1. Technical seminar on
Light-Emitting Diodes (LEDs) in Post
Harvest Quality Preservation
By
Thongam Sunita, Shaghaf Kaukab, Th. Bidyalakshmi Devi, K.
Bembem
ICAR-Central Institute of Post Harvest Engineering & Technology, Ludhiana,
Punjab-141004
1
2. Contents
• Introduction
• LED fundamentals
• Advantages and disadvantages
• Mechanism of microbial inactivation
• Applications
• LED treatment units
• Conclusions
2
3. Introduction
• Light-emitting diode (LED) technology is nonthermal
food processing technique
• It utilizes light energy with wavelengths from 200-780 nm
• LED technology has shown antimicrobial efficacy in food
systems
3
Fig.1 Electromagnetic spectrum
4. 4
Introduction (contd.)
• LED is used as a highly efficient ultraviolet (UV)
decontamination technology
• UV-LEDs emit monochromatic light enabling customised
UV-LED disinfection systems
Fig. 2 Ultraviolet sub-divisions and applications
5. 5
Introduction (contd.)
• LEDs are an alternative source of ultraviolet (UV) light
• LEDs are used in agriculture and food industry
• LEDs offers high performance, robustness, long lifetime
(> 50,000 h), low power use and cost effectiveness
Fig.3 LED treatment of carrot
(Source: https://www.foodonline.com/doc/germicidal-leds-a-viable-light-source-for-food-
safety-0001. Accessed on 11/10/2020)
6. LED Fundamentals
• Light-emitting diode (LED): semiconductor device that emits light
when current flows through it.
6
Fig. 4 Components of (a) conventional dual-in-line package and (b) modern high-power LED
7. LED Fundamentals (contd.)
7
Fig. 5 Working principle of an LED
• Principle of working : electroluminescence (emission of light upon
application of an electric or a magnetic field)
8. LED Fundamentals (contd.)
•Different semiconductor materials emit different colours (wavelength) of
light
8
Fig. Electronic symbol
Fig. 6 Types of LED
9. LED Fundamentals (contd.)
9
Table 1: Semiconductor of LEDs emitting light of different wavelengths
GaAs:Gallium arsenide; AlGaAs:Aluminum gallium arsenide; GaAsP:gallium arsenide
Phosphide; AlGaInP:aluminum gallium indium phosphide; GaP:gallium phosphide;
InGaN:Indium gallium nitride; SiC:silicon carbide; AIN:Aluminum nitride;
AlGaN:aluminum gallium nitride; AlGaInN: aluminum gallium indium nitride;
