胡萝卜片微波-热风滚动床干燥物料特性研究

Drying Characteristics of Carrot Slices during Microwave-Hot-airflow Rolling Drying

摘要:

为了改善微波干燥果蔬的物料特性，通过搭建的微波-热风滚动床干燥（Microwave-hotairflow rolling drying, MARD）试验台，研究了胡萝卜片在MARD不同干燥阶段的热像变化，通过低场核磁共振分析与成像（Low-field nuclear magnetic resonance analysis and imaging, NMR/MRI）研究了胡萝卜片在MARD不同干燥阶段水分状态和水分分布，试验还测得在对应干燥阶段胡萝卜片介电常数ε′和介电损耗因子ε″的变化规律。通过分析物料的脱水过程和干燥品质发现，MARD过程干燥速度逐渐降低，物料温度分布均匀，随着干燥进行温度稳定在设定范围；NMR波谱下的水分信号量逐渐降低且主峰向左移，水分的活跃程度降低；MRI信号显示，MARD干燥过程中水分分布均匀；随着MARD进行，物料介电常数ε′和介电损耗因子ε″显著降低，边缘部位介电损耗比心部低，随着干燥的进行，这种差别逐渐减小，说明由介电特性差异导致的微波干燥不均的影响在MARD过程中减弱。

Abstract:

In order to improve the drying quality of fruit and vegetables, microwave-hot-airflow rolling drying (MARD) device was developed, using which the thermal image of carrot slices during drying was measured. In addition, the moisture state and distribution in different drying stages were detected with low-field nuclear magnetic resonance analysis and imaging (NMR/MRI). The dielectric constantε′and dielectric loss factor ε″of carrot slices in the corresponding drying stage were also measured. The dehydration process and drying quality of the materials were analyzed by comprehensive indexes, and the results showed that the drying speed of carrot slices was decreased gradually, and the drying temperature was distributed evenly, and floated in the set range. In NMR spectrum, the water signal was decreased gradually and the main peak was shifted to the left, when the water was changed to the direction of compact combination with dry matter. The MR signal showed that the water distribution was uniform during MARD. With the development of MARD, the ε′and ε″of materials were decreased significantly, and the dielectric loss at the edge was lower than that at the core. With the drying processing, the difference was decreased, indicating the effect of non-uniform microwave drying caused by the difference of dielectric properties would be weakened in the MARD process. The research provided a reference for improving the efficiency and quality of microwave drying of fruits and vegetables.