Laser beams predict apple ripeness

Rana Nassif

Laser beams predict apple ripeness

In the 1989 movie Honey, I Shrunk the Kids, a hobby scientist played by Rick Moranis accidentally blows up an apple with the laser in his shrink ray machine. Now, scientists have found a better use for lasers trained on apples: measuring their ripeness. In a technique known as biospeckle, researchers shined a helium-neon laser on the surface of golden apples and then analyzed how the light was reflected (seen above). The laser wasn’t very powerful—just a couple of milliwatts stronger than the average laser pointer—but it picked up tiny imperfections on the apple’s smooth skin, which caused the laser light to bounce irregularly and result in a grainy appearance at small scales. As the fruits ripened, the “grains” in the pattern became smaller and smaller, the team reports this month in Applied Optics. They attribute the shrinking to a rise in an apple’s cellular activity during the ripening process—the study notes that cellular respiration, for instance, is known to increase as fruits ripen. To confirm that the smallest grains occurred during peak ripeness, the team also monitored the apples’ production of ethylene gas—a known byproduct of the ripening process that peaks just as the fruit reaches optimal edibleness. Once the apples were past their prime, ethylene gas production slowed, apple activity decreased, and the size of the reflected grains began to increase. Because traditional methods of assessing ripeness either destroy the fruit or rely on subjective visual cues, the researchers suggest that the technique could eventually help farmers accurately harvest their crops at optimal times and predict how long a fruit can be stored.

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