New sensor can accurately measure fruits’ ripeness.

New Tecnology helping prevent loss of produce from spoilage. Sensor can detect concentrations of ethylene as low as 0.5 parts per million. 

Every year, U.S. supermarkets lose roughly 10 percent of their fruits and vegetables to spoilage, according to the Department of Agriculture. To help combat those losses, Massachussets Institute of Technology (ITT), have built a new sensor that could help grocers and food distributors better monitor their produce.

The new sensors, can detect tiny amounts of ethylene, a gas that promotes ripening in plants. Swager envisions the inexpensive sensors attached to cardboard boxes of produce and scanned with a handheld device that would reveal the contents’ ripeness. That way, grocers would know when to put certain items on sale to move them before they get too ripe.

“Food is something that is really important to create sensors around, and we’re going after food in a broad sense,” Swager says. He is also pursuing monitors that could detect when food becomes moldy or develops bacterial growth, but as his first target, he chose ethylene, a plant hormone that controls ripening.

Plants secrete varying amounts of ethylene throughout their maturation process. For example, bananas will stay green until they release enough ethylene to start the ripening process. Once ripening begins, more ethylene is produced, and the ripening accelerates. If that perfect yellow banana is not eaten at peak ripeness, ethylene will turn it brown and mushy.

Detecting ripeness

Researchers built a sensor consisting of an array of tens of thousands of carbon nanotubes: sheets of carbon atoms rolled into cylinders that act as “superhighways” for electron flow.

To modify the tubes to detect ethylene gas, the researchers added copper atoms, which serve as “speed bumps” to slow the flowing electrons.

Copper atoms slow the electrons a little bit, but when ethylene is present, it binds to the copper atoms and slows the electrons even more. By measuring how much the electrons slow down — a property also known as resistance — the researchers can determine how much ethylene is present.

To make the device even more sensitive, the researchers added tiny beads of polystyrene, which absorbs ethylene and concentrates it near the carbon nanotubes. The researchers can detect concentrations of ethylene as low as 0.5 parts per million. The concentration required for fruit ripening is usually between 0.1 and one part per million.

The researchers tested their sensors on several types of fruit — banana, avocado, apple, pear and orange — and were able to accurately measure their ripeness by detecting how much ethylene the fruits secreted.


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