It is useful to boost our knowledge in the field of preservation of food material using pulse light technology.

1. PULSED LIGHT TECHNOLOGY IN FOOD PROCESSING
PRESENTED BY
GOPAL KUMAR
AGRICULTURAL AND FOOD ENGINEERING DEPARTMENT
IIT KHARAGPUR

2. Contents
• Introduction
• Principle
• Mechanism microbial inactivation
• Factors affecting the microbial inactivation
• Design of pulsed light system
• Uses of the technology
• Conclusions
• References

3. Introduction
• Developed as a non-thermal food processing technique, that involves
discharge of high voltage electric pulses (upto 70 kV/cm) into the
food for few seconds.
• Aims at reducing the pests, spoilage microorganisms and pathogens
from food.
• Used mainly to inactivate surface micro-organisms on foods,
packaging material and equipments.
• Uses light energy in concentrated form and exposes the substrate to
intense short bursts of light (pulses).
• Pulsed light is an improved form of ultraviolet-C that is being given
to foods.

4. Fluence rate: Energy received from the lamp by the sample per unit area per
second. watt/meter2 (W/m2).
Fluence / Dose: Energy received from the lamp by the sample per unit area
during the treatment. Joule/meter2 (J/m2).
Pulse width: Time interval (fractions of seconds) during which energy is
delivered.
Exposure time: Time period in seconds during which treatment is given.
Peak power: It is measured as pulse energy divided by the pulse duration.
Its unit is Watt (W).
Pulse-repetition-rate (prr): Number of pulses per second (Hz) and
commonly expressed as pps (pulses /second).
Technical Terms

5. Several names
• Pulsed ultraviolet light (Sharma and Demirci, 2003)
• High intensity broad-spectrum pulsed light
(Roberts and Hope, 2003)
• Pulsed light (Rowan et al., 1999) and
• Pulsed white light (Marquenie et al., 2003)

6. Principle
 The principle involves the generation of pulsed light with gradually
increasing from low to high energy and then releasing the highly
concentrated energy as broad spectrum bursts.
 Within fraction of second, the electromagnetic energy gets stored in the
capacitor and is then released in the form of light within a billionth of a
second, which results in power amplification and minimum additional
energy consumption

7. Mechanism of microbial inactivation
Photochemical effect Photothermal effect
• Pulsed Light
• rich broad spectrum ultraviolet content,
• short duration,
• high peak power and
• the ability to regulate the pulse duration and frequency output
• Ultraviolet plays a vital role in the microbial cell inactivation.
• The ultraviolet spectrum comprises of three wave ranges:
• Long-wave ultraviolet -A (320-400 nm),
• Medium-wave ultraviolet -B (280-320 nm) and
• Short-wave ultraviolet -C (200-280 nm)
• The lethal effect of pulsed light can be due to
• Photochemical or
• Photothermal mechanism or
• Both may exist simultaneously.

8. Mechanism of microbial inactivation
Photochemical effect Photothermal effect
conjugated carbon-
carbon double
bonds
Ultraviolet
light absorbed
No
enzymatic
Repair
changes the
DNA and RNA
structures.
• As DNA is the target cell for ultraviolet wavelengths so
Primary target -nucleic acid
• Dimers inhibit the formation of new DNA chains in the
process of cell replication resulting in the chologenic death
of affected microorganisms by ultraviolet.

9. Figure 1. Formation of Thymine Dimer, Thymine-cytosine dimer and mixed dimer
(Setlow et al., 1966).
In the ultraviolet-C range of 250-260 nm, alterations in DNA take place due to
pyrimidine dimers mainly thymine dimers.
Ultraviolet irradiation usually generates
•thymine dimers in large quantity,
•cytosine dimers in low quantity and
•mixed dimers at an intermediate level

10. Mechanism of microbial inactivation
Photochemical effect Photothermal effect
• This hypothesis become evident by (Wekhof et al., 2001) when they showed
electron-microscope photographs of flashed Aspergillus niger spores
presenting severe deformation and rupture.
• The ruptured top of spore become evident of an escape of an overheated
content of the spore, which became empty after such an internal ‘‘explosion’’
and ‘‘evacuation’’ of its content took place during the light pulse.
fluence >0.5
Joule/cm2
absorption of
all ultraviolet
light
temporary
overheating
rupture of
bacteria

11. Design of pulsed light system
The pulsed light system consists of several common components.
• A high voltage power supply:
provides electrical power to the storage capacitor
• A storage capacitor:
stores electrical energy for the flash lamp
• A pulse-forming network:
determines the pulse shape and spectrum characteristics
• Gas discharge flash lamp
• A trigger signal:
initiates discharging of the electrical energy to the flash
lamp, which is the key element of a pulsed light unit.

