不同干燥方法下红枣蜜饯水分状态变化研究

Study on Changes of Moisture State of Preserved Jujube Fruit by Different Drying Methods

基于低场核磁共振(LF-NMR)技术研究热风干燥与真空微波干燥下红枣蜜饯内部水分分布及干燥过程中水分迁移规律、水分状态及含量的变化,为其干制提供理论依据。结果表明:MRI图像可以清晰反映水分分布情况,枣中含有3种状态的水,分别是结合水、不易流动水和自由水,成熟鲜枣中94%以上的水都是自由水,红枣蜜饯热风干燥最初2 h自由水含量显著降低,干燥后期自由水向组织内迁移减弱,最终不易流动水含量增加至43.9%,自由水含量散失降至55.99%;红枣蜜饯真空微波干燥过程中自由水快速向不易流动水迁移,6 min时自由水含量为0,结合水含量降低,不易流动水含量高达99.94%,因此真空微波干燥较热风干燥具有时间短、效率高的优势。

The water distribution in jujube preserved fruit by hot air drying and vacuum microwave drying and the law of water migration,the changes of water state and content in jujube fruit during drying were studied by LF-NMR to provide a theoretical basis for jujube preserved fruit drying.The results showed that MRI images could reflect the water distribution clearly.There were three states of water in the jujube:bound water,less mobile water and free water,and more than 94%of the water in ripe fresh jujube was free water,the free water content decreased significantly in the first two hours of hot-air drying,the migration of free water into the tissues weakened in late drying,and finally the less mobile water fraction increased to 43.9%and free water content decreased to 55.99%respectively.While during the process of vacuum microwave drying,the free water migrated rapidly to the less mobile water,at 6 min,the free water content was almost 0,the bound water content reduced,and the less mobile water was as high as 99.94%.Therefore,vacuum microwave drying had the advantages of shorter time and higher efficiency compared with hot air drying.