Researchers have discovered a new way to detect the earliest signs of ripening in fruit and vegetables, and in real-time – a discovery that could substantially reduce the amount of food loss occurring throughout the supply chain.
Writing in the journal ACS Central Science, the researchers describe their invention: a portable sensor made out of carbon nanotubes, which can detect ethylene – the hormone plants emit as they ripen – in minuscule quantities, just seconds after it’s released. The new tool senses ethylene emissions of just 15 parts per million (ppm): this incredibly high sensitivity could help farmers, food carriers, and grocery stores make smarter decisions about how to manage and use fruit and veg before it rots.
“Knowing [ethylene] emissions can help to manage the inventory at [grocery] stores, and make decisions about transportation and distribution,” explains Timothy Swager, lead author on the study, and professor of chemistry at the Massachusetts Institute of Technology. “It is also clear that plants in distress can give off ethylene, and you could imagine monitoring plant health with micro sensors based on our materials.”
To develop the new sensor, he and his team used nanotubes made out of carbon, combined with the metal, palladium. In the presence of ethylene, palladium triggers a process called oxidation, which causes ethylene to lose some of its electrons, which then flow to the metal. In turn, the palladium then passes these electrons onto the carbon nanotubes, making those tubes more conductive. That drives a measurable change in the current that can be correlated to the precise amount of ethylene that’s present in the air.
An earlier version of the sensor, which the researchers developed in 2012, could only detect ethylene at 500 ppm – so this new iteration is notably finer-tuned. This could enable much closer management of fruits and vegetables as they make their way through the supply chain.
Overall, this could have huge practical benefits. The Food and Agriculture Organization estimates that in developing countries, between 30 to 40% of food is lost before it even reaches the market. The researchers add that an estimated 50% of a farm’s production value can potentially be lost thanks to failures along the supply chain. So this industry is ripe (excuse the pun) for interventions like these.
There are probably other expensive chemical sensors out there that can detect ethylene at similar levels, Swager says. But this is the first portable sensor to reliably do this with such sensitivity, he adds. That could give it more widespread practical value in the food industry.
The root of the researchers’ discovery lies, unexpectedly, in flowers, which were the basis of the experiment. Flowers emit small amounts of ethylene just before their petals unfurl – making them ideal candidates for helping determine the sensor’s reactivity. Using carnations and lisianthus, the researchers enclosed the blooms inside a chamber along with the sensor, which revealed that it could detect the spike of ethylene in real-time, shortly before the flowers bloomed.
Having recently patented their new hypersensitive invention and licensed it to a start-up for production, Swager thinks the sensor could one day find multiple uses in everything from fruit ripening and cold storage facilities, to grocery stores – “and even in your refrigerator,” he says.
Bit by bit, inventions like these could help to bring down the devastating and unnecessary loss and waste that haunts our food systems.
