• Food quality is a sensory property that includes appearance, taste, nutritional value
(nutrient content), health benefit (functional ingredient) or safety (chemical,
• It includes those attributes which affect consumer‟s choice for a product.
Need For Quality Food
•Major challenge for food industry is to maintain the food quality ; the reason being
well aware consumers.
•For this reason food industry has to adopt certain techniques in order to meet the
growing need of maintaining food quality; this is known as food quality control.
•The main issue which is considered while quality control process is to deteriorate the
level of microbes and other contaminants in food.
Ultrasound : Energy derived from sound waves
Irradiation: Energy derived from ionising radiations
Cold Plasma Technique: Energy derived from plasma
What is Ultrasound?
• It is a form of energy generated by sound waves of frequencies
that are too high to be detected by human ear, i.e. above 16 kHz.
•Ultrasound can propagate in gases, liquids and solids.
•Considered to be technologies that were developed to minimize
processing and maximize quality and safety in food
•These applications include improvement in microbial
inactivation, food preservation, manipulation of food texture and
Physics of Ultrasound
• The sound waves travel effectively through liquids which are comprised of closely compacted
• Sound is transmitted as sequential sine waves whose height represents amplitude or loudness.
• A single full cycle is measured from peak to peak, and the number of these cycles per one
second represents the frequency. The frequency is described in Hertz [Hz] which by convention
is in honor of the German physicist Heinrich Hertz for his work on electromagnetic
How can Ultrasound be applied in Food ?
• Ultrasound when propagated through a biological structure induces compressions and
depressions of the particles and a high amount of energy is imparted.
In food industry, the application of ultrasound
can be divided based on range of frequency:
low power ultrasound
high power ultrasound
Low Power Ultrasound:
• Low energy [low power, low intensity] ultrasound
Principles of LPU for Food Analysis:
• It uses a small power level that the waves cause no physical and chemical alteration
in the properties of the material through which it passes.
• This property is been utilized for non-invasive analysis and monitoring of various
food materials during processing and storage to ensure quality and safety.
• Ultrasonic velocity (v) is determined by density (ρ) and elasticity (E) of the medium,
according to the Newton-Laplace equation (Blitz, 1963).
•The Newton-Laplace equation is the starting point for the determination of
isentropic properties of solution, using the speed of sound u and density (ρ).
•This equation implies that the ultrasound velocity of the solid form of a material
is larger than that of its liquid form.
•In food industry, the sensitivity of ultrasound velocity to molecular
organizations and intermolecular interactions makes UVM – Ultrasound Velocity
Measurements suitable for determining composition, structure, and physical state
of different food materials.
•It also helps in detection of foreign bodies and defects in processed and
Why Low Power ?
• Can provide information about the physiochemical
properties of food materials, their composition,
structure and physical state.
• The major advantage of this technique over other
traditional techniques is that the measurement is
so rapid and non-destructive.
Applications of Low Power Ultrasound
• In Meat Technology
• In Fruits and Vegetables
• In Cereal products
• Ultrasonic monitoring for food freezing
High Power Ultrasound:
• High energy [high power, high intensity] ultrasound
• 20 and 500 kHz
• Disruptive and enforce effect on the physical, mechanical, or
biochemical properties of foods. These effects are promising in food
processing, preservation and safety.
The chemical and biochemical effects are effective tools for sterilizing equipments, preventing
contamination of food processing surfaces by pathogenic bacteria and removal of bacterial
Principle of HPU
Factors that affect power ultrasound are energy, intensity, pressure, velocity and temperature.
Where, Pa is the acoustic pressure (a sinusoidal wave), which is dependent on time (t),
frequency (f) and the maximum pressure amplitude of the wave.
Pa max is related to the power input or intensity (I) of the transducer:
I = Pa max/ 2ρv , where ρ is the density of the medium and v is the sound velocity in the
Mechanical Chemical and Biological Effects:
Why HPU ?
Ultrasonic Inactivation of Microorganism
• The most common techniques currently used to inactivate microorganisms in food
products are conventional thermal pasteurization and sterilization.
• Thermal processing does kill vegetative microorganisms and some spores; however, its
effectiveness is dependent on the treatment temperature and time.
• The magnitude of treatment, time and process temperature is also proportional to the
amount of nutrient loss, development of undesirable flavors and deterioration of
functional properties of food products.
• High power ultrasound is known to damage or disrupt biological cell walls which will
result in the destruction of living cells.
