Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Experimental Investigations of Microwave Plasma UV Lamp for Food Applications Montserrat Ortoneda*, Sinead O’Keeffe, Jeff D. Cullen, Ahmed I. Al-Shamma’a and David A. Phipps 1 RF and Microwave Group, General Engineering Research Institute, Liverpool John Moores University, Liverpool, L3 3AF, UK * [email protected] The food industry is keen to have new techniques that improve the safety and/or shelf life of food products without the use of preservatives. There is considerable interest in developing UV light and ozone (O3) treatments to enhance shelf life. A microwave radiation device that is a novel source of germicidal UV and O3 suitable for the food industry has been developed, which offers speed, cost and energy benefits over existing sources. With this system comes the need to monitor a number of conditions, primarily UV intensity and ozone gas concentrations. The effectiveness of intense UV exposure for short periods of time was assessed on different microorganisms. Culture plates were exposed to a range of doses of UV-C light, and the reduction in numbers of surviving microorganisms was recorded. The results on the biocidal capacity of the microwave generated UV light are presented. Submission Date: 17 January 2008 Acceptance Date: 1 August 2008 Publication Date: 4 November 2008 INTRODUCTION Each year the food distribution chain has an increased demand for fresh products such as minimally processed vegetables [Ragaert et al., 2004]. The economical losses related to highly perishable products such as fresh processed lettuce are substantial because this type of product is likely to lose quality during processing and distribution. Food producers and supermarkets are always looking for improved production methods allowing better preservation of these products and longer shelf lives [Corbo et al., 2005; Yahia et al., 1988]. At the same time, these treatments need to preserve, or even enhance the sensorial and nutritional qualities of the fresh product. Aspects such as general appearance, texture, off-odours, aroma, browning, colour and Keywords: Microwave plasma UV lamp, optical fibre, bacteria, food packaging International Microwave Power Institute taste are important for consumers, and therefore affect the sales of the products [Allende et al., 2004; Ragaert et al., 2004]. One of the main factors influencing the lifespan of fresh products is the microbial content of the product. Fresh fruits and vegetables normally carry non-pathogenic, epiphytic microflora. Although it does not represent a threat for human health, it can contribute to the shortening of the product’s lifespan [Corbo et al., 2005]. That is the reason why these products are routinely decontaminated using different protocols. On the other hand, these products can become contaminated with pathogens, occasionally. This contamination can occur during production on the farm (dirty irrigation water or use of raw manure), and also at any stage of product handling from harvest to point sale (washing, cutting, slicing, packaging) [James, 2006]. Minimally processed foods such as packaged 42-4-13 salads present specific challenges because cutting and slicing removes the natural protective barriers of the intact plant, thus accelerating the decay of the product [Allende et al., 2006]. Typical decontamination methods such as washing with hypochlorite or commercial surfactant formulations, have a limited success with only a 1 to 2-log reduction (90 – 99 % killing). Other methods such as washing with hydrogen peroxide reduce the microbial contamination by 3-logs (99.9 %) [Sapers et al., 2000]. Traditional detergents are known to be partially effective in removing pathogens, however each type of disinfectant varies both in efficiency and in allowable maximum concentration [Beuchat, 1998]. The use of a nonselective treatment for the destruction of pathogens on the surface of fresh fruits and vegetables that leaves no residue would be desirable. Ozone is one of several new sanitizing agents recently used in post harvest management systems [Xu, 1999]. It decomposes spontaneously to non toxic products and it can be used in combination with other disinfection treatments to reduce the presence of pathogenic and non pathogenic