Pulsed vacuum drying of rhizoma dioscoreae slices

- Increasing number of pressure drops could, but not always, boost drying rate.
- Pulsing ratio was optimized based on pressure, sample temperature and drying rate.
- The amount of pressure drops affected drying rate more than temperature.
- Weibull model and Dicner model well described pulsed vacuum drying of Chinese yam slices.
- Prolonged vacuum duration resulted in less browning and better rehydration.

This research explored the application of pulsed vacuum technology on drying of rhizoma dioscoreae slices. Influences of thickness, temperature and pulsing ratio on drying characteristics and rhizoma dioscoreae quality (color, rehydration characteristics and microstructure) were analyzed. Increasing temperature and decreasing thickness resulted in higher drying rate. Pulsing ratio was adjusted according to relationships between material temperature and chamber pressure, as well as drying rate which agreed well with Weibull model. The optimized condition, that product temperature increased during atmospheric pressure period and then decreased because of moisture evaporation through the whole vacuum period, was obtained according to rhizoma dioscoreae temperature-time curve with highest drying rate and best retention of product quality. The amount of pressure drops was found to be more influential than material temperature in accelerating drying rate. Prolonged vacuum duration was helpful in inhibiting browning of rhizoma dioscoreae slices, forming puffed structure and accordingly obtaining better rehydration characteristics.