Study on vacuum drying characteristics and hygroscopic properties of Huangqi ( A.mongholicus Bunge) slices

The drying characteristics of Huangqi ( A. mongholicus Bunge) was studied under the conditions of different drying temperatures, vacuum degrees, and atmosphere maintaining time, respectively by vacuum drying technology. The model of vacuum drying process of Huangqi was built. The change of color degree 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 drying stage and the decreasing rate drying stage. The different drying conditions significantly affected the drying process. The higher temperature, the higher vacuum degree and the shorter atmosphere maintaining time caused the shorter drying time.The linear and Weibull composed model fitted the vacuum drying process of Huangqi well and the interval of the coefficient R2 was 0.9802 ~ 0.9997. The analysis of the colour showed that the lightness of Huangqi dried was brighter than before.But the red & green value and blue & yellow value were lower than before.The drying temperature had a significant effect on the brightness value and the brightness value decreased when the drying temperature increased.The dried Huangqi's water activity was lower than 0.3. And there were no significant changes in the hygroscopic properties of Huangqi powder under different drying conditions. The results provides theoretical support to the vacuum drying process of the Huangqi.