microorganisms in fresh products [Selma et al., 2007]. Modified atmosphere packaging (MAP) is another method that improves the environment of the food whilst preventing potential bacterial growth. Fruit, vegetables, salads, poultry, fish and red meat are just some of the food products that can benefit from a modified atmosphere. However, there is a major concern about the safety of foods packaged using MAP because it suppresses the growth of spoilage organisms, but it seems to have no effect on slow growing pathogenic bacteria such as Yersinia enterocolitica, Aeromonas spp. and Listeria monocytogenes. In this case, removing the spoilage microorganisms would favour the growth of the pathogenic ones when present in the product [Allende et al., 2006]. One alternative process is the use of germicidal ultraviolet light at a wavelength of 200–280 nm (UV-C), alone or combined with other treatments such as ozone, mild thermal treatements or MAP. Ultraviolet light is a non chemical disinfectant 42-4-14 system that uses an extremely rapid physical light energy of a specific wavelength to destroy microorganisms. The microwave plasma UV lamp (MPUVL) developed in a research project supported by the EU, is able to produce both UV light at the germicidal region (254 nm) and at the Ozone forming region (185 nm), simultaneously. The system has proven to have higher efficiency than both a conventional UV lamp and the low pressure electrical DC discharge lamp [Cullen et al., 2006]. Pathogens associated with fresh produce Epidemiologic evidence shows a relationship between some foodborne pathogens and specific food products. Numerous pathogens have been isolated from a variety of fresh fruits and vegetables. For example, Aeromonas hydrophila, A. caviae, Campylobacter jejuni, Clostridium botulinum, C. perfringens, Cryptosporidium parvum, E. coli O157:H7, Giardia lamblia, Listeria monocytogenes, Salmonella spp., Shigella spp., Staphylococcus aureus and Yersinia enterocolitica have been found in lettuce and mixed salads and have been associated with outbreaks in different countries [Archer and Young, 1988]. These microorganisms will affect people with a weak immune system, such as children and elderly people, and those with underlying diseases [McCabe-Sellers and Beattie, 2004]. The diseases caused by these pathogens range from self limited diarrhoea, abdominal pain and fever, to more serious diseases such as severe diarrhoea, kidney failure (caused by E. coli O157:H7), respiratory and musculoskeletal paralysis (caused by Clostridium) or meningitis, infection of the nervous system and miscarriages (caused by Listeria) [Archer and Young, 1988; Tauxe, 1997]. Use of UV light in food technology UV light has been used to sterilize a wide range of materials and surfaces for years [Andersen Journal of Microwave Power & Electromagnetic Energy ONLINE Vol. 42, No. 4, 2008 et al., 2006]. In the food industry it is used in a broad range of antimicrobial applications including disinfection of water, air, food preparation surfaces and containers [Wang et al., 2005]. The germicidal properties of UV irradiation are situated in the UV-C region of the spectrum (200-280 nm), and more specifically around 254 nm. This wavelength is absorbed by the nucleic acids (DNA and RNA) present in all living organisms and provokes the formation of pyrimidine dimers and other nucleic acid lesions. These lesions in the DNA and RNA inhibit replication and transcription and prevent the microorganism from multiplying [Hinjen et al., 2006]. UV light is effective against a wide range of microorganisms, including pathogens that do not respond to chlorine treatments in drinking water such as oocysts of Cryptosporidium and Giardia [Hingen et al., 2006]. Treatment with ultraviolet energy offers several advantages to available washing and sanitizing methods, as it does not leave a residue, have legal restrictions and does not require extensive safety equipment to utilize [Yousef and Marth, 1988]. The use of UVC light could be useful as a treatment step in HACCP protocols because it is effective at reducing microbial numbers on the surface of fresh fruits and vegetables [Yaun et al.,2004 , Allende et al., 2004, Allende et al., 2006, Gomez-Lopez et al., 2005] and can be applied in a continuous