A promising pulse-spouted microwave freeze drying method used for Chinese yam cubes dehydration: quality, energy consumption, and uniformity

Pulse-spouted microwave freeze drying (PSMFD) used for Chinese yam cubes was evaluated at three microwave power levels (400, 600, and 800 W). The drying characteristics, energy consumption, and quality of dried yam cubes were assessed and compared with freeze dried samples. Moreover, the drying uniformity of PSMFD and static microwave freeze drying (MFD) was contrasted. Results showed that drying time decreased and drying rate increased with increasing microwave power levels, furthermore drying rate curves contained three stages. Compared to the freeze drying (FD) process, PSMFD (800 W) could shorten drying time by 55%, and appropriate microwave power (400 and 600 W) contributed to the improvement of crispness. The retention of ascorbic acid and total phenol content of yam cubes dried at 600 W was higher than that of samples dried at 400 and 800 W. In addition, the drying uniformity of PSMFD was improved compared with that of MFD. Considering the high efficiency and comparable quality compared with FD evaluated by principal component analysis (PCA), PSMFD is a promising drying technique.