Use of dielectric mixture equations for the characterization of uncleaned peanuts

Authors: JULRAT, SAKOL - Oak Ridge Institute For Science And Education (ORISE); Trabelsi, Samir

Submitted to: Measurement: Food
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2022
Publication Date: 1/19/2022
Citation: Julrat, S., Trabelsi, S. 2022. Use of dielectric mixture equations for the characterization of uncleaned peanuts. Measurement: Food. https://doi.org/10.1016/j.meafoo.2022.100022.
DOI: https://doi.org/10.1016/j.meafoo.2022.100022

Interpretive Summary: Rapid and nondestructive determination of physical characteristic which are used for the grading of peanuts is very useful and provides the means for better decision making which in turn result in significant cost savings. Among the most important peanut grading parameters are kernel moisture content and foreign material content. Kernel moisture content is used at peanut buying points to declare the peanut load a sale or no sale. In Georgia, kernel moisture content has to be less thank 10.49% to meet the sale requirement. Foreign material content is used to determine whether the peanut load needs further cleaning or not. Our research has shown that microwave sensing technology an be used to determine both kernel moisture content while still in the pod and foreign material content. This is achieved through accurate measurement of the dielectric properties which represent the electrical finger print of the material. When peanuts are brought to the buying point they are a mixture of peanut pods and foreign materials (sticks, shells, peanut raisins, and stones). And therefore, the measured dielectric properties are those of the mixture. As in all indirect methods modeling is crucial for moving from the measured parameters, in this instance the dielectric properties, to the target physical characteristics. In this paper, several mixture equations which correlate the measured dielectric properties to the individual volume fraction and dielectric properties of each constituent in the mixture are investigated with the objective of identifying analytical equations to determine foreign material content in uncleaned peanuts. Among the mixture equations tested, the logarithmic dielectric mixture model showed the best estimates for all types of foreign material-peanut mixtures. Therefore, it can be programmed in a microwave meter for rapid and nondestructive determination of foreign material content in uncleaned peanuts from measurement of their dielectric properties at a single microwave frequency.

Technical Abstract: A dielectric mixtures study of foreign materials such as peanut shells, sticks, peanut raisins and stones mixed with cleaned unshelled peanuts is presented. The dielectric properties of the foreign materials mixed with cleaned unshelled peanuts were measured by microwave free-space transmission technique at 10 GHz. Dielectric mixture equations, linear, quadratic, cubic and logarithmic were used to describe the mixtures of the foreign materials and cleaned unshelled peanuts. Volume fractions of foreign materials and cleaned unshelled peanuts, and the dielectric constants of foreign materials and cleaned unshelled peanuts were used in the models. Physically, the volume fractions of foreign materials are related to the mass and the density of foreign materials, as well as the volume fraction of cleaned unshelled peanuts. The effective dielectric properties of mixtures of single and multiple types of foreign materials with cleaned unshelled peanuts were determined and compared to measurement data. Results of the logarithmic dielectric mixture model showed the best estimates for dielectric constant of all types of foreign material-peanut mixtures.