• Unfortunately very high intensities are needed if ultrasound alone is to be used for
permanent sterilization. However, the use of ultrasound coupled with other
decontamination techniques, such as pressure, heat or extremes of pH is highly
Thermosonic (heat plus sonication),
manosonic (pressure plus sonication),
and manothermosonic (heat plus pressure plus sonication) treatments are likely the best
methods to inactivate microbes, as they are more energy – efficient and effective in
The advantages of ultrasound over heat pasteurizationinclude:
Minimizing of flavor loss, greater homogeneity and significant energy savings.
The effectiveness of an ultrasound treatment is dependent on the type of bacteria
being tested, amplitude of the ultrasonic waves, exposure time, volume of food being
processed, the composition of food and the treatment temperature.
Ultrasound in Food Industry
• Major Significance to Industry and Consumers
• Better quality and Healthy Food
• High Efficiency
• Saves Energy and Costs
• packaged food is passed through a radiation chamber on a conveyor belt
• It is passed through a radiation beam, like a large flashlight, instead of
coming in direct contact with the radioactive materials
How does Food Irradiation Works?
• Food is exposed to a carefully measured amount
of intense ionizing radiation.
• When food is irradiated, the radiation energy
breaks the bonds in the DNA molecules of
microorganism. Thus, the organism dies or
becomes unable to reproduce.
• Frozen foods take larger radiation dose to kill
• The effectiveness of the process depends on the
organism‟s sensitivity to irradiation.
• The food irradiation process uses three types of ionizing radiation sources:
cobalt-60 gamma sources : most commonly used as they can deeply penetrate
electron beam generators
• Absorbed dose is measured as the quantity of radiation imparted per unit of mass of a
• The unit of absorbed dose is the gray (Gy) where 1 gray is equivalent to 1 joule per
• Low doses (up to 1 kGy) inhibit sprouting in tuber, bulb and root vegetables, inhibit
the growth of asparagus and mushrooms, and delay physiological processes (ripening,
etc.) in fruits
• Medium doses (1 to 10 kGy) extend the shelf life, eliminate spoilage and pathogenic
• High doses (10 to 50 kGy) can be used for industrial sterilization and decontamination
of certain additives or ingredients
• Parasites and insect pests, which have large amounts of DNA, are rapidly killed by
an extremely low dose of irradiation.
• It takes more irradiation to kill bacteria, because they have less DNA.
• Viruses are the smallest pathogens that have nucleic acid, and they are, in general,
resistant to irradiation at doses approved for foods.
• Another useful effect: it can be used to prolong the shelf life of fruits and vegetables
because it inhibits sprouting and delays ripening.
It has been studied that when irradiation is used as
approved on foods:
• Disease-causing microorganisms are reduced or
• The nutritional value is essentially unchanged
• The food does not become radioactive
• Irradiation is a safe and effective technology that can
prevent many food borne diseases.
Considering its potential role in the reduction of post-harvest losses, providing safe
supply of food and overcoming quarantine barriers, food irradiation has received
wider government approvals during the last decade.
There is also a trend towards increased commercialization of irradiated food.
Currently, there are 47 irradiation facilities in some 23 countries being used for
treating foods for commercial purposes.
• kill many insects and pests that infest foods like grains, herbs and spices without
appearing to affect them
• kill or considerably reduce the level of dangerous micro organisms in foods such as
salmonella and campylobacter in raw meat and poultry.
• Listeria in ready to eat foods like hot dogs
• Delay or stop normal ripening and decay processes so that foods can be stored for
• Irradiation can successfully replace the fumigation treatment of cocoa beans and
coffee beans and disinfest dried fish, dates, dried fruits, etc.
• One of the most important advantages of food irradiation processing is that it is a
cold process which does not significantly alter physico-chemical
characters of the treated product.
• It can be applied to food after its final packaging
Are irradiated foods still nutritious?
• Their nutritional value doesn’t change
• levels of the Vitamin - Thiamine are slightly reduced, but not enough to result in
• no significant changes in the amino acid, fatty acid, or vitamin content of food.
• the changes induced by irradiation are so minimal that it is not easy to determine
whether or not a food has been irradiated.
• A big advantage of irradiated food, is that it is a cold process: the food is still
essentially “raw”, because it hasn‟t undergone any thermal process.