12. Figure 2. Functional diagram of a high-intensity pulsed-light system.
(Adapted from Xenon Corp., 2005)

13. Design of pulsed light system (Flash lamp)
Envelope • Converts 45% to 50% of the input electrical
energy to pulsed radiant energy (xenon
corp., 2005).
• Filled with an inert gas such as xenon or
krypton.Electrodes
Seals
Figure 3. Schematic representation of a xenon-filled flash lamp

14. Design of pulsed light system (Flash lamp)
The envelope is a jacket that contains the filling
gas and also surrounds the electrodes.
The envelope must be
• transparent to the radiations that are emitted
by the lamp,
• impervious to the filling gas as well as air,
• able to withstand high temperatures and
thermal shocks and have mechanical
strength.
Envelope
Electrodes
Seals

15. Design of pulsed light system (Flash lamp)
Metallic electrodes protrude into each end of
the envelope and are connected to the capacitor
which is charged to a high voltage. The
electrodes provide electric current into the gas.
The lifetime of the lamp is determined by the
cathode and is hence an important component.
Envelope
Electrodes
Seals

16. Design of pulsed light system (Flash lamp)
• The whole assembly of the flash lamp
needs to be sealed.
• Commonly used seals include, solder
seals, rod seals and ribbon seals.
Envelope
Electrodes
Seals

17. Generation of Pulsed Light
A very large pulse of current is sent through the ionized gas, which excites the
electrons surrounding the xenon atoms, causing them to jump to higher energy
levels. The electrons release this energy and drop back to a lower orbit by producing
photons.
The pulsed operation of xenon discharge lamps is characterized by two stages.
• Plasma formation near the anode
• Plasma decay stage
Figure 3. Schematic representation of a xenon-filled flash lamp
(nn= number of neutral atoms; ne= number of electrons; n+= number of ionized xenon atoms).

18. Factors affecting the microbial inactivation
Type of micro-
organism
The distance
from the light
source
Interaction
between light
and the
substrate
Optical properties of cells, e.g.
• degree of scattering and
• absorption of light
The incident beam of light undergoes
refraction due to difference in the optical
density between the substrate and the
surrounding air.
There are also some micro-organisms resistant
to pulsed light.

19. Factors affecting the microbial inactivation
Type of micro-
organism
The distance
from the light
source
Interaction
between light
and the
substrate
•For transparent and coloured food materials,
refraction is particularly relevant
•Opaque food materials, reflection
•For smooth surfaces specular reflection.
•For rough surfaces diffuse reflection.
•For translucent materials, scattering.
Figure 4. Interaction between light and the food

20. Factors affecting the microbial inactivation
Type of micro-
organism
The distance
from the light
source
Interaction
between light
and the
substrate
The quantitatively distribution of light dose inside
a substrate is described by the term Optical
penetration depth, which represents the distance
over which light decreases in fluence rate to 37%
of its initial value.
•Shorter wavelengths → Deeper penetration into
the food
Distance from light source
and depth of the substrate
Absorption and scattering

21. What can it be used for?
Products
Liquid foods (cold pasteurization of liquid food
such as milk, juices) and
Solid foods (fruits, vegetables, eggs, shell, fish and
meat)
Operations Disinfection and preservation of food products.
Solutions
for short
comings
• Rapid and energy saving
• Decontamination of the food products and food
related packaging and equipments.
• Replacement of the traditional thermal and
chemical disinfection technologies

22. What can it NOT be used for?
Products
Operations
Other
limitations
Risks or
hazards
• Light sensitive products
• High protein or oil content foods
• Carbohydrate and water content of food
products has variable effects on microbial
destruction of the PL treatment depending
on the type of microorganisms
• Coloured food powders (i.e., black pepper,
wheat flour)
• Foods with rough or uneven surfaces,
crevices or pores
• Seeds (cereals, grains, and spices)

23. What can it NOT be used for?
Products
Operations
Other
limitations
Risks or
hazards
The PL technology is a non-thermal
technology. However, heating may occur
accidentally during the use of PL
technology. In order to avoid this effect, the
following recommendations are desirable:
• use of a limited number of pulses
• use of lower duration pulses
• an appropriate cooling period between
pulses
• a low IR content of the spectrum for the
pulses
• cooling of light sources

24. What can it NOT be used for?
Products
Operations
Other
limitations
Risks or
hazards
Uniformity of the treatment is limited
by the product geometry and opacity.

25. What can it NOT be used for?
Products
Operations
Other
limitations
Risks or
hazards
PL technology is considered free of any health
risks. However, more research is needed on the
nutritional consequences and on the applicability
of photosensitization to foods.
PL is safe to apply but some precautions have to
be taken to avoid exposure of workers to light
and to evacuate the ozone generated by the
shorter UV wavelengths.

