are applied to preserve foods for a long
time and heat treatment is the most widely used method due to its
high efficiency on microbial and enzyme inactivation.
There are a lot of food products that present a threat of bacterial or
viral intoxication for which processing by heat may not be
desirable.
Such thermally sensitive food products on exposure to heat
treatment may undergo physical, chemical, and microbial changes
such as modification of flavor, color, and texture.
4
Introduction

5. Ultrasound is known as a green novel technology due to its role
in environmental sustainability. Sound waves exceeding the
audible frequency range i.e. greater than 20 kHz are termed as
‘Ultrasound’. The lowest ultrasonic limit is 20 kHz (1 Hz = 1 cycle
per second) and the upper limit of ultrasound frequencies for
gases is 5 and 500 MHz for liquids and solids
When the acoustic waves propagate through a medium, they
generate compressions and rarefaction (decompressions) in the
medium particles. This, in turn, produces a high amount of
energy, due to turbulence, and increase in mass transfer.
Ultrasound
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Ultrasonic waves are characterized by their frequency and
wavelength. The product of these parameters is the speed of the wave
through the medium:
c = λf
where c is speed of sound, f is frequency, and λ is wavelength.
The speed of sound increases with the density of the media. Some
advantages of the use of ultrasound in the food industry include
minimization of flavor loss, homogenization effects, and significant
energy saving

7. Ultrasound is an emerging sustainable technology that
enhances the rate of several processes in the food processing
industry, and their efficiency. It can also be applied in
combination with temperature (thermosonication) and
pressure (manosonication) to produce a synergistic effect,
which further enhances its efficacy.
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Ultrasound

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METHODS OF ULTRASOUND
Ultrasound can be used for food preservation in combination with
other treatments by improving its inactivation efficacy. There have
been many studies combining ultrasound with either pressure,
temperature, or pressure and temperature.
1. Ultrasonication
2. Thermosonication
3. Manosonication
4. Manothermosonication

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1. Ultrasonication
Ultrasonication (US) is the application of ultra- sound at low temperature.
Therefore, it can be used for the heat sensible products.

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Thermosonication (TS) is a combined method of
ultrasound and heat.
The product is subjected to ultra- sound and moderate
heat simultaneously.
Thermosonication

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Manosonication (MS) is a combined method in which
ultrasound and pressure are applied together.
Ma- nosonication provides to inactivate enzymes and/or
mi- croorganisms by combining ultrasound with
moderate pressures at low temperatures.
Its inactivation efficiency is higher than ultrasound alone
at the same temperature.
Manosonication

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Manothermosonication
Manothermosonication (MTS) is a combined method of heat,
ultrasound and pressure.
MTS treatments inactivate several enzymes at lower temperatures
and/or in a shorter time than thermal treatments at the same
temperatures.
Applied temperature and pressure maximizes the cavitation or bubble
implosion in the me- dia which increase the level of inactivation.
MTS has been demonstrated to be very effective in inactivation of
enzymes associated with food spoilage which otherwise endure the
conventional thermal treatment.
This method can significantly decrease the activity of many enzymes
like pectin esterase (PE) enzyme of various fruit juices at the
moderate pressure (100-300 kPa) and temperature below 100°C.

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1. Manothermosonication

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Fig. E. coli K12 cells observed with
environmental scanning electron
microscopy (ESEM): (a) control
(50,000 magnification), (b) and (c)
manosonication at 40 °C and 500 kPa
for 2 min (80,000 magnification), (d)
thermosonication at 61 °C and 100 kPa
for 0.5 min (80,000 magnification), and
(e) and (f) manothermosonication at 61
°C and 500 kPa for 0.25/0.5 min
(50,000 and 80,000 magnification for (e)
and (f), respectively).
Ref - Hyoungill Lee, Inactivation of
Escherichia coli cells with sonication,
manosonication, thermosonication, and
manothermosonication: Microbial
responses and kinetics modeling,
Ultrasonics Sonochemistry Volume
37, July 2017, Pages 216-221

