Submitted to: Journal of Microwave Power and Electromagnetic Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/1996
Publication Date: N/A
Citation: Interpretive Summary: Nondestructive testing and automatic sorting are important factors in harvesting, handling, and marketing of fruit and vegetable products. They are important in reducing costs of operation and postharvest losses, and in determining and maintaining product quality. Electrical properties of fruits and vegetables can be rapidly sensed with appropriate electronics equipment. If these properties can be correlated with important quality factors, such equipment can be designed to rapidly determine quality, and then adapted to automatic sorting equipment. Exploratory research to establish the range of the electrical properties of several fruits and vegetables at microwave frequencies has shown differences attributable to stage of maturity. These data have been subjected to further analysis, and results of these "dielectric relaxation" studies are being reported. Rough correlations were found between some of the new data and quality factors of fmoisture content and total soluble solids, a measure of sweetness in fruit and some vegetables. Further research, involving wider ranges of quality factors is needed to establish useful correlations for specific fruits or vegetables, but these studies are reported as important initial steps in determining the potential usefulness of such techniques for practical application.
Technical Abstract: The Debye equation and its derivatives were used to analyze experimental permittivity data of twenty-three kinds of fresh fruits and vegetables over the frequency range from 2 to 20 GHz. Cole-Cole plots and the linear relationship between the dielectric constant and the product of angular frequency and loss factor were found useful in determining how well experimental data fit the Debye-type relaxation. Estimates of dielectric parameters provided by the linear relationship between the dielectric constant and the quotient of loss factor and angular frequency were subject to problems attributed to ionic conduct and sensitivity to measurements errors at the lower frequencies.