RF Impedance Method for Estimating Moisture Content in Small Samples of In-Shell Peanuts

摘要

Control of moisture content (MC) in peanuts is important in preserving quality and preventing spoilage in postharvest peanuts. Rapid means of MC determination is therefore necessary during the drying of freshly harvested peanuts and, thereafter, during storage, marketing, and processing. Current practice requires the shelling and cleaning of peanut samples for moisture measurements on kernels in commercial moisture meters. New research has shown that MC can be determined nondestructively by RF impedance measurements on a parallel-plate capacitor containing small samples (seven or eight pods), thus rapidly providing results within 1% MC of the reference standard oven MC on 70%-100% of the pods over the moisture range from 5% to 23% MC. Moisture contents are predicted by computer calculation from capacitance and phase angle measurements at three frequencies of 1, 5, and 9 MHz, with an equation relating MC to differences in capacitance and phase angle at the three frequencies and empirically determined calibration constants. A practical instrument using these principles would be useful in drying, storage, marketing, and processing of peanuts