Process performance and quality attributes of temperature and step-down relative humidity controlled hot air drying of Panax notoginseng roots

Dalong Jiang,Sara Zielinska,Yanhong Liu,Congcong Li,Zhi’An Zheng,Zhenjiang Gao,Rongyan Wang

doi:10.25165/j.ijabe.20211406.6198

Abstract

The effects of temperature and step-down relative humidity controlled hot-air drying (THC-HAD) on the drying kinetics, energy efficiency and quality, i.e., rehydration ratio (RR), color parameters (L*, a*, b*), total color difference (ΔE*), Panax notoginseng saponins (PNS) content, and ginsenosides content (R1, Rg1, Re, Rd, Rb1) of Panax notoginseng roots were evaluated. The drying time was significantly affected by the drying temperature followed by the relative humidity (RH) of the drying air. Special combination of drying conditions, i.e., drying temperature of 50°C, relative humidity of 40% for 3 h and then continuous dehumidification from 40% to 8% allowed to shorten the drying time by 25% compared to drying at the same temperature and continuous dehumidification. The longer was the drying time under constant high RH of drying air, the lower was the RR of dried samples. The step-down RH strategy contributed to the formation of a porous structure, enhancement of drying efficiency and quality improvement. Generally, the ginsenosides content increased with the increase in temperature, while no obvious trend was recorded for ginsenoside R1. The contents of the ginsenoside R1, Rg1, Rb1 and PNS decreased with the increase in the drying time under constant high RH. Taking into account the drying time, energy consumption and quality attributes, drying at the temperature of 50°C, constant RH of 40% for 3 h and then step-down RH from 40% to 8% was proposed as the most favorable combination of drying conditions for dehydration of whole Panax notoginseng roots. Keywords: Panax notoginseng (Burk.) F. H. Chen (Araliaceae) roots, step-down relative humidity, hot air drying, process performance, quality attribute DOI: 10.25165/j.ijabe.20211406.6198 Citation: Jiang D L, Li C C, Zielinska S, Liu Y H, Gao Z J, Wang R Y, et al. Process performance and quality attributes of temperature and step-down relative humidity controlled hot air drying of Panax notoginseng roots. Int J Agric & Biol Eng, 2021; 14(6): 244–257.

Highlights

It includes the following process parameters: 1) Drying temperature DT, °C; 2) Drying time Dt, h; 3) Rehydration ratio (RR); 4) the content of Panax notoginseng saponins (PNS), %; 5) R1 is the content of ginsenoside R1, %; 6) Rg1 is the content of ginsenoside Rg1, %; 7) Re is the content of ginsenoside Re, %; 8) Rd is the content of ginsenoside Rd, %; 9) Rb1 is the content of ginsenoside Rb1, %; 10) specific energy consumption (Sec), kW·h/kg; 11) heat accumulation (Ha), °C·h; 12) shrinkage ratio (Sr), %; 13) lightness L*; 14) yellowness b*; 15) redness a*; 16) total color difference (ΔE*)
Note: DT is the drying temperature, °C; Dt is the drying time, h; RR represents the rehydration ratio; PNS represents the content of Panax notoginseng saponins, %; R1 is the content of ginsenoside R1, %; Rg1 is the content of ginsenoside Rg1, %; Re is the content of ginsenoside Re, %; Rd is the content of ginsenoside Rd, %; Rb1 is the content of ginsenoside Rb1, %; Sec represents the specific energy consumption, kW·h/kg; Heat accumulation (Ha) represents the heat accumulation, oC·h; Sr represents the shrinkage ratio, %; L*is the white-black value; b*is the yellow-blue value; a*is the red-green value; ΔE* is the total color difference
Step-down relative humidity (RH) convective hot air drying of whole Panax notoginseng roots was experimentally investigated

Summary

Objectives

The aims of this study were to evaluate the effects of temperature and humidity controlled hot-air drying (THC-HAD) i.e., constant drying temperature, constant relative humidity and step-down relative humidity on 1) the drying characteristics of whole Panax notoginseng roots; 2) quality attributes, such as color (L*, a*, b*, ΔE*), rehydration ratio, shrinkage, texture, ginsenosides contents (R1, Rb1, Rd, Re, Rg1, PNS), and microstructure, as well as 3) specific energy consumption. The aims of this study were to evaluate the effects of temperature and humidity controlled hot air drying (THC-HAD) on the drying characteristics of whole Panax notoginseng roots, quality parameters and specific energy consumption

Methods

Results

Conclusion