Processing Technology

Taking advantage of UV light benefits to control microorganisms


By Tatiana Koutchma on 12/24/2012

Foodborne and waterborne pathogens are the largest group of microorganisms that present health hazards in the food industry. Some of these organisms can become airborne during processing and settle on raw, semi-finished or final products, thereby becoming amenable to control by ultraviolet (UV) light in the air as well as on surfaces.

Nearly every meat processing facility can benefit from use of UV light to control microbial hazards through treatments of air, non-food, food contact surfaces, processing water, ingredients, raw and finished products. Here is what processors need to know before installing a UV system.

Science of UV light

Ultraviolet light (UV) is a portion of the electromagnetic spectrum between 100 and 400nm.  UV-light can be further divided into UV-A, -B, and -C sub-diapasons that are characterized by various wavelengths and energy levels of photons and thus differ in their produced effects.

The UV-A range from 315 to 400nm may cause changes in human skin, whereas light in the UV-B range from 280 to 315 nm definitely affects skin and may lead to skin cancer. The germicidal UV-C range from 200 to 280 nm effectively inactivates bacterial, viral and protozoan microorganisms. The vacuum UV is from 100 to 200 nm and can be absorbed by almost all substances and thus can be transmitted only in a vacuum. When vacuum UV and UV-C photons are absorbed by oxygen atoms, the energy exchange causes the formation of ozone.

UV light has low penetrating power because its inherent energy of photons is minor in comparison with ionizing radiation; it belongs to non-ionizing radiation. Absorption of non-ionizing radiation leads solely to electronic excitation of atoms and molecules as opposed to ionizing radiation that can lead to ionization. However, the excitation energy of UV photons is much higher than the energy of thermal motions of the molecules at physiological temperatures.

Gas discharges are responsible for the light emitted from UV lamps. A gas discharge is a mixture of non-excited atoms, excited atoms, cations and free electrons formed when a sufficiently high voltage is applied across a volume of gas. Low-pressure mercury (LPM) sources emit 90 percent of their UV-energy at 253.7 nm. LPM sources are monochromatic, relatively cheap and have reasonably long life of up to 6,000 of hours. More powerful options are high intensity monochromatic amalgam lamps (LPA) and polychromatic medium pressure mercury (MPM) lamps. MPM sources are mainly used in water treatment industry. The life of amalgam lamps can be twice as long – up to 12,000 hours.

How to maximize your UV system

UV light emitted from the gas discharge of a UV source propagates away from atoms and ions interacting with the materials through absorption, reflection, refraction and scattering. This explains why correct positioning of the UV source and distance from the treated meat product is critical to maximize the efficacy of UV treatments. Any obstruction to the path of the light, such as dust, shadowing or clumping of bacteria, may reduce efficacy. So UV light isn’t as effective on a rough surface than it is on a smooth one.

The characteristics of UV source such as wavelength or the levels of UV light photons energy, the number of photons or UV intensity and exposure time will define UV process lethality. It was found that the following product parameter – temperature, pH, chemical composition and physical structure – affect UV light’s effectiveness to control microorganisms.

Additionally, the efficacy of UV sources against different groups of pathogenic and spoilage organisms varies in different matrices such as air, water, surfaces or fluid foods. Adenovirus is considered as the most UV-resistant organism in water treatment, whereas bacteria and mold spores are characterized by the highest UV resistance in air and food matrices.

Effects on various pathogens

In recent studies, UV light was reported to be effective against non-spore forming pathogenic microflora on raw meats and poultry surfaces. UV-C at 0.5 J/cm2 reduced the initial populations of C. jejuni, L. monocytogenes,and S. typhimurium by 1.3-1.2 log CFU/g respectively on chicken breasts.

Similarly UV treatment of raw chicken fillet at 0.2 J/cm 2 reduced C. jejuni, E. coli, serovar Enteritidis, total viable counts, and Enterobacteriaceae by 0.76, 0.98, 1.34, 1.76, and 1.29 log CFU/g, respectively. Following UV treatment of packaging and surface materials, higher reductions of up to 3.97, 4.50, and 4.20 log CFU/cm2 were obtained for C. jejuni, E. coli, and serovar Enteritidis, respectively.

These studies indicate that UV may be beneficial in working areas of meat and poultry processing plants to reduce the level of aerobic and non-spore forming pathogens and may be applied to decontaminate cut-up products moving on conveyors, associated packaging and surface materials.

According to USDA, contamination of foods with L. monocytogenes is likely to occur in all RTE meat and poultry products that are exposed to post-lethality processing environment. These post-lethality processing environments are the areas into which products are routed after complete treatments and may include slicing, peeling, dicing, re-bagging and brining. As an example of UV post-lethality application, packaged RTE product can be exposed to UV to avoid of risk of cross or recontamination. Knowledge of light permeability of the packaging material is critical when such a process is developed.

To demonstrate the efficacy of UV technology to FSIS, the UV dose requirements to achieve specific log reduction requirements need to be evaluated first. This information will allow selecting not only a correct UV source but also the effective design of a system depending on the application.

Conclusion

Although there are several benefits of UV light in the meat and poultry industry, cost-saving opportunities that include energy, processing water and enhanced safety need to be carefully considered in each case for successful technology implementation and to assure positive benefits.

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