Quality formation mechanism of shiitake mushrooms during multiphase microwave drying (MMD)

Our previous studies have demonstrated that multiphase microwave drying (MMD) can simultaneously achieve high drying efficiency and superior product quality. This study further investigated the quality formation mechanism during the MMD process. Results indicated that with increasing drying time, free and bound water were progressively removed, resulting in the formation of a uniform and well-connected porous structure and a marked improvement in rehydration capacity. Micro-CT and TEM analyses confirmed that MMD enabled efficient dehydration while largely preserving cell wall integrity. FTIR and DSC results indicated that the secondary structure and thermal stability of mushroom proteins remained generally stable throughout the drying process. Texture analysis together with LF-NMR and Micro-CT results indicated that drying for approximately 90 min achieved the best balance between structural stability and rehydrated texture, as reflected by the formation of a well-connected porous network, enhanced rehydration capacity, and coordinated hardness and springiness. Metabolomic analysis further revealed that drying time primarily regulated amino acid, lipid, and carbohydrate metabolic pathways, thereby promoting the formation of flavor precursor compounds. Overall, this study elucidates the intrinsic relationships among moisture migration, structural evolution, and quality formation during MMD, providing a theoretical basis for parameter optimization and high-quality processing of shiitake mushrooms.