Frequency, moisture content, and temperature dependent dielectric properties of potato starch related to drying with radio-frequency/microwave energy

Abstract To develop advanced drying methods using radio-frequency (RF) or microwave (MW) energy, dielectric properties of potato starch were determined using an open-ended coaxial-line probe and network analyzer at frequencies between 20 and 4,500 MHz, moisture contents between 15.1% and 43.1% wet basis (w.b.), and temperatures between 25 and 75 °C. The results showed that both dielectric constant ( ε ′) and loss factor ( ε ″) were dependent on frequency, moisture content, and temperature. ε ′ decreased with increasing frequency at a given moisture content or temperature. At low moisture contents (≤25.4% w.b.) or low temperatures (≤45 °C), ε ″ increased with increasing frequency. However, ε ″ changed from decrease to increase with increasing frequency at high moisture contents or temperatures. At low temperatures (25–35 °C), both ε ′ and ε ″ increased with increasing moisture content. At low moisture contents (15.1–19.5% w.b.), they increased with increasing temperature. The change trends of ε ′ and ε ″ were different and dependent on temperature and moisture content at their high levels. The penetration depth ( d p ) decreased with increasing frequency. RF treatments may provide potential large-scale industrial drying application for potato starch. This research offers useful information on dielectric properties of potato starch related to drying with electromagnetic energy.