Density-independent radiofrequency dielectric models for moisture estimation in grain sorghum

Accurate on-line moisture content measurement in modern industrial processing of cereal grains to flour or other food products can maximize efficiency of energy use. However, installation of automated, unattended moisture monitoring systems has not been widespread in snack food and baking industries. In any automatic control system it is the measurement of the controlled variable which is the primary key to success, and regrettably the sensors currently available has not always led to the desired accuracy of control. The most reliable solution to measure the moisture content of flowing granular products continuously and non-destructively is the use of microprocessor-based instruments designed to use bulk density-independent dielectric functions. The object of this study was to investigate the suitability of the Meyer and Schilz dielectric function [(epsilon' - 1)/epsilon ''] for indirect moisture content measurement of grain sorghum in the frequency range from 75 kHz to 5 MHz, where epsilon' and epsilon '' are the dielectric constant and the loss factor of the dielectric, respectively. The most satisfactory dielectric model could estimate sorghum moisture content from 11 to 21 % w.b. with standard errors of estimate and prediction of 0.8 percentage point moisture.