SENSING MOISTURE-CONTENT OF PECANS BY RF IMPEDANCE AND MICROWAVE RESONATOR MEASUREMENTS

The moisture content of in-shell pecans, Carya illinoensis (Wangenh.) K. Koch, was measured by radio-frequency (RF) impedance measurements of a parallel-plate capacitor with a pecan between the plates and by microwave resonant cavity measurements with a pecan in the resonant cavity. Impedance measurements were also taken on pecan kernel halves. Nuts of six pecan cultivars, four from the United States and two from Israel, with kernel moisture contents ranging from 3 to 11% (w.b.) were included in the study. Although equilibrium moisture contents (m.c.) of pecan kernels and shells differ greatly, and proportions of total nut weight represented by the kernel and shell vary significantly among cultivars, a high correlation was found between total nut m.c. and kernel m.c. Standard errors of calibration (SEC) of 0.6% m.c. and 1.5% m.c. were obtained for determination of entire nut moisture content with electrical measurements on the whole nuts for the RF impedance and microwave cavity measurements, respectively. RF impedance measurements on kernel halves and on the in-shell pecans predicted kernel moisture contents equally well with SEC values of 0.6% m.c for both measurements.