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Decontamination of Foods by Pulsed Ultraviolet Light
Ali Demirci Department of Agricultural and Biological Engineering, The Pennsylvania State University, University Park, PA 16802
PULSED UV-LIGHT BASICS
ABSTRACT Pulsed Ultraviolet (UV)-Light is an emerging technology, which has a potential to be used for decontamination food products. The recent studies suggest pulsed UV light inactivates microorganisms not only by photo-chemical reactions, but also by other mechanisms associated with the use of high intensity pulses such as photo-thermal and photo-physical mechanisms, Microbial cells become inactive with conventional UV induced photochemical reactions have taken place, but the cell structures remain intact after UV treatment. However, pulsed UV light also damages the cell structures for some of the pulsed UV treated cells. Therefore, pulsed UV-light can be considered a powerful tool for inactivation of microorganisms on food surfaces or liquids. Many studies have demonstrated the effectiveness of pulsed UV-light on microbial loads on food surfaces. In our lab, various studies have been performed for the applications of pulsed UV-light treatment including fruits, poultry products, hard cheeses, pure water, and wastewater.
ACKNOWLEDGEMNENT The research presented here was funded in part by Penn State Experiment Station, USDA Special Research Grants, U.S. Highbush Blueberry Council, Pennsylvania Poultry Check-off Program and The Scientific and Technological Research Council of Turkey (TUBITAK). Special thanks to XENON Corporation (Wilmington, MA) for providing technical assistance for the pulsed UV systems used for these projects.
PULSED UV STUDIES AT PENN STATE Inactivation of Staphylococcus aureus
Electrical energy compressed into short pulses > pulsed light emitted
Spectrum range: deep UV – infrared (100-1100 nm) Rich and efficient in the UV<400 nm
(germicidal) Consists of short light pulses
delivered by Xenon gas lamp Pulse duration: a few hundred
microseconds Inactivates pathogens in very short
time. Approved by FDA in 1999 (Federal
Register, 1999).
INTRODUCTION Pulsed ultraviolet (UV) light is a novel technology, which offers effective inactivation of pathogens on the food surfaces in very short periods of time. Basically, pulsed UV-light lamp produces a continual broadband spectrum from the deep UV to infrared, which are emitted as very short light pulses. These pulses involve UV-light below 400 nm, which is germicidal. Pulsed UV-light does not involve chemicals, and is safer and more efficient than conventional continuous UV-light. Pulsed UV-light may be utilized for the inactivation of microorganisms on raw and minimally-processed foods because this technology is considered to be a non-thermal for short processing times. It is also considered to be an alternative decontamination technique to irradiation. In 1999, pulsed light treatment of food was approved by FDA.
Decontamination of small fruits
Effect of Depth on Energy Dose and Inactivation in agar and denatured whey protein isolate (DWPI) gel
Pulsed UV-Light Systems
Control panel
sample
UV lamp
Cooling air
UV chamber
XENON SteriPulse-XL®3000
Quartz glass separation
UV lamp
Annular space for test liquid (Water)
Water Inlet
Water outlet
Flow-Through System
Static System
XENON Steripulse® -RS 4000
Commercial Pulsed UV System
XENON Alfa®
Photo-chemical effect: UV-light component forms thymine dimers (Bank et al., 1990; Jay, 1997; Miller et al., 1999)
Photo-thermal effect:
Visible and infrared portion of the pulsed UV-light cause localized heating of the bacterial cell (Fine and Gervais, 2004)
Photo-physical effect:
Constant physical disturbances due to the pulses result in structural damages on cell (Krishnamurthy et al., 2007)
INACTIVATION MODES
S. aureus after a 5-s treatment with pulsed UV-light
Untreated S. aureus
Effects of pulsed UV-light treatment on S. aureus after 5-s treatment with pulsed UV-light
A. untreated S. aureus B. cell wall rupture C. lack of cell wall D. cytoplasm shrinkage and damage on cell wall E. cytoplasm shrinkage and membrane damage F. cell wall damage and cellular content leakage
Krishnamurthy, K., S. Jun, J. Irudayaraj, and A. Demirci. Food Bioprocess Technol. 3:93–104 (2010)
Krishnamurthy, K., A. Demirci, and J. Irudayaraj. J. Food Prot.67:1027-1030 (2004)
0.00
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0 5 10 15 20 25 30Time (sec)
log 1
0 CFU
/ml r
educ
tion
12 ml24 ml48 ml
0.00
1.00
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0 5 10 15 20 25 30Time (sec)
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0 CFU
/ml r
educ
tion
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0 5 10 15 20Time (sec)
Tem
pera
ture
(o C)
Phosphate buffer - 12 ml
Baird parker agar
00.10.20.30.40.50.60.70.80.9
1
0 2 4 6 8 10 12
Agar Depth (mm)
Ener
gy (J
/cm
2 /s)
0.00%
10.00%
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60.00%
% D
eclin
e
00.10.20.30.40.50.60.70.80.9
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0 2 4 6 8 10 12
DWPI Depth (mm)
Ener
gy (J
/cm
2/s)
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eclin
e
Reduction of E. coli O157:H7 on Blueberries Reduction of Salmonella on Strawberry
5 10 30 45 6013cm
5cm0.000.501.001.502.002.503.003.504.004.50
Log10
Reduction
Time (s)
13cm8cm5cm
Velocity (cm/min)
Log Reduction of E. coli
(CFU/ml rinse solution)
78 (30-s) 0.87 52 (45-s) 0.96 39 (60-s) 1.00 26 (90-s) 1.17 20 (120-s) 1.31 13 (180-s) 1.43
0
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0 5 10 15 20 25
Log
Red
uctio
n (C
FU/m
l)
Flow Rate (L/min)
E. coli
B. subtilis
% Removal Turbidity SS COD TOC
E. coli (10 L/min)
20.0 57.8 49.5 16.3
B. subtilis (6 L/min)
12.5 39.3 41.4 7.0
Raw w. water (10 L/min)
50.5 55.8 79.8 35.0
-4-3.5
-3-2.5
-2
-1.5-1
-0.50
0 20 40 60 80 100 120
Treatment Time (s)
log 1
0(S)
2 mm4 mm6 mm8 mm10 mm
Agar -1
-0.8
-0.6
-0.4
-0.2
00 20 40 60 80 100 120
Treatment Time (s)
log 1
0(S)
2 mm4 mm6 mm8 mm10 mm
DWPI
Bialka, K.L., P. N. Walker, V. M. Puri, and A. Demirci. Transactions of the ASABE. 51: 195-204 (2008)
Decontamination of Poultry Carcass
Decontamination of Pure Water and Municipal Wastewater Effluent
Flow meter
Blower for cooling
Pump
Inlet
Outlet Control Unit
Flow adjustment valve
Flow rate (L/min)
B. subtilis (Log CFU/ml)
Growth after enrichment
0 5.5 – 6.5 Yes
2 0 No 4 0 No 6 0 No 8 0 No
10 0 No 14 0 No
Pure Water
Municipal Wastewater Effluent
Bialka K. L., A. Demirci. Journal of Food Science 72(9): M391-M396 (2007)
13
8
30.001.002.003.004.005.006.007.00
5 10 30 45 60
Log10 Reduction
Time
Bialka K. L., A. Demirci. Journal of Food Science 73(5):M201-M207 (2008)
Keklik, N. M., A. Demirci, and R. Bock. Transactions of ASABE. 54(3): 993-1000 (2011)
Demirci, A. and K. Krishnamurthy. Ultrapure Water Journal. 24 (1): 35-40 (2006)
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