mode or in pulses to the food samples. Reducing the number of bacteria and other microorganisms is especially significant in the case of minimally processed products, where UV together with refrigeration and several modifications in packaging, including modified atmospheres, can play a very important role in increasing lifespan and decreasing the risk of food poisoning. Although high doses of UV-C radiation are harmful to plant tissues, low doses can help reduce the number of microorganisms that would cause spoilage and shorten the lifespan of the food product or could represent a health risk [Krishnamurti et al., 2004]. At the same time, this type of light induces a series of changes in International Microwave Power Institute the plant tissues as a defence mechanism against this type of radiation that can delay senescence in several types of fruits and vegetables [Erkan et al., 2001, Marquenie et al., 2003]. Germicidal kinetics The survival (S) of microorganisms when exposed to either UV or ozone is represented by two rates of decay, as shown in equations 1 and 2 [Koller, 1965]. This relationship is illustrated in Figure 1. S=C exp(-KD) for D <D0 S=C exp(-mD) for D<D0 (1) (2) The dosage D is the product of the UV or ozone intensity and duration (t) of exposure. There is an initial rapid rate of kill (k) to a level (1-C) and this is followed by a much slower kill rate (m). The value of C is of the order of 10-3. Figure 2 shows a comparison of the dosages (Do) required for UV, ozone and chlorine required to achieve a 99.9% kill level when compared with the dosage for the Escherichia Coli (E coli) in water. They show comparative responses with a range of microorganisms. The most likely explanation for the tailing off of the survival curves is the clumping effect suggested by various investigators, which is the tendency of micron-sized particles to clump together naturally. The clumping of bacteria cells protects a small percentage of bacteria and causes them to behave as if they had much higher resistance to both UV and ozone. EXPERIMENTAL PROCEDURES Experimental setup of the Microwave Plasma UV Lamp The microwave power is produced by a magnetron source operating at 2.45 GHz. Figure 3 shows the main MPUVL components. The 42-4-15 Figure 1. Survival curve of microorganisms in response to UV radiation. Figure 2. Comparative mortalities of bacteria and other pathogens in response to UV radiation, ozone and chlorine treatments in water sterilisation. 42-4-16 Journal of Microwave Power & Electromagnetic Energy ONLINE Vol. 42, No. 4, 2008 Figure 3. Microwave plasma Ultraviolet Light system setup. custom made lamps utilise a high purity GE214 quartzTM glass [Cullen et al., 2006)] that allows 254 nm and 185 nm UV light to pass through. Inside the lamp, there is a low pressure mixture of Argon gas combined with Mercury vapour produced by double-distilled liquid Mercury drops (considered safer than the extremely toxic and volatile fumes). The lamp itself does not contain any electrodes, as in the case of the commercial lamps. The cavity was connected to the magnetron with a low loss coaxial RG214 cable with N-Type connectors. The microwaves are generated by a magnetron 200 power supply. This is a variable supply which is capable of outputs up to a maximum of 200 Watts CW or 300 W (peak power) pulsed with a 4 kHz frequency repetition rate. The unit is also equipped with an incident power meter and reflected power meter. The microwave power is coupled to the lamp via a tunable resonant cavity using the fundamental TE010 mode. The E-field propagated into the cavity resonator is a radial mode and propagates through the quartz tube via a surface wave [Al-Shamma’a et al., 2001]. In the MPUVL, the electric field component is transverse with standing wave present compared with the longitudinal electric field of the commercial lamp; this leads the lamp International Microwave Power Institute to emit UV of an order of magnitude higher in intensity with power per unit length of at least 250W/m [Kraszewski, 1967]. The high rate of power per unit length allows for the setting up of the lamp for the investigation of various cases of bacteria inactivation. In addition, the resonant cavity of the MPUVL can be designed to allow one or more lamps to be used