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ARS Home » Southeast Area » Dawson, Georgia » National Peanut Research Laboratory » Research » Publications at this Location » Publication #152419


item Kandala, Chari

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2003
Publication Date: 6/30/2003
Citation: Kandala, C. 2003. Determination of peanut pod and kernel moisture contents by rf impedance mesurements. American Society of Agricultural Engineers Meetings Papers.

Interpretive Summary: Peanut is a major crop in three regions of the U.S., particularly the Southeast. Peanuts have become an important food item, and the U.S. peanut industry strives to produce high quality edible products for domestic and foreign customers. To assess their quality, peanuts are inspected and graded by trained inspectors before farmer marketing. One of the prominent factors, not only in the grading but also in the storage and utilization of the peanuts, is their moisture content. Moisture content is presently measured with commercial moisture meters that measure average moisture content for samples that are about 200g. Single kernel moisture contents at farmer marketing lots could be high. This may be an indication of improper curing that would affect the quality of the peanuts. Single kernel moisture measurements would be useful in estimating the variation of moisture content among individual kernels as an indicator of peanut quality. The variation of single kernel moisture within a farmer stock lot could be a parameter in further handling, such as additional drying or immediate transport to the shelling plant. It would be very useful if the peanut kernel moisture could be estimated from physical measurements made on the pod itself. This would save the time required to shell the peanuts and clean the kernels before they can be used for measurements. Earlier experiments showed a good correlation between the peanut pod and the kernel moistures as measured by the standard oven method. In this work the peanut pod moisture was calculated from RF Impedance measurements, and the kernel moisture content was derived using a simple equation. There was a fair agreement between the moisture content values thus obtained and the standard air-oven values. This method is rapid and nondestructive and offers a basis on which a practical instrument could be developed.

Technical Abstract: Moisture content (mc) of individual peanut kernels, Arachis hypogaea L., was earlier determined by measuring the complex impedance of a parallel-plate capacitor with a kernel held between the plates. The method was based on measuring the capacitance, dissipation factor, and/or phase angle of a parallel-plate capacitor with a single peanut between the plates at 1.0 and 4.5 MHz. These values were used in an empirical equation to calculate the mc of the kernels ranging between 5 and 15% moisture. The calculated mc values were within 1% of the air-oven values for 90% of the kernels tested and were independent of kernel size. In this present work similar impedance measurements were made at two frequencies, 1 and 5 MHz, on single peanut pods as well as on each of the kernels taken out of the pods. Two empirical equations were developed, one for estimating the mc in single pods and the other for single kernels. The mc values thus obtained were compared with the values obtained by the standard oven method in each case and agreed well enough for practical use.