SENSING MOISTURE CONTENT AND QUALITY OF GRAIN AND OTHER AGRICULTURAL PRODUCTS BY DIELECTRIC PROPERTIES
Location: Quality and Safety Assessment Research Unit
Title: Study of Melon Permittivities for Quality Sensing
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 15, 2009
Publication Date: June 1, 2009
Citation: Proceedings of the 8th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances (ISEMA 2009), June 1-5, 2009, Espoo, Finland. Study of Melon Permittivities for Quality Sensing. Symposium Proceedings. Nelson, S.O, Trabelsi, S. 2009. pp. 19-22.
Interpretive Summary: Study of Melon Permittivity for Quality Sensing
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 10 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.
Permittivities (dielectric constants and dielectric loss factors) were determined at frequencies between 10 MHz and 20 GHz for mature cantaloupe, honeydew melons, and watermelons grown during three consecutive years and studied in relation to the sweetness of the edible tissue as determined by soluble solids content (SSC). High correlations were noted between SSC and moisture content in the tissues of all three kinds of melons, with SSC increasing linearly with decreasing moisture content. Dielectric properties were similar for all three melon types, and they reflect the influence of the dielectric behavior of free water. No obvious correlations were noted between the dielectric properties and the SSC that are useful for sensing the quality of the melons.