Strawberries

New approach to slowing rot doubles berry shelf life

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 thanks to LED technology.

A research team from the US Department of Agriculture’s (USDA) Food Components and Health Laboratory in Beltsville, Md, and Sensor Electronic Technology (SETi) in Columbia, SC, has demonstrated that low irradiance ultra-violet (UV) light directed at strawberries over long exposure periods at low temperature and very high humidity – typical home refrigerator conditions – delays spoilage.

The team used a novel device incorporating light-emitting diodes (LEDs) that emit UV at wavelengths found in sunlight transmitted through Earth’s atmosphere.

The results, which will be presented next week at the Conference on Lasers and Electro-Optics (CLEO: 2013 in San Jose, Calif), 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.

strawberry shelf life

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.
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SETi has developed a special technology to fabricate UV LEDs across the entire UV spectrum from UVA to UVC. This flexibility allowed them 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, who will present the work at CLEO: 2013.

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.

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,” states Remis Gaska, president and CEO of SETi.

Source: The Optical Society