Microwave-assisted drying techniques to enhance the drying efficiency and quality of dried Gastrodia elata

Gastrodia elata (G. elata) is highly valued for its health and medical effects. A timely and efficient drying process helps improve the quality of dried G. elata. Prior to drying, G. elata was steamed at 100 °C for 20 min to improve final product quality. In this study, microwave drying (MD), microwave hot-air rolling-bed drying (MHARD), microwave infrared vibrating-bed drying (MIVBD) and pulse-spouted microwave vacuum drying (PSMVD) were used to dry G. elata. The effects of drying techniques on drying kinetics, moisture state, color profile, microstructure, glass transition temperature, active ingredients (total phenol, total flavonoids, total sugar, gastrodin and p-hydroxybenzyl alcohol contents) and antioxidant properties of dried samples were investigated.

The results revealed that steaming increased the proportion of free water in G. elata and facilitated its migration to the sample surface during drying. Among the various drying techniques, MIVBD achieved the shortest drying time of 44.7 min and it accelerated drying by 21.16%, 39.02% and 59.36% compared to MD, PSMVD and MHARD methods, respectively. PSMVD resulted in a minimal color change (ΔE = 21.5) and the dried sample had a porous structure. Drying process reduced the antioxidant activity, and MHARD-dried samples showed the highest total phenol and gastrodin contents.

The results of this study indicate that MIVBD significantly improved the drying efficiency of G. elata, while MHARD maximumly preserved the bioactive compounds. It aims to provide theoretical support for the microwave drying of G. elata. © 2025 Society of Chemical Industry.