Location: Quality Safety and Assessment ResearchTitle: Historical development of grain moisture measurement and other food quality sensing through electrical properties.
|NELSON, STUART - Retired ARS Employee|
Submitted to: IEEE Instrumentation & Measurement Magazine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2015
Publication Date: 1/22/2016
Citation: Nelson, S.O., Trabelsi, S. 2016. Historical development of grain moisture measurement and other food quality sensing through electrical properties. IEEE Instrumentation & Measurement Magazine. pgs. 16-23.
Interpretive Summary: When the electrical properties of materials are well correlated with other properties or characteristics of those materials that are important, it is often possible to use properly designed instruments for rapidly measuring those nonelectrical properties of interest. This may be accomplished by the use of electric fields in sensing the electrical properties of the material and then obtaining estimates of the nonelectrical properties through appropriate correlations. In the agricultural and food industries, these kinds of measurements have been used for many years for rapid determination of moisture content in grain and seed. Research has been conducted seeking useful correlations between quality attributes of other food materials and their electrical properties, but they have generally been less successful than the determination of moisture content. In this article, an overview of the historical development of such measurement methods and techniques is presented with respect to grain and seed and other agricultural products and food materials. Sensing and measurement of grain and seed moisture content has been the most successful application, which is used world-wide. Sensing of sweetness and other qualities of fruits and vegetables has been studied, but practical applications have so far not been convincingly demonstrated.
Technical Abstract: A review of the use of electrical properties of agricultural products for sensing moisture content and other qualities shows that their use for rapid measurements of the moisture content in grain and seed has been the most successful application. Discovery of useful correlations between the moisture content of grain and its electrical resistance or conduction provided the basis for development of widely used practical grain moisture meters in the grain seed industry. With the development of radio-frequency applications and measurements, the dielectric properties of grain and seed were also found to have useful correlations with moisture content, giving rise to the development of grain moisture meters utilizing measurements at radio frequencies in the range of 1 to 20 MHz. These capacitance- and impedance-sensing moisture meters have been used for many years, and accuracies have been improved through better understanding of the behavior of the grain and seed dielectric properties with respect to frequency, moisture content, temperature, and bulk density of the grain and seed samples. More recent studies of the dielectric properties of grain and seed have revealed significant advantages in using measurements at microwave frequencies, which show promise for simultaneous sensing of moisture content and bulk density in both static and flowing materials, providing moisture content independent of bulk density. Because of advantages offered by measurement at the higher frequencies, commercial development of new moisture meters for grain and seed can be expected to improve the reliability and utility of such instruments in the grain and seed industries. Nondestructive sensing of quality in fruits and vegetable through their electrical properties has also been explored for a number of products. Correlations between dielectric properties and sweetness (soluble solids content, mostly sugars) have been examined for peaches, apples, and melons at radio and microwave frequencies. Although some interesting correlations were noted, none have yet proved useful for practical development. Moisture content sensing in onions for potential assistance in managing the curing process has shown some potential promise, and moisture sensing in dates to automate sorting processes to separate dates of different moisture levels has shown some feasibility, in principle, but neither application has been developed for practical use.