利用低场核磁共振技术分析月柿果片微波间歇干燥过程中的内部水分变化

Analysis of Internal Moisture Changes of Persimmon Slices during Intermittent Microwave Drying Using Low-Field NMR

为探究广西月柿果片在微波间歇干燥过程中的水分变化规律和干燥效果,应用低场核磁共振技术,测定在不同的微波功率密度下果片干燥过程中的横向弛豫时间T_(2)反演谱,进而分析其内部的水分赋存状态及迁移规律。结果表明:新鲜月柿果片中主要存在三种状态的水,即自由水、不易流动水、结合水;月柿果片微波间歇干燥过程包括前期加速、中期恒速和后期降速阶段。当微波功率密度为3.1、2.7、2.3 W/g时,随着微波功率密度的增大,失水速度逐渐加快,干燥至终点所需的时间分别为210、240、300 min;随干燥时间的延长,T_(2)弛豫时间均向左迁移,峰总面积减小。根据MRI图像可知柿子的失水方向是由表面向内部逐步进行,最先消失的是最外侧的部分,中心部位直到干燥后期才逐渐减少直至消失。

Magnetic analysis and nuclear magnetic resonance imaging were used to analyze the water migration rule of persimmon slices in the intermittent microwave drying process.The experimental results showed that:In the persimmon slices,there were mainly three types of water:free water,semi-combined water,the most closely bound water in persimmon slices.Persimmon slices intermittent microwave drying process showed the acceleration,constant speed and speed down the three stag.When the microwave power density was 3.1,2.7,2.3 W/g,as the microwave power density increased,the water loss rate gradually increased,and the time required for drying to the end point was 210,240,300 min.With the prolongation of drying time,the relaxation time of T_(2) shifted to the left,and the total peak area continued to decrease.According to the MRI images,the water loss direction of persimmon was gradually from the surface to the interior,the most lateral part disappeared first,and the central part gradually decreased until the late drying stage.