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Blue glow reveals rice quality

21 Jul 2005

The variety, region of origin and chemistry of rice is revealed by its blue-green photoluminescence.

Checking the quality and purity of rice could become easier thanks to a photoluminescence (PL) imaging system that can reveal any contamination or non-uniformity. Scientists in Japan have shown that blue-green (462 nm) emission given off by rice excited with UV (365 nm) light changes depending on its type, where its grown and its mineral content.

The rice is simply illuminated with UV light from a mercury lamp and the resulting PL signal is collected by a filtered CCD camera and then analysed on a computer. Similar optical schemes are already used to check the ripeness of fruit ( Lasers test the sweetness of fruit (May 2005)).

In experiments, the research team from Toyo University found that they could successfully distinguish between grains of glutinous and non-glutinous (akita-komachi and koshihikari). What’s more the strength of the signal depends on the source of the rice and its nutritional value.

“The local atmospheric variations over the plant fields such as temperature, sunshine, wind and rainfall which influence the growth of the plants seem to be responsible for the variations,” say researchers from the university’s Sensor Photonics Research Center in a paper on the topic (Review of Scientific Instruments 76 073702 2005).

“It is also reasonable that the relative contents of amylopectin and amylase, concentration of amino acids and inorganic minerals such as calcium, sodium and potassium may influence the PL intensity of rice.”

The quick and non-invasive nature of the inspection process means that it could be ideal for use in a factory environment.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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