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

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0 5 10 15 20 25 30Time (sec)

log 1

0 CFU

/ml r

educ

tion

12 ml24 ml48 ml

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

0 5 10 15 20 25 30Time (sec)

Log 1

0 CFU

/ml r

educ

tion

0

5

10

15

20

25

30

35

40

45

50

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%

20.00%

30.00%

40.00%

50.00%

60.00%

% D

eclin

e

00.10.20.30.40.50.60.70.80.9

1

0 2 4 6 8 10 12

DWPI Depth (mm)

Ener

gy (J

/cm

2/s)

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

% D

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

1

2

3

4

5

6

7

8

9

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)