26. Effects of PL on Food Products
Liquid
Foods
Other
Foods
Solid
Foods
Packaging
Materials
• Water-has a high degree of transparency to a
broad range of wavelengths including visible
and UV light, while Sugar solutions and
wines, exhibit a more limited transparency.
• Increasing the amount of solids will diminish
the intensity of penetration of the UV
radiation. In an aqueous solution, the lower
the transparency, the less effective the PL
treatment.
• Liquids with high UV absorbance must be
treated as a thin layer in order to reduce
radiation absorption by the liquid.

27. Effects of PL on Food Products
Liquid
Foods
Other
Foods
Solid
Foods
Packaging
Materials
• The log reductions for spinach, celery, green
paprika, soybean sprouts, radicchio, carrot,
iceberg lettuce, and white cabbage with PL of 7
J pulse intensity were between 0.21 and 1.67
• 80% increase in the respiration rate of lettuce,
whereas the respiratory rate of cabbage was not
affected.
• The model predictions indicate that maximum
4.93 log reduction could be obtained when the
treatment time was 100 s at a distance from the
strobe of 3 cm and a maximum energy of 5.6 J
cm−2 per pulse.

28. Effects of PL on Food Products
Liquid
Foods
Other
Foods
Solid
Foods
Packaging
Materials
• PL treatments achieved high levels of
microbial inactivation on relatively simple
surfaces, while generally showed only 1–3 log
reductions on complex surfaces such as
meats.
• Part of the radiation may have been absorbed
by proteins and lipids, thus decreasing the
effective radiation dose on microorganisms
• Beef steaks treated with PL using 5 J cm−2 to
each side and stored 3 days at 4–5 °C exhibited
2 log reductions in microbial counts.

29. Effects of PL on Food Products
Liquid
Foods
Other
Foods
Solid
Foods
Packaging
Materials
• PL technology is applicable to sterilize or
reduce microbial population of packaging
material surfaces or food contact materials in
processing plants. On the surface of different
packaging materials inoculated with 10–1,000
CFU cm−2, a single pulse of 1.25 J cm−2
inactivated S. aureus, while B. cereus and
Aspergillus spores were inactivated with
intensities greater than 2 J cm−2.
• McDonald et al. (2000) reported almost
identical inactivation levels of Bacillus subtilis
for the decontamination of surfaces with 4*10−3
J cm−2 PL and 8*10−3 J cm−2 continuous UV
light treatments.

30. Advantages
• The intensity of light, that lasts for only a second, is
20,000 times brighter than sunlight, but there is no
thermal effect, so quality and nutrient content are
retained.
• For the treatment of foods that require a rapid
disinfection.
• The lack of residual compounds and the absence of
applied chemicals disinfectants and preservatives.
• Foods with smooth surfaces such as fresh whole fruit
and vegetable commodities, hard cheeses, or smooth
surface meat slices are suitable for treatment with PL
where surface contamination is a concern for
microbial contamination.

31. Limitations
• Effective penetration is still a challenge to this technology.
• Limited efficacy for controlling food heating.
(Heating limited the treatment of alfalfa seeds, grated carrots
and raw salmon fillets.)
• Thermal effect in food powders.
• Limited PL efficiency because of the shadow effect.
• Foods with rough or uneven surfaces, crevices, or pores are
unsuitable for PL.
• Not an adequate technology for cereals, grains and spices
due to their opaque nature.

32. Conclusions
• The pulsed light processing is a new concept and has
many applications in the food industry as a non-thermal
technique of food preservation.
• This technology is fast and environment friendly.
• Its most important technological problems are to find
ways to control food heating, and to treat homogeneously
foods.
• There are some microbial species resistant to the pulsed
light processing technique and so such species should be
studied and also the foods they contaminate be considered
separately for processing.
• More research is needed on the nutritional consequences.

33. References
• Abida, J., Rayees, B. and Masoodi, F. A., Pulsed light technology: a novel method
for food preservation, International Food Research Journal 21(3): 839-848 (2014).
• Gemma Oms-Oliu, Olga Martín-Belloso & Robert Soliva-Fortuny, Pulsed Light
Treatments for Food Preservation: A Review, Food Bioprocess Technol (2010)
3:13–23.
• N.Elmanasser, S.Guillou, F.Leroi, N.Orange, A.Bakhrouf, M.Federighi, Pulsed-
light system as a novel food decontamination technology: A review, Can. J.
Microbiol. 53 (2007) 813-821.
• Vicente M. Gomez-Lopez, Peter Ragaerta, Johan Debevere and Frank
Devliegherea, Pulsed light for food decontamination: a review, Trends in Food
Science & Technology 18 (2007) 464-473.