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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Quality and Safety Assessment Research Unit » Research » Publications at this Location » Publication #299183

Title: Dielectric properties-based method for rapid and nondestructive moisture sensing in almonds

item Trabelsi, Samir
item MCKEOWN, MURAT - US Department Of Agriculture (USDA)
item NELSON, STUART - Collaborator

Submitted to: Journal of Microwave Power and Electromagnetic Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2016
Publication Date: 6/10/2016
Citation: Trabelsi, S., Mckeown, M.S., Nelson, S.O. 2016. Dielectric properties-based method for rapid and nondestructive moisture sensing in almonds . Journal of Microwave Power and Electromagnetic Energy. doi:10.1080/08327823.2016.1190153.

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 microwave frequencies ranging from 5 to 15 GHz. The effect of temperature was taken into account in the moisture calibration equations. Results are presented for measurements on shelled almonds at temperatures ranging from 5 to 45 oC. Accuracies of the rapid microwave tests were between 0.47% and 0.96% 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 is presented for moisture determination in almonds independent of bulk density. The dielectric properties of almond were measured between 5 and 15 GHz, with a 1-GHz increments, for samples with moisture contents ranging from 4.8% to 16.5%, wet basis, bulk densities ranging from 0.565 g/cm3 to 0.7 g/cm3, and temperatures ranging from 5.2 oC to 45 oC. A density-independent calibration function expressed in terms of the dielectric properties was used to predict moisture content in almond kernels from measurement of their dielectric properties. Moisture calibration equations are given at each frequency, at room temperature (25 oC) and with temperature compensation for temperatures between 5.2 oC and 45 oC, along with their respective standard errors of calibration, which ranged from 0.47% to 0.96% depending on frequency.