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. A research team from the US Department of Agriculture’s (USDA) Food Components and Health Laboratory in Beltsville, Maryland (US) and Sensor Electronic Technology, Inc. (SETi) in Columbia, South Carolina (US) has demonstrated that low irradiance ultraviolet (UV) light directed at strawberries over long exposure periods at low temperature and 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 the Earth’s atmosphere. The results will be presented next week at the Conference on Lasers and Electro-Optics (CLEO) 2013 on 9-14 June at the San Jose Convention Centre in San Jose, California (US). They are significant because previous attempts using traditional UV light sources for storage of produce resulted in severe drying, and it was unknown whether 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 and to their ability to span the wavelength range from near UV to infrared (IR). 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 company to tune the emitted light to the wavelengths most effective for this application.
Photo 2: UVC treatment exacerbated existing damage in the strawberries while inhibiting mould growth. Credit: Sensor Electronic Technology Inc (SETi).
Photo 3: UVB (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).
According to lead USDA researcher Steven Britz, UV-LEDs provided an opportunity to use low power devices that work well in the cold and can fit in small spaces, such as refrigerator compartments. 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 that the UV-treated berries extended their shelf life twofold (i.e., 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.
The CLEO 2013 presentation ATh3N.3, “Deep Ultraviolet (DUV) Light-Emitting Diodes (LEDs) to Maintain Freshness and Phytochemical Composition During Postharvest Storage,” will be given by Stephen Britz on Thursday, 13 June at 2:45 p.m. in the San Jose Convention Centre.
Photo 1: The control sample shows mould growth on the strawberries after seven days. Credit: Sensor Electronic Technology Inc (SETi).
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