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A Nano-Nose To Keep Our Fruit Fresh Longer

Detecting ripening fruit–and then slowing the process–could prevent incredible amounts of wasted food. A new super-sensitive device might be able to pick up telltale signs earlier than ever.

A Nano-Nose To Keep Our Fruit Fresh Longer
Elena Itsenko/Shutterstock

Here’s an undeniable fact: Most of us like eating fruits and vegetables when they’re ripe. Here’s another undeniable fact: When produce gets too ripe, it starts to rot. That stinks. In the produce business, they call that shrink. Shrink cuts into everyone’s bottom line. Shrink means wasted food and this kind of garbage accounts for a remarkable percentage–an estimated 30%–of what farmers grow.

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Timothy Swager is a chemistry professor who has made a name for himself at MIT’s Institute for Soldier Nanotechnologies by developing ultra-trace-sensing equipment: high-tech bomb sniffing equipment. He’s spent years developing systems that surpass the average particle detectors in airports, equipment that mimics a dog’s sense of smell, technology that can sniff out minuscule “chemical vapor signatures.” He’s never heard of shrink, but Swager’s lab recently developed sensors that act sort of like high-tech Labrador retrievers capable of sniffing out ripening produce. (Even if these pups existed, which they don’t, what kind of a hairnet would Fido the Fruit Sniffer have to wear to conform with food safety guidelines?)

The sensors use nanotechnology to detect ethylene, the plant hormone responsible for releasing enzymes that convert starches into sugars (amalase), reduce acidity (kinase), and soften flesh (pectinase). Ethylene gas is responsible for ripening in parts per million–the gaseous equivalent of one drop from an eye-dropper in the average kitchen sink–but until now, its chemical make-up made it notoriously difficult to detect a tiny whiff of its dank, day-after-a-keg-party smell.

Two researchers in Swager’s lab–Jan M. Schnorr and Birgit Esser–created the sensor by connecting carbon nanotubes between two gold electrodes. (“They’re a little flexible,” Swager says, “somewhere between cooked spaghetti and uncooked spaghetti.”) They then attached copper-containing molecules to these tubes to catch ethylene, allowing the gas to be measured, and thereby detecting the difference between ripe and rotten. “If you control this, you can manage food in terms of distribution, storage, and strategic ripening,” he says. “If you can measure ethylene better, then that has big implications for probably one of the most important commodities: Food.”

The sensors are smaller than a conventional UPC bar code. They require little energy and can be built for a matter of cents. As such, Swager believes wireless RFID (radio-frequency identification) could send information from the nano-sniffing produce stickers to truckers, distributors, and storage facilities–telling them when to add fresh air or start pumping in ethylene gas. “You can slow things down or let them ripen faster when you have a system that can tell you when to ventilate,” he says. “You could even put a sensor on your own refrigerator at home.”

Before the remote ethylene sensors become a commercial reality and start to shrink our mountains of wasted shrink, the lab needs to put some finishing touches on its prototype. Swager says, “If you’re going to put this in anybody’s hands, you have to be able to dump beer on it and still have it work.” And if all goes as planned, he says he has another innovation that could transform the future of mushroom foraging. “I have a dream of developing a sensor so you don’t have to use dogs to find truffles.”

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