Comparison of Permittivity Between Traditional and High-oleic Runner-type Peanuts at Microwave Frequencies

Authors: Lewis, Micah; Trabelsi, Samir

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2021
Publication Date: 10/15/2021
Citation: Lewis, M.A., Trabelsi, S. 2022. Comparison of Permittivity Between Traditional and High-oleic Runner-type Peanuts at Microwave Frequencies . Transactions of the ASABE. https://doi.org/10.13031/trans.14323.
DOI: https://doi.org/10.13031/trans.14323

Interpretive Summary: Towards the end of the 20th century, different varieties of peanuts were developed with different compositions of oleic and linoleic acids. It was determined that increasing oleic acid levels and decreasing linoleic acid levels in peanuts would improve shelf life by deterring lipid oxidation. This would also prevent the creation of off flavors. Thus, peanuts with such composition are called high-oleic peanuts. Substantial testing has been done to analyze what effects such change in composition would have on peanuts from a chemical, sensory, and allergenic perspective. Tests have shown minimal differences, if any. However, analysis has not been performed to determine the effect of such compositional change on the permittivity of the peanuts. Complex permittivity is the ability of a material to store and dissipate electric energy. Correlations between permittivity and moisture content are commonly used to develop calibrations for moisture sensing using indirect methods. Therefore, any change in permittivity caused by the high-oleic trait would affect such calibrations. Complex permittivity measurements were taken in the laboratory on traditional and high-oleic runner-type peanuts (shelled and unshelled). Measurements were taken at 23 °C between microwave frequencies of 5 and 9 GHz. Analysis of the measured parameters and other properties showed that at microwave frequencies, the change in levels of oleic and linoleic acid within the peanuts had minimal to no effect on their permittivity. Therefore, moisture calibrations developed for traditional runner-type peanuts can be applied to high-oleic varieties.

Technical Abstract: Different cultivars of peanuts were developed containing higher amounts of oleic acid to improve oxidative stability and overall peanut quality. Increasing oleic acid levels and decreasing linoleic acid levels in peanuts deters lipid oxidation, preventing the creation of off flavors and increasing shelf life. Since their conception, high-oleic peanuts have been tested from a chemical and sensory perspective to observe differences between them and traditional peanuts. Such tests have shown minimal differences, if any. However, tests to observe the effect of changing the levels of oleic and linoleic acid on permittivity have not been reported. Thus, a vector network analyzer (VNA) was used to take free-space transmission measurements of the complex permittivities of high-oleic and traditional runner-type peanut pods and kernels. Measurements were taken at 23 °C between 5 and 9 GHz. Measurements yielded the dielectric constant and loss factor, terms which are often correlated to moisture content. Analysis was performed to compare the change of the dielectric constant, loss factor and loss tangent with moisture content for the high-oleic and traditional peanuts. Linear trends were observed for each parameter with increasing moisture content for both cultivars. Results from the complex plane showed values for coefficients of determination greater than 0.9 for pods and kernels. Therefore, at microwave frequencies, the change in levels of oleic and linoleic acid within the peanuts was observed to have minimal to no effect on their permittivity. Thus, moisture calibrations based on correlations between dielectric properties and moisture content for traditional runner-type peanuts can be applied to high-oleic cultivars.