ARS | Publication request: Design and Performance of an Impedance Analyzer for Nondestructive Moisture Content Determination of In-Shell Peanuts

Submitted to: IEEE Instrumentation & Measurement Society
Publication Type: Proceedings
Publication Acceptance Date: February 12, 2008
Publication Date: June 12, 2008
Citation: Kandala, C., Butts, C.L. 2008. Design and Performance of an Impedance Analyzer for Nondestructive Moisture Content Determination of In-Shell Peanuts. IEEE Instrumentation & Measurement Society. (2008) 2:240-246.

Interpretive Summary: MC is a significant factor in the assessment of the quality of peanuts used to make edible products and is measured at various stages such as at harvest, drying, processing and storage. MC measurement is presently done using capacitance type moisture meters. For this method, the peanuts have to be shelled and cleaned, and this is time-consuming. The test samples are usually discarded, resulting in cumulative loss of edible peanuts. A method was developed earlier to determine the MC of in-shell peanuts (peanut pods) from the impedance measurements made on a parallel-plate system holding the peanuts between them, using either a commercial impedance meter. The measurements made were on seven or eight pods held between the parallel-plates and thus it was possible to measure the average moisture of a small sample. This small parallel-plate system would be useful for detecting any high moisture peanuts blended in a larger sample of peanuts that might have escaped detection while MC measurements were made on bulk samples (300 to 500 g). However, it would be convenient to measure MC on moderately large quantities of peanut pod samples, say 100 to 150 g, which would yield better estimation of the average MC of peanuts being dried in a large trailer. While the commercial impedance meters performed well in the establishment of the impedance method for moisture determination, they have several extra features that are not needed for this work which make them expensive. Thus a low-cost meter that would measure the impedance parameters at the required frequencies on a moderately large sample of in-shell peanuts would be useful in the estimation of their moisture content. From the peanut pod moisture values the MC of the peanut kernels, the parameter presently measured and monitored in the industry, can be estimated to an acceptable accuracy.

Technical Abstract: Moisture content (MC) in peanuts is measured at various stages of their processing and storage in the peanut industry. A method was developed earlier that would estimate the MC of a small sample of in-shell peanuts (peanut pods) held between two circular parallel-plates, from the values of capacitance and phase angle measured by a commercially available impedance analyzer, at three frequencies 1, 5 and 9 MHz. These values were used in an empirical equation, developed using the capacitance and phase angle values of samples of known MC levels, to obtain the average MC values of peanut samples with moisture contents in the range of 6 to 20%. In the present work, a low-cost impedance analyzer, designed and assembled in our laboratory was used to measure the impedance and phase angles at 1, 5 and 9 MHz. The MC values predicted by the analyzer were compared with those obtained by the standard air-oven method. For 93% of the samples tested in the moisture range between 9% and 20% the MC values were found to be within 1% of the air-oven values. Ability to determine the average MC of in-shell peanuts without shelling and cleaning them, with a low-cost instrument, will be of considerable use in the peanut industry.