Abstract: Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were employed to investigate the pattern of moisture distribution and mobility during the microwave drying of Morchella esculenta slices. The study also analyzed changes in the microstructure and quality of dried mushroom slices at microwave power densities of 1, 2, 3, and 4 W/g. The results indicated that there were three types of water in fresh M. esculenta slices: bound, immobilized, and free water. Throughout the drying process, free water continuously decreased while immobilized and bound water initially increased and then decreased. At the end of drying, free water was completely removed, leaving only bound water and a small amount of immobilized water. Higher microwave power densities accelerated the removal of free and immobilized water. MRI pseudo-color images revealed uneven moisture distribution in the early drying stage, which became more uniform in the later stage. Under different microwave power densities, the total peak area showed a strong correlation with the dry-basis moisture content of the slices. A moisture content prediction model was established for each microwave power density. Therefore, in practical production, drying parameters could be adjusted based on inversion spectra of transverse relaxation time (T2) and linear equations to improve production efficiency and maintain product quality. Based on comprehensive analysis of drying efficiency and product quality, the optimal microwave power density for drying M. esculenta slices was determined to be 2 W/g. This condition ensured the physicochemical quality of the final product while reducing the drying time, resulting in good quality of dried M. esculenta slices. Thus, these findings provide a theoretical foundation for optimizing the drying process of M. esculenta slices.

Key words: Morchella esculenta slices; microwave drying; low-field nuclear magnetic resonance; moisture; quality