On The Road To A New Sensor, Students Monitor Bananas

Note: See this story on the Web at http://www.umaine.edu/mainesci. Photos of the experiment backlit by fluorescent light are available from the Department of Public Affairs.

ORONO, Maine -- A new sensor research project at the University of Maine has students and faculty going bananas. In their effort to develop a fruit ripeness sensor that could be useful for growers and food processors, they are monitoring bananas for natural emissions of ethylene gas.

John Vetelino, a professor in the Department of Electrical and Computer Engineering (ECE), says that ethylene is an indicator of the ripening process in many fruits and vegetables. A sensor that detects minute quantities of the tell-tale gas could save the food products industry money by providing precise information about the best time to pick, store and process produce. Vetlino is a pioneer of UMaine’s sensor program in the Laboratory for Surface Science and Technology (LASST).

"This is a pilot project to determine if the technology will work for this purpose," he says. The project is funded by a $49,918 grant from the U.S. Department of Agriculture. Vetelino is working with Al Bushway of the UMaine Department of Food Science and Human Nutrition, Bruce Segee of ECE, and three electrical engineering students: Jeremy Thiele, a sophomore from Hollis, Maine; Jie Zhou, a master’s student from Wuhan, People’s Republic of China; and Stephanie Pitcher, a junior at the University of Colorado from Colorado Springs.

Pitcher came to UMaine in the summer of1999 as part of the Research Experience for Undergraduates (REU) program which Vetelino has coordinated over the past two decades with National Science Foundation funding. She returned to Orono during the holiday vacation to continue working on the project and intends to enroll as a master’s student at UMaine after graduation.

"The benefit to industry would be having a non-destructive way to monitor food quality," says Bushway. "The end result will be better products the consumer."

"This is a new direction for the laboratory," says Vetelino. "We’ve got major projects going with the Department of Defense in the area of chemical and biological sensors and the National Institutes of Health in sensors related to human health. Our science is driven by practical applications, and this project has gotten lots of support from people in the food industry."

A ripeness sensor could be a boon to growers by indicating when crops are ready to pick. Ideally, harvesting should be done at the peak of ripeness. However, large commercial farms must often pick early, just as produce begins to ripen. There is a danger, however. If they pick too early, the produce may not ripen at all.

"As fruits and vegetables start ripening, they emit very small concentrations of ethylene, in the parts per million range," says Vetelino. "Our sensors have to be sensitive enough to detect that level."

Food processors face similar issues, he adds. As produce is held in storage, peak ripeness occurs as ethylene concentrations reach a maximum. For most purposes, that is the ideal time to begin processing.

"If processors wait too long, you get fermentation and alcohols and other compounds that are generally undesirable," says Vetelino.

The goal of the banana monitoring experiments is to determine how ethylene gas concentrations correspond to different stages of ripeness, says Vetelino. Researchers will use the data to calibrate sensors. Students have placed the bananas in sealed jars, and the gases emitted by the fruit are analyzed by high performance gas chromatography. The procedure is being carried out in the Water Research Institute which occupies the Sawyer Environmental Research Center with LASST.

The project is in a very early stage of development, and Vetelino knows that a number of difficult issues still need to be addressed. For example, the sensor must respond to ethylene and not any of the other compounds that are emitted by fruits and vegetables.

The sensor also has to be able to perform continuously without becoming "poisoned." That can occur when the sensing element becomes clogged with the chemical being detected. In fact, some sensors are designed to be used once and then discarded. In that case, being "poisoned" is not a problem. However, for constant monitoring of produce, the sensor must be able to indicate varying levels of ethylene gas as products ripen.

Ultimately, gas levels detected by the prototype sensor will be translated by an intelligent software program to give a clear indication of ripeness. Bruce Segee, an expert in such systems, will supervise that part of the project.

The sensor program in LASST has also tackled several other USDA funded food quality projects in the past year. In collaboration with the Sensor Research and Development Corporation (SRD) in Orono, LASST scientists are working on a device to monitor compounds emitted from fish as an indicator of freshness. Another team led by David Frankel, senior scientist at LASST, is working on a sensor to detect pesticide residues on fruits and vegetables. Graduate and undergraduate students are involved in each of these projects.

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