pulsed light and application in food process industry

1. course teacher
ASST. PROF SREEJA. R
Credit seminar -1 semr.3201 (0+1)
Pulsed Light
Applications
in Food Processing
Presented by :
HARIKRISHNAN M.P
2015-06-009
S6 B.Tech food engineering

2. Contents
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What is pulsed light (PL) technology
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Mechanism involved in destruction of
micro organism by PL
Factors effecting the efficiency of PL system
Applications of PL technology for food processing
Case study

3. Introduction
Food processing is the transformation of raw
ingredients, by physical or chemical means into
food, or of food into other forms
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4. With the increase in consumer awareness, demand for minimally
processed foods and eco friendliness is increasing day by day
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The conventional thermal preservation and processing techniques appears adversely
affecting the food quality, organoleptic properties and nutrients
Food processing
Thermal processing Non thermal processing

5. Non thermal processing
• Producing fresh like foods by replacing thermal treatments
• Produces minimally processed food with fresh quality and
higher nutritive value with retention of colour and flavour
-High hydrostatic pressure (HHP)
-Ultrasound processing
-Irradiation
-Pulsed electric field
- PULSED LIGHT
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6. Pulsed light technology
Pulsed Light (PL) technology is an innovative method of
purification and sterilisation of food items by using very high-power
and very short-duration pulses of light emitted by inert gas flash
lamps
This technique has received several names in the scientific literature:
Pulsed UV light, high intensity broad-spectrum pulsed light,
pulsed light and pulsed white light
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7. Pulsed Light
Emits broadband radiation that ranges
from 100-1100 nm
PL technology involves accumulation of
electromagnetic energy in the capacitor
during fraction of seconds followed by its
release in the form of light within a short
time nanoseconds to milliseconds
Applying in order to kill bacteria, yeasts,
molds, and viruses
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8. Development of PL technology
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1970
Inert-gas flash
lamps generating
intense and short
pulses of UV for
microbial
inactivation in
Japan
1984
First patented by
Hiramoto
(US Patent 4464996)
Later rights
purchased by
Purepulse
technologies
1989
Development of
broad spectrum
PL technology
Patented as
PureBright
(US Patent4871559)
1996
PL has been
approved by
the FDA and
adopted in food
industry

9. PL terminologies
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Fluence rate : It is the energy received from the lamp by the sample per unit area per second.
Its unit isWatt/meter2 (W/m2)
Pulse width : It is the time interval (fractions of seconds) during which energy is delivered
Exposure time : It is the time period in seconds during which treatment is given
Peak power : It is measured as pulse energy divided by the pulse duration. Its unit isWatt (W)
Pulse-repetition-rate (prr): It is the number of pulses per second (Hertz [Hz]) or commonly
expressed as pps (pulses per second)
Fluence / Dose : It is the energy received from the lamp by the sample per unit area during
the treatment. Its unit is Joule/meter2 (J/m2)

10. Target
Electric pulse forming
(switches)
Pulsed light source
(inert gas flash lamps)
Electric energy storage
(capacitors)
Electric energy supply
(convertor)
Line
High power pulsed light
High power high – voltage high DC pulsed electric current
Low- Power high-voltage high DC continuous electric current
Low power low-voltage low AC continuous electric current
Low power high voltage low DC continuous electric current
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High
voltage
power
supply
capa
citor Flash lamp
Sample
Pulse shaping device
Pulsed Light system components

11. Pulsed light generation
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High voltage application the gas inside the flash lamp
undergoes ionisation
These broad spectrum photons are targeted t
samples
High-current electrical pulse and plasma formation takes place
near the anode by the electrons travelling towards it
The electrons while jumping back to their lower energy
levels, release quanta of energy producing photons
A very large current pulse formation occurs and this is sent
through the ionised gas
Excitation of the electrons surrounding the gas atoms,
causing them to jump to higher energy levels

12. x
d
Incident radiation E0 Reflected radiation rE0
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Transmitted energy Ex
Absorbed energy Ed
PL interaction with food material

