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

Abstract

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 °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 △E), the contents of ginsenosides (R1, Rg1, Re, Rd, Rb1), 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 °C, relative humidity of 12%, and air flow rate of 0.3 m/s. PVD at 75 °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 °C and PVR of 9:13 resulted in the highest PNS content, i.e., 9.03%. Among different drying conditions, the temperature of 65 °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.