SENSING MOISTURE CONTENT AND QUALITY OF GRAIN AND OTHER AGRICULTURAL PRODUCTS BY DIELECTRIC PROPERTIES
Location: Quality and Safety Assessment Research Unit
Title: Stability and Type-Independence Analysis of Density-Independent Calibration Fuctions for Microwave Moisture Sensing in Unshelled and Shelled Peanuts
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: May 20, 2010
Publication Date: June 20, 2010
Citation: Trabelsi, S., Lewis, M.A., Nelson, S.O., Tollner, E.W. 2010. Stability and Type-Independence Analysis of Density-Independent Calibration Fuctions for Microwave Moisture Sensing in Unshelled and Shelled Peanuts. ASABE Annual International Meeting Paper No 1009857, Pittsburg, Pa. 2010.
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 10.49 percent, they cannot be sold 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. 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 lots, including Virginia and Valencia types and Runner type cultivars grown in Georgia and Texas were measured over wide ranges of frequency, moisture content, and bulk density. Density-independent moisture calibration functions, independent of peanut type, were determined for unshelled and shelled peanuts of these lots. The stability and type-independence of these calibrations was determined in terms of the coefficients of determination and standard errors. The best stabilities were noted in the frequency range from 5 to 11 GHz. The findings support the use of a single calibration 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.
Free-space-transmission measurements were used to measure the relative complex permittivities of shelled and unshelled peanuts of various types at 23°C between 5 and 15 GHz. Moisture content was estimated with three different calibration functions and compared to standard oven moisture determinations: two of these functions are permittivity-based, and the other is expressed in terms of attenuation and phase shift. The stability of these three functions for individual peanut types and type-independence was evaluated over broad ranges of frequency, moisture content and bulk density. Coefficients of determination and standard errors of calibration are presented for each function.