Objective: To research the feasibility of freeze-drying technique under low vacuum in preservation of fresh herb of Chinese medicines. Method: Rehmanniae Radix with thermal instability indigrents and Zingiberis Rhizoma Recens with volatile indigrents were choosed as the research objects and divided into two groups(freeze-drying group dried by freeze-drying technique under low vacuum and electric thermostatic drying group dried by electric thermostatic drying technique).Differences between the two groups were compared by contrasting the appearance

microstructure

water content

content of active ingredients and rehydration after drying. Result: Crude drugs of freeze-drying group had bright color and intact shape

while electric thermostatic drying group had dark color and distorted shape.Water content in freeze-drying group was lower than that of electric thermostatic drying group.Microstructure of the two groups did not destroy.Retention rates of catalpol and 6-gingerol in freeze-drying group were higher than those in electric thermostatic drying group

but the retention rate of volatile indigrients in the two groups was very close.As for rehydration

Rehmanniae Radix in freeze-drying group had a 292% weight gain in 1 h

when the crude drug' water absorption came up to constant weight

it had a 300% weight gain;while Rehmanniae Radix in electric thermostatic drying group had a 220% weight gain in 4 h

then the weight of which was sustained. Conclusion: Products of freeze-drying technique have high quality

good appearance

low water content

complete microstructure

high retention rate of index ingredients and strong rehydration.All of the above statements prove that it is an excellent drying technology with high potential in preservation of fresh herb of Chinese medicines.