and in any shape. A twin MPUVL system arrangement can be seen in Figure 4. The lamp arrangement does not induce any severe losses to the microwave coupling, and the power is divided equally among the lamps of which the thermal burden of the lamps reduced. An optical detector system, based on a transimpedance amplifier, was developed to monitor the UV intensity at 254 nm. A UV enhanced photodiode was used with a narrowband optical filter that transmits light at 254 nm. A similar system can be developed to monitor the optical signal at 185 nm [O’Keeffe et al., 2007]. Figure 5 shows the microwave UV lamp system set-up for bacteria-killing experiments. The lamp has been positioned horizontally based upon the testing requirements. One end of the lamp is energised by microwave power and the other end has a computer controlled stepping motor for a lamp shutter, which controls the UV exposure time against various types of bacteria. 42-4-17 Design of a parabolic reflector The samples that have to be irradiated would normally be situated underneath the lamp in a fixed position or moving over a conveyor belt. With the initial design of the lamp, most of the UV radiation emitted by the lamp was wasted, since only the portion directed to the area below the lamp had an effect on the samples. To maximize the efficiency of the lamp, a parabolic reflector was designed. The intensity of UV radiation on the surface under the lamp (60 mm from the lamp) was measured with and without the parabolic reflector. Figure 6 shows the intensity map for the lamp with no cover. The lamp shows the highest intensity directly under the lamp and nearest the microwave cavity (15-16 W/m2). Along the length of the lamp it decreases slightly where the Primarc lamp tapers in the middle. The intensity of the UV light decreases rapidly as the sensor moves away from under the lamp. At 10 mm from the lamp, the intensity is approx. 10-12 W/m2. At 20 mm from the lamp, the intensity is approx. 4-6 W/m2. Beyond 30 mm the intensity is negligible. Figure 7 shows the results of the intensity map for the Primarc lamp with a parabolic cover in place. The parabolic cover was designed to be 12.5 mm from the lamp centre, therefore it was placed 3.5 mm from the outside of the lamp. Given the design of the lamp holder, this is the closest the parabolic cover can be placed to the lamp. It is clear that the parabolic cover significantly improves the intensity of the UV light and the overall efficiency of the lamp. The UV light directly under the lamp is 16-20 W/m2 when the reflector is in place. As the sensor is moved away from under the lamp the UV intensity remains high. Where previously, without a cover, at 30 mm there was negligible UV intensity, this is now increased to 10-14 W/m2. The intensity remains high until 90 mm either side of the lamp. The cover ends at 100 mm, thus the UV intensity outside this range is minimal. The intensity 42-4-18 Figure 4. The twin MPUVL system arrangement. Figure 5. The MPUVL set-up. increases slightly at 70-80 mm, which may be due to the uneven surface of the parabolic cover used. Microorganisms used The study of pathogens in a laboratory is important for the understanding of their biology and specific characteristics. It is unsafe, though, to work with virulent strains and very strict safety measures need to be observed. Due to this, surrogate organisms are sometimes used instead of the pathogenic strains. Surrogate strains are tools in assessing fresh fruit and vegetable safety and the effectiveness of Journal of Microwave Power & Electromagnetic Energy ONLINE Vol. 42, No. 4, 2008 Figure 6. Intensity map (J/m2) for the Primarc Microwave Plasma UV Lamp at 60 mm without the parabolic reflector. Figure 7. Intensity map (J/m2) for the Primarc Microwave Plasma UV Lamp at 60 mm with the parabolic reflector. International Microwave Power Institute 42-4-19 microbial control measures because they mimic growth and survival patterns of a pathogen and can help in studying what occurs with a pathogen during handling and storage. They are important tools used when studying the effects and responses to specific processing treatments, such as the effectiveness of a produce wash or other decontamination processes. In this study we have used the strain E. coli