Abstract
A gas sensor array, consisting of seven Metal Oxide Semiconductor (MOS) sensors that are sensitive to a wide range of organic volatile compounds was developed to detect rotten onions during storage. These MOS sensors were enclosed in a specially designed Teflon chamber equipped with a gas delivery system to pump volatiles from the onion samples into the chamber. The electronic circuit mainly comprised a microcontroller, non-volatile memory chip, and trickle-charge real time clock chip, serial communication chip, and parallel LCD panel. User preferences are communicated with the on-board microcontroller through a graphical user interface developed using LabVIEW. The developed gas sensor array was characterized and the discrimination potential was tested by exposing it to three different concentrations of acetone (ketone), acetonitrile (nitrile), ethyl acetate (ester), and ethanol (alcohol). The gas sensor array could differentiate the four chemicals of same concentrations and different concentrations within the chemical with significant difference. Experiment results also showed that the system was able to discriminate two concentrations (196 and 1964 ppm) of methlypropyl sulfide and two concentrations (145 and 1452 ppm) of 2-nonanone, two key volatile compounds emitted by rotten onions. As a proof of concept, the gas sensor array was able to achieve 89% correct classification of sour skin infected onions. The customized low-cost gas sensor array could be a useful tool to detect onion postharvest diseases in storage.
Highlights
Onion is an important vegetable crop around the world [1]
Onions are kept in cold storage with a dry and well-ventilated atmosphere for a period ranging from a few weeks to six months before processing
Metal Oxide Semiconductor (MOS) sensors were not commercially available to detect the specific volatiles released by onions when they are healthy or diseased
Summary
Onion is an important vegetable crop around the world [1]. Once harvested, onions are kept in cold storage with a dry and well-ventilated atmosphere for a period ranging from a few weeks to six months before processing. Major types of gas sensors include MOS, conducting polymer, surface or bulk acoustic wave (SAW or BAW) sensors, and metal oxide field effect transistors (MOSFET). Commercial E-nose technology was used to evaluate the quality of fruits and vegetables, such as detecting and classifying post-harvest diseases in blueberry fruits [20], quality of apples and oranges [21], and to differentiate various types of Allium based on their headspace volatiles and pungency [22]. They are not specific to onion post-harvest disease detection To fill this gap, a customized gas sensor array was developed, which consists of multiple MOS gas sensors, a gas delivery mechanical system, an automated electronic circuit board, and user friendly software. Two specific objectives were to: (1) develop the gas sensor array consisting of a mechanical system, electronic system, and software program; (2) characterize and test the developed gas sensor array
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