ARS | Publication request: Phase angle and Impedance Measurements for Nondestructive Moisture Content Determination of In-Shell Peanuts Using a Cylindrical Sample Holder

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: January 15, 2007
Publication Date: June 17, 2007
Citation: Kandala, C., Butts, C.L. 2007. Phase angle and Impedance Measurements for Nondestructive Moisture Content Determination of In-Shell Peanuts Using a Cylindrical Sample Holder. ASABE Annual International Meeting. Paper Number 076215.

Interpretive Summary: Moisture content (mc) in peanuts is presently determined using capacitance type meters. The peanut samples need to be shelled and cleaned before they are placed in the sample holder of these meters for mc measurement. Cleaning and shelling of samples involves considerable time and labor. Also these samples, once shelled and cleaned, are usually discarded after the mc measurement. Thus large quantities of edible peanuts are lost during these tests. It would be useful if the mc of the peanuts could be determined by physical measurements on the in-shell peanuts itself. In this work a parallel-plate electrode system fitted inside an acrylic cylinder that measures the mc of in-shell peanuts in conjunction with a low cost impedance meter is described. The system was initially calibrated using peanut pod samples of known mc values in the moisture range of 7 to 17%. The calibration constants generated were used in a semi-empirical equation developed, and the mc of peanut pod samples were calculated using the measured impedance values at the frequencies of 1 and 5 MHz. The calculated mc values of these samples were compared with the mc values of the samples obtained by the standard air-oven method and were found to be within 1% of the air-oven values for over 90% of the samples tested. This method is rapid and nondestructive.

Technical Abstract: Two parallel-plate electrodes were mounted inside a cylinder, made of a non-conducting material. The space between the plates was filled with peanut pods and the capacitance and phase angle of this system was measured with a prototype low-cost impedance meter, designed for this purpose. Measurements were made at frequencies of 1 and 5 MHz on peanut pod (in-shell) samples of known moisture content between 7 and 17% (wet basis). Using these measured values an empirical equation was developed from which the average moisture content of a peanut pod sample could be calculated from its impedance values. The calculated moisture content values were compared with their air-oven values and were found to be within 1% of the air-oven values for over 90% of the samples tested. The size of the sample used was about 100 g and no shelling or cleaning of the sample is involved. This method is rapid and nondestructive.