ATCC 25922. This is a non pathogenic strain that is considered to be a surrogate of the enterotoxigenic strain of E. coli O157:H7 [Duffy et al., 2000]. It has the same UV sensitivity/resistance as three pathogenic strains of E. coli O157:H7 and it was used to evaluate the response to UV-C light emitted by a Microwave Plasma Ultraviolet Lamp (MPUVL) developed previously in our lab [Cullen et al., 2006]. Other organisms used in this study are: Pseudomonas aeruginosa NCTC 10662, Bacillus cereus (vegetative cells and spores) and Staphylococcus aureus NCNTC 6571. Overnight liquid cultures were adjusted to different concentrations (106-108 cfu/ml) and 0.1 ml was plated on to Nutrient Agar plates. The plates were then exposed to the UV light for a certain time and immediately placed in the 37ºC incubator. Surviving colonies were counted the next day. RESULTS AND DISCUSSION The maximum intensity of the UV radiation emitted by the lamp is 10 W/m2 in the area below the lamp. This intensity is lower in the areas not directly below the lamp. To correlate the intensity of ultraviolet radiation emitted by the MPUV lamp with its biocidal power, an experiment was designed in which the plates containing the E. coli cells were placed in five different locations in the area illuminated by the lamp (three were placed directly underneath the lamp, covering the whole length of the lamp, one was placed 20 cm in front and another 20 cm at the back, forming a cross shape) and exposed for 5 seconds to the UV light. Two sets of plates were exposed to UV light: the first set of 42-4-20 plates (low inoculum) contained approximately 2x105 cfu/plate. These plates did not develop any colonies, meaning that all the cells were killed by the UV radiation. The second set of plates, containing a high inoculum of 2x107 cfu/plate, showed a significant reduction in the number of colonies, though this reduction was not homogenous for all the plates. In the plates situated at the back and in the centre row (left, centre and right), there was a 6 log reduction. Although the results for these three plates were in the same range, the reduction in survival was slightly smaller in the plate situated at the right. The plate situated at the front only had a 5 log reduction, showing that the intensity of the light is not equal in all the areas, which agrees with the distribution of intensities observed for the lamp. This shows that in order to get accurate and highly reproducible results, the position of the samples has to be maintained constant. The germicidal effect of the UV-C light emitted by the microwave powered lamp was assessed on 4 different microorganisms. Culture plates containing from 105 to 107 cfu (colony forming units) of the bacteria were exposed to a range of doses of UV-C light. The culture plates were placed in the area directly underneath the lamp, at 10 cm distance. Plates were then exposed to the UV light for different amounts of time depending on the microorganism. For example, E. coli and P. aeruginosa plates were exposed for 2 to 8 seconds. Both organisms are gram-negative and have similar membrane structure. S. aureus was also exposed to UV light for 2 to 8 seconds. In the case of B. cereus the exposure times were longer because it is known that gram positive bacteria, and more specially the members of the genus Bacillus, are highly resistant to UV light. Procaryotic cells divide by a process called binary fission (invagination of the plasma membrane and the laying down of new cell wall to produce two separate daughter cells). Some bacteria, though, are able to produce endospores (spores) when there are no nutrients available. These are highly heat-resistant, dehydrated Journal of Microwave Power & Electromagnetic Energy ONLINE Vol. 42, No. 4, 2008 Figure 8. Growth of E. coli on Nutrient Agar plates after exposure to different doses of UV light. resting cells formed intracellularly in members of the genera Bacillus and Clostridium. Spores are not metabolically active and can remain in that state for long periods of time. To distinguish the active cells from the inactive spores, cells are also called vegetative cells. For our experiment, spores were obtained from 2-3 week old plates, and the abundance of vegetative cells and spores was measured using