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Open AccessArticle

Effects of Moisture, Temperature, and Salt Content on the Dielectric Properties of Pecan Kernels during Microwave and Radio Frequency Drying Processes

1
Tobacco Research Institute, Chinese Academy of Agricultural Sciences (CAAS), Qingdao 266101, China
2
School of Plant Protection, Anhui Agricultural University, Hefei 230036, China
3
Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences (CAAS), Beijing 100193, China
*
Author to whom correspondence should be addressed.
Foods 2019, 8(9), 385; https://doi.org/10.3390/foods8090385
Received: 12 August 2019 / Revised: 27 August 2019 / Accepted: 28 August 2019 / Published: 2 September 2019
(This article belongs to the Special Issue Application of Novel Thermal Technology in Foods Processing)
Dielectric properties of materials influence the interaction of electromagnetic fields with and are therefore important in designing effective dielectric heating processes. We investigated the dielectric properties (DPs) of pecan kernels between 10 and 3000 MHz using a Novocontrol broadband dielectric spectrometer in a temperature range of 5–65 °C and a moisture content range of 10–30% wet basis (wb) at three salt levels. The dielectric constant (ε′) and loss factor (ε″) of the pecan kernels decreased significantly with increasing frequency in the radio frequency (RF) band, but gradually in the measured microwave (MW) band. The moisture content and temperature increase greatly contributed to the increase in the ε′ and ε″ of samples, and ε″ increased sharply with increasing salt strength. Quadratic polynomial models were established to simulate DPs as functions of temperature and moisture content at four frequencies (27, 40, 915, and 2450 MHz), with R2 > 0.94. The average penetration depth of pecan kernels in the RF band was greater than that in the MW band (238.17 ± 21.78 cm vs. 15.23 ± 7.36 cm; p < 0.01). Based on the measured DP data, the simulated and experimental temperature-time histories of pecan kernels at five moisture contents were compared within the 5 min RF heating period. View Full-Text
Keywords: pecan; dielectric properties; radio frequency (RF) heating; simulation pecan; dielectric properties; radio frequency (RF) heating; simulation
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MDPI and ACS Style

Zhang, J.; Li, M.; Cheng, J.; Wang, J.; Ding, Z.; Yuan, X.; Zhou, S.; Liu, X. Effects of Moisture, Temperature, and Salt Content on the Dielectric Properties of Pecan Kernels during Microwave and Radio Frequency Drying Processes. Foods 2019, 8, 385.

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