SENSING MOISTURE CONTENT AND QUALITY OF GRAIN AND OTHER AGRICULTURAL PRODUCTS BY DIELECTRIC PROPERTIES
Location: Quality and Safety Assessment Research Unit
Title: Type-Independent Calibration Method for Microwave Moisture Sensing in Unshelled and Shelled Peanuts
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: April 28, 2008
Publication Date: June 21, 2009
Citation: Lewis, M.A., Trabelsi, S., Nelson, S.O., Tollner, E.W. 2009. Type-Independent Calibration Method for Microwave Moisture Sensing in Unshelled and Shelled Peanuts. ASABE Annual International Meeting.
Interpretive Summary: Electrical characteristics, known as dielectric properties, of grain and oilseeds, are closely related to the amount of water that they contain. Consequently, instruments can be designed to sense these dielectric properties and be calibrated to read moisture content. Such instruments, called moisture meters, are widely used in the grain and seed trade for rapid determination of moisture content. Moisture content is especially important in the sale and storage of peanuts so that spoilage and development of toxins can be avoided. If kernel moisture contents of peanut lots exceed 10.5 percent, sale is unlawful in the United States. Microwave dielectric properties of peanuts are being studied for use in development of microwave moisture meters for use in the peanut industry. In particular, the microwave measurement technique provides a method for reliably measuring the moisture content of the peanut kernels from measurements on the unshelled peanut pods. In these studies, moisture content of kernels from such measurements over a range from 6 to 22 percent moisture content were determined with accuracies of one-half of one percent moisture content. Current moisture meters require the shelling of samples to determine moisture content of the kernels. At peanut buying points, samples go through a thorough grading process before the moisture content is determined, and at that time the decision is made as to whether the peanut lot can be sold Thus, the new microwave moisture technique offers a real advantage in peanut grading operations, because moisture content can be determined at the beginning of the grading process, and if it is too high, the time and labor lost in grading those samples can be avoided. In this new work, dielectric properties of four peanut types, Runner, Spanish, Virginia, and Valencia, from various growing locations in the United States were measured and moisture calibrations were determined for each type. Then a calibration was developed independent of peanut type with accuracies of less than 1 percent moisture content over the range from 6 to 22 percent.. Thus, a single calibration can be used for all types of peanuts, which is a real advantage for moisture meter manufacturers and users of such instruments. The new microwave moisture meters offer promise for improving efficiencies of grading and processing as well as preventing losses due to spoilage and will be useful tools for peanut farmers, handlers, and processors, thus providing safe and high quality products for consumers.
A microwave dielectric method was used for nondestructive and instantaneous determination of moisture content in shelled and unshelled peanuts from measurement of their relative complex permittivities in free space at 6.0 GHz and 23°C. Moisture content was determined independent of bulk density with the use of a density-independent calibration function. Statistical analysis provided the moisture calibration equations for each type with high coefficient of determination. The effectiveness of this method was further shown with the provision of a single moisture calibration equation for various types in shelled and unshelled peanut samples. Therefore, by using microwave moisture sensing, moisture content can be accurately predicted in different peanut types with a single calibration equation.