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AlGaN UV LEDs double berry shelf life

SETi is planning to commercialise its aluminium gallium nitride LEDs for use in refrigerators to delay the spreading of mould
Strawberry lovers rejoice: the days of unpacking your luscious berries from the refrigerator only to find them sprouting wispy goatees of mould may be numbered.

This is thanks to developments by a research team from the U.S. Department of Agriculture's (USDA) Food Components and Health Laboratory in Beltsville, Maryland, and Sensor Electronic Technology, Inc. (SETi) in Columbia, South Carolina.

The scientists directed low irradiance ultra-violet (UV) light at strawberries over long exposure periods at a low temperature and very high humidity. These are typical home refrigerator conditions. They found an extension in the berry shelf life over strawberries kept in a darkened atmosphere.

The team used a novel device incorporating LEDs that emit UV at wavelengths found in sunlight transmitted through Earth’s atmosphere. The results are significant because previous attempts using traditional UV light sources for storage of produce resulted in severe drying, and it was unknown if the advantages of long exposure to low-level UV light would be effective against rot.

LEDs are now commonplace thanks to their long life and energy efficiency, as well as their ability to span the wavelength range from near UV to infrared. The full UV spectrum, however, had presented challenges for LED manufacturers - until recently.

SETi developed a special technology to fabricate UV LEDs across the entire UV spectrum from UVA to UVC. This flexibility allowed the firm to tune the emitted light to the wavelengths most effective for this application.

"UV-LEDs presented the opportunity to try low power devices that work well in the cold and can be engineered to work in small spaces such as refrigerator compartments," says lead USDA researcher Steven Britz.

Using strawberries purchased from a local supermarket, Britz’s team placed one batch in a dark refrigerator and one batch in a refrigerator exposed to UV-LEDs. Results showed the UV-treated berries had their shelf life extended twofold - nine days mould-free - over darkened berries, as judged by weight, moisture content, concentration of select phytochemicals, visible damage, and mould growth.

UV-B (equal energy) treatment prevents damaged areas from spreading while also inhibiting mould growth. This is a critical aspect of the technology - the ability to "tune" the UV to the most effective part of the spectrum, something that would be difficult and much less efficient using a typical mercury UV source. (Credit: Sensor Electronic Technology Inc (SETi).)

Based on these encouraging results, the team is working to commercialise the technology for home refrigerators.

“These findings are expected to have a major impact on the appliance business to extend the shelf life and preserve nutritional value of fresh produce while reducing waste and saving money for every household,” explains Remis Gaska, president and CEO of SETi.

The team will discuss its work at the Conference on Lasers and Electro-Optics (CLEO: 2013), which is taking place between June 9th and 14th at the San Jose Convention Centre.

CLEO: 2013 presentation ATh3N.3. “Deep Ultraviolet (DUV) Light-Emitting Diodes (LEDs) to Maintain Freshness and Phytochemical Composition During Postharvest Storage” by Stephen Britz will take place on Thursday, June 13th at 2:45 p.m.

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