Integrating MAP with new germicidal techniques 317 Filament Filament se face to base face length Fig. 15.4 Conventional low-pressure mercury lamp eproductive functions and thus inactivate the microorganisms. The most common source for producing light within a germicidal region is the low pressure mercury vapour lamp. At room temperature approximately 73% of the output radiation produces 254nm UV radiation, 19% produces 185nm UV radiation and 8% is output as a series of wavelengths 313, 365, 405, 436 and 546nm This is shown in Fig. 15.4. It operates with the same principle as a fluorescent lamp but without the phosphor coating. A voltage applied across the lamp generates an electric field E within the lamp which ionises the mercury vapour to produce UV light emission. The bulb is made of type 219 quartz which excludes light below 220nm. When operating at a temperature of 40oC this lamp emits 92% of its radiation at 254nm wavelength. The characteristics of this family of lamps are given in Table 15.3. They operate using ac.(50Hz)mains power and produce an output of no more than 25w per metre lamp length Microwaves are high frequency electromagnetic waves generated by magnetrons, which can be stored in a resonance cavity made of metal or dielectric material (Wilson 1992). The principle is illustrated in Fig. 15.5 in which microwaves are launched into the lamp via a coupled metal cavity resonator. The electric field(E) ionises the mercury vapour in the lamp to produce the UV emission. The microwave frequency is 2.46GHz and is the same as that used in a microwave oven. This allows low cost magnetrons to be used (Kraszewski 1967). The lamps differ significantly from conventional UV lamps because they have no warm-up time, do not deteriorate with age, have adaptable shapes and can be used in pulsed mode. There is also the possibility of producing ozone and UV from the same lamp to produce a synergistic effect Table 15.3 Conventional UV lamp characteristics Lamp and Lamp wattage Lamp current UV output UV output arc length 1000mm uW/cm- 212.131 0 425 2.9 24 287,206 425 3.9 436.356 425 793.711 37 425 12.8
reproductive functions and thus inactivate the microorganisms. The most common source for producing light within a germicidal region is the low pressure mercury vapour lamp. At room temperature approximately 73% of the output radiation produces 254nm UV radiation, 19% produces 185nm UV radiation and 8% is output as a series of wavelengths 313, 365, 405, 436 and 546nm. This is shown in Fig. 15.4. It operates with the same principle as a fluorescent lamp but without the phosphor coating. A voltage applied across the lamp generates an electric field E within the lamp which ionises the mercury vapour to produce UV light emission. The bulb is made of type 219 quartz which excludes light below 220nm. When operating at a temperature of 40ºC this lamp emits 92% of its radiation at 254nm wavelength. The characteristics of this family of lamps are given in Table 15.3. They operate using a.c. (50Hz) mains power and produce an output of no more than 25W per metre lamp length. Microwaves are high frequency electromagnetic waves generated by magnetrons, which can be stored in a resonance cavity made of metal or dielectric material (Wilson 1992). The principle is illustrated in Fig. 15.5 in which microwaves are launched into the lamp via a coupled metal cavity resonator. The electric field (E) ionises the mercury vapour in the lamp to produce the UV emission. The microwave frequency is 2.46GHz and is the same as that used in a microwave oven. This allows low cost magnetrons to be used (Kraszewski 1967). The lamps differ significantly from conventional UV lamps because they have no warm-up time, do not deteriorate with age, have adaptable shapes and can be used in pulsed mode. There is also the possibility of producing ozone and UV from the same lamp to produce a synergistic effect. Fig. 15.4 Conventional low-pressure mercury lamp. Table 15.3 Conventional UV lamp characteristics Lamp and Lamp wattage Lamp current UV output UV output @ arc length W mA W 1000mm, (mm) W/cm2 212, 131 10 425 2.9 24 287, 206 14 425 3.9 35 436, 356 23 425 7.0 69 793, 711 37 425 12.8 131 Integrating MAP with new germicidal techniques 317
