Submitted to: Sensing and Instrumentation for Food Quality and Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2008
Publication Date: August 8, 2008
Citation: Kandala, C., Butts, C.L. 2008. Design and performance of a capicitor sensor and impedance analyzer for nondestructive moisture content detemination. Sensing and Instrumentation for Food Quality and Safety. DOI 10.2007. Interpretive Summary: Peanuts are dried artificially in large numbers of trailers that have a perforated floor and an air plenum till they dry to the required moisture level. This process involves considerable time, energy and expenditure. At some drying facilities, more than 80 trailers at a time are in use. During the drying process, the MC of the peanuts in each trailer must be measured at regular intervals to determine whether the desired MC level has been obtained and when the dryers can be turned off. Drying the peanuts for a longer time after the required MC level has been reached not only increases the drying costs but also may lower the quality of the peanuts. To make a MC measurement, a peanut sample of about 500 grams from a trailer is collected by an operator, the peanuts are shelled and cleaned, and the kernels are placed in the sample holder of the moisture meter. This method is laborious and time consuming. In this work an alternative rapid, nondestructive method is presented. By measuring capacitance, phase angle, and dissipation factor of a parallel-plate system fitted inside a non-conducting cylindrical tube, the average moisture content of approximately 100g of peanuts could be predicted rapidly and nondestructively. The moisture range of the peanuts tested was between 6% and 20% and the predicted MC values were within 1% of the air-oven MC values for 90% or more of the samples tested. For this method there are no requirements for the sample weight or volume. The samples need not be shelled and cleaned. This method is quick and nondestructive and provides a basis for the development of a practical instrument that can measure MC of in-shell peanuts.
Technical Abstract: This paper describes a method to determine the moisture content of in-shell peanuts with a parallel-plate electrode system fitted inside a cylinder by using impedance measurements made on the system. Two parallel-plate electrodes were mounted inside a cylinder, made of acrylic material, and the space between the plates was filled with in-shell peanuts (80 to 100 g). The impedance measurements were made on the parallel-plate system at 1 and 9 MHz, and the average moisture content (MC) of the peanut pods (in-shell peanuts) was determined from a semi-empirical equation. The calculated MC values were compared with standard oven-determined values and were within 1% of the standard oven values for 90% of the samples tested in the moisture range between 6% and 20%. Two parallel-plate sensors with different plate separations and peanuts from the 2004 and 2005 harvests, were used in these measurements. The method, being rapid and nondestructive, is suitable for the development of a practical instrument for measurement of moisture content in in-shell peanuts.