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

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 T₂ 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.