A novel low-frequency microwave assisted pulse-spouted bed freeze-drying of Chinese yam

The efficacy of low-frequency microwave (915 MHz) assisted pulse-spouted bed freeze-drying (MFD-915) with high processing capacity was investigated. A multi-stage variable microwave power loading scheme was developed based on the dielectric properties of Chinese yam to avoid gas discharge. The MFD-915 trials with different spouting intervals (10, 20 and 30 min) was performed. MFD-915 with spouting interval of 10 min that had best performance reduced the drying time by 41.38% compared to freeze-drying (FD). In terms of energy consumption, the MFD-915 saved up to 34.4% of total energy consumption compared to FD. Compared with high-frequency microwave (2450 MHz) assisted pulse-spouted bed freeze-drying (MFD-2450), the specific energy consumption was greatly reduced due to the large sample processing capacity per unit time. MFD-915 produced dried yam products with the same quality (color, rehydration ratio, total phenols and total flavonoids content) as FD and MFD-2450, and a short spouting interval was more conducive to improving drying uniformity. This study demonstrated that MFD-915 had the advantages of producing high quality products, saving energy, reducing time and increasing processing capacity, which provided a basis for industrial production. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.