American consumers are becoming increasingly aware of the safety-enhancing methods used on food and beverage products before their arrival at retail outlets: pasteurization by heat and high-pressure treatment, and irradiation by gamma rays, X-ray or electron beams. But they may not know much about ultraviolet radiation (UV), which is gradually becoming more common as a relatively inexpensive and, depending on the type product on which it’s used, effective method of reducing or eliminating pathogens. UV is electromagnetic radiation with a wavelength of between 100-400 nanometers, a nanometer being one-billionth of a meter. It can come from the sun or artificial sources, with the danger level to humans increasing as the wavelength gets shorter. UV is classified into three general areas by wavelength: UV-A, UV-B and UV-C. UV-A has the longest wavelength range (320-400 nanometers) and is the type of radiation responsible for sunburns and is linked to skin cancer. UV-B, at 280-320 nanometers, also plays a role in skin tanning and burning, but it’s a minor one compared to UV-A. UV-C, at 100-280 nanometers, has the shortest wavelength range of the three and is the type applied to food and beverages, although the technology has long been known and used for other industrial applications. For example, UV-C has been used for many years to disinfect or sanitize drinking water, wastewater, air, and food contact surfaces. (The photo shows a ceiling-mounted UV-C lamp being used to sanitize the air in a food-processing plant.) Wider application of UV-C as a pathogen-reduction technology for food and beverages is more recent, with the U.S. Food and Drug Administration (FDA) approving it for “cold pasteurization” of juices about a dozen years ago. FDA’s action was prompted by E. coli outbreaks linked to unpasteurized apple cider and contaminated fruit juices. The agency issued a rule in 2001 requiring most juice producers to follow Hazard Analysis and Critical Control Points (HACCP) controls, with UV-C treatment as one of the acceptable methods. Those regulations went into effect in 2002 for all but small and very small juice producers, which came under the rules in 2003 and 2004, respectively. FDA calls UV-C at 200-280 nanometers the “germicidal range” because it “effectively inactivates bacteria and viruses.” FDA explains that the “germicidal properties of UV irradiation are mainly due to DNA mutations induced through absorption of UV light by DNA molecules.” Today UV-C is commonly used on juices and apple cider, grains, cheeses, baked goods, frozen products, fresh produce (except lettuce, which wilts), liquid egg products and other foods and beverages. Soda manufacturers use it to treat drink sweeteners, and it’s also being used on french fries and tortillas. UV has been used on food products for more than 50 years. While organic food may not be legally irradiated, notes the Organic Consumers Association, many other commonly consumed foods (and their ingredients) are, even though retail purchasers may not know it. Federal regulations do not require products treated with UV-C irradiation to be labeled as such. However, some states do require it. Dr. Tatiana Koutchma, a food processing research scientist for Agriculture and Agri-Food Canada and an authority on UV, said she found such a label on a beverage product she purchased. “I think it depends on state rules,” she said. “I recently bought some cider in Vermont, which Vermont is famous for, and it said, ‘Treated with UV radiation.’ I took a picture of this.” Vermont’s legislature adopted the following regulation in 1985:
“All fruits, vegetables, meats, poultry, eggs, dairy products and other natural and processed products offered for sale at retail or wholesale in Vermont for human or animal consumption which indicate pursuant to federal law that they have been subjected to an irradiation process shall be labeled ‘Treated with radiation’ or ‘Treated by irradiation.'”
UV-C has been shown to reduce or eliminate E. coli, Salmonella, Listeria, Cryptosporidium, Vibrio and molds. However, its effectiveness depends on exposure time, level of irradiation and the specific technology used.
Koutchma said that UV-C is effective on juices in particular and takes very little time to work its magic. Using a tubular flow unit, she said that it would take only 24 seconds to treat 4,000 liters of juice. “It’s very fast,” she noted. Koutchma has written several scientific papers on UV applications in food processing and presented her findings at conferences. She believes there’s a “bright future” for the technology. “When I started 10 years ago, UV didn’t penetrate opaque liquids (like milk, for example). Right now, the systems are available after 10 years to treat opaque liquids in a tubular flow or well-mixed that deliver liquid to a source so all volumes of the liquid will be exposed. Knowledge is accumulating,” she said. Similiar views are held by Dr. Robert Scheir, a medical microbiologist and president of Cerritos, CA-based Steril-Aire, Inc. He said that UV applications for food and beverages are perfectly safe, are a relatively cheaper method of reducing pathogens and other contaminants on food, and can significantly improve product shelf life. Scheir’s interest began about 25 years ago after observing what he suspected was Aspergillus mold on the rooftop air-conditioning system at a California children’s hospital. Knowing that such exposure could be fatal to young children, he decided to apply his scientific expertise to help reduce it. Food-processing applications came later, including working with baked-good manufacturers. “What happens is the refrigeration units are growing mold and bacteria and putting it into the cooling areas,” he explained. “Cooling actually sucks in the air, so they’re actually inoculating the product with the mold that’s growing on the refrigeration coils. So we put our product on the refrigeration coils and it cuts down on mold.” Scheir has developed high-output UV-C emitters built into so-called “tumbling machines,” which are manufactured in Idaho. These tumblers (shown in the photo) use a rotating drum or screw conveyor to completely expose food surfaces to the light and “have the proven ability to kill or inactivate mold, yeast, viruses and bacteria including Listeria, E. coli, Staphylococcus, Salmonella, Pseudomonas and phage.” According to the manufacturer, these machines can be used on:
- Frozen products – vegetables, fruits, meats, sea food, bakery products, etc.
- Fresh products – vegetables, fruits, meats, sea food, grains, etc.
- Cooked and refrigerated products – pasta, deli, cheese
- Products prior to bulk storage – potatoes, onions, fruit and other produce.
Because development and application of UV-C has been relatively slow in this country, Scheir indicated that he would like to live long enough to experience greater acceptance and use of the technology. “The traction is growing. I hope I can outlive the curve. It should be growing a lot faster, but it’s happening,” he said. Scheir noted that he is seeing increased interest in UV-C from a variety of industrial quarters, although there can be resistance to the upfront costs involved. “The biggest problem in the food industry, as well as in the medical industry and commercial buildings and schools, is that they’re all run by CFOs and purchasing people who are fixated on first costs,” he explained. “You go in and say it’s going to cost $25,000, but the payback will be 10-15 days, and they say they can’t afford $25,000.” Other obstacles to increasing UV-C use may be due to terminology. Wider consumer acceptance may be forthcoming if the technology were called “light treatment” instead of “irradiation.” But, whatever it’s called, experts say that UV-C treatment has been already proven effective in making food products safer. “It shouldn’t be labeled,” Scheir said. “There’s no after-product and no byproduct. There’s zero safety hazard. It’s just a short-wavelength light.” “It is extremely useful,” Koutchma said. “It’s not a new area, but it’s a new application. I really like it because it is complementary to improved safety of food.”