a microscope. Plates containing >95% spores were scraped and the spores suspended in a buffered solution. Spores and vegetative cells were treated for 10 to 60 seconds. After exposure to UV-C light, the plates were incubated overnight at 37ºC. Surviving bacteria developed a colony, which were then counted. An example of this can be seen in Figure 8. The plates situated on the top row were inoculated with 105 E. coli bacteria, and exposed for different amounts of time to UV light. After incubation, surviving bacteria developed colonies, which can be seen in Figure 8. The longer the plates were exposed to UV light, the lower the amount of bacteria that were able to survive. Figure 9 shows the reduction in the numbers for the 4 different microorganisms tested. Experiments were performed in triplicate, and the average values are shown. The exposure times for the plates varied from 2 to 8 seconds for E. coli, P. aeruginosa and S. aureus, and International Microwave Power Institute from 10 to 60 for B. cereus. A reduction of up to 6 Log in the number of living microorganisms was observed for E. coli and P. aeruginosa in less than 2 sec exposure, which corresponds to less than 20 J/m2. S. aureus was slightly more resistant, and needed between 20 and 50 J/m2 to obtain the same Log reduction. Vegetative cells of Bacillus were more resistant to UV radiation, and an exposure to 600 J/m2 was needed to produce a 6 log reduction in the number of surviving microorganisms in the test plates. When spores of B. cereus were used to perform the tests, they proced to be highly resistant to damage by UV light, and very high doses of radiation (600 J/m2) were needed to observe a reduction of even 2 Log in the number of surviving microorganisms. Due to aggregation of bacteria, which occurs naturally due to their very small size, some of the bacteria that happen to be in those clumps may survive the exposure to UV-C light. This is why there is a “trailing” effect observed, and after a high kill rate observed for the first seconds, this kill rate decreases and it is difficult to find plates with 0 colonies, mainly when the inoculums is high. However, the 6 log reduction observed for three of the studies species after only 2- 5 seconds of exposure, which equals a 99.9999 % killing, should be sufficient for most food products to achieve a long lifespan without any 42-4-21 Figure 9. Effect of UV radiation on different bacterial species. The diagrams show the number of surviving bacteria after exposure to different doses of UV light (grey and white bars), compared to the initial number of bacteria (dark bars). Error bars represent standard deviation of the mean. Experiments were performed at least in triplicate. detectable spoilage effects. Microorganisms like Bacillus cereus are more resistant to UV light, and their spores especially might respond better to other type of treatments, alone or combined with UV light. CONCLUSIONS AND FUTURE WORK The MPUVL used in these experiments has proven to be an alternative to the commercial ultraviolet irradiation systems. It can significantly reduce the microbial contamination in surfaces. The next steps are to evaluate the biocidal capacity of the lamp with real samples, such as various lettuce types, and other vegetables as well. The effect of the reduction of microbiological contamination and its relationship to an increase of shelf life will also be evaluated using different packaging techniques and storage conditions. ACKNOWLEDGMENTS The authors would like to thank the EU for their kind fund toward the Micro-GMAP Project 42-4-22 contract MTKD-CT-2006-042609. REFERENCES Allende, A., E. Aguayo and F. Artes (2004). “Microbial and sensory quality of commercial fresh processed red lettuce throughout the production chain and shelf life.” Int. J. Food Microbiol., 91(2), pp.109-117. Allende, A., J.L. McEvoy, Y. Luo, F. Artes and C.Y. Wang (2006). “Effectiveness of two-sided UV-C treatments in inhibiting natural microflora and extending the shelf-life of minimally processed ‘Red Oak Leaf’ lettuce.” Food Microbiol, 23(3), pp.241-249. Al-Shamma’a, A.I., I. Pandithas and J. Lucas (2001). “Low-pressure microwave plasma ultraviolet lamp for water purification and ozone applications.” J. Phys D: Appl. Phys., 