Abstract: In order to improve the drying efficiency and the quality of shiitake mushrooms under microwave drying, numerical simulation and bench test were used to study the absorption pattern of microwave energy in shiitake mushrooms at different microwave intensities and to investigate the variation characteristics of temperature and moisture during the drying process. The results showed that the characteristics of microwave drying temperature involved three stages: rising, remaining constant, and rising once again. The same trend was observed for the drying rate. As the temperature rose to 80–100 ℃ at the late stage of drying, the thermal runaway phenomenon appeared, and the internal temperature of shiitake mushrooms rose sharply. Hot spots appeared at the center of shiitake mushrooms during the drying process, and the internal microwave volume heat was significantly higher than that on the surface. In order not to exceed the temperature for thermal runaway, microwave drying should be carried out at microwave intensity of 2.4 W/g first and then 0.8 W/g with a 5 min interval, giving the highest drying uniformity and drying efficiency. The research results provide valuable guidance for the microwave drying of shiitake mushrooms.

Key words: shiitake mushrooms, microwave drying, thermal runaway, simulation, process optimization