2. Ultrasonics - science of sound waves above the limits of human
audibility.
Sound is the propagation of pressure wave through some physical
elastic medium.
The pressure waves are generated from some type of mechanical
disturbance.
Mechanical energy is being converted to a waveform that radiates
energy away from the disturbance.
3. Mechanical vibrations become vibrating pressure waves,
transferring energy to the medium and to objects that the wave
contacts.
Ultrasound with a frequency of between 25 kHz and 2 MHz has
been shown to have a remarkable effect on many physical and
chemical processes.
Frequency ranges of sound
4. Ultrasound waves are similar to sound waves but have a frequency that is above
16 kHz and cannot be detected by the human ear.
Ultrasound has the properties of sound waves, such as reflection, interference,
adsorption, and scattering, and can be propagated through solids, liquids, and
gases.
low-intensity ultrasound (1 Wcm-2
) - used as a non-destructive analytical method
to assess the composition, structure or flow rate of foods and
High-intensity ultrasound (10–1000 Wcm-2
) - used at higher frequencies (up to
2.5MHz) to cause physical disruption of tissues, create emulsions, clean
Equipment or promote chemical reactions (e.g. oxidation).
5. Sound waves can be longitudinal and transverse waves (shear waves).
Transverse waves - particle motion is perpendicular to the direction of
wave propagation.
As liquids and gases do not support shear stress under normal conditions,
transverse waves can only propagate through solids.
The velocity of these waves depends on the material and is relatively low
compared to longitudinal waves.
Longitudinal (shear) waves - the direction of particle motion is the same
as the wave motion.
These waves are capable of travelling in solids, liquids, or gases, and are
thus widely used in ultrasonic applications.
6.
7. THE NATURE OF SOUND WAVES
The compression and expansion cycle of ultrasound
8. ULTRASOUND
INSTRUMENTATION
Transducers
A transducer is a device that converts one form of
energy into another form.
In ultrasonic applications, the transducers are
designed to convert mechanical or electrical
energy into high-frequency sound.
There are two main types of transducers:
mechanical and electroacoustic .
9. Mechanical transducers rely on either the flow of a
liquid or gas through a siren, rotor, turbine, or whistle
to generate ultrasound.
Electromechanical transducers are based on the
inherent electrostrictive phenomenon in certain
materials to produce piezoelectric or magnetostrictive
transducers.
10. ULTRASONIC EQUIPMENT
To introduce ultrasonic energy into a system requires an ultrasonic
transducer and an ultrasonic power supply or "generator."
The generator supplies electrical energy at the desired ultrasonic
frequency.
The ultrasonic transducer converts the electrical energy from the
ultrasonic generator into mechanical vibrations.
12. Modern ultrasonic generators can produce frequencies of as high as
several gigahertz (several billion cycles per second) by transforming
alternating electric currents into mechanical oscillations, and
scientists have produced ultrasound with frequencies up to
about10GHz.
Higher frequencies have shorter wavelengths, which allows them to
reflect from objects more readily and to provide better information
about those objects.
14. Piezoelectric transducers convert alternating electrical energy
directly to mechanical energy through use of the piezoelectric effect
in which certain materials change dimension when an electrical
charge is applied to them.
Electrical energy at the ultrasonic frequency is supplied to the
transducer by the ultrasonic generator.
This electrical energy is applied to piezoelectric element(s) in the
transducer, which vibrate.
These vibrations are amplified by the resonant masses of the
transducer and directed into the liquid through the radiating plate.
The vast majority of transducers used today for ultrasonic cleaning
utilize the piezoelectric effect.
15. CAVITATION
In the liquid media, the best-known effect of ultrasound is cavitation.
When an intense sound wave passes through a liquid, it creates regions
of compression (positive pressure) and rarefaction (negative pressure).
If the negative pressure during rarefaction is high enough, a cavity or
bubble can form in the liquid.
There are two main types of cavities: transient (also called “inertial”)
and stable (also called “noninertial”).
Each of them demonstrates a different type of behavior of a gas bubble
that is subjected to an ultrasonic field.
16. Transient cavitation occurs when a cavity experiencing vibration
increases in size progressively over a number of compression and
rarefaction cycles, until it reaches a size where it collapses
violently .
The bubbles grow during rarefaction and collapse during
compression cycle when a critical bubble size is reached for that
particular condition.
During cavity collapse, there are occurrences of very high, but
localized temperatures (theoretically estimated at up to 10,000 K),
pressures (theoretically estimated at up to 100 MPa; experimentally
estimated at 0.01–0.5 MPa), and cooling rates (1010
K/s) .
It is also reported that an electrical field can occur at the interface
when a cavity fragments.
17. Long-lived gas bubbles are called stable cavities and exist for many
compression and rarefaction cycles.
They are produced at relatively low ultrasound intensities (1–3
W/cm-2
) and will oscillate for a number of cycles often nonlinearly
about some equilibrium size without collapsing.
While the conditions within stable cavities are not as extreme as
transient cavities, relatively high pressures and temperatures
(estimated at about 1650 K) still occur, which allows them to
contribute to influence chemical reactions.
20. METHODS OF ULTRASOUND
1) Ultrasonication (US) is the application of
ultra- sound at low temperature. Therefore, it can
be used for the heat sensible products. However, it
requires long treatment time to inactivate stable
enzymes and/or microorganisms which may cause
high energy requirement. During ultrasound
application there may be rise in temperature
depending on the ultrasonic power and time of
application and needs control to optimize the
process
21. Thermosonication (TS) is a combined method of
ultrasound and heat. The product is subjected to
ultra- sound and moderate heat simultaneously.
This method produces a greater effect on
inactivation of microorganisms than heat alone .
When thermosonication is used forpasteurization or
sterilization purpose, lower process temperatures
and processing times are required to achieve the
same lethality values as with conventional
processes
22. Manosonication (MS) is a combined method in
which ultrasound and pressure are applied
together. Manosonication provides to inactivate
enzymes and/or microorganisms by combining
ultrasound with moderate pressures at low
temperatures. Its inactivation efficiency is higher
than ultrasound alone at the same temperature.
23. 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 pressuremaximizes the cavitation
or bubble implosion in the media which increase the
level of inactivation. Microorganisms that have high
thermotolerance can be inactivated by
manothermosonication. Also some thermoresistant
enzymes, such as lipoxygenase, peroxidase and poly-
phenoloxidase, and heat labile lipases and proteases
from Pseudomonas can be inactivated by
manothermosonication
24. ULTRASOUND IN FOOD
PROCESSING
Low-power, high-frequency ultrasound (1
W/cm2
; >100 kHz) is normally used to monitor
food products or processes.
High-power, low-frequency ultrasound (10–
1000 W/cm2
; 20–100 kHz) is normally used to
alter the properties of a material or affect the
progress of a process.
25. ULTRASONICATION IN DAIRY
TECHNOLOGY
Ultrasound treatment is applied in dairy
industry for removal of fat from dairy wastewater
using enzyme (Lipase z) as a catalyst
Improvement in whey ultrafiltration,
Cutting of cheese blocks,
Crystallization of ice and lactose,
Cleaning of equipment,
Pasteurization, and homogenization which
involve minimum loss of flavor, and increased
homogeneity and considerable savings in energy
26. ULTRASONICATION IN FRUIT AND
VEGETABLE PROCESSING
Ultrasonication is used to maintain both pre- and
post-harvest quality attributes in fresh fruits and
vegetables and is considered a substitute for
washing of fruit and vegetable in food industry
Improving the nutritional value of fruit juices
Ultrasonication has proved to be one such
technique Effect of ultrasound on different
quality parameters of apple juice and is reported
to retain fresh quality, nutritional value, and
microbiological safety in guava juice
27. Ultrasound treatment can also be used to recover
the nutrient loss occurred during blanching,
resulting in achieving the collaborative benefit of
both the techniques
Ultrasonication cleaners (20–400 kHz) have been
efficiently used to produce fruits and vegetables
free of contamination and at 40 kHz, it has been
applied on strawberry fruits in which decay and
infection was considerably reduced along with
quality maintenance
28. ULTRASONICATION IN MEAT
TECHNOLOGY
A large number of applications of ultrasonic
treatment are reported in meat technology like,
reduction of meat toughness due to large propor,
examining the composition of fish, poultry, raw,
and fermented meat products by supporting
genetic enhancement programs in case of
livestock tion of connective tissue and in the
tenderization of meat products.
30. PROCESSING OF PROTEIN FOODS
Ultrasound can be used to enhance the processing of
materials containing proteins, such as the tenderization of
raw meat, destruction of microorganisms, homogenization,
protein extraction from cells, and enhancement of
membrane filtration.
The ultrasound mechanisms that can enhance these
processes, such as localized or bulk heating, microjet
formation, high shear, liquid agitation, polymer chain lysis,
and free radical formation, can also denature the proteins
present.
31. ANTIMICROBIAL TREATMENT
The antimicrobial effect of ultrasound is largely due to
the localized, but extreme, pressures and
temperatures produced during cavitation leading to
damage to cell walls, with possible contributory effects
due to direct thermal effects from the localized
heating, production of free radicals causing damage to
DNA, and microstreaming causing thinning of cell
membranes.
34. ENHANCEMENT OF HEAT
TRANSFER
Sound and ultrasound can be used to enhance the rate of
heat transfer during freezing, thawing and cooking. In the
case of thawing and cooking, ultrasound assists the
process by increasing the rate of heat transfer with the
surrounding medium and by absorption of sonic energy by
the material.
By contrast, in samples being frozen, the absorption of
energy from sound waves, which will reduce the cooling
rate, needs to be balanced against the improved heat
transfer coefficient and also improved product quality
produced by increasing ice crystal nucleation.
35. ADVANTAGES OF ULTRASOUND
Minimizing of flavor loss,
greater homogeneity
significant energy savings,
the reduction of pathogens at lower temperatures
higher product yields,
shorter processing times,
reduced operating and maintenance costs
36. DISADVANTAGE OF ULTRASOUND
Ultrasound application needs more input of
energy which makes industrialists to think over
while using this technique on commercial scale
Ultrasound induces physicochemical effects
which may be responsible for quality impairment
of food products by development of off-flavors,
alterations in physical properties, and
degradation of components.
37. Frequency of ultrasound waves can impose
resistance to mass transfer
Ultrasonic power is considered to be responsible
for change in materials based on characteristics
of medium. So, this power needs to be minimized
in food industry in order to achieve maximum
results
38. CONCLUSION
Ultrasound being non-toxic and ecofriendly is an
emerging technology which is considered as
green technology as it saves lot of energy and
maximizes production.
Ultrasound finds a diverse application in science
and food technology which has been employed in
studying food composition (fruits, vegetables, and
dairy products) and detecting contamination by
foreign extraneous materials in canned and dairy
foods.
39. A lot of research has been conducted on
ultrasound technologies in food technology, but
still a great deal of future research is necessary
in order to produce industrial-automated
ultrasound systems that will help in reduction of
labor, cost, energy, and should ensure the
maximum production of high value and safe food
products.
