SENSING MOISTURE CONTENT AND QUALITY OF GRAIN AND OTHER AGRICULTURAL PRODUCTS BY DIELECTRIC PROPERTIES
Location: Quality and Safety Assessment Research Unit
Title: CORRELATING HONEYDEW MELON QUALITY WITH DIELECTRIC PROPERTIES
Submitted to: Transactions of the ASABE
Publication Type: Proceedings
Publication Acceptance Date: April 25, 2006
Publication Date: July 9, 2006
Citation: Nelson, S.O., Trabelsi, S., Kays, S.J. 2006. Correlating honeydew melon quality with dielectric properties. American Society of Aagricultural and Biological Engineers Paper Series. Paper No. 066122
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 the honeydew melon, 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 honeydew melons 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 might exist that could be correlated with maturity. 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 mature honeydew melon tissue were measured over the frequency range from 10 MHz to 1.8 GHz along with refractometer determinations of soluble solids content (SSC). A high correlation was found between SSC and the dielectric properties as expressed in a complex-plane plot of the dielectric constant and loss factor, each divided by SSC. Through this mathematical relationship, SSC can be calculated from measured dielectric properties independent of tissue density, moisture content, and temperature. Problems in using this new principle for practical nondestructive sensing of honeydew melon quality are considerable, 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.
Honeydew melons were grown and harvested with a range of maturities for measurement of tissue permittivities (dielectric constant and loss factor) to study possible correlations between the dielectric properties and soluble solids (sweetness) for nondestructive sensing of maturity. Permittivities of tissue samples from 38 melons were measured at 25 degrees Celsius over the frequency range from 10 MHz to 1.8 GHz along with refractometer determinations of soluble solids content (SSC), and tissue density and moisture content. A high correlation (correlation coefficient r = 0.96) was found between SSC and the permittivity as expressed in a complex-plane plot of the two components of the relative complex permittivity, each divided by SSC. Through this mathematical relationship, SSC can be calculated from measured permittivity values independent of tissue density, moisture content, and most likely independent of temperature as well.