Don't Squeeze the Oranges Please!

?A new device that can accurately measure the ripeness of different types of fruit by detecting the presence and amounts of ethylene gas could spell the end of squeezing fruit.

If the tests of a new device developed by chemists at the Massachusetts Institute of Technology bear out, you’ll never need to squeeze an orange or other fruits to test their ripeness at your local grocery store again. The new measuring device from the MIT researchers can accurately measure the ripeness of several different types of fruit by detecting the presence and amounts of ethylene, a gas that promotes ripening in plants. So far the new sensors have been tested on bananas, avocados, apples, pears and oranges, and were able to accurately measure the ripeness of all of them without a hitch.

In fruit maturation, various fruits emit ethylene gas that causes the ripening process to begin. Once the ripening process begins, more and more ethylene is released, and the fruits respond by quick ripening. The science of measuring the ethylene in fruits is not new however, and produce warehouses have long been using expensive and complicated gas chromatography or mass spectroscopy equipment to measure ethylene levels and gauge the ripeness of fruits that are in storage. The new ethylene measuring device from MIT device is small and inexpensive in comparison, and could be used at the retail level in grocery stores to help shopkeepers determine which batches of fruit need to be sold first in order to minimize losses due to spoilage.

The MIT ethylene measuring device uses tens of thousands of tiny carbon nanotubes with copper atoms attached to them to measure the ethylene content.  The electrons will all flow freely through the nanotubes excepting any ethylene molecules present. Instead of flowing out, the ethylene molecules will bond with the copper atoms, and obstruct the flow of the electrons. The MIT device also uses small polystyrene beads to absorb the ethylene and concentrate it near the nanotubes where it can be more easily measured. In this way the sensors can determine ethylene concentrations as low as 0.5 parts per million. Those measurements work well with fruits because a concentration of between 0.1 and one part per million is required for most types of fruit to ripen.

The cost and size advantages of the newer and smaller MIT ethylene measuring device are apparent when you consider that the MIT chip and sensor combined swill only cost about $1, compared to the larger, $1,200 gas chromatography or mass spectroscopy systems. Because they are much smaller too, the sensors could eventually be built into the cardboard boxes used to store fruit, and equipped with radio-frequency identification (RFID) chips that would transmit ripeness data to inexpensive handheld reading devices used by retail stores. When new technology enters the science of food production, it seems everybody wins, and if the ripeness-detecting ethylene measuring devices pan out commercially, the MIT researchers will begin working on new monitors based on the same technology that would be able to detect when food products become moldy or develop bacterial growth.