RF impedance method to estimate moisture content in small samples of in-shell peanuts

It was earlier determined that moisture content (mc) in a single in-shell peanut (peanut pod) can be estimated from the complex impedance measurements on a parallel-plate capacitor with the pod held between the plates. In this method capacitance (C), phase angle (θ), and/or dissipation factor (D) were measured with the pod between the plates at two frequencies of 1.0 and 5.0 MHz, and these values were used in an empirical equation to calculate the mc of the pod. Moisture content values obtained by this method were independent of variation in the size of the peanut pods, and the mc of the pods tested was between 5% and 20%. The predicted moisture contents were within 1% of the standard air-oven values for over 85% of the single pods tested. In the new work reported in this paper, the feasibility was assessed for estimating the average mc of a small sample of peanuts, consisting of seven or eight pods, from the complex impedance measurements made on a parallel-plate capacitor holding the pods, at the frequencies 1, 5 and 9 MHz.