Dielectric properties of chestnut flour relevant to drying with radio-frequency and microwave energy

Abstract Dielectric properties of compressed chestnut flour samples with 11.6–48.0% w.b. moisture content were determined with a network analyzer and an open-ended coaxial-line probe over a frequency range from 10 to 4500 MHz and a temperature range from 20 to 60 °C. The results showed that the permittivities of chestnut flour were a function of frequency, moisture content and temperature. Both dielectric constant and loss factor decreased with increasing frequency but increased with increasing moisture content and temperature. The relationship between permittivities and moisture content and temperature at 27, 40, 915 and 2450 MHz could be described by second- or third-degree polynomial models, with the coefficients of determination higher than 0.993. The analysis of variance showed that moisture content and temperature had strong significant effects on permittivity values. The penetration depth decreased with increasing frequency, moisture content and temperature. Large penetration depth at radio frequencies below 100 MHz may provide practical large-scale dielectric drying of chestnut.

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