318 Novel food packaging techniques MPUVL To sensor power supply UV radialion 0-200245GHIL pp) power microwave DVM Fig. 15.5 The microwave UV lamp Two different lamp designs are shown in Fig. 15.6. The lamps are energise om one end and operate in free space to emit both 185nm and 254nm by using 214 quartz glass or can emit only 254nm by using 219 quartz glass(Al- Shammaa et al. 2001). Because the microwaves produce a transverse electric field compared with the longitudinal electric field of the conventional lamp, the microwave lamp is able to emit UV of an order of magnitude higher in intensity e.g., at least 250W/m UV light can be detected by silicon photodiodes having enhanced responses in the 190 to 400nm wavelength range. The 5.8mm detector area is housed in a metal can package whilst the 33.6 and 100mm* devices are housed in ceramic packages(RS Components 1998). All packages incorporate a quartz window for enhanced spectral response. The device is illustrated in Fig. 15.7 with all The UV flat lamp The UV cylindrical lamp Fig. 15.6 Microwave UV lamp shapes
Two different lamp designs are shown in Fig. 15.6. The lamps are energised from one end and operate in free space to emit both 185nm and 254nm by using 214 quartz glass or can emit only 254nm by using 219 quartz glass (AlShamma’a et al. 2001). Because the microwaves produce a transverse electric field compared with the longitudinal electric field of the conventional lamp, the microwave lamp is able to emit UV of an order of magnitude higher in intensity, e.g., at least 250W/m. UV light can be detected by silicon photodiodes having enhanced responses in the 190 to 400nm wavelength range. The 5.8mm2 detector area is housed in a metal can package whilst the 33.6 and 100mm2 devices are housed in ceramic packages (RS Components 1998). All packages incorporate a quartz window for enhanced spectral response. The device is illustrated in Fig. 15.7 with all Fig. 15.5 The microwave UV lamp. The UV flat lamp The UV cylindrical lamp Fig. 15.6 Microwave UV lamp shapes. 318 Novel food packaging techniques
Integrating MAP with new germicidal techniques 319 Active are 0.45p Metal can package Cathode -Anode Fig. 15.7 The Uv detector diode(mm units) dimensions being given in mm. It operates with a voltage of 5V and a maximum current of 10mA. The electrical characteristics are given in Table 15.4 and the responsitivity in Fig. 15.8. The device produces a current output which is linear with input UV power UV light is able to kill microorganisms by using wavelengths within the germicidal region. The 254nm wavelength emitted from a mercury discharge is ideal for this action. The kill rate is usually represented by a logarithmic value of Table 15.4 de characteristics Active ity amp/watt(typical) @245mm@340nm responsivity 2.4×2.4 950nm 33.6 58×5.8 0.14 950nm 006 Wavelength. nanome Fig. 15.8 Typical spectrum response and typical quantum efficiency curves
dimensions being given in mm. It operates with a voltage of 5V and a maximum current of 10mA. The electrical characteristics are given in Table 15.4 and the responsitivity in Fig. 15.8. The device produces a current output which is linear with input UV power. UV light is able to kill microorganisms by using wavelengths within the germicidal region. The 254nm wavelength emitted from a mercury discharge is ideal for this action. The kill rate is usually represented by a logarithmic value of Fig. 15.7 The UV detector diode (mm units). Table 15.4 Diode characteristics Active area Responsivity amp/watt (typical) Peak mm2 mm @ 190nm @ 245nm @ 340nm responsivity (typical) 5.8 2.4 2.4 0.12 0.14 0.19 950nm 33.6 5.8 5.8 0.12 0.14 0.19 950nm Fig. 15.8 Typical spectrum response and typical quantum efficiency curves. Integrating MAP with new germicidal techniques 319
