Characterization of Moisture Transformation and Distribution in Mushroom (Lentinus edodes) During Hot-Air Drying

Dehydration is widely used for shelf-life extension of mushrooms. We examined the moisture distribution and transformation mechanism in mushrooms (Lentinus edodes) during process with six different hot-air drying methods, including isothermal drying, uniform rise drying, nonuniform rise drying, uniform intermittent drying, nonuniform intermittent drying and combined drying. Nuclear magnetic resonance and 2D proton density imaging were used to analyze moisture transformation and distribution during the whole drying processes. The results showed that freezable and nonfreezable moisture were active while bound moisture was stable during drying processes. The key step to improve drying efficiency is to accelerate moisture transform from nonfreezable moisture status into freezable status. Combined drying was finally selected as the best treatment due to the observed homogeneous moisture distribution and its positive effect on mushroom's sensory quality. Practical Application Moisture content and status (free water and hydroxyl bond water) are the key parameters that affect the dehydrated foods such as dehydrated mushroom. As known, hot-air drying is commonly used in the dehydrated mushroom process, including isothermal drying (ID), combined drying (CD), etc. It is very critical to find out the difference in dehydration mechanism of the mentioned methods, and make clear how these mechanisms finally affect the moisture content and status of mushroom, and find out the principle that water transformation mechanism. Because these mechanisms may also affect the drying efficiency, finally affect the quality of dehydrated mushroom. So the present research focus on the details that happened during drying process use NMR and 2D proton density imaging, especially the moisture distribution and transformation mechanism, by which we hope to give the industry a basic guidance while face different hot-air drying methods and different product requirements.