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Japanese mandarin orange producers use ultraviolet rays to slow spoilage

This photo shows the machine that applies ultraviolet rays to mandarin oranges in Yuasa, Wakayama Prefecture, on Nov. 16, 2020. (Mainichi/Satoshi Mogami)

YUASA, Wakayama -- "Mikan" mandarin orange producers in this west Japan town have begun using machines that can expose the fruit to ultraviolet rays and slow spoilage.

    The apparatus was developed by Saika Technological Institute Foundation, a general incorporated foundation based in the city of Wakayama. To ensure its invention could be installed on conventional shipment lines, the foundation has made the machine smaller than its prototype.

    Mikans on the conveyor belt pass through the machine and are bathed in ultraviolet rays. The exposure causes the citrus skin to produce "scoparone," an organic compound and type of polyphenol with an antibacterial effect. The foundation started developing the machine in 2017, and in 2019 published their research results. The device can apply ultraviolet to about 700 kilograms of mikan mandarin oranges per hour.

    In their experiments, the foundation stored 40 mandarin oranges that had been cut in half in 20 degrees Celsius and 90% or more humidity for a week. One group of mikans was treated with ultraviolet rays, while the other was not. They found that mikans exposed to the light were less spoiled, and that even though some had rotted, the speed at which they did was slower.

    Mitsuhiro Oakada, a 57-year-old mikan farmer from Yuasa who primarily ships his produce to supermarkets in the Tokyo metropolitan area, has implemented the machine to apply ultraviolet rays to the mikans right before they're boxed. He expressed his expectations for its effectiveness, saying, "I wanted to take a chance on the possibility that the quality (of the mikans) improves, even if just by a little."

    The foundation is also developing a machine to screen for scarred oranges.

    (Japanese original by Satoshi Mogami, Wakayama Bureau)

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