ARS | Publication request: Microwave dielectric method for moisture sensing almonds

Submitted to: Microwave International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 6, 2010
Publication Date: July 15, 2010
Citation: Trabelsi, S., Nelson, S.O. 2010. Microwave dielectric method for moisture sensing almonds. 44th Annual Microwave Symposium Proceedings; Denver, Colorado; July 14-16, 2010, pp. 161-166.

Interpretive Summary: Moisture content is the most important parameter that determines the quality and safety of agricultural and food products. Therefore, accurate determination of moisture content is key in defining optimum conditions for better handling, processing and storage of these products. For almonds, initial moisture content and moisture migration are critical to the preservation of their quality and safe storage. Among nondestructive and rapid methods for moisture determination, dielectric-based microwave methods are the most promising. They rely on correlating intrinsic electrical properties of the material, called dielectric properties, with water content. The dielectric properties are those properties that determine how materials interact with electric fields. A common example of this interaction is the way materials heat differently in microwave ovens. The dielectric properties of materials are dependent on frequency, temperature, composition, and, for granular and particulate materials, they are also dependent on bulk density. In this study, a density-independent calibration function developed in research on microwave moisture sensing in grain and seed was used to predict moisture in almond kernels from measurement of their dielectric properties at a single microwave frequency. The effect of temperature was taken into account in the moisture calibration equation. Results are presented for 8-GHz measurements on shelled almonds at temperatures ranging from 5 to 45 oC. Accuracies of the rapid microwave tests were about 0.5% moisture content for the entire temperature range. Thus, the research indicates good potential for development of microwave moisture meters for almonds that would be helpful to growers and processors in providing high quality almonds for consumers.

Technical Abstract: A dielectric –based method was developed for rapid and nondestructive determination of moisture content in almond kernels independent of bulk density from measurement of their dielectric properties at a single microwave frequency. Calibration equations for moisture determination with temperature compensation is given at 8 GHz along with the standard errors of calibration at 25 oC and for temperatures ranging from 5 oC to 45 oC.