Dielectric Spectroscopy of Melons for Potential Quality Sensing

Authors: Nelson, Stuart; Trabelsi, Samir; KAYS, STANLEY - UGA

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2009
Publication Date: 2/2/2009
Citation: Nelson, S.O., Trabelsi, S., Kays, S.J. 2009. Dielectric Spectroscopy of Melons for Potential Quality Sensing. Transactions of the ASABE. 51(6):2209-2214.

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. Electrical characteristics of fruit tissue known as dielectric properties can be sensed with electric fields for possible detection of fruit quality. Therefore 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 exist that could be correlated with maturity. Dielectric properties were measured both on the external surface of the melons and on internal tissue samples. The best criterion for 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. The dielectric properties of melon tissues were measured over the frequency range from 200 MHz to 20 GHz along with refractometer determinations of soluble solids content (SSC). New information was obtained on the dielectric properties of melon tissues and their dielectric behavior with respect to frequencies applied. However, no obvious correlations were noted between the melon dielectric properties and sweetness. Therefore, further research is necessary for quality sensing, but development of such a melon quality meter would be helpful to melon growers and handlers in the marketing of high quality produce for American consumers.

Technical Abstract: 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. Electrical characteristics of fruit tissue known as dielectric properties can be sensed with electric fields for possible detection of fruit quality. Therefore 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 exist that could be correlated with maturity. Dielectric properties were measured both on the external surface of the melons and on internal tissue samples. The best criterion for 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. The dielectric properties of melon tissues were measured over the frequency range from 200 MHz to 20 GHz along with refractometer determinations of soluble solids content (SSC). New information was obtained on the dielectric properties of melon tissues and their dielectric behavior with respect to frequencies applied. However, no obvious correlations were noted between the melon dielectric properties and sweetness. Therefore, further research is necessary for quality sensing, but development of such a melon quality meter would be helpful to melon growers and handlers in the marketing of high quality produce for American consumers.