Optimization of microwave freeze drying strategy of mushrooms (Agaricus bisporus) based on porosity change behavior

For dehydrated foods, porosity is a crucial parameter which affects mass and heat transfers, and is related to the product quality. It is important to monitor porosity change behavior to optimize the drying process. To achieve faster drying along with high product quality, microwave freeze drying (MFD) was applied to mushrooms dehydration processing. The relationship between porosity (include total, open-, and closed-pore porosity) and dried mushroom qualities was studied, and a suitable microwave loading strategy was obtained. It was found that lots of open pores could transform to closed pores while the moisture content (MC) was below 0.25 ± 0.05 g/g (db), and the closed-pore porosity was arrived at a relatively stable level at moisture content below 0.17 ± 0.03 g/g (db). Both total porosity and closed-pore porosity had a significant influence (P < 0.01) on texture of MFD mushroom, and open-pore porosity had a significant effect (P < 0.01) on rehydration ratio of MFD mushroom. According to the porosity change behavior of mushrooms, a dynamic microwave loading strategy can be used to reduce drying time and keep product quality during MFD process.