C:Diamond
Semiconductor Wavelength (nm) Color
GaAs, AlGaAs > 760 Infrared
AlGaAs, GaAsP, AlGaInP,
GaP
610–760 Red
GaAsP, AlGaInP, GaP 590–610 Orange/ amber
GaAsP, AlGaInP, GaP 570–590 Yellow
GaP, AlGaInP, AlGaP 500–570 Green
InGaN, SiC 450–500 Blue
InGaN, 400–450 Violet
AlN, AlGaN, AlGaInN, C 200-400 Ultraviolet
10. LED Fundamentals (contd.)
• Irradiance (I) of the LED: radiant power exposed to unit
surface area of the sample
• Energy dose (E): product of the irradiance and the exposure
time (t)
E (mJ/cm²)= I (mW/cm²) × t (s)
• Photon Flux: No. of photons received per unit area per
second (µmol mˉ²sˉ¹ or µE mˉ²sˉ¹)
10
11. 11
Advantages and Disadvantages of LED
Advantages
• Long lifetime (50,000 to 100,000 hours)
• High luminous efficacy
• Energy efficient
• Negligible heat emission
• No warm-up time
• Shock resistance
• Smaller size (< 2mm²)
• Directional light emission
• Various color of light
Disadvantages
• Expensive than other lighting technologies
• Requires accurate voltage and constant current flow
12. 12
Mechanism of inactivation
• LED produce photodynamic inactivation due to
photosensitization of light absorbing compounds
Fig. 7 Effect of LED treatments on bacteria
(Reactive oxygen species)
damage
13. 13
Applications
• Delay of Senescence in Vegetables
• Accelerating ripening
• Delaying of ripening
• Enhancing or delaying loss of nutritional content
• Preventing food spoilage
• Surface disinfection
14. 14
Table 2: Inactivation of food pathogens using UV LEDS
Food
pathogen
Wavlen
gth
(nm)
Treatme
nt media
Irradianc
e (mW
cmˉ²)
UV
fluence
(mJ
cmˉ²)
Log
count
reductio
n
Referenc
es
Escherichi
a coli
DH5α
365 Cabbage
tissue
125 675000 3.23 Aihara
(2014)
Listeria
monocytog
enes
271 Sliced
cheese
surface
0.004 3.0 3.94 Kim
(2016)
Salmonella 395 Wheat
flour
- 1199000 3.67 Samir et
al. (2020)
15. UV-LED unit
15
Fig.8 Schematic view of experimental set-up (Samir et al., 2020)
• Wavelength range
(nm): 275, 365,395 &
455
• Distance between
sample & LED head:
2 cm
•Treatment time:
30min
16. 16
Light emitting diode (LED) illumination system
Fig. 9 Schematic diagram of 405 ± 5-nm illumination system (Kim et
al.2017a) (Housing: Acrylonitrile butadiene system)
Salmonella Enteritidis in phosphate buffered
saline
• 1.4–2.1 log CFU/ml , 0.45 kJ/cm2 (for 7.5 h)
• 1.58–3.80 kJ/cm2 (for 20–48 h)
• 0.8–0.9 log CFU/cm2 at 3.80 kJ/cm2,
4°C
17. 17
Table 3: Blue Light LEDs for microbial inactivation
Organism Wavelength
(nm), Dose
(kJ cmˉ²)
Treatment
media
Log count
reduction
References
Escherichia coli 460 nm,
(10W),
3.8°C, 37.8
min
Milk >5 Srimagal
et al. (2016)
Salmonella spp. 405 nm
1.3-1.7 kJ
cmˉ²
36-48 h, 4°C
Fresh-cut
papaya
1.3 Kim et al.
(2017b)
Escherichia coli
Staphylococcus
aureus
462±3 nm
0.013 kJ
cmˉ²
Photosensitizer
Curcumin
5.91 Bhavya et al.
(2019)
18. 18
Light emitting diode (LED) illumination system
Fig.10 Schematic diagram of the batch type LED experimental set up
(Srimagal, Ramesh and Sahu, 2016)
19. UV-LED unit for treatment of L. monocytogenes on
the surface of apple and lettuce
19
Fig 11. Schematic diagram (A) and photo of the custom UV LED unit (B) (Aquisense,
KY) (Koutchma & Popovic, 2019).
• 18 UV-C LED (277nm)
• 2 circular chips (9 LEDs each)
20. 20
Table 4: LEDs in delaying of senescence in vegetables
Food LED
(wavelength)
Intensity Treatment
time
Effectiveness References
Broccoli
(Brassica
oleracea)
White and blue
LED
20 μmol
mˉ²sˉ¹
Continuous Generally higher
chlorophyll, carotenoid,
fructose, glucose, and
sucrose content
compared to dark control
Hasperué
et al.
(2016)
Lettuce
(Lactuca
sativa)
Red (660 nm)
and Blue
(455 nm)
5 μmol
mˉ²sˉ¹
Continuous Overall visual quality was
rated unacceptable
after 15 d for butterhead
lettuce irradiated with
red and blue LEDs and 19
d for iceberg lettuce
irradiated with blue LED
Woltering
and Seifu
(2015)
21. 21
Table 5: LEDs in accelerating ripening processes
Food LED
(wavelength)
Intensity Treatment
time
Effectiveness References
Strawberrie
s (Fragaria
ananassa)
Blue (470 nm) 40 μmol
mˉ²sˉ¹
Continuous Increase in ethylene
production, respiration,
color development, total
antioxidant activity,
and antioxidant enzyme
activity
Xu et al.
(2014)
Peach
(Prunus
persica)
Blue (470 nm) 40 μmol
mˉ²sˉ¹
Continuous Increase in ethylene
production, total soluble
solids content, color
development, and
decrease in firmness,
titratable acidity
Gong et al.
