Design and performance of an impedance analyzer for nondestructive moisture content determination of in-shell peanuts

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.