ASABE Technical Library - Abstract

Abstract. This research explored the application of pulsed vacuum technology on drying of Chinese yam. Chinese yam slices were dried at three thickness (3, 5 and 7 mm), three temperatures (55, 60 and 65°C) at predetermined pulsing ratio based on former researches. Influences of above factors on drying characteristics and Chinese yam quality (color, rehydration ratio and microstructure) were analyzed. Increasing temperature and decreasing thickness resulted in higher drying rate. The best quality retention was obtained at temperature of 60°C and thickness of 5 mm. The effects of vacuum and atmospheric pressure duration were complicated. 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 Chinese yam temperature-time curve during drying process, on which highest drying rate and best retention of product quality were obtained. During the pulsed vacuum drying experiments based on the optimum thickness and temperature, vacuum duration and atmospheric pressure durations were adjusted according to relationship between material temperature and chamber pressure, as well as drying rate of Chinese yam. 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 yam slices, forming puffed structure and accordingly obtaining better rehydration ratio.