怀山药微波冻干过程的水分扩散特性及干燥模型

Water Diffusion Characteristics and Microwave Vacuum Freeze-Drying Modelling of Chinese Yam(Dioscorea opposite) Tubers

为探究怀山药干燥过程中的水分扩散特性,以怀山药为原料,使用微波真空冷冻干燥技术进行干燥,同时采用低场核磁共振的横向弛豫时间(T_2)反演谱分析怀山药切片在干燥过程中内部水分的变化,并结合有效水分扩散系数、水分含量、干燥速率的变化规律对微波真空冷冻干燥过程中怀山药的内部水分扩散特性进行分析。结果表明:干燥过程中水分由自由度高向自由度低的方向迁移;不同微波功率(1.5～4.4 W)下怀山药干燥过程的有效水分扩散系数变化范围在1.129×10^(-9)～5.439×10^(-9) m^2/s之间,随着微波功率的增大,有效水分扩散系数升高,水分扩散迁移的速度增大,非结合水向结合水方向转化逐渐增多。采用Page、Newton等模型与实验数据进行拟合,结果表明Page拟合度较高,R^2大于0.99,可以较好地对怀山药微波真空冷冻干燥过程进行预测和控制。本实验为怀山药干燥过程的水分实时监测及实现精准干燥提供了理论依据。

This study was undertaken in order to explore the water diffusion characteristics of Chinese yam tubers during microwave vacuum freeze-drying. Low field nuclear magnetic resonance (LF-NMR) was used to analyze water distribution change during the drying process. In addition, changes in water effective diffusion coefficient, water content and drying rate were measured. The results showed that moisture migration from high degree of freedom to low degree of freedom occurred during the drying process. Water effective diffusion coefficient increased from 1.129 × 10^-9 to 5.439 × 10^-9 m^2 /s as the microwave power increased from 1.5 to 4.4 W. Similarly, moisture diffusion coefficient, water migration rate and the amount of unbound water converted to bound water increased with increasing microwave power. The Page and Newton models were fitted to the experimental data. Our comparative evaluation showed that the Page model could better describe the drying process with excellent goodness of fit and R^2 of greater than 0.99. This study can provide a theoretical basis for real-time monitoring of moisture in the drying process of Chinese yam tubers.