Light based technologies started to emerge in food processing practices due to their broad antimicrobial action, low cost and non-thermal purely physical nature. The techniques such as continuous UV-C at 254 nm, pulsed light (from 170 to 1000 nm) and pulsed UV (from 200 to 400nm), and recently light emitting diodes (LEDs, in the range of 255 to 405 nm) utilize different wavelengths of electromagnetic spectrum, have different intensity and treatment times, and can differ in their anti-microbial efficacy. Even though the term “irradiation” is frequently used for UV treatments, UV also considered as a light and cannot be associated with ionizing radiation. Often, the term “illumination” is preferred to avoid consumer confusion.
After discovery of germicidal properties of light in UV range and its effects on microbial DNA, the development of mercury filled discharge lamps led to the applications of UV mainly in drinking and waste water disinfection. As a water treatment technique, UV is known to be effective against bacteria, viruses and protozoans like, Giardia lamblia cysts or Cryptosporidium oocysts. Also, UV has been used commercially for many years for air and food contact surfaces sanitation in food industry.
Compared to the water and air decontamination, the application of UV-light to processing foods is a relatively new and challenging area. Low-pressure mercury and amalgam electroded lamps that emit 90 % of light at 253.7 4nm are mainly adapted by the food industry because they are readily available at comparatively low cost and life time up to 12,000 hours. The light treatments may include prolongation of the shelf life and prevention of food-borne diseases in juices, drinks and beverages, fresh produce, meat, poultry and seafood; retardation of ripening and ageing of fruit and vegetables.
Despite light being known for its low penetration, a lot of interest has been focused at the uses of UV-C as an alternative means of pasteurization of fluid products. The benefit of non-thermal UV is a better quality product with minimum change of nutritional value and fresh like taste. UV-light can be effective in treating relatively high UV transparent liquids such as clarified juices and soft drinks, but is less effective in treating turbid liquids with particulates and compounds (e.g., citrus juices) where UV-light is strongly absorbed, scattered or reflected. In order to achieve high efficacy of light in products with low UV transmission, the new engineering approaches have been developed that differ from those normally employed for water. Due to this challenge, UV systems use thin film laminar, annular turbulent or Dean flow in coiled tubes to treat juices, milk, liquid egg products and sweeteners. The main challenge for food processors interested in using UV technology becomes to select the most appropriate UV light system for their application. The next step is to validate the UV system and to establish processing conditions to achieve product safety and shelf-life objectives and in the same time to provide the required level of quality and retain nutritive constituents, product sensory and structure attributes.
In present time, the UV treatment found a great value in the productions that are using liquid sugars and sweeteners and can replace traditional heat treatments.
Also, US FDA approval of UV emitted by low pressure mercury lamps at 254 nm for treatment of juice products, opened new opportunities at the growing market of premium cold pressed fruit and vegetable juices. UV is a continuous process that may extend shelf-life of popular leafy green, fruit and vegetables blends, almond and coconut based beverages while using various types of glass packaging.
UV treatment is a promising technology for milk and cheese processors that can provide added value as compared to heat pasteurization. The research showed that UV was effective against typical pathogenic bacteria in milk without impacting essential milk enzymes and protein thus maintaining the essential healthy properties of natural milk.
In 2016, the European Food Safety Agency (EFSA) concluded that novel UV process of treating pasteurized milk to produce ESL product with increased vitamin D content is safe under the intended specified conditions. This decision opens new opportunities for further technology commercialization in dairy applications.
Pulsed light is delivered in several flashes per second with the intensity about 20,000 times higher than the intensity of UV light. This allows achieving fastthroughput, low energy usage and lower cost packaging decontamination solutions. In industrial scale, the PL is applied for decontamination of caps, cups, lids and ultra-clean and ESL packaging lines.
More research on validation of commercial UV units is necessary to accelerate UV technology acceptance.
In recent years, LEDs have been developed with the following advantages: small size, up to 80% energy-efficiency, easy control of emission, point of use applications, and no mercury and glass. UV LEDs are the next wave in the LED revolution that brings not only the advantages to the UV-A, UV-B and UV-C regions but also UV-C LEDs can be used at the optimal germicidal wavelength tuned against specific organisms. The germicidal effects against several common bacteria and fungi already have been demonstrated along with the first applications for disinfections in hospital rooms, water and sterilizing bottles. In food treatment, the effectiveness of LEDs in UV and visible range has been shown against pathogens on the surfaces of raw and finished meat and poultry products, and post harvest treatment of fresh produce. LEDs can enhance the nutritive quality of foods in the postharvest stage, as well as manipulate the ripening of fruits, and reduce fungal infections.
Despite several challenges and limitations, UV LEDs are being presented as a new
technological solution with enormous potential in food processing and cold storage
operations to control pathogens and shelf-life.
About The Author
Dr. Tatiana Koutchma is a Research Scientist at Agriculture and Agri-Food Canada, focusing
on applied research related to novel processing technologies, development and validation of
new processes for industry. She is an internationally recognized expert in high pressure,
ultraviolet light, and other advanced thermal and non-thermal methods.