Effects of different drying methods on drying characteristics, microstructure, quality, and energy consumption of Panax Notoginseng roots (Araliaceae)

Abstract

The effects of three different drying tecnologies (PVD, THC-HAD, and IR-HAD) on drying kinetics, microstructure, energy consumption, and quality, that is, rehydration ratio (RR), color parameters (L*, a*, b*), total color difference (△E), Panax Notoginseng saponins (PNS) content, and ginsenosides content (R1, Rg1, Re, Rd, Rb1) of Panax Notoginseng roots were examined experimentally. As expected, the drying time decreased with increase of drying temperature from 40 to 70 °C, and PVD needed the shortest drying time, followed by THC-HAD and IR-HAD. The drying time of PVD was reduced by 22.9% and 30.2% compared with THC-HAD and IR-HAD at 60 °C, respectively. PVD can effectively shorten the drying time, and the dried samples had better brightness (about 50.2 ± 1.3), rehydration ability (range from 1.6 to 2.1) through promoting the porous structure formation of dried roots. But PVD is not the most suitable drying technology in terms of ginsenosides content preservation and energy consumption, when compared to THC-HAD and IR-HAD. For Panax Notoginseng roots need to be used as medicine, IR-HAD is a promising drying technology, especially at 50 °C, as it allowed high retention of PNS (about 12.5%) and low unit energy consumption (about 19.5 kW·h/kg). Therefore, the current findings indicate that IR-HAD drying has the potential to produce high-quality dried Panax Notoginseng roots on commercial scale.