Microwave Nondestructive Sensing of Moisture Content in Shelled Peanuts Independent of Bulk Density with Temperature Compensation

Authors: Trabelsi, Samir; Nelson, Stuart; Lewis, Micah

Submitted to: Sensing and Instrumentation for Food Quality and Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2009
Publication Date: 2/4/2009
Citation: Trabelsi, S., Nelson, S.O., Lewis, M.A. 2009. Microwave Nondestructive Sensing of Moisture Content in Shelled Peanuts Independent of Bulk Density with Temperature Compensation. Sensing and Instrumentation for Food Quality and Safety.

Interpretive Summary: Dielectric properties of materials are those electrical characteristics that determine how they interact with electromagnetic fields. For example, some materials are heated much more rapidly in a microwave oven than others. Those materials that heat rapidly have a higher dielectric loss factor than materials that do not absorb much energy from the microwave fields. The dielectric properties of materials such as grain and oilseeds are also 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 determinations of moisture content. Research has shown that microwave frequencies may offer advantages for the development of new reliable moisture meters. Moisture content is especially important in the sale and storage of peanuts so that spoilage and development of toxins can be avoided. For example, it is well known that aflatoxin represents a major heath risk to both humans and animals. Rapid means for moisture assessment are essential in minimizing aflatoxin risk during storage and improvement of kernel quality and profitability to peanut growers. This paper reports success in rapidly and nondestructively measuring moisture content of shelled peanuts through microwave measurements. Three dielectric-based algorithms for sensing moisture content in shelled peanuts without knowledge of their bulk density and with temperature compensation are presented. New moisture meters might be developed using these principles that would be helpful in preventing losses due to spoilage and provide useful tools to peanut farmers, handlers, and processors, thus providing high quality products for consumers.

Technical Abstract: Dielectric methods for rapid and nondestructive sensing of moisture content in shelled peanuts from free-space measurement of attenuation and phase shift, and their corresponding dielectric properties at 10 GHz, are presented. These methods provide moisture content independent of bulk density and compensate for temperature effects. Results of moisture prediction with three density-independent moisture calibration functions are compared. For each function, the moisture calibration equation with temperature compensation is given along with corresponding standard errors of calibration. Also, the frequency behavior of each of these calibration functions was examined in the frequency range between 8 GHz and 14 GHz. Keywords – Nondestructive sensing, moisture content, shelled peanuts, dielectric properties, density independence, temperature compensation.