关键词: 黑莓, 微波干燥, 介电性能, 含水率, 温度, 频率, 穿透深度

Abstract: Dielectric properties of blackberries samples with 20%-80% w.b. moisture content were determined with a network analyzer and an open\|ended coaxial\|line probe over the frequency ranged from 1 to 3 000 MHz and the temperature ranged from 20 to 100 ℃. The effect of frequency， moisture content and temperature on the relative permittivity （ε′）and dielectric loss factor （ε″）were investigated， the penetration depth was measured， and the relation model of dielectric properties of blackberries and the main influence factors was established， in order to inspect the precision and feasibility of moisture content prediction based on dielectric parameter. The results showed that both ε′ and ε″ of blackberries decreased with increasing frequency. ε′ increased with increasing moisture content and decreased with increasing temperature， however， ε″ increased with increasing temperature but decreased with increasing moisture content. The penetration depth decreased with increasing temperature and frequency， but increased with increasing moisture content. The relationship between dielectric parameter and main influence factors could be described by binary quadratic equations， and the determination coefficients of each model were higher than 0.96， indicating that the model could well describe the relationship， thus it is feasible to predict the moisture content of blackberries based on dielectric parameters and temperature.

Key words: blackberries, microwave drying, dielectric properties, moisture content, temperature, frequency, penetration depth