Pear review: Organic UVC cleanup

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  • Published: Aug 1, 2015
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
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Scrubbing up well

Light treatment for organic fruit to remove lethal pathogens (Credit: Roopesh Syamaladevi, WSU)

Some kinds of organic fruit can be scrubbed of food borne pathogens, such as the potentially debilitating and sometimes lethal Escherichia coli O157:H7 and Listeria monocytogenes, that are often present on their skins using ultraviolet-C radiation, according to a new study from researchers at Washington State University published in the International Journal of Food Microbiology.

Sodium hypochlorite, chlorine dioxide and peroxyacetic acid solutions are often used to purportedly "disinfect" fresh food produce. Unfortunately, these substances have rather limited efficacy in removing human pathogens from the surfaces of such food, despite fruit packers making several applications and even scrubbing produce. Efficacy is even more limited for soft fruits, such as raspberries and strawberries, bean sprouts and other produce. There is a critical need to develop novel disinfection technologies that substitute for conventional washing and sanitizing techniques," says Shyam Sablani of the School of Food Science, at WSU in Pullman, Washington and colleagues.

Irrespective of the pros and cons of so-called "organic" food, there is a market for such fruit and vegetables, and as such there is a certain urgency in ensuring those products are safe for public consumption. The discovery that UVC can eradicate certain important pathogenic microbes should be welcome news for organic fruit processors who generally seek alternatives to chemical sanitizers but must comply with the US Food Safety Modernization Act to help prevent food borne diseases.

Solar solution

"UVC radiation is present in sunlight; however, it is completely absorbed by the ozone layer and Earth's atmosphere," Sablani explains. "“It has germicidal properties and can be effective against bacteria, mould and viruses." Because UVC cannot penetrate opaque solid objects either, it can be used to sanitize surfaces. Indeed, it has been used for several years to sanitize food contact surfaces as well as drinking water and contaminated air. It was already known that UVC can disrupt pathogen DNA and stop them multiplying but Sablani's research also now shows that it does not affect the chemical or physical quality of the fruit.

The team demonstrated proof of principle with apples, pears, strawberries, raspberries and cantaloupe melon to determine the lowest UVC dose necessary to effectively remove contamination with mixed strains of E. coli and Listeria. They found that UVC light kills 99.9 percent of pathogens on apples and pears, although Listeria was more resistant than E. coli.

Rough skin

“If you have smoother skinned fruit, then this technology is really great,” Sablani explains. "If the fruits are very rough and if the level of contamination is low, it also works quite well." Indeed, inactivation was only at 90 percent on rough-surfaced fruit such as strawberries and raspberries; the very fruit on which conventional sanitization fails.

"For food safety standards, you don’t want any pathogens on the fruit," Sablani adds. Rough surfaces of strawberries, raspberries and cantaloupe melons offer places where pathogens can hide, reducing the effects of UVC light. If bacterial contamination levels are high, then UVC technology alone may not be sufficient to achieve the desired level of effectiveness. Sablani says that research is currently underway to increase the effectiveness of UVC light on these types of fruit.

Fundamentally, this simple technology could be useful to the industry but would not require significant changes on the fruit-packing lines other than addition of UVC lamps and protective screens. The research was funded partially by the Biological and Organic Agriculture (BIOAg) program of the WSU Center for Sustaining Agriculture and Natural Resources.

"The next step is to look into industrial implementation related challenges of this technology and we ultimately want to achieve improved safety of fresh produce and reduce the number of cases of foodborne illnesses on consumption of fresh produce," Sablani told SpectroscopyNOW.

Related Links

Int J Food Microbiol 2015, 210, 136-142: "Ultraviolet-C light inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on organic fruit surfaces"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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