The zNose Knows Ripeness

For some fruits, degree of ripeness is evident just by looking—bananas, anyone? For others, such as peaches and pears, a mere touch can tell you what your eyes might not—squish!

But melons are another matter. Their rinds don’t change color as they ripen, and if you Google “How do you know when a melon is ripe?” you’ll find dozens of techniques: Shake them, thump them, look for a dent on the stem end, and so on.

Now, an electronic nose may hold the secrets to melon ripeness and could provide the answer much more quickly than the previous scientific method—gas chromatography—which takes up to an hour to analyze a single sample.

Both gas chromatography and the electronic nose, known as zNose and produced by California-based Electronic Sensor, analyze the characteristic volatile blend of aromas given off by a melon that is ripe. Scientists in the laboratory of Florence Negre-Zakharov, PhD, assistant professor in the department of plant sciences at the University of California-Davis, studied zNose to see if its one-minute “sniff” was as accurate as gas chromatography. It was.

“Not only is gas chromatography time-consuming, it’s also a very expensive instrument that requires specialty training. But with very little training, almost anyone could learn to use the zNose pretty quickly,” said Simona Vallone, PhD, a postdoctoral associate in Dr. Negre-Zakharov’s lab and the lead author on a recent study of the technology. “The rapidity of the measurement, along with how portable the instrument is, makes it very useful for industry and perhaps even in the field by farmers.”

Dr. Vallone noted that, in addition to melons, mangoes are another fruit for which external characteristics like color change don’t necessarily correlate with ripeness. “Our main goal is to help industry and growers increase the consumption of their products,” she said. “People might not buy a product if they’re not able to determine if a fruit is ripe or not, or they might not repeat the purchase if they’ve had a bad experience.”

Dr. Vallone said the group thinks the technology could be made even more sensitive. They plan more field tests to determine how sensitive the technology will be when background smells like soil, air, and other produce compete for its sniffing skills.

The research was published March 30 in the Journal of Visualized Experiments.

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