13. Contd…
According to the Beer- Lambert law The energy E(x) of light transmitted to a distance
x below the surface of a material body decreases with x
E(x) = (1 - r) E0 e-[α]x
Where
E(x)= Energy of light transmitted
r= Reflection coefficient
α= Extinction coefficient
which measures the transparency or the opacity
of the material for each given λ
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14. The energy Ed absorbed by a layer of depth d below the distance x is:
Ed = E(x) [1 – e-[α]d ]
The absorbed light energy is generally dissipated as heat, resulting in a
temperature increase equal to:
∆T=Ed / ρ Cp Ad
where ρ and Cp are the density and the specific heat of the material and A is the
surface area
Contd…
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15. Microbial inactivation
The lethality of Pulsed Light attributed to its rich broad spectrum ultraviolet content, its
short duration, high peak power and the ability to regulate the pulse duration
The inactivation of micro organism includes several mechanisms such as
Photo chemical mechanism – Due to UV region in PL
Photo thermal mechanism –Temperature increment
Photo physical mechanism – Due to pulsing effect
Generally photo chemical and photo thermal mechanism acts simultaneously to create a
required microbial reduction
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16. Photo chemical mechanism
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Attributed to UV components of
pulsed light.
UV-A:Long wave (320-400 nm)
UV-B:Medium wave (280-320 nm)
UV-C: Short wave (200-280 nm)
UV light damages the bacterial DNA by
forming thymine dimers, leading to cell
death or spore inactivation.

17. Photo thermal mechanism
• The energy of light pulses penetrate through a food product is absorbed
by the layers nearest to the surface and dissipated as heat, causing in
such thin layers a certain increase in temperature
• Microbial cells have a higher absorption of the pulsed light than that of
the surrounding medium (water), which causes a localized rapid heating
of microorganisms
• Very high pulse power values can reach temperatures sufficient to cause
their overheating, rupture and death
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Takeshita et al., 2003
. TEM of S. cerevisiae. (a) Unirradiated, (b) irradiated with two flashes pulsed light at 0.7 J/cm2/flash and three flashes a 0.7
J/cm2/flash(c), (d) irradiated with UV light (3 s at 60 mW/cm 2/s).

18. Photo physical mechanism
Photo physical effect due to pulsing effect of high
intensity light
The high intensity pulses cause membrane damage,
vacuole expansion, elution of protein and structural
damages in micro organisms
The microbial damages are similar to PEF system
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Ramos-Villarroel et al., 2012
TEM micrographs of (a) E. coli cells from untreated fresh-cut mushrooms (b) fresh-cut mushrooms treated with 6
J/cm2 full spectrum and (c) treated fresh-cut mushrooms with 12 J/cm2 full spectrum (cells with alteration of
cytoplasmic content and cell wall) at 0 day of processing.

19. Design parameters
PULSED LIGHT SYSTEM
PARAMETERS
Light pulse intensity
 Pulse number and duration
 Light spectral composition
 Light source positioning
 Distance to the sample
SAMPLE PARAMETERS
Sample thickness
Initial microbial population
Optical characteristics
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20. Fluence rate
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Impact of the number of light pulses and total fluence on L.
innocua inactivation in a flow-through unit.
Fluence rate
TemperatureMicrobial
reduction
Temperature increment during PL treatment
(Parato et al., 2011)Innocente et al., 2014

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Effects of thickness of sample & Distance from the
light source on PL

22. The quantitatively distribution of light dose inside a
substrate is described by the term Optical
penetration depth
Optical penetration depth represents the distance
over which light decreases in fluence rate to 37% of
its initial value
Impact of the thickness and flow rate on L. innocua
inactivation in a flow-through unit.
Artíguez et al., 2011
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Influence of distance from the light source (cm) in the
inactivation of E. coli at a thickness of 15cm from the lamp
Preetha et al., 2017

23. Effects of PL on nutritional properties
• Pulsed light treatment did not show any sever adverse effect on quality
of product
• Inactivation of enzymes reduce oxidation and browning effects
• Some products showed enhanced anti oxidant and polyphenol content
after PL treatment
• UV treatments reported reduction of vitamin C content whereas PL
treatment did not cause higher reduction
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24. Applications of PL technology
 Surface decontamination
Packaging material sterilisation
Food equipment sterilisation
Sterilisation of egg shells, fruits and vegetables
Microbial inactivation in water, milk and fruit
juices
Pulsed light treatment of meat product
Decontamination of food powders, seeds

