银杏白果干燥过程中水分分布及迁移的变化

Moisture distribution and migration of Ginkgo biloba seeds during air drying process

【目的】探讨银杏白果在干燥过程中水分分布、迁移规律及低场核磁共振信号量与含水量之间的关系,为银杏白果水分传递模型的建立以及储存过程中含水量的快速测定提供依据。【方法】利用低场核磁共振技术,对不同热风干燥温度(50、60、70、80、90℃)处理的银杏白果中氢核的横向弛豫衰减信号进行测试,并利用SIRT模型对数据进行反演,得出横向弛豫时间T2的反演数据。利用自旋回波脉冲序列对银杏白果的质子密度加权成像。【结果】银杏白果中的水分主要有3种存在状态,分别为结合水(0.79~7.32 ms)、束缚水(13.67~89.07 ms)和自由水(109.70~1 072.27 ms)。经过热风干燥处理改变了银杏白果中水分的结合状态,水分发生明显迁移,自由水和束缚水的信号幅值随干燥温度的升高而逐渐减弱。不同含水率银杏白果的反演峰总面积不同,随着干基含水率的增加,核磁共振信号增强、峰面积增大,两者具有显著的相关性,拟合方程为y=7 436.46x+153.32(R2=0.993)。核磁共振成像技术通过图片明暗的不同,直观地呈现出不同阶段的水分含量。【结论】干基含水率与核磁共振横向弛豫时间、弛豫峰面积之间有较好的相关性,可以利用低场核磁技术快速检测出银杏白果中的水分含量。通过核磁共振图谱也可以直观地观察银杏白果内部水分含量的变化。

【Objective】 The water composition of Ginkgo biloba seeds plays an important role in its physiological metabolism and affects its quality. Information about moisture distribution and migration in G. biloba seeds during hot air drying can provide data to optimize drying and rapidly determine the water content during storage. 【Method】The Carr-Purcell-Meiboom-Gill decay signals were obtained during hot air drying of G. biloba seeds by low-field nuclear magnetic resonance(NMR) equipped with a 0.5 T permanent magnet and proton resonance frequency of 21 MHz at a temperature of 32℃. The transverse relaxation time(T2) was calculated based on the decay signal data using the SIRT algorithm, which provides the position and area of each peak. NMR images were obtained by SE imaging sequence. 【Result】 The drying rate increased with an increase in the air temperature during hot air drying. For all states of water, T2 followed a decreasing trend during drying. The states of water could be classified into three main categories: bound water(0.79-7.32 ms), weakly bound water(13.67-89.07 ms), and free water(109.70-1 072.27 ms). The moisture state of G. biloba seeds changed, and free water and weakly bound water were gradually removed during hot air drying. Increased water content significantly correlated with stronger NMR signals and larger peak areas. This phenomenon can be described by this equation: y = 7 436.46 x + 153.32(R2 = 0.993). NMR imaging was used to visualize proton images at different stages in the light and dark. 【Conclusion】 There is a high correlation between moisture content and NMR relaxation peak value. The water content of G. biloba seeds can also be observed directly using a nuclear magnetic map.