Novel sensing system catches the dud spud

One bad spud can ruin the whole pile. But now, a simple electrical sensor can detect the culprit. A new device can determine that a single potato’s infected with rot-causing bacteria even while it’s buried in a crate filled with hundreds of healthy tubers.

The disease, soft rot, can run wild in a potato pile once it gets into just one bruised or otherwise damaged tuber. Spreading to neighboring potatoes, the bacterium Erwinia carotovora can turn their flesh into soft, wet mush before anyone notices the infection. Eventually, the spuds will emit a strong-smelling gas with such components as ethanol and acetone.

Soft rot can be one of the most important pathogens of potatoes in storage, comments Gale E. Kleinkopf of the Kimberly Potato Storage Research Facility in Kimberly, Idaho. “It can take an entire storage out in a matter of weeks,” he says.

Now, researchers in England have developed an instrument that detects the vapors from infected potatoes long before a human nose does, they report in the December Measurement Science and Technology. The device, consisting of ceramic-based sensors, reveals an increase in the concentration of telltale gases above a potato bin.

Each match-head-size sensor has a particular electrical resistivity, which varies with the amount of oxygen at its surface. When soft-rot bacteria attack a potato, the resulting gases react with oxygen near the sensor. This, in turn, leads to easily detectable changes in the sensor’s resistivity.

After testing various sensors differing in thickness and chemical composition, the team constructed a new prototype device that includes the three best performers. Then, they infected several potatoes and placed each with a bunch of healthy tubers. The instrument could detect even a single infected potato in a pile of about 900, says team member Ben de Lacy Costello of the University of the West of England in Bristol.

Such a method could eventually be used commercially to identify early signs of spoilage. This could be especially valuable where potatoes are stored year-round for making such processed foods as french fries and potato chips, he says.

The researchers appear to have come upon a suitable set of sensors that detect several different gases at once, comments Richard Jones of the Agricultural Research Service in the U.S. Department of Agriculture in Beltsville, Md. However, he notes, it’s still unclear whether these gases are specific to bacterial soft rot, since the team hasn’t reported tests on any other type of tuber infection.

According to figures from the Economic Research Service of the USDA, each person in the United States eats an average of about 50 pounds of fresh potatoes a year. If processed potatoes, such as those used for chips and fries, are included, the 1999 per capita tally comes to about 140 pounds of spuds.

“Anything that would give us an earlier look at problems in storage would really be beneficial,” says Kleinkopf.

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