Biosystems Engineering (2006) 93 (2), 153–160 doi:10.1016/j.biosystemseng.2005.11.001 PH—Postharvest Technology Dielectric Properties of Flaxseeds as affected by Moisture Content and Bulk Density in the Radio Frequency Range K. Sacilik 1 ; C. Tarimci 2 ; A. Colak 1 1 Department of Agricultural Machinery, Faculty of Agriculture, Ankara University, 06130, Aydinlikevler, Ankara, Turkey; e-mail of corresponding author: sacilik@agri.ankara.edu.tr 2 Department of Engineering Physics; e-mail: Faculty of Engineering, Ankara University, 06100, Tandog˘an, Ankara, Turkey; e-mail: tarimci@eng.ankara.edu.tr (Received 21 February 2005; accepted in revised form 8 November 2005; published online 4 January 2006) The dielectric properties of flaxseed were determined in the ranges of 592–2218% dry basis (d.b.) for moisture content, 5867–7229 kg m 3 for bulk density and 50 kHz–10 MHz for frequency of applied electric field using a parallel-plate capacitor sample holder. Effects of the parameters such as moisture content, bulk density and frequency on the dielectric properties were studied. The relative permittivity, loss factor, loss tangent and the a.c. conductivity were greatly influenced by the moisture content, bulk density and frequency. The moisture content was the most significant factor affecting the dielectric properties of flaxseeds. The relative permittivity and loss factor increased with an increase in moisture content and bulk density and with a decrease in frequency. The dependence of the loss factor and loss tangent on frequency was less regular than that of the relative permittivity. The a.c. conductivity was observed to increase more rapidly with increasing moisture contents than with increasing frequencies. The relative permittivity and loss factor of flaxseeds were adequately estimated by empirical equations composed of moisture content, bulk density and frequency. Also, both models provided a practical and suitable way to predict the relative permittivity and loss factor within the experimental range of study. r 2005 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd 1. Introduction Flaxseed or linseed (Linum usitatissimum L.) is an annual oilseed crop that belongs to the family Linaceae and the small flat oval seed from flax. It is a rich source of a-linolenic acid, averaging 18% of the total seed weight and constituting 53% of the total fatty acids and soluble and insoluble fibres. Therefore, it is of consider- able nutritional value for human and animal diet. It has been gaining popularity in the health food market because of its reported health benefits and disease prevention properties attributed to flaxseed compo- nents. In addition, use of whole flaxseeds in bakery products and breakfast cereals has increased in recent years (Wanasundara et al., 1999; Li–Chan & Ma, 2002; Mustafa et al., 2002). The flaxseed is one of the most important oilseed crops grown worldwide. The annual world production of flaxseeds was estimated at about 21 Mt from 25 million ha of land. The four leading flaxseed producing countries are Canada with the largest production of 754 400 t, followed by China with 466 000 t, USA with 264 830 t and India with 172 600 t (FAO, 2003). Dielectric properties of agricultural materials and products are increasingly applied as new technology is adapted for use in agriculture and related industries. The dielectric properties of these materials are impor- tant in the design of electrical and electronics equip- ment, and suitable techniques for measuring these properties for various applications have been developed as they were needed (Nelson, 1999). The dielectric properties of cereal grains and oilseeds are essential for understanding their electric behaviour, and the devel- opment of indirect non-destructive methods for deter- mining their physical properties (Trabelsi & Nelson, 2003). In agriculture, the dielectric properties of grains ARTICLE IN PRESS 1537-5110/$32.00 153 r 2005 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd