Effect of pulsed vacuum drying on drying kinetics and quality of roots of Panax notoginseng (Burk.) F. H. Chen (Araliaceae)

In order to explore the feasibility to enhance drying kinetics, the effects of pulsed vacuum drying (PVD) under different temperatures (55, 60, 65, 70, and 75 degrees C) and pulsed vacuum ratio (PVR) (3:16, 6:16, 9:16, 12:16, 9:10, 9:13, and 9:19 min/min) on the drying kinetics, energy consumption, and quality attributes of Panax notoginseng roots in terms of color parameters (L*, a*, b*, and oE), the contents of ginsenosides (R-1, R-g1, R-e, R-d, R-b1), and Panax notoginseng Saponins (PNS) are evaluated. The results were compared with those obtained under hot air drying (HAD) conducted at the temperature of 60 degrees C, relative humidity of 12%, and air flow rate of 0.3 m/s. PVD at 75 degrees C and PVR of 9:16 min/min resulted in the shortest drying time, i.e., 26.6 h, while PVD at the temperature of 65 degrees C and PVR of 9:13 resulted in the highest PNS content, i.e., 9.03%. Among different drying conditions, the temperature of 65 degrees C and PVR of 9:16 min/min are recommended as the most suitable ones for drying of whole Panax notoginseng roots in terms of drying time, energy consumption and quality of final product.