Study on vacuum pulsation drying characteristics of Huangqi(A. mongholicus Bunge)

Abstract.

The drying characteristics of Huangqi(A. mongholicus Bunge) was studied under the conditions of different drying temperatures: 50, 60, 70, 80℃, vacuum degrees: -0.06, -0.07, -0.08, -0.09Mpa, pulsation ratio30:0,25:5,20:10, respectively. The model of vacuum drying process of Huangqi was built. The change of color of Huangqi dried was analyzed and the effect of different drying conditions on the hygroscopic properties of Huangqi powder was discussed. The results showed that the vacuum drying process of Huangqi had two stages: the constant rate stage and the decreasing rate stage. The different drying conditions significantly affected the drying process. The higher temperature, the higher vacuum and the shorter atmosphere keeping time caused the shorter drying time. The linear and Weibull composed model fitted the Huangqi vacuum drying process well. Colour analysis showed that the of dried Huangqi was brighter than before. But the red & green value and blue and yellow value were lower than before. The drying temperature had significant effect on the brightness value and the brightness value decreased when the drying temperature increased. And there were no significant changes in the equilibrium hygroscopic rate of Huangqi powder under different drying conditions. The results support the Huangqi vacuum drying technology.