Abstract To develop a novel combination drying method combining radio frequency (RF) with vacuum and osmotic dehydration (OD), information on dielectric properties is essential so as to understand the interaction between the electromagnetic field and the matrix undergoing drying. In this paper, the dielectric properties of kiwifruit samples were determined across the frequency range of 10 and 3000 MHz using an open-ended coaxial-line probe and impedance analyzer at moisture contents ranging from 19.8% to 79.6% on a wet basis (w.b.) and temperatures between 20 and 80 °C. The effect of pre-treatments including OD and hot air drying (AD) on the dielectric properties, physicochemical properties and RF-vacuum drying characteristics of kiwifruit were also studied. The results showed that both the dielectric constant and loss factor decreased with decreasing moisture content and increasing frequency. At high moisture contents (above 65% w.b.), the dielectric constant decreased slightly with increasing temperature, whereas at lower moisture contents (below 50% w.b.), the dielectric constant increased sharply with increasing temperature. In addition, the OD resulted in less kiwifruit quality deterioration than AD in terms of titratable acidity, ascorbic acid, soluble solids and color. Although dielectric permittivities of OD treated kiwifruits were slightly lower than those of AD treated samples, the effect of the OD treatment on RF energy coupling was negligible compared to the AD. Therefore, OD may provide an alternative way for AD as a pre-treatment before RF drying for kiwifruits with high-quality characteristics.

中文翻译：

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与射频真空和渗透干燥相结合的猕猴桃的介电特性

摘要 要开发一种将射频 (RF) 与真空和渗透脱水 (OD) 相结合的新型组合干燥方法，介电特性的信息对于了解电磁场与进行干燥的基质之间的相互作用至关重要。在本文中，猕猴桃样品的介电特性在 10 到 3000 MHz 的频率范围内使用开放式同轴探头和阻抗分析仪在湿基 (wb) 的 19.8% 到 79.6% 的水分含量范围内测定温度在 20 至 80 °C 之间。还研究了 OD 和热风干燥 (AD) 等预处理对猕猴桃介电特性、理化特性和射频真空干燥特性的影响。结果表明，介电常数和损耗因子都随着水分含量的降低和频率的增加而降低。在高水分含量（高于 65% wb）下，介电常数随着温度的升高而略有下降，而在低水分含量（低于 50% wb）下，介电常数随着温度的升高而急剧增加。此外，在可滴定酸度、抗坏血酸、可溶性固形物和颜色方面，OD 导致猕猴桃质量下降比 AD 少。尽管 OD 处理的猕猴桃的介电常数略低于 AD 处理的样品，但与 AD 相比，OD 处理对 RF 能量耦合的影响可以忽略不计。所以，