25. Application of PL technology to solid foods
• Surface topography of solid foods
• Part of radiation absorbed on rough surface leads to reduction
of effectiveness
• Solid foods with simple surfaces leads to higher microbial
reduction
• On complex surfaces like meat PL is not effective
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26. 26
Pulsed light 2.1 J/cm2 death of
Salmonella cells on the surface
Slight increase in the temperature
10.5 J/cm2 did not cause penetration
of Salmonella cells to the egg contents
from the shell
Sensory qualities and functional
properties were not affected
Decontamination of egg surface
(Lasagabster et al., 2011)

27. Application of PL technology to food powders
Composition and colour of powder effects PL treatment
Coloured powder absorbs more PL radiation and will reduce the
effectiveness
Thermal effects occurring due to absorption of PL result in microbial
reduction
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28. System for surface inactivation of
microorganism
System consists of three components
I. Power source
II. Energy storage capacitor
III. Treatment chamber
Treatment chamber is of 250cm diameter and there are 8 xenon lamps
arranged on the periphery of the chamber, the distance between
the samples and the xenon lamps was 13.5 cm
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29. Pulsed Light treatment system for sea foods
System consists of
• Power supply
• Controller module
• Treatment chamber
• Cooling blower
The cooling blower used for removal
accumulated heat along with removal of bad
odour
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cheigh et al., 2013
treated untreated

30. Application of PL technology to Liquid foods
Increasing the solid content of product diminishes the PL
penetration
Liquid foods with high UV absorbance must be treated
as thin layer
With increase in number of UV absorbing components in
sample reduces effectiveness
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31. Continuous pulsed light system for fruit juices
• The system was developed by Dunn et al.
(1989) and it was patented as a system for
sterilisation of pumpable foods such as fruit
juices
• Sample passed through space present between
the inner cylinder and outer cylinder
• The inner cylinder contains the flash lamps,
outer cylinder is made of highly reflective
material in order to allow maximum light
through the food
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32. Decontamination of food processing equipments
• Surface topography effects the PL treatment
• Smoothest finish surfaces are not suitable for PL
treatment
• Highly hydrophobic and reflective nature leads to cell
clustering
• Stainless steel knife surface contacting meat infected
with Listeria monocytogenes and Escherichia coli O157:H7
showed a highest effectiveness of inactivation of 6.5 log
colony forming units (CFU)/side of knife
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(Rajkovic et al., 2010)

33. Decontamination of packaging materials
• PL treatment depends on nature of packaging material and type of
microorganism
• Packaging material should be chemically stable (should not undergo
depolimarisation)
• The material should be transparent in order to allow the light to pass
into the food
• Packaging system does not require high melting temperature for
heat seal
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34. Surface sterilisation systems for packaging
material
STERILISATION OF FLEXIBLE
FILMS STERILISATION OF
CONTAINERS
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35. 35

36. Pulsed light
• The wavelength ranges between (110-1100 nm)
• Produce a peak power distribution as high as 35
MW.
• Reduced temperature build up due to short pulse
duration and cooling period between pulses.
• Better penetration depth and high emission power.
• Total absence of photo reaction after treatment.
• More effective and rapid for microbial inactivation.
• Limited oxidation reaction.
• Flash lights are used for light generation.
Ultraviolet radiation
• The wavelength ranges between 200-400 nm.
• Power emission ranged from 100 to 1,000 W.
• Accumulation of heat during continuous
treatment.
• Poor penetration depth and low emission power.
• Possibility of photoreaction after treatment.
• Effective microbial inactivation.
• Possibility of oxidation reaction.
• Mercuric vapour lamps are used for UV generation.
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37. Limitations of PL system.
• Generally for non transparent media pulsed light can only
be used as a surface treatment for first 2μm
• Limited efficiency for controlling food heating
• Limited efficiency due to shadow effect and shielding effect
• Foods with rough or uneven surfaces, crevices or pores
unsuitable for PL treatment
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38. Case study I
• Title: The role of pulsed light spectral distribution in the inactivation of Escherichia coli
and Listeria innocua on fresh-cut mushrooms
• Authors: AnaY. Ramos-Villarroel, Nicoleta Aron-Maftei, Olga Martín-Belloso, Robert
Soliva-Fortuny
• Journal: Journal of food control, year 2012, volume 24, 206-213
• Objectives:
To determine the spectral range of pulsed light (PL) treatments causing microbial
inactivation and its effect on quality of fresh-cut mushrooms (Agaricus bisporus)
inoculated with E. coli or L. innocua
To study the effect responsible for their action on bacterial cells using Transmission
Electron Microscopy (TEM) was also studied
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39. Materials and methods
• Microbiological analysis
• Changes in colour values
• Transmission Electron Microscopy (TEM) 39
Pulsed light treatments:
Filter Wavelength range
2-mm thick Pyrex glass filter (PF) without UV-C light
(305-1100 nm)
Makrolon polycarbonate plastic filter
(MF)
VIS-NIR light
( 400-1100 nm)
Without any filter Full spectrum
( 180-1100 nm)

