Abstract: In order to make full utilization of Rehmannia glutinosa Libosch leaf resource, improve its added value and provide optimal drying method for Rehmannia glutinosa Libosch leaves extract, single-factor design was used to explore the effects of microwave power and drying time on water content of dried products, followed by process optimization for the microwave vacuum drying of the extract by orthogonal array design based on multi-index comprehensive evaluation. Results indicated that the optimal microwave vacuum drying parameters were initial water content in extract of 45%, microwave power of 2 kW, heating time of 18 min, rotating speed for loading tray of 90 r/min, intermittent ratio of 3:1 and loading amount of 110 g. Under the optimal drying conditions, water content, retention rate of verbascoside and retention rate of total glycosides were 2.89%, 95.98% and 89.41%, respectively. Compared with vacuum oven drying, vacuum belt drying and freeze drying, microwave vacuum drying has the remarkable advantages of low water content, less loss rate of bioactive components, short drying time, high retention rate of bioactive components and simple operation, which exhibits promising application value in the field of industry due to its stability and reliability.

Key words: Rehmannia glutinosa Libosch leaves, microwave vacuum drying process, verbascoside, total glycosides, multi-index comprehensive evaluation