34, pp.2775-2778. Andersen, B.M., H. Banrud, E. Boe, O. Bjordal and F. Drangsholt (2006). “Comparison of UV C light and chemicals for disinfection of surfaces in hospital isolation units.” Infect. Control Hosp. Epidemiol., 27, pp.729-734. Archer, D.L. and F.E. Young (1988). “Contemporary issues: diseases with a food vector.” Clin. Microbiol. Rev., 1, pp.377-398. Journal of Microwave Power & Electromagnetic Energy ONLINE Vol. 42, No. 4, 2008 Beuchat, L.R. (1998). “Surface decontamination of fruits and vegetables eaten raw: a review.” World Health Organization (Geneva). Corbo, M.R., M.A. Del Nobile and M. Sinigaglia (2005). “A novel approach for calculating shelf life of minimally processed vegetables.” Int. J. Food Microbiol., 106(1), pp.69-73. Cullen, J., A.I. Al-Shamma’a and M.G. Jones (2006). “Microwave-Generated UV Light as a Biocide.” 40th IMPI Annual Microwave Symposium (Boston). Duffy, S., J. Churey, R.W. Worobo and D.W. Schaffner (2000). “Analysis and modelling of the variability associated with UV inactivation of Escherichia coli in apple cider.” J. Food Prot., 63(11), pp.1587-1590 Erkan, M., C.Y. Wang and D.T. Krizek (2001). “UVC irradiation reduces microbial populations and deterioration in Cucurbita pepo fruit tissue.” Environ. Exp. Bot., 45, pp.1-9. Gomez-Lopez, V.M., F. Devlieghere, V. Bonduelle and J. Debevere (2005). “Intense light pulses decontamination of minimally processed vegetables and their shelf-life.” Int. J. Food Microbiol., 103(1), pp.79-89. Hijnen, W.A., E.F. Beerendonk and G.J. Medema (2006). “Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: a review.” Water Res., 40(1), pp.3-22. Review. James, J. (2006). Microbial Hazard Identification in Fresh Fruit and Vegetables, John Willey & Sons. Koller, L.R., (1965). Ultraviolet Radiation, 2nd Ed, John Wiley & Sons, New York. Kraszewski, A., (1967). Microwave gas discharge devices, Iliffe Books Ltd., 2nd Ed. Krishnamurthy, K., A. Demirci and J. Irudayaraj (2004). “Inactivation of Staphylococcus aureus by pulsed UV-light sterilization.” J. Food Prot., 67, pp.10271030. Marquenie, D., A.H. Geeraerd, J. Lammertyn, C, Soontjens, J. F. Van Impe, C.W. Michiels and B.M Nicolai (2003). “Combinations of pulsed white light and UV-C or mild heat treatment to inactivate conidia of Botrytis cinerea and Monilia fructigena.” Int. J. Food Microbiol., 85(1-2), pp.185-196. McCabe-Sellers B.J. and S.E. Beattie (2004). “Food safety: emerging trends in foodborne illness surveillance and prevention.” J. Am. Diet Assoc. 104(11), pp.1708-1717. O’Keeffe S., J. Cullen, A.I. Al-Shamma’a, C. Fitzpatrick, E. Lewis, M. Ortoneda. and D.A. Phipps (2007). “Optical Fibre Sensor System for the online International Microwave Power Institute monitoring of a Microwave Plasma UV Lamp Food Treatment System.” Proc. XIV Sensors & their Applications Conf. Ragaert, P., W. Verbeke, F. Devlieghere and J. Debevere (2004). “Consumer perception and choice of minimally processed vegetables and packaged fruits.” Food Quality and Preference, 15, pp.259-270. Sapers, G.M., R.L. Miller, M. Jantschke and A.M. Mattrazzo (2000). “Factors limiting the efficacy of hydrogen peroxyde washes for decontamination of apples containing Escherichia coli.” J. Food Sci., 65(3), pp.529-532. Selma, M.V., D. Beltran, A. Allende, E. Chacon-Vera and M.I. Gil (2007). “Elimination by ozone of Shigella sonnei in shredded lettuce and water.” Food Microbiol., 24(5), pp.492-499. Tauxe, R.V. (1997). “Emerging foodborne diseases: an evolving public health challenge.” Emerg. Infect Dis., 3(4), pp.425-34. Review. Wang, T., S.J. MacGregor, J.G. Anderson and G.A. Woolsey (2005). “Pulsed ultra-violet inactivation spectrum of Escherichia coli.” Water Res., 39, pp.2921-2925. Xu, L. (1999). “Use of ozone to improve the safety of fresh fruits & vegetables.” Food Technol., 53, pp.58-61. Yahia, E.M., C. Barry-Ryan and R Dris (2007). “Production Practices and Quality Assessment of Food Crops.” Volume 4: Proharvest Treatment and Technology, Springer, Netherlands. Yaun, B.R., S.S. Sumner, J.D. Eifert and J.E. Marcy (2004). “Inhibition of pathogens on fresh produce by ultraviolet energy.” Int. J. Food Microbiol., 90(1), pp.1-8. Yousef, A.E. and Marth, E.H. (1988). “Inactivation of Listeria monocytogenes by ultraviolet energy.” J. Food Sci., 53, pp.571-573. 42-4-23