40. Results
Influence of light spectral composition on the counts of 1. E. coli (Log cfu/g), 2. Listeria innocua in PL- treated
fresh-cut mushrooms (A: 6 J/cm2; B: 12 J/cm2) stored at 5ºC during 15 days. FS (180-1100 nm), PF (305-1100 nm)
and MF (400-1100 nm). 40
Microbiological analysis

41. Changes in L* colour value
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Influence of light spectral composition on changes in lightness
(L*) of PL-treated fresh-cut mushrooms (A: 6 J/cm2; B: 12
J/cm2)
12j/𝐶𝑀2
6j/𝐶𝑀2

42. Transmission Electron Microscopy (TEM)
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Transmission electron microscopy micrographs of (a) L. innocua /E. coli cells untreated from fresh-cut mushrooms (undamaged
cells), (b) fresh-cut mushrooms treated with 6 J/cm2 full spectrum (damage cell slight) and (c) fresh-cut mushrooms treated with 12
J/cm2 full spectrum (cells with alteration of cytoplasmic content and cell wall) at 0 day of processing.

43. Conclusion
The use of PL treatments has found effectiveness against the two tested microorganisms but in
different degrees. High fluencies (12 J/cm2) were required to reduce in more than 3 and 2 log cycles
the population of E. coli and L. innocua respectively
The bacterial inactivation and quality parameters were dependent mainly on the UV component of
the PL spectrum (especially UV-C light). Thus, NIR or VIS wavelengths did not have a quantifiable
effect on the overall microbial inactivation
TEM studies showthat PL treatments affect E. coli and L. innocua cells generating an agglutination
of cytoplasmic content with disruption of cell membrane, which leads to microbial death
This work is a contribution to understanding the specific mechanisms of bacterial inactivation.
Results suggest that the photophysical effect exists and is part of the mechanism of bacterial
inactivation caused by PL treatments
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44. Case study-II
• Title: Bacterial inactivation in fruit juices using a continuous flow Pulsed
Light (PL) system
• Authors: G. Pataro , A. Munoz , I. Palgan , F. Noci , G. Ferrari , J.G. Lyng
• Journal: Food Research International , volume-44, pages: 1642–1648, year
2011
• Objectives:
 This experimental study deals with microbial inactivation by PL in a
continuous flow system.
It aims at investigating the lethal and effects of PL treatments depending
on the energy dose and absorption properties of two different fruit juices
inoculated with a Gram-positive and a Gram-negative bacterial strain.
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45. Materials and methods
Flow rate
(ml/min)
Residence
time(s)
Number
of pulses
Energy
doses(J/cm2)
38.4 0.49 1.5 1.8
27.0 0.70 2.1 2.5
20.8 0.91 2.7 3.3
17.0 1.11 3.3 4.0
13.4 1.41 4.2 5.1
12.5 1.51 4.5 5.5
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Developed PL system Treatment combination
ST- stirrer, US-un treated sample, P- Pump, WIB-Water ice bath, SC- sterilisation chamber, XL- Xenon lamp, QT-
Quartz tube, ML- Metal enclosure, CS- Cooling system, CM- Power control module, Ts- Treated sample, DL- Data
logger, PC-computer

46. Results
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Variation in sample temperature
Steady state profiles of the temperature increase of the fruit juice (●) and the air surrounding the quartz
tubes inside the chamber (○) as a function of the energy dose in the presence of the cooling system
Typical profiles of the temperature increment in orange juice obtained with (dashed
lines) and without (solid line) cooling as a function of the running time of the
PL sterilisation system

47. Bacterial inactivation in apple and orange juices
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Inactivation curves of E. coli DH5-α
in apple (●) and orange juice (▼)
and of L. innocua 11288 in apple (○)
and orange juice (Δ) as a function of
the energy dose .

