Radio Frequency(RF) dielectric properties of honeydew melon and watermelon juice and correlations with sugar content

In order to understand the relationship between dielectric properties and sugar content of juices, dielectric properties of juice of three honeydew melon cultivars and four watermelon cultivars with different maturities were measured with an open-ended coaxial-line probe and impedance analyzer over the frequency range from 10 MHz to 1.8GHz. Soluble solids content of fruit juice and moisture of fruit pulp were also measured. The correlation between dielectric properties and soluble solids content was analyzed. Results show that the dielectric constant and loss factor of fruit juice decrease monotonically as frequency increase, and they are influenced by the difference of cultivars. The best linear relationships, with the coefficients of determination of 0.784, are found between loss tangent and soluble solids content for honeydew melons at 1.8 GHz. Better correlation is not noticed between dielectric properties and soluble solids content of watermelons. Obvious linear relationships between soluble solids content and moisture are found in honeydew melons and watermelons, with coefficients of determination of 0.973 and 0.906, respectively. Hope the research offer some useful information in developing sugar sensors for juice based on dielectric properties.