Influence of ultrasonic pretreatments on microwave hot-air flow rolling drying mechanism, thermal characteristics and rehydration dynamics of Pleurotus eryngii.

Background: In order to improve the drying efficiency and reduce the drying energy consumption of Pleurotus eryngii, microwave hot-air flow rolling drying (MHARD) coupled with ultrasonic pretreating time (0, 20, 40, and 60 min) was used to investigate the drying profile, thermal characteristics, water migration, microstructure and rehydration dynamics of P. eryngii using differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (LF-NMR) analysis and scanning electron microscopy (SEM).

Results: Results showed that the drying time of P. eryngii was 80, 70, 60 and 50 min, accordingly. Energy consumption was significantly reduced by ultrasonic pretreatment, and moisture effective diffusivity (D ) was increased with the increase of ultrasonic pretreating time. DSC curves showed that the drying process was accelerated by ultrasonic pretreatment significantly by enhancing the heat transfer. Meanwhile, SEM images showed that the cell was broken and numbers of irregular holes appeared in the ultrasound-pretreated samples. In terms of rehydration dynamics, Page model could well model the rehydration kinetics of dried P. eryngii with R  > 0.99.

Conclusion: The findings indicate that ultrasonic pretreatment is a promising method for MHARD of P. eryngii as it can enhance the drying process, and show potential for industrial application. © 2021 Society of Chemical Industry.