(2015)
22. 22
Table 6: LEDs in accelerating ripening processes (Contd.)
Food LED
(wavelength)
Intensity Treatment
time
Effectiveness References
Satsuma
mandarins
(C. unshiu)
Red (660 nm) 12 μmol
mˉ²sˉ¹
Continuous Acceleration of color
development in the rind
of irradiated fruit
compared to those stored
in the dark
Yamaga et
al. (2016)
Fig.12 Experimental setup of blue LED irradiation in vitro (left) and in vivo (right)
23. 23
Table 7: LEDs in Delaying of ripening
Food LED
(wavelength)
Intensity Treatment
time
Effectiveness References
Mature green
tomatoes
(Solanum
lycopersicum)
Blue (440–
450 nm)
85.7 μEmol
mˉ²sˉ¹
Continuous A slower rate of color
change from green to
red and more firmness
observed compared to
red light
Dhakal and
Baek
(2014)
Fig.13 Color changes in mature green tomatoes with darkness and
continuous irradiation of blue and red light.
24. 24
Table 8: LEDs in Enhancing or delaying loss of postharvest nutritional content
Food LED
(wavelength)
Intensity Treatment
Time
Effectiveness References
Peach
(Prunus
persica)
Blue (470 nm) 40 μmol
mˉ²sˉ¹
Continuous Greater total carotenoid,
zeaxanthin and
b-carotene, b-
ryptoxanthin, and lutein
content compared to dark
control after 20 days
Cao et al.
(2017)
25. 25
Conclusions
• Food chiller equipped with LEDs can preserve fresh-cut fruits
• LEDs can replace the fluorescent lights
• Capability to design customised UV reactors
• Environmental friendly solutions to save energy, water, reduce
costs, lower reliance on toxic chemicals and improve safety
• Extend fruit and vegetable shelf life
• UV LEDs present a new technological solution for control
of pathogens and spoilage
26. 26
References
• Kim MJ, Ng BXA, Zwe YH, Yuk HG (2017a) Photodynamic inactivation of Salmonella
enterica Enteritidis by 405 ± 5-nm light-emitting diode and its application to control
salmonellosis on cooked chicken. Food Control 82:305–315
• Kim MJ, Bang WS, Yuk HG. (2017b). 405 ± 5 nm light emitting diode illumination causes
photodynamic inactivation of Salmonella spp. on fresh-cut papaya without deterioration.
Food Microbiol 62:124–132.
• Josewin SW, Ghate V, Kim MJ, Yuk HG (2018) Antibacterial effect of 460 nm light-emitting
diode in combination with riboflavin against Listeria monocytogenes on smoked salmon.
Food Control 84:354–361.
• Moretti, C., Tao, X., Koehl, L., & Koncar, V. (2016). Electrochromic textile displays for
personal communication. In Smart Textiles and their Applications (pp. 539-568). Woodhead
Publishing.
• Subedi, S., Du, L., Prasad, A., Yadav, B., & Roopesh, M. S. (2020). Inactivation of Salmonella
and quality changes in wheat flour after pulsed light-emitting diode (LED) treatments. Food
and Bioproducts Processing, 121, 166-177.
27. 27
References
• Gupta, S. D., & Agarwal, A. (2017). Light Emitting Diodes for Agriculture (pp. 273-303).
Singapore: Springer.
• Woltering EJ, Seifu YW (2015) Low intensity monochromatic red, blue or green light
increases the carbohydrate levels and substantially extends the shelf life of fresh-cut
lettuce. Acta Hortic 1079:257–264.
• Gong D, Cao S, Sheng T (2015) Effect of blue light on ethylene biosynthesis, signalling and
fruit ripening in postharvest peaches. Sci Hortic 197:657–664.
• Dhakal R, Baek K-H (2014b) Short period irradiation of single blue wavelength light
extends the storage period of mature green tomatoes. Postharvest Biol Technol 90:73–77
• Yamaga I, Shirai Y, Nakajima T, Kobayashi Y (2016) Rind color development in satsuma
mandarin fruits treated by low-intensity red light-emitting diode (LED) irradiation. Food Sci
Technol Res 22:59–64