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Fig. Rhodosporidium toruloides cells
observed with scanning electron
microscopy (SEM), 50,000
magnification.
Ref-
A. Meullemiestre, Manothermosonication
as a useful tool for lipid extraction from
oleaginous microorganisms , Ultrasonics
Sonochemistry 37 (2017) 216–221

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Ultrasound waves are classified into four different categories based
on the
mode of vibration of the particles in the medium, with respect to the
direction of propagation of the wave, viz.,
longitudinal waves,
transverse waves,
surface waves, and
plate waves .

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Depending upon/Based on the
intensity (frequency of the
sound ) and frequency
ultrasound waves used in food
application can be categorized
into two categories:
 Low intensity ultrasoun and
High-intensity ultrasound.

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Low-Intensity Ultrasound
This is also known as ‘‘diagnostic’’ or ‘‘high-frequency’’ ultrasound,
and involves low-amplitude sound waves. Low-power ultrasound uses
very high frequencies of 100 kHz to 10 MHz or more, with low
sound intensities of 100 mW cm−2 to 1 W cm−2. It measures the
velocity and attenuation of the wave.
Some applications of low-power ultrasound in the food industry are in
processing, quality assurance, and nondestructive food inspections.
food quality assessment (ripeness, composition)

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High-Intensity Ultrasound
produces sound intensities of high power which rank from 10 to 1000
W cm−2, Also known as ‘‘power ultrasound,’’ this uses lower
frequencies (20– 100 kHz) and with amplitudes ranging from 5 to 50
mm .
This kind of ultrasound treatment has enough energy to break
intermolecular bonds. Some applications in food processing
operations include emulsification, homogenization, modification of
viscosity, defoaming, extrusion etc.

23. Generation of ultrasound
The most basic component employed in the generation of ultrasound
is a transducer which converts electrical pulses into acoustic energy of
required intensity.
There are two types of transducers are mainly used for the generation
of ultrasound
Magnetostrictive and
Piezoelectric
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24. A magnetostriction transducer is a device
that is used to convert mechanical energy
into magnetic energy and vice versa. Such
a device can be used as a sensor and also
for actuation as the transducer
characteristics is very high due to the bi-
directional coupling between mechanical
and magnetic states of the material.
Magnetostrictive Transducers act as
electroacoustic transducers for the
generation of ultrasonic waves. These
transducers work on the principle of
magnetostriction which is described as
the subsequent alteration in length per
unit length.
Magnetostrictive Transducers
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25. Piezoelectric Transducer deals with the
inter-conversion of acoustic and
electrical energies.
The working principle of a Piezoelectric
Transducer is based on the fact that
when a mechanical force is applied on a
piezoelectric crystal, a voltage is
produced across its faces. Thus,
mechanical phenomena is converted
into electrical signal. No external
supply is required for this transducer to
work.
Piezoelectric Transducer
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The most commonly produced piezoelectric ceramics are lead
zirconate titanate (PZT), barium titanate, and lead titanate

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Microbial Inactivation
Thermal treatment (i.e. pasteurization, ultra high tem-
perature) is generally considered to be main method for
the inactivation of bacteria but often result in some un-
desirable results such as formation of unwanted flavors
and loss of nutrients.
Nowadays, ultrasound is used for inactivation of
microorganisms to overcome the undesirable results of
thermal processing.
Microbial inactivation mechanisms of ultrasound is
simply explained by cavitation phenomena that caused by
the changes in pressure.

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That the ex- tremely rapid creation and collapse of
bubbles formed by ultrasonic waves in a medium creates
the antimicrobial effect of ultrasound.
During the cavitation process, localized changes in
pressure and temperature cause break- down of cell walls,
disruption and thinning of cell mem- branes, and DNA
damage via free radical production.
In fact, type of bacteria is an important criteria that
changes the effectiveness of an ultrasound treatment.
Different kinds of microorganisms have different
membrane structure.

