ARS | Publication request: Examination of dielectric spectroscopy data for correlations with melon quality

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: July 27, 2011
Publication Date: August 7, 2011
Citation: Trabelsi, S., Lewis, M. 2011. Examination of dielectric spectroscopy data for correlations with melon quality. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE). ASABE Paper No. 110851.

Interpretive Summary: Techniques for nondestructive determination of quality of agricultural products are helpful to producers, handlers and processors, those marketing the produce, and consumers. Visible and physical characteristics of many fresh fruits and vegetables are available for correlation with quality, and some of these, such as color, size, weight, density, elasticity, and firmness are used in automatic sorting of some produce into different categories for the market. For melons, however, no useful characteristics of this type have been found for reliable correlation with quality. The best criterion for melon quality is the measurement of soluble solids, which are mostly sugars and therefore a measure of sweetness. This requires the extraction of tissue samples from the melons and measurement of expressed juice with a refractometer instrument, which has been calibrated to indicate percentage of soluble solids. Electrical characteristics of fruit tissue known as dielectric properties can be sensed with electric fields for possible detection of fruit quality. Therefore, in earlier studies, several cultivars of cantaloupe, honeydew melons, and watermelons were grown and harvested with a range of maturities for dielectric spectroscopy measurements of the melon tissue to learn whether differences in the dielectric properties (electrical characteristics) might be correlated with quality. Dielectric properties were determined from measurements on the external surface of the melons and on internal tissue samples at frequencies in the range from 10 MHz to 20 GHz along with refractometer determinations of soluble solids content (SSC). These dielectric properties of melons obtained in earlier measurements were re-examined for any correlations with SSC. Because of low correlations between the dielectric properties and sweetness of the melons and high attenuation of electrical signals in the melon tissue, the study did not reveal any liklihood for nondestructive melon quality sensing through their dielectric properties.

Technical Abstract: Earlier dielectric spectroscopy data measured in the frequency range from 10 MHz to 20 GHz on honeydew melons, cantaloupe, and watermelons were re-examined for correlations with soluble solids content (sweetness) that might be useful for nondestructive sensing of melon quality. The study did not reveal any correlations deemed useful for nondestructive melon quality sensing through their dielectric properties. Though better coefficients of variation were obtained for higher frequencies, they were not judged great enough to be very useful, and the attenuation of RF signals in the melons prevents access to internal edible tissues for useful sensing of quality.