Effect of vacuum drying on drying kinetics and quality of the aqueous extracts of Callicarpa nudiflora Hook. et Arn.

To explore the feasibility to enhance drying kinetics and keep the active ingredients of the aqueous extracts of Callicarpa nudiflora Hook. et Arn., the effects of vacuum drying under different vacuum pressure (8, 20, 50 kPa), drying temperature (80, 95, 110 °C), and the thickness (4, 8, 12 mm) on the drying kinetics, energy consumption and the contents of verbascoside and galuteolin of the aqueous extracts were evaluated. Boiling heat transfer and low-pressure mass transfer of the aqueous extracts during drying were analyzed. Among different drying conditions, the vacuum pressure of 20 kPa, drying temperature of 110 °C and the thickness of 4 mm were recommended as the most suitable ones for vacuum drying of the aqueous extracts of Callicarpa nudiflora Hook. et Arn. in terms of the moisture ratio and the quality of final product.