用低场核磁分析胡萝卜切片干燥过程的内部水分变化

Analysis on internal moisture changes of carrot slices during drying process using low-field NMR

为研究胡萝卜切片在干燥过程中内部水分变化的特征,采用电热恒温干燥箱在40、50、60、70和80℃的条件下对胡萝卜切片进行热风干燥试验,应用低场核磁共振(low field nuclear magnetic resonance,LF-NMR)的横向弛豫时间(T2)反演谱分析胡萝卜切片在干燥过程中内部水分的变化。试验结果表明:干燥过程改变了胡萝卜样品中水的结合状态,自由度高的水分向自由度低的迁移;随着干燥温度升高,干燥速率加快,但温度为80℃时,由于物料表面结壳阻碍了水分的外迁从而影响干燥速率。试验数据为果疏变温联合干燥工艺和干燥转换点的确定提供参考。

In order to investigate the characteristics of internal moisture change of carrot slices at different temperatures during drying process, an hot air drying experiment on carrot slices using the electric heating thermostatic drying oven at different temperatures, which were respectively 40, 50, 60, 70 and 80℃, have been carried out. The internal moisture changes from the perspective of transverse relaxation time （T 2 ） inversion spectrum of low-field nuclear magnetic resonance were analyzed. Results showed that moisture states and moisture distribution changed in drying process and the moisture with high degree of freedom moved to the moisture with low degree of freedom. The drying rate was accelerated with the rise of drying temperature, however, the drying rate was restrained because the material surface crusting hindered the outmigration of water at 80℃. This research can provide theoretical basis for drying technology and conversion point of variable temperature combination drying of fruits and vegetables.