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Such as, Gram-positive and Gram-negative bacteria do
not show same behaviour against ultrasonic waves due to
their different cell and membrane structures.
Effect of ultrasound on microbial inactivation also de-
pends on intensity and frequency of ultrasound applied.
Generally, frequency range of 200 - 600 kHz enhanced
the effects of ultrasound on microorganisms.
Wordon, et al. suggested that high frequency of
ultrasound was more effective in irradiation of
microorganisms.

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Enzyme Inactivation
Enzymatic reactions produce undesirable changes in
many foods during processing and storage periods.
Heat treatment to eliminate enzymes is the commonly
used method but it also destroys nutrients and may cause
loss of food quality.
For this reason, nonthermal technologies are being tested
as an option for reducing the enzymatic activities in
foods.

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its inactivation mechanism was explained by cavitation.
Since then, it has been proven that ultrasound is an
effective method in the inactivation of enzymes when it is
used alone or with temperature and pressure.
There are many enzymes inactivated with ultrasound
such as
•glucose oxidase ,
•peroxidase ,
•pectin methyl esterase
•protease and lipase
•watercress peroxidase and
• poly- phenoloxidase

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Transmission electron microscopy
FIG 5 TEM photographs of E. coli cells. (a) Untreated
bacteria. (b, c, and d) Bacteria treated with ultrasound for
20 min.
FIG 6 TEM photographs of S. aureus cells. (a) Untreated
bacteria. (b, c, and d) Bacteria treated with ultrasound for
20 min.

33. Application of Ultrasound
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Applications Principle Products
Filtration Vibrations Liquid food products eg.
Juices
Freezing / Crystallization Uniform Heat Transfer Milk products
Fruits & Vegetables
Meat
Thawing Uniform heat Transfer Frozen products
Brining/Pickling Cheese, meat, fish etc
Drying Uniform Heat Transfer Dehydrated Food Products
Foaming Dispersion of gas bubbles Protein
Degassing / Deaeration Agitation Carbonic beverages, aqueous
solutions.
Cooking Uniform Heat Transfer Meat Products
Vegetables
Emulsification Cavitation Phenomenon Emulsions eg. Mayonnaise
Cutting Cavitation Phenomenon Soft Products eg. Cheese,
Bread
Sterilization / Pasteurization Uniform Heat Transfer Milk, Juice
Extraction Diffusion Food and plant material
Rehydration Absorption Dried vegetables, grains etc.

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Heat generation : electrical resistance heating
The need to conduct heat is the limiting factor in the
sterilization of particles. Volumetric techniques, in which
heat is generated with In the material , offer ways of
circumventing the problem.
It is possible to generate heat using microwave heating
[4],in which a high-frequency electric field excites the
water molecules within the material, or by electrical
resistance heating ('ohm cheating').

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The principle of electrical resistance heating is shown in
Figure10.1. In this process, an electric current is passed
through the material, which then heats throughout its
volume, as a result of its electrical resistance.
The process is more energy efficient than microwave
heating, because nearly all of the electrical energy goes in
to the food as heat.
Whereas microwave heating requires no physical
contact, however, resistance heating requires electrodes
in good contact with the food.

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Advanced Thermal Processing Technique :
Ohmic Heating
 Ohmic heating is an advanced thermal processing
method where in the food material, which serves as an
electrical resistor, is heated by passing electricity through
it.
 Electrical energy is dissipated into heat, which results in
rapid and uniform heating.
 Ohmic heating is also called electrical resistance heating,
Joule heating, or electro-heating.

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Principles of Ohmic Heating
 Ohmic heating is based on the passage of
alternating electrical current (AC) through a
body such as a liquid-particulate food system
which serves as an electrical resistance in which
heat is generated.
 The rate of heating is directly proportional to
the electrical conductivity.