UV Light Keeps Strawberries Fresh in the Fridge

Strawberry Fields may live forever in the Beatles' song, but fresh strawberries survive for only two or three days in the refrigerator. Now experiments with specially-produced LEDs have shown how ultraviolet light can keep the fruit mold-free for as many as nine days.

UV lights in refrigerators have been tried before, but have failed to extend the life of stored fruits and vegetables because they dried the produce out. But new research being presented next week at the Conference on Lasers and Electro-Optics (CLEO: 2013) suggests that low-level LED-based UV light could lengthen the shelf life of strawberries without the drying problem.

"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 Steven Britz, lead researcher at the U.S. Department of Agriculture (USDA), in a press release.

LEDs have already shone a bright light on efforts to boost food production—different colors of LEDs have already helped Dutch researchers to hack tomato plants in a way that affects size, height and color. But the recent USDA tests represent the latest in a long line of attempt to use irradiation to preserve the safety and shelf life of food.

The UV-LEDs, which were created by Sensor Electronic Technology, Inc. (SETi), can be made to replicate the entire UV spectrum—from UVA to UVC—in a way that allowed the USDA team to see which UV wavelength proved most effective for preventing produce from rotting.

Tests took place with one batch of strawberries placed in a dark refrigerator and another placed in a refrigerator exposed to UV-LEDs. The UV-treated berries had a significantly longer shelf life based on factors such as visible damage, mold growth, concentration of certain chemicals that naturally occur in fruit, weight and moisture content.

The UVB wavelengths proved especially effective in both blocking mold growth and preventing damaged areas of the strawberries from spreading. By comparison, UVC light blocked mold growth but worsened the existing damage on the strawberries.

Researchers plan to begin commercializing the UV-LEDs for use in home refrigerators. Luxury fridges such as the high-end Sub-Zero refrigerators already use UVC light as part of their air purification systems. But apparently few, if any, commercial fridges expose the fruits and veggies to direct UV light.

It's not difficult to imagine "smart" refrigerators of the near future actively texting or emailing homeowners about when the strawberries or other produce are about to expire. Better food preservation could provide a small part of the solution for cutting down on the huge amounts of food that goes to waste—about 1.3 billion metric tons worldwide every year, or a third of all food produced for human consumption.

Photo: Brian Prechtel | USDA