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 (dp) 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.
Highlights
Starch is a major agricultural product that is consumed and/or used on a daily basis in the whole world
It was found that both ε′ and ε′′ were influenced by frequency. ε′ decreased with increasing frequency at all moisture contents (Fig. 1a)
Same change trend was noted on the potato starch samples at other temperatures
Summary
Starch is a major agricultural product that is consumed and/or used on a daily basis in the whole world. The high endothermic temperature increased with decreasing moisture content, and the low endothermic temperature was found at 66 °C It indicates that drying below 65 °C is helpful to obtain potato starch with high quality. Study on dielectric properties of agriculture products is necessary and crucial to develop effective RF or MW drying process[15] and to improve dielectric heating uniformity. The objectives of this study were: (1) to obtain the dielectric properties of potato starch at moisture contents between 15.1% and 43.1% w.b. and at temperatures between 25 and 75 °C over a frequency range from 20 to 4,500 MHz, (2) to analyze the relationship between dielectric properties and penetration depth with above-mentioned factors, and (3) to provide information on designing drying process and on deciding treatment sample thickness for drying potato starch with RF/MW energy
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