Dielectric spectroscopy studies on fresh fruits and vegetables

In connection with quality sensing in fruits and vegetables, the dielectric properties of mature-green and full-ripe peaches at 2.45 GHz were examined to see whether these properties might be useful in distinguishing degree of maturity. Permittivity measurements at 2.45 GHz did not offer promise for detecting quality factors. Following permittivity characterization measurements for twenty-three kinds of common fresh fruits and vegetables over the frequency range from 200 MHz to 20 GHz at 23°C, similar measurements were taken over a narrow range of peach maturity, and evidence for possible distinction of maturity degree was obtained. A permittivity-based maturity index was suggested, based on differences in both components of the permittivity, the dielectric constant ε´ at the low end of the frequency range and the loss factor ε´ at 10 GHz near the higher end of this frequency range. More research and developmental work was recommended for determining the potential for practical use of the technique, including measurements at frequencies lower than 200 MHz, since the curves for the dielectric constants of the different maturities appeared to be diverging as they approached the lower end of the frequency range.