科学美国人60秒:Laser Zap Determines Fruit Ripeness

Ever throw an avocado in a paper bag with a banana to get the avocado to ripen faster? That trick works because both of them are what’s called "climacteric" fruits. Meaning they release ethylene gas as they mature—and the gas in turn accelerates ripening. At maximum ethylene release, the fruit reaches peak ripeness: ideal taste and texture. After that, the fruit's cells begin to die, molds move in, and it rots.

So how to determine the best time for picking—and eating? Today’s high-tech farmers might sample the ethylene released by the fruit, as it sits in an airtight container. Or use a color meter, to track a fruit's progression towards "ripe color."

But now researchers have devised what might be a simpler and more scientifically accurate technique—shooting fruit with lasers. When they zapped golden delicious apples, what bounced back was a speckled pattern of black and red dots: a measure of how the fruit's cells and water absorbed and reflected the laser light. That pattern changed over time, right in step with the fruit's release of ethylene. Meaning these images could be a good proxy for ethylene measurements, and let farmers know the best time to harvest. The study is in the journal Applied Optics. [Rana Nassif et al, Detection of Golden apples’ climacteric peak by laser biospeckle measurements]

Next, the researchers hope to develop a handheld laser for farmers, so they can shoot fruit right on the tree. It remains to be seen if laser measurement of bananas will have…appeal. 

—Christopher Intagliata

[The above text is a transcript of this podcast.]