320 Novel food packaging techniques Table 15.5 Ultraviolet energy levels in microwatt-seconds per square centimetre at wavelength of 254nm required for 99.9% destruction of microorganisms Mould grobacterium tumefaciens 8500 Mucor ramosissimus(white 35200 Bacillus anthraci Bacillus subtilis(vegetative) 1 1000 Penicillum roqueforti(green) 26400 6500 gae Escherichia col 7000 3500 gionella dumoffii 5500 Chlorella vulgaris 22000 Legionella gormon 4900 Legionella mcdade 3100 Legionella longbeachae Legionella 3800 Viruses Legionaires disease Leptospira interrogans 6000 (Infectious Jaundice Mycobacterium tuberculosis 6600 Neisseria cattarhalis virus 8000 Proteus vulgaris vIrus Pseudomonas aeruginosa poliovirus 21000 aboratory strain) Pseudomonas aeruginosa 10500 Rotavirus 24000 (environmental strain) Rhodospirillum rubrum 6200 Yeast Salmonella enteritidis Salmonella paratyphi 6100 Baker's yeast (Enteric fever) Salmonella typhimurium 15200 Brewers yeast Salmonella typhosa (typhoid fever) 26400 Saccharomyces var ellipsoideus 13200 Serratia marcescens 17600 Shigella dysenteriae(Dysentery) 4200 Shigella flexneri (Dysentery) sonnel Staphylococcus epidermidis Staphylococcus aureus with a sub-micron filter taphylococcus faecalis 10000 the EPCB filter by PURA Staphylococcus hemolyticus Staphylococcus lactis Viridans streptococci 3800 Cysts include Giardia, Llambila and Vibrio cholerae(Cholera 6500 Chryptosporidiun the kill rate with 90% being 1, 99% being 2,99.9% being 3. Table 15.5 gives the 3 log kill rate for a wide range of microorganisms. The UV light power is given in microwatts per cm" and a typical value would be 6000 u W/cm- for bacteria Higher kill rates can be obtained by increasing the UV light dosage(intensity x time)but there is usually a limit attained for the kill rate
the kill rate with 90% being 1, 99% being 2, 99.9% being 3. Table 15.5 gives the 3 log kill rate for a wide range of microorganisms. The UV light power is given in microwatts per cm2 and a typical value would be 6000 W/cm2 for bacteria. Higher kill rates can be obtained by increasing the UV light dosage (intensity time) but there is usually a limit attained for the kill rate. Table 15.5 Ultraviolet energy levels in microwatt-seconds per square centimetre at wavelength of 254nm required for 99.9% destruction of microorganisms Bacteria Mould spores Agrobacterium tumefaciens 8500 Mucor ramosissimus (white 35200 Bacillus anthraci 8700 gray) Bacillus megaterium (vegetative) 2500 Penicillum expensum 22000 Bacillus subtilis (vegetative) 11000 Penicillum roqueforti (green) 26400 Clostridium tetani 22000 Corynebacterium diphtheriae 6500 Algae Escherichia coli 7000 Legionella bozemanii 3500 Legionella dumoffii 5500 Chlorella vulgaris 22000 Legionella gormonii 4900 Legionella micdadei 3100 Legionella longbeachae 2900 Legionella pneumophila 3800 Viruses (Legionaires disease) Leptospira interrogans 6000 (Infectious Jaundice) Mycobacterium tuberculosis 10000 Bacteriophage (e. coli) 6600 Neisseria cattarhalis 8500 Hepatitis virus 8000 Protius vulgaris 6600 Influenza virus 6600 Pseudomonas aeruginosa 3900 Poliovirus 21000 (laboratory strain) Pseudomonas aeruginosa 10500 Rotavirus 24000 (environmental strain) Rhodospirilium rubrum 6200 Yeast Salmonella enteritidis 7600 Salmonella paratyphi 6100 Baker’s yeast 8800 (Enteric fever) Salmonella typhimurium 15200 Brewer’s yeast 6600 Salmonella typhosa 6000 Common yeast cake 13200 (typhoid fever) Sarcini lutea 26400 Saccharomyces var. ellipsoideus 13200 Serratia marcescens 6200 Saccharomyces sp 17600 Shigella dysenteriae (Dysentery) 4200 Shigella flexneri (Dysentery) 3400 Cysts Shigella sonnei 7000 Staphylococcus opidermidis 5800 Cysts normally cannot be killed with UV, Staphylococcus aureus 7000 but are removed with a sub-micron filter Staphylococcus faecalis 10000 such as the EPCB filter by PURA Staphylococcus hemolyticus 5500 Staphylococcus lactis 8000 Viridans streptococci 3800 Cysts include Giardia, Llambila and Vibrio cholerae (Cholera) 6500 Chryptosporidiun 320 Novel food packaging techniques