RF impedance method for nondestructive moisture content determination for in-shell peanuts

Abstract

A method was developed earlier for estimating the moisture content (mc) in samples of wheat, corn and peanut kernels, nondestructively, by measuring their complex impedance values. In this method, capacitance (C), phase angle (θ) and dissipation factor (D) were measured with an impedance analyser at 1 and 5 MHz on a parallel-plate capacitor holding a few kernels of a particular commodity between the plates. These values were then used in an empirical equation based on the parameters C, θ and D, and the moisture content was calculated. The calculated mc values were within 1% of the air-oven values for about 85% of the kernel samples tested in the moisture range from 6% to 20% for wheat, corn and peanuts. However, it would be useful during drying and processing of peanuts, if the mc could be determined without shelling them. In this work, the feasibility of determining the moisture content of in-shell peanuts (pods) by similar impedance measurements was investigated. Values of capacitance, phase angle and dissipation factor measured at 24 °C and at three frequencies were used in a modified prediction equation and the moisture content was estimated within 1% of the air-oven values for over 90% of the pod samples tested in the moisture range from 6% to 25%. The method is rapid and nondestructive and may be used in the development of a commercial instrument.