• Is used on a very limited range of foods as it is an expensive technology
• Affects some important constituents of foods, for example, vitamin E levels can
be reduced by 25% after irradiation and vitamin C by 5-10%
• Radiation doses at the levels recommended will not kill all micro organisms, 90%
may be destroyed so need to handle with care otherwise remaining organisms can
• Ineffective against viruses - as they are the smallest pathogens that have DNA or
RNA, and they are relatively resistant to irradiation at the levels approved for
• Prions, such as the one that causes “mad cow” disease (bovine spongiform
encephalopathy, or BSE), have no DNA, so they also are not affected by irradiation
at the levels approved for foods.
• Can create new substances called Radiolytic products. While this does not mean
that the food is radioactive, there is considerable controversy over whether these
products are unique and if so whether they are dangerous.
• Preferences of the consumers have shifted
towards healthy, tasty foods, which are readily
available, ready to eat and easily stored
• Challenge to Food Industries – providing such
foods in a form suitable for distribution and
mass production without affecting texture,
flavour, and color, is technically complex and
What is Cold Plasma Technology ?
• Cold Plasma Technology is a novel, non thermal food processing technology that uses
energetic and reactive gases to inactivate contaminating microbes in food products ( E.g..
meat, poultry, etc.,)
• Plasma is a mixture of positive and negative charges as well as neutral particles and
photon. Plasma exist over a massive range in temperatures and densities.
• It is estimated that 99% of the known universe is in a plasma state. The sun and stars are
examples of natural plasmas
Generation of Plasma
• Man-made plasma can be generated at low temperatures typically by applying a
voltage to a gas. The electric field generated from the applied voltage can accelerate
any free electrons in the gas.
• Accelerated electrons collide with gas atoms to excite or ionise them. Ionisation of
gas atoms releases more electrons; this cascaded reaction can generate a rich
abundance of highly reactive chemical species which are capable of inactivating a
wide range of microorganisms including food borne pathogens and spoilage
Cold Plasma Technology in Foods
• Cold Plasma Technology in food Industry
relies on gas discharge technology - an
effective, economical, environmentally safe
method for critical cleaning.
• The vacuum ultraviolet (VUV) energy is very
effective in the breaking most organic bonds
(i.e., C-H, C-C, C=C, C-O, and C-N) of surface
contaminants. This helps to break apart high
molecular weight contaminants.
• A second cleaning action is carried out by the oxygen
species created in the plasma (O2+, O2-, O3, O, O+,
O-, ionised ozone, excited oxygen, and free electrons).
• These species react with organic contaminants to form
H2O, CO, CO2, and lower molecular weight
• The resulting surface is ultra-clean/sterilised. The
plasma activated atoms and ions cause molecular
„sandblasting‟ and can break down organic
Cold plasma can be used for decontamination of
products where micro-organisms are externally located.
Unlike light ( UV decontamination), plasma flows
around objects, which means „Shadows Effects‟ do not
occur ensuring all parts of a product are treated.
For products such as cut vegetables and fresh meat,
there is no mild surface decontamination technology
available currently, cold plasma could be used for this
Can also be used to disinfect surfaces before packaging
or included as packaging process
• Illustration – Sterilization capability of Cold
• E.coli – inoculated in to 3 Petri dishes.
• One dish was left as a control with no plasma
exposure, another was exposed for 30s of plasma
treatment, and a third was exposed for 120
• The bacterial kill zone was
progressively higher with longer
• Common pathogen – Unprocessed meat – 70%
• Plasma Torch - Applied for 180s,
• Plasma eliminated or subsequently reduced low levels
of bacteria from both skinless chicken and chicken
• Plasma is used as a method for killing Salmonella on
• Askild Holck, senior research scientist at Nofima:
“By using plasma treatment, we have
succeeded in removing 99.5 per cent of all
bacteria on the egg shell but because this is a
gentle method, the egg yolk and white are unaffected."
Bacteria‐free eggs with plasma technology.
• Important aspects of this technology are still immature,
particularly with respect to its use with food nutrition
• We do not know how cold plasma inactivates spores or how
the cold plasma – specifically the electronically excited
molecules – interact with the food or packaging materials, or
the stability of the plasma for large-scale commercial
• Need to determine optimum operating conditions for a given
application - Safety of treated products.
T.J. Mason, L. Paniwnyk, J.P. Lorimer. Ultrasonics Sonochemistry 3 (1996), The uses of
ultrasound in food technology, Pages S253-S260
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