48. Conclusion
• The temperature of both the juice and air inside the sterilisation
chamber may increase significantly during processing, unless an
efficient cooling system is incorporated into the equipment.
• PL treatment can be successfully applied to obtain high levels of
destruction with respect to the selected food borne pathogens and the
treatment efficiency strongly depended on the energy dose that is
actually absorbed by the microorganisms.
• The occurrence of sublethally injured cells after PL treatment.
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49. References
• Aguero, M.V., Jagus, R.J., Martin-Belloso, O., and Soliva-Fortuny, R. 2016. Surface decontamination of
spinach by intense pulsed light treatments: Impact on quality attributes. Postharvest Biol. Technol. 121:
118–125.
• Artíguez, M.L., Lasagabastera, A., and Marañón, I.M. 2011. Factors affecting microbial inactivation by
Pulsed Light in a continuous flow-through unit for liquid products treatment. Proc. Food Sci. 1: 786-791.
• Cheigh, C., Park, M., Chung, M., Shin, J., and Park, Y. 2012. Comparison of intense pulsed light and
ultraviolet (UC-C)-induced cell damage in Listeria monocytogenes and Escherichia Coli O157:H7. Food
Cont. 25: 654-659.
• Dunn, J.E., Clark, W.R., and Asmus, J.F. 1989. Methods for preservation of foodstuffs. Maxwell
Laboratories Inc., San Diego, USA. US Patent 4871559.
• Innocente, N., Segat, A., Manzocco, L.M., Marino, M., Maifreni, I., Bortolomeoli, A., Ignat, and Nicoli,
M.C. 2014. Effect of Pulsed light on total microbial count and alkaline phosphatase activity of raw milk.
Int. Dairy J. 39: 108-112.
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50. • Manzocco, L., Panozzo, A., and Nicoli, M. C. 2013. Inactivation of poliphenoloxidase by pulsed light. Food Eng. Phys. Prop.
78:183–187.
• Lasagabster, A., Arboleya, J.C., and Martinez, D.M. 2011. Pulsed light technology for surface decontamination of eggs, Impact
on Salmonella inactivation and egg quality. Innov. Food Sci. Emerg.Technol. 12 (2): 124-128.
• Parato, G., Munoz, A., Palgan, I., Noci, F., Ferrari G., and Lyng, J.G. 2011. Bacterial inactivation in fruit juices using a
continuous flow pulsed light (PL) system. Food Res. Int. 44: 1642-1648.
• Preetha, P., Varadharaju, N., Kennedy, Z.J., Malathi, D., and Shridar, B. 2016. Non-thermal Inactivation of Escherichia coli in
Pineapple juice by Pulsed LightTreatment. InternationalJ. Food Ferment.Technol. 6(1): 57.
• Takeshita, K., Shibato, J., Sameshima, T., Fukunaga, S., Isobe, S., Arihara, K., and Itoh, M. 2003. Damage of yeast cells induced
by pulsed light irradiation. Int.J. Food Microbiol. 85:151-158.
• Rajkovic, A., Tomasevic, I., Smigic, N., Uyttendaele, M., Radovanovic, R., and Devlieghere, F. 2010. Pulsed ultraviolet light as
an intervention strategy against Listeria monocytogenes and Escherichia coli O157:H7 on the surface of a meat slicing knife. J.
Food Eng. 100: 446-451.
• Ramos-Villarroel, A.Y., Aron-Maftei, N., Martın-Belloso, O., and Soliva-Fortuny, R. 2012. The role of pulsed light spectral
distribution in the inac- tivation of Escherichia coli and Listeria innocua on fresh-cut mushrooms. Food Cont. 24: 206–213.
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