Quality Evaluation of Shiitake Mushrooms Dried by Vacuum Microwave Treatment

Abstract

We applied a vacuum microwave drying (VMD) process to shiitake mushrooms under different pressure conditions below 20 kPa, and investigated drying time, hardness and rehydration characteristics, extracted guanylic acid, color, and sensory evaluation. The samples were subjected to different microwave treatments at different levels of power (25 W/g dry matter, 50 W/g dry matter, and 75 W/g dry matter) and absolute pressures (3 kPa, 10 kPa, and 20 kPa). VMD reduced drying time by approximately 13 to 70 times compared with hot air drying (HAD). Decreasing the pressure tended to soften the rehydrated samples, whereas the amount of guanylic acid extracted from samples treated at 20 kPa was the largest. The sensory evaluation score of VMD-treated shiitake mushrooms was larger than HAD-treated mushrooms. Collectively, these results suggest that VMD is more suitable and useful than HAD